SOURCE ASSESSMENT DOCUMENT
NO. 2 4
RUBBER PROCESSING
Authors
Mr.
T. W -
Hughes
Mr.
t. ]•;.
Ctvrtnicok
Mr.
D. A.
Horn
Dr.
R. VI.
Ser th
Program Manager
Dr. R. C. Binning
EPA Projcct 0ffIcor
Dr. Dole A. Denny
EPA Project Leader
Mr. Kenneth Baker
Prepared for
Chemical Processes Section
Particulate and Chemical Processes Branch
Industrial Environmental Research Laboratory - RTP
U.S. Environmental Protection Agency
Research Triangle Park, North Carolina. 27711
Contract 68-02-1874
August 19 7 5
MONSANTO RESEARCH CORPORATION
DA Y T 0 N L A13 0 RA T 0 RY
Dayton., Ohio 4 54 07
A
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CONTENTS
See tion Page
I Introduction 1
II Summary 2
III Source Description 4
A. Source Definition 4
13. Process Description 8
1. Feed Material 3
2. Fabrication 36
3. Tire Manufacture 57
C. Geographical Distribution 67
IV Emissions 7 4
A. Locations and Descriptions 7 4
.1.. Compounding 7 4
2. Curing 7 6
3. Under Tread Cementing 92
4. Green Tire Spraying 92
5. Other Processing Emission Points 93
B. Emission Factors 93
C. Definition of a Representative Source 97
D. Source Severity 9 8
.1. Maximum Ground Level Concentration 93
2. Severity Factor 100
3. Contribution to Total Air Emissions 101
4. Population Exposed to High Pollutant 107
Concen tration s
V Control Technology 10 9
A. liydroca ebon 109
1. Adsorption 109
2. Absorption 115
3. Incineration 115
4. Vapor Condensation 120
i 1
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Page
V Control Technology (continued)
B. Particulate 121
1. Wet Scrubbing ]_21
2. Fabric Filtration 2.30
3. Mist Eliminators ^32
VI Growth and Nature of the Industry 135
A. Present Technology 13 5
13. Emerging Technology 136
C. Marketing Strengths and Weaknesses 138
1. Tires 13S
2. Molded and Extruded Products 139
3. Hose and Belting 14 2
4. Natural Rubber 144
5. Total New Rubber Consumption 144
VII Appendix
Rationale Cor a Sampling Plan
VIII Conversion Factors 14 8
IX References 149
lii
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LIST OP TABLES
Table Page
1 U.S. Consumption oi: Natural and Synthetic 9
rubber, 19 71
2 Class! i:j.ca t ion of rubbers 12
3 Typical Mixtures for Synthetic Rubber 15
P roduc L" ion
4 Commercial Antioxidants 20
5 Pigments used in Rubber Compounding 2-1
G .Typical Softeners and Plasticixers used 27
in Rubber Compounding
7 Commercial Accelerators 29
8 Commercial Antiozonants 3 2
9 Blowing Agents Which Release Nitrogen 34
10 Organic Activators 35
11 Commonly used Retarders 35
12 Preparation of a Dispersion of Amino:; 46
Suitable for Latex Compounding
13 Preparation of a Dispersion of Methazate 4 6
Suitable for Latex Compounding
14 Preparation oE a Maugav.'hite Emulsion 47
Suitable for Latex Compounding
15 Preparation of an Oi.l Emulsion Suitable 4 7
for Latex Compounding
16 Typical Compound Compositions for Tire 62
Parts
17 Typical Tire Cord Dip Solution 64
18 Summary of.Rubber Producing Plants by 68
Product Type
19 State by State Production of Rubber Goods 72
20 Materials Emitted During Rubber VuJ.can.i- 78
zation
2.L Curing Concentrations of Selected 79
Compounds
22 Melting Points of Common Antioxidants 80
IV
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LIST GF TABLES (Continued)
Table Page
2 3 Melting Points of Common Accelerators 31
2A Passenger Tire Tread Formulations 84
25 Passenger Tire Formulations for Black 85
Sidewalls
26 Passenger Tire Formulations Cor White 86
SidewalIs
27 Definitions of Commercial Ingredients 87
23 Estimated Emissions of Volatile Compounds 88
from Hypothetical Passenger Tire with 10 kg
Combined Weight of Tread and Sidewall Stocks
29 Tread Stock Formulation Used by Rappaport 90
30 Volatilization of Green Tread Stock During 91
Vulcanization at Temperatures Between
160°C and 200°C
31 Summary o C Emissions Data Reported in the 94
Literature for Rubber Processing
32 Emission Factors Cor Compounding in a 95
Tire Plant
33 F,mission Factors for Curing in a Tire Plant 96
3 4 Maximum Ground Level Concentrations of 9 9
Different Emissions from Rubber Processing
35 Time-Averaged Maximum Ground Level Con- 102
centrations and Severity Factors for
Emissions from Rubber Processing
36 Total Emissions of Hydrocarbons and 103
Particulates Resulting from Rubber
Processing Operations by State
37 Percent Contribution oC Emissions of 105
Hydrocarbons and Particulates from Rubber
Processing to Corresponding State Emissions
from Point Sources
3 8 Area and Population Exposed to Pollutants 10 8
for Which v/F > 1 and v/F > 0.1
39 New Rubber Consumption 14 2
40 Rubber Consumption Forecast for 1980 14 5
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LIST OF FIGURES
Figure Page
1 Cross Section of a Banbury Internal 3S
Mixer Mounted Over a Rubber Mill
2 Diagram of the Calendering Process 41
3 Extrusion Processes 4 3
4 Processing Steps in the Production of 54
Molded Goods
5 Cross Section of a Tire 58
6 Variations of Tire Construction 59
7 Tire Plant Process Flow Diagram 61
8 Geographic Distribution of Rubber Product 7 0
Plants in the U.S.
9 Carbon Adsorption System 114
10 Catalytic Afterburner 119
11 Centrifugal Spray Scrubbers 125
12 Impingement Plate Scrubber 126
13 Ventun Scrubber 127
14 Packed Bed Scrubbers 12 9
15 Centrifugal Fan Wet Scrubber 131
16 Domestic Market Estimates and Forecasts 141
Molded, Extruded, Lathe Cut Products
17 Market Potential for Rubber Hose Belting 143
18 Total Mew Rubber Consumption, Snythetic 14 6
vs Natural Source
vi
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SECTION I
INTRODUCTION
Rubber must be processed to convert rubber polymers into
finished, saleable products. This practice constitutes a
source of air pollution. The objective of this work was to
assess the environmental impact of rubber processing in the
United States and to produce a reliable and timely Source
Assessment Document for use by EPA in deciding whether there
is a need for additional control technology development.
Tins document was prepared by acquiring and analyzing
information on: (1) the materials used in rubber process-
ing; (2) the basic rubber processing steps; (3) source
sites; (4) emissions produced; (5) effects on air quality;
(6) the state of the art and future considerations in pollu-
tion control technology; and (7) the projected growth and
anticipated technological developments in this practice.
[In this document, the effects on air quality resulting from
rubber processing were determined using estimated emission
factors derived from limited emission data available in the
literature. More complete and more reliable data could be
obtained by further sampling and analysis of: (1) chemical
substance'emissions; (2) particulate emissions and (3) other
, a
emissions.J
Information shown in brackets ,_ ( ] , in this preliminary
document may not appear in the final Source Assessment
Documen t.
1
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SECTION II
SUMMARY
Rubber processing is performed to convert rubber (natural
and synthetic) into finished, saleable products. It is
estimated that approximately *1500 plants perform some type
of rubber processing. The products manufactured include:
(1) tires and inner tubes; (2) footwear; (3) hose and
belting; (4) fabricated rubber products; (5) reclaimed
rubber; (G) gaskets and packing; (7) nonferrous wire drawing
and insulation; and (8) tire retreading and repairing.
Rubber processing plants are concentrated in the industrial-
ized states such as Ohio and California.
Rubber processing involves a number of steps such as: (1)
compounding, (2) iniLling, (3) molding, (<1) cementing, (5)
spraying, and (6) -wiring. These processing steps generate
hydrocarbon and particulate emissions. Hydrocarbons consist
of rubber chemicals and solvents which are volatilized
during the processing. Particulates consist of carbon
black, soapstone, zinc oxide, etc., which are generated
during compounding and milling operations.
Emissions from rubber processing constitute 0.34?o of the
national total of hydrocarbon emissions from point sources.
Hydrocarbon emissions in the following states exceed 15 of
2
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of the total state hydrocarbon emissions: Alabama, .Mississippi,
Ohio, and Tennessee.
A severity factor, S, was defined zo indicate the hazard
potential of each emission source':
where y is the tiroe-ovoraqcci maximum ground level co.icen-
tration of each pollutant emitted f tons a representative
rubber processing source, and F is the primary ambient air
quality standard c-r a "corrected" threshold limit value
(TLV@-3/2'1 • 1/100 ) depending on the type and composition of
the pollutant-3
The representative source \vds defined as p. --ire plant vith
an annual capacity cf 1.7 rf.il lion units. In rubber pro-
cessing the sever_ty factor equals 1.2 for hydrocarbons, but
it is less than 0.1 for =11 erii-ted hydrocarbon cr.ernioal
substances. ("Ihis includes only those species for which
TLA''s have been established . ] The popul? t.ior. that is aff ectsd
by the emissions for v.0.1 is for hydrocarbons.
Control technology for rubber processing consists of absorp-
tion, adsorption, condensation, compression, incineration,
and fabric filtration of the materials emitted.
TL'v'C", /'.ncritan Conference of Govcrriiucrstcil. Industrial
Hyg j.en is ts.
->
J
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SECTION III
SOURCE DESCRIPTION
A . SOU RC E D E F !I MITIO N
This source is identified as Rubber Processing and includes
the cicjht industries shov/n below. The definitions of these
industries correspond with their Standard Industrial
Classifications (SIC's) as defined by the U.S. Department
of Commerce.
Tires and Inner Tubes (SIC 3011)
This industry "includes establishments primarily
engaged in manufacturing pneumatic casings, inner
tubes, and solid and cushion tires for all types of
vehicles, airplanes, farm equipment, and children's
vehicles; tiring; and camelback and tire repair
and retreading materials."1
Preliminary Report, 1972 Census of Manufactures, Industry
Series, Tires and Inner Tubes,, SIC 3011, U.S. Department
of Commerce, Social and Economic Statistics Administration,
Bureau of the CEnsus, Washington, D.C., March 1974.
4
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Rubber ancl Plastics Footwear (SIC 3021)
This industry "includes establishments primarily
engaged in manu fac taring all rubber and plastics
footwear, . . . having rubber or plastic soles
vulcanized to the uppers."2 (Processes specific to
the utilization of plastics within the rubber and
plastics footwear industry are excluded from
further consideration in the assessment of the
rubber processing source.)
Reclaimed Rubber (SIC 30 31)
This industry "includes establishments primarily
engaged in reclaiming rubber from scrap rubber
tires, tubes, and miscellaneous waste rubber
articles by processes which result in devulcan-
ized, depolymcrized or regenerated replasticized
products containing added ingredients. These
products are sold for use as a raw material
in the Manufacture of rubber goods with or with-
out admixture with crude rubber or synthetic
rubber . "
Rubber and Plastics Hose and Bolting (SIC 3041)
This industry "includes establishments primarily
engaged in manufacturing rubber and plastics
"Prelimina.ry Report, 197 2 Census of Manufactures, Industry
Series, Rubber and Plastics Footwear, SIC 3021, U.S.
Department of Commerce, Social and t'conoinic Statistics
.Administration, Bureau of the Census, Washington, D.C.,
i-iarch 1974.
^Preliminary Report, 1972 Census of Manufactures, Industry
Series, Reclaimed Rubber, SIC, 3031, U.S. Department of
Commerce, Social and Economic Statistics Administration
Bureau of the Census, Washington, D.C., February 1974.
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hose and belting, including garden hose."1'
(Processes specific to the utilization oil
plastics within the rubber and plastics hose
and belting industry arc excluded from further
consideration in the assessment of the rubber
processing source.)
Fabricated Rubber Products N.E.C.3 (SIC 30G9)
This industry "Includes establishments primarily
engaged in manufacturing industrial and mechan-
ical rubber goods, rubberized fabrics and
vulcanized rubber clothing, and miscellaneous
rubber specialties and sundries."5
Gaskets, Packing and Sealing Devices (SIC 3293)
This industry "includes establishments primarily
engaged in manufacturing gaskets, gasketing
materials, compression packing, molded packings,
oil seals, and mechanical seals. Included arc
gaskets, packing and scaling devices made of
leather, rubber, metal, asbestos, and plastics.""'
aNot elsewhere classified.
''Preliminary Report, 197 2 Census of Manufactures, Industry
Series, Rubber and Plastics Hose and Belting, ST.C 3 041,
U.S. Department of Commerce, Social and Economic Statis-
tics Administration, Bureau of the Census, Washington, D.C'. ,
February 1974.
-"Preliminary Report, 1972 Census of r-ianu f ac tur cs , Industry
Series, Fabricated Rubber Products, N.E.C., SIC 3069, U.S.
Department of Commerce, Social and Economic Statistics
Administration, Bureau of the Census, Washington, D.C.,
March 1974.
^Preliminary Report, 1972 Census of Manufactures, Industry
Series, Gaskets, Packing and -Sealing Devices, SIC 3293, U.S.
¦Department of Commerce, Social and Economic Statistics Ad-
ministration, Bureau of the Census, Washington, D.C., March 1974.
6
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Nonferrous Wiredrawing and Insulating (SIC 3357)
This industry "includes establishments primarily-
engaged in drawing and insulating, and insulating
wire and cable of nonferrous metals from purchased
wire bars, rods, or wire."7
Tire Retreading and Repair Shops (SIC 7 534)
This industry "includes establishments primarily
engaged in repairing and retreading automotive
tires. Establishments classified here may cither
retread customers' tires or retread tires for
sale or exchange to the user or the trade."8
Consumption of new rubber by the .industry is reported in
three parts: (1) tires and tire products including pneu-
matic and solid tires, inner tubes, retread and repair
materials, flaps, and sundries; (2) other products including
footwear, belts, hose, mechanical goods, foam, sponge, and
sundries; and (3) wire and cable. This breakdown permits
observation of trends in total new rubber consumption.
It also illustrates the dominant position of tires and
tire products which consistently use 62o to 66% of all
new rubber each year. Wire and cable use a small part
of the total which has remained constant in absolute terms
but has declined from 3% to 1% over the years from 1958
to 1972. The other products consume the remainder (about
Preliminary Report, 1972 Census of Manufactures, Industry
Series, Nonferrous Wiredrawing and Insulating, SIC 3357,
U.S. Department of Commerce, Social and Economic Statistics
Administration, Bureau of the Census, Washington, D.C.,
March, 1974.
Preliminary Report, 1972 Census of Manufactures, Industry
Series, Tire Retreading and Repair Shops, SIC 7534, U.S.
Department of Commerce, Socia-J: and Economic Statistics Admin-
istration, Bureau of the Census, Washington, D.C. (To be
pub.Lished . )
7
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one-third) of total new rubber production in manufacturing a
great variety of items.^
The tires and inner tubes industry is thus the major industry
of this.source, accounting for 66% of finished product
weight of the entire fabricated rubber products industry.
The breakdown of consumption of natural and synthetic rubber
by oiid use as of 1971 xs indicated in TabLe 1.
B. PROCESS DESCRIPTION
1. Feed Material
a. Rubber and Rubber Latex -
(1). Natural rubber - Rubber represents a primary material
input to the rubber processing source. Natural rubber is
obtained by tapping the tree lievea Bra ni.liev. sis and collecting
latex from which the rubber is separated by the process
known as coagulation. Coagulation occurs when various acids
or salts are added. The rubber separates from the rubber
serum as a white, doughlike mass, which is then milled and
sheeted to remove contaminants and to enable drying. This
rubber is known as natural rubber, which chemically is built
of 5000 isoprene units j.n a cia (designated herein as cis)
configuration.
JPettigrew, R. J., and F. H. Roninger. Rubber Reuse and
. Solid Waste Management, Solid, Waste Management in the
Fabricaced Rubber Products Industry, 19 63. Environmental
Protection Agency. Publication SW-22c. 1971. 120 p.
8
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Table 1. U.S. CONSUMPTION OF NATURAL AND SYNTHETIC
RUB13KR, 197110
Weight 1
Rubber end use
oE total
Cumulative Z
Tires and related products
66 . 0
66 . 0
Molded goods
Au tonio tive
4 . 6
70 . 6
0 ther
5.2
75.0
Foam rubber
3 . 2
79 . 0
Shoe products
1. . 9
30 . 9
Hose, tubing
]_. 9
82 . 8
Rubber footwear
1 . 6
8 4.4
0-ir.ings, packing gaskets
1 . 5
8 5 . 9
Sponge rubber products
1.4
n ~r
O J . J
Solvent and latex cement
1.3
88 . 6
iielts and belting
1 . 1
39.7
Wire and cable
1. 1
90 . 3
Coated fabrics
1. J.
91 . 9
Floor and wall coverings
0 . 8
9 2.7
Pressure-sensitive tapes
0 . 5
93.2
Industrial rolls
0 . 5
93.7
Athletic goods
0 . 5
9 •'! . 2
Military goods
0 . 5
9 4.7
Thread (bare)
0. 5
95 . 2
Drugs and medical sundries
0 . 4
95.6
Toys and balloons
0 . .'1
96 . 0
All other
4 . 0
100 . 0
1 0 Richard son, J., and M. Herbert. Fovccasbnq in the
Rubber Industry. (Paper CMRA 877 presented at joint ¦
meeting of the Chemical Marketing- Research Association
and the Commercial Development Association. Nev? York,
May 19 7 4.)
9
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Because natural latex is very sensitive to bacterial
action, a preservative must be added to protect it. The
most commonly used preservative is dilute ammonia. Ammonia
can also be used in combination with formaldehyde (0.15% to
1.30%) or- sodium pen tachlorophena te (0.3%) Santobri te"3 based
on latex.
Further latex processing consists of concentrating the
solids. Centrifugincj (90%) and creaming are mostly used
for this purpose, with a very small amount of concentration
being done by evaporation. In the creaming process, a
small quantity of gum, such as ammonium alginate, gum
tragacanth or Irish moss, is added. Concentration by
evaporation requires the addition of stabilizers, alkalis,
and soap to the latex. The evaporation route differs from
the other two methods in that all. ingredients in the
original latex plus any stabilizing additives remain in
the finished product. Essentially all latexes are con-
centrated to G2% to 08% total solids before sale. The
latex is transported in its concentrated form for use in the
production of foam, latex-dipped goods, adhesives, etc.
Dry rubber is produced by stabilizing the latex with
preservatives such as sodium sulfide, diluted to about
15% and coagulated by the addition of dilute formic or acetic
acid. The agglomerate is then either washed or dewatered
in mills. "Pale crepe," "smoked sheets" and other different
grades of rubber including bark, earth scrap and factory-
salvage are thus produced.
Natural rubber is still used in the United States for
truck tires because of its heat-buildup resistance. Other
reasons for the use of natural rubber are its excellent
10
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properties, such as a gums took, and overall balance of
desirable properties, and a.'l.so because rubber making
machinery was designed to handle this material.
(2) Synthetic rubber - The First synthetic rubbers to be
commercially available in the United States were "thiokol"
and l!neoprene." Those rubbers were introduced in the early
1930's and both of; them are still produced commercially
because they have special properties that are not matched
by natural rubber. Other types of synthetic rubber followed
and their chemical formulations, properties, and preferred
uses are summarized in Table 2.
Several other elastomers are available. They are considered
specialty rubbers, and are mostly limited by their cost to
use in areas where specific properties are desired. Ex-
amples of these elastomers are listed below:
Thiokol (T) is a polysulfide rubber which has
outstanding oil and solvent resistance. How-
ever, its other properties are poor.
Silicone rubbers have excellent high and low
temperature resistance, good anecharCcal proper-
ties at high temperaturer low compression sat, and
fair oil resistance. Thoir cost, however, restricts
use mainly to aircraft and outer space equipment.
Due to their inertness and non-toxicity the silicone
rubbers are also used for some food and surgical
applications.
EPR (EPM) is ethylene propylene rubber with
good aging, abrasion, and heat resistance. It
exhibits excellent resistance to oxygen,
11
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ozone, acids, alkalis and other chemicals
over a wide range of temperatures. It is not oil
resistant and its full utilization potential is
not fully defined.
Po.Lyurethane rubber (A'U) is a polyurethane diiso-
cyanate with exceptional abrasion, cut and tear
resistance, high modulus and hardness. It is
not suited for normal tire service because
abrasion resistance decreases rapidly with
increasing temperature. The material is used
in some small solid tires, but its main appli-
cations are in foams and surface coatings.
llypalon (CSH) is chlorosulfonated polyethylene
with excellent resistance to ozone and strong
chemicals like nitric acid, sulfuric acid, chromic
acid, hydrogen peroxide and strong bleaching
agents. It has good heat resistance and mechan-
ical properties, limited colorab.il i ty , fair oil
resistance and poor low temperature resistance.
Uses include conveyor belts, steam hose tubes,
o-rings and gaskets in ozone generators, mis-
cellaneous molded goods and coated fabrics for
outdoor use.
Fluoroelastomers (FDM) arc fluorinated hydro-
carbons with excellent high temperature resis-
tance, particularly in air and oil. They arc
of limited use for cooking utensils.
13
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Synthetic rubbers can be produced either in an emulsion
process (butadiene-styrene, polybutadiene, polybutadiene-
acrylonitrile, neoprene) or a non-aqueous process (butyl
rubber, silicone rubbers, polyisoprene, polybutadiene,
polvurethanc, polyolefm, solution butadiene-styrene
rubbers). In the emulsion polymerization process, the
monomer (or the mixture of monomers in copolymerization) is
mixed with an appropriate emulsifying solution, catalyst,
and modifying agent. When the required conversion of the
monomers is achieved the reaction is stopped by the
addition of some material such as hydroquinone which des-
troys the catalyst and arrests further polymerization. 7\t
this stage the rubber is contained in a stable milky
suspension known as synthetic latex.
The latex is then stripped of unreacted monomers and
antioxidant is added. Rubber can be isolated from the
latex by coagulation with salt, salt acid, or aluminum
sulfate solution. Table 3 shows some mixtures commonly
used to prepare synthetic rubbers. The finished product
rubber contains fatty acids, rosin acids, antioxidants,
moisture, and some inorganic materials (mainly sodium
chloride and perhaps some minute quantities of materials
used in its preparation) .
Non-aqueous processes cover the largest spectrum of methods
extending from those which produce an insoluble polymer that
separates during polymerization (butyl rubber) to the poly-
mers which remain in solution (bunas). The polymerization
reaction takes place in solution with the proper solvent.
The solution polymerization for making synthetic rubber
has been the source of many varieties oE new products. Thus,
in the production of butyl rubber, the catalyst (aluminum
chloride) is added as a dilute, solution in methyl chloride.
14
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Tabic 3. TYPICAL MLMTURES FOR SYNTHETIC RUDDER PRODUCTION! ?
Rubbe i:
Componen t
Parts per
100 monomer
a 1
SBR (BK, Buna W)
.Butadiene
7 5.0
(hot polymeriza-
S tyrene
25. 0
tion at 501>C)
Wa ter
180.0
Soap
5.0
"Lorol." me reap tan
0. 50
(n-C; ?_il, .,S!1)
Potassium persulfate
o
o
SBR (cold polymeri-
Butadiene
7] . 5
zation below 30°C)
Styrene
2 8.5
Water
2 0 0.0
Mixed tart-mercaptans
0. 125-0.15
Potassium fatty acid soap
4 . 7
"Daxad-11"
0.1
KCl
0.5
FeSOi, 7M20
0.00 4
Sodium fornuildehyde
0.0228
sulfoxylate (SFS)
Ethylene diamine tetra-
o
o
acetic acid (Sequestrenc
i\ A)
NaOll
0. 00 2 4
D a .1. s o p r o p y 1 b e n 7. e n e
0.03 -0.L0
'nydroperoxj.de
Sodium dimethyl dithio-
0.10
carbamate (SDD) stopping
ayen t
CR (cold polymeri- [j
Chloroprene
100
zat.ion be Low 3 0°C)
U-Woocl rosin
'1. 0 | Dissolved in
Sulfur
0.6 ( the monomer
Water
150 '
S o d i i.i m h y d i: oi d e
0.8
Sodium salt of
0.7
naph thalene su1 Con i c
condensation product
Potassium persulfate
0
1
o
a
SBR = styrene - butadiene rubber; BR = butnd.icne rubber;
Buna N = butadiene - acrylonitrLie rubber. In the recipe
for CR, styrene is omitted; for Buna M, styrene is
substituted v;ith ac ryJ oni tr .i le .
b
CP. = chloroprene rubber.
15
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Produced polymer precipitates out of the solution and is
slurried with hot water, whereupon monomer flashes off and
is recovered. An antioxidant is added to prevent deterior-
ation during drying and storage and the rubber then is
dried. -Butyl rubber latex is not produced during the pro-
duction of this material, but butyl rubber dispersions have
been prepared indirectly by dissolving the rubber in a
solvent, dispersing the solution, and subsequently removing
the solvent to leave a dispersion of butyl rubber in water.
The synthesis of polyisoptenc was not successful until 1955.
Difficulties were associated with synthesizing cis-1,4-poly-
isoprene and minimizing the formation of trans-(designated
herein as trans) polyisoprene units. The catalyst used and
reported to be specific for synthesis of cls-polymer was
lithium metal, melted in petroleum jelly and mixed with pure
dry isoprene (0.1 part lithium/100 parts monomer). Alkyl-
alumium with titanium tetrachloride in hydrocarbon medium,
tr .iisobu tylalumi nura and tricthyl aluminum have been used
since then. After polymerization is completed the catalyst
is deactivated using isopropyl alcohol and an antioxidant is
added. The product is dried and cleaned to contain less
than 1% volatile material. The•synthetic polyisoprene
simulates very well the properties of natural rubber.
However, it does not contain fatty acid. This is later
compensated for in the compounding recipe.
Polybutadiene rubbers utilize organolithium and Ziegler-
type catalysts. Alkyl or aryllithium catalysts are reported
to produce essentially the same polybutadienes; butyllithium
is 'used most frequently. Ziegler catalysts consist of
alkylaluminum compound with titanium tetrachloride or
titanium trichloride. Other transition metals such as
16
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vanadium, molybdenum, cobalt, and nickel are also used.
Commercial practice seems directed toward the reaction
products of TiCli, and rL'iI!( with alkylaluminum compounds,
alkylaluminum halides with cobalt compounds, and aluminum
trihalides with cobalt compounds.1'
Polvurethane is an example of: a condensation- polymer. In
condensation polymerization diispcuamate and dialcohol,
react and eliminate simple molecules such as HoO or ammonia.
Some reactions are performed where no compound js eliminated.
Butadiene-styrene rubbers (SBR) can also be polymerized in
solution (hexane). Alkyllithiufn catalysts have been used
in this process. Polyolefin rubbers utilize alkylaluminum
catalysts in mixtures of vanadium chlorides (VCli. , VCI3,
VOCI3, V-tr iaceta te) or titanium chlorides (TiCli. , TiClj)
in a hydrocarbon solvent.
Silicone rubbers are generally prepared by conversion of
dimethyl dichlorosilane by addition of water in the presence
of small proportions of iron chloride, sulfuric acid, or
sodium hydroxide. These chemicals arc later washed out of
the polymer.
(3) Reclaimed rubber - The third important feed material
in the rubber processing industry is reclaimed rubber, or
vulcanized rubber reworked to render it suitable as raw
material. Reclaimed rubber is obtained from rubber scrap,
natural or synthetic in origin, which is segregated into
separate and compatible rubbers and then graded according
to quality and intended use. It is not profitable to use
17
-------
reclaimed rubber unless it costs no more than half as much
as virgin rubber. Its utilization therefore fluctuates
depending on the costs of virgin rubbers.
Reclaimed rubber is manufactured in various ways, the
simplest "being digestion of scrap (to which oil has been
added) either in caustic soda or zinc chloride to remove
non-rubber products. The rubber is then milled. New
reclamation involves removal of fabric by mechanical
means. The rubber is then ground, mixed with oil and
extruded.
The significance of individual rubber feed materials to
the rubber processing industry may be demonstrated by
percentages of these materials processed in the United
States. Of the total 3.4 Tg3 of rubber processed in the
United States in 1972, 6% was reclaimed rubber, 76% was
synthetic rubber, and the remainder was natural rubber.
The total includes imports.
b. Rubber Chemicals - The commercial application of
either raw natural dry rubber or raw synthetic rubber is
very limited. For the great majority of users, the rubber
must be modified, usually by the addition of chemical agents
with specific functions. Exceptions include such uses as
crepe rubber shoe soles; cement, as in the familiar rubber
adhesives; and adhesives in masking tape.
Rubbers in prescribed proportions are blended to obtain
rubber of required qualities. The desirable properties
achieved by rubber compounding are plasticity, elasticity,
toughness, softness, hardness, impermeability, resistance
to abrasion, etc. The variety of chemicals added in the
1 Tg = 101^ grams; other metric system prefixes are
shown in Section VIII.
18
-------
compoundir.g 3i3p dapends on the type of processing that
v.-iil follow and on final product use. The £olloving is
an example of a rubber compound:
Ingredient
Parts on
v.'eicr. t basis
Rubber [such as SBR)
Sal Cur
Zinc oxide
Stearic acid
Accelerator
Loading or filling pigment
Reclaim, softeners, extenders
/\s recuireu
100 . 0
50. 0
2 . 0
5 . 0
1.5
3.0
colors, blowing agents, anti-
oxidants , antiozonants, odorants,
etc.
To identify the materials that are used irs the fabrication
of rubber products, the following sections present the
individual compounds and their functions in rubber pro-
cessing .
(1) Antioxidants and stabilizers - Antioxidants and
stabilisers are needed to protect the rubber during its
handling and shipment. Generally, stabilizers are used to
protect polymers during their isolation and s;oracrs. The
antioxidants protect the rubbers both during processing and
in the finished product. Most antioxidants give good pro-
tection as stabilizers, bur nor all stabilisers give
satisfactory antioxidant activity. Natural rubber needs
antioxidants oniy, but the synthetic polymers require r>o'ch.
Table 4 summarizes the commercially important rubber anti-
oxidants and stabilizers according to the three principal
19
-------
Table 4. COMMERCIAL ANTIOXIDANTS11'
Chemical name
Trade names or trade-
marked names
Aldehyde
-amine type
7\ldol-l~'r>aphthylamine
AgeRi te Resin, Aceto AM
Bu tyraldehyde-aniline
product
Ant ox
/^cetaldehyde-aniline
produc t
Cry lerse
Aldol-aniline product
Re sis to:-:
p,p'-Diaminodiphenyl-
methane
Tonox
Kctone-
amine type
1,2-Dihydro-2,2,4 -trimethyl-
quinoline resin
AgeRite Resin D, Flectol 11,
Aceto POD
1, 2-D.ihydro-2 , 2 , 4- tri-
methyl-6-e thoxyquinoli.ne
Santoflex AW, Polyflex
1,2-Dihydro-2,2,4-tri-
methy1-6-phenylquinoline
Santoflex B
1,2-Dihydro-2,2,4-tri-
in.e thy 1- 6-dodecy 1-
quinoline
Santoflex DD
Diaryldiamine type
Nr N'-diphenyl-p-phenylene-
diamine
AgeRite DPPD, OZF
N , N 1 -di- (3-naphthyl-p-
pheny1enediamine
AgeRite White, Aceto DIPP
W , "N1-dialkylphenyl-p-
phenylenediamine
Wingstav 100, Wingstay 200
Diary1amine type
Phenyl-1-naph thylamina
Neozone A, Aceto PAN
Phenyl-2-naph thylamine
Neozone D Special, AgeRite
Powder, PBN, Aceto PBM
Alkylated diphenylamine
AgeRite Stalite, Octamine,
Pennox A, Wytox ADP,
Poly1i te
14Kirk-Othmer Encyclopedia of,-Chemical Technology, 2nd
Edition. Vol. I?. New York, In ter science Publisners,
John Wiley & Sons, Inc., 1968.
2 0
-------
Table 4 (continued). COMMERCIAL ANTIOXIDANTS111
Trade name or trade
Chemical name marked names
Ketone-dicirylamine type
Diphenylamine-acetone,
high-temperature product
Diphenylamine-acetone, low-
temperature product
Phenyl-2-naphthylamine-
ace tone , low-temperature
produc t
Diphenylamine-acetone-
aldehyde product
AgeRite Superflex, BLE-25,
Meozone L, Cyanoflex 100
Amino:
Betanox Special
BXA
Substituted phenol type
2 , 6-Di-t-buty1-4-methyl-
phenol
Butylated hydroxyanisole
2-a-Methylcyclohexyl-4 , 6-
dimethylphenol
Styrenated phenol
Hindered phenol
Butylated styrenated m,p-
cresol
CAO-.l, DBPC, Tenamene 3,
lonol, Amoco 533, Dalpac 4,
Deenax, Tenox BUT, CAO-3,
Tenox BI-IA, Sustane BHA
Nonox WSL
AgeRite Spar, Wingstay S,
Styphen 1
Wingstay T, Nevastain A,
Cvanox LF, Santowhite 5 4
Wingstay V
Bisphenol type
4, 4'-bis(2,6-t-Butylphenol)
2,2'-Methylenebis(4-methyl-
6-t-butylphenol)
2,2'-Methylenebis(4-ethyl-
6-t-butylphenol)
4,4'-Me thylenebis(6-1-
butyl-2-methylphenol)
4,4'-Me thylenebis(2,6-d i-t-
butylphenol)
Ethyl 712
Plastanox 2246, CAO-5
Plastonox 4 25
Ethyl 7 20
Binox M, Ethyl 7 02, lonox 22 0
21
-------
Table 4 (continued). COMMERCIAL ANTIOXIDANTS1"
Chemical name
Trade name or trade-
marked name
Bisphenol
type (continued)
4,4' -Butyl.ideneb.is (6 — t—
butyl-3-methylphenol)
Santov/hite powder
2,2'-Thiobis (4-methyl-6-
t-butylphenol)
CAO-4
4,41-Thiobis(6-t-butyl-2-
methylphenol)
Ethyl 7 3G
4,4'-Thiobis(6-t-butyl-3-
methylphenol)
Santov/nite Crystals
4,4'-Thiobis(3,6-di-sec-
amylphenol)
Santowhite L
Hindered bisphenol
AgeRite Superlite, Naugawhite,
Pennox D
4,4'-Dioxydiphenyl
Antioxidant DOD
Alkylated polyphenol
Wingstay L
Hydroquinone type
Hydroquinone
Tecquinol
Monobenzyl ether of hydro-
quinone
AgeRite Alba
2, 5-Di-t-amvlhydroquinone
Santovar A
Aminophenols
N-butvl-p-aminophenol
Tenamene 1
N-lauroy1-p-aminophenol
Suconox 12
2,6-Di-t-butyl-a-d imethyl-
amino-4-methylphenol
Ethyl 703
4-Isopropoxy dipheny1amine
AgeRite Iso
Phosphite type
Modified high-molecular-
v/eight hindered phenol
phosphite
AgeRite Geltrol
Tri (nonylphenyl)phosphite
Polygard
2-Ethylhexv1 octylpheny1-
ohosphite
i—I
1
CJ
>
22
-------
groups: ary'lamines, phenols, and phenolphosphides. Trade
names of these compounds are also given for easier compound
identification. Concentration levels of the stabilizers
range from 0.5 to 1.25 parts of stabilizer/100 parts of
rubber.
(2) Pigments - Any solid material' that is mixed into the
rubber, except for vulcanizing agents, may be referred to
as a pigment. Dry pigments can be classified as either
reinforcing agents or filling materials. The reinforcing
agents improve the properties of the vulcanizates v/hile
the filling agents serve as diluents. Commonly used
pigments and their average particle sizes are given in
Table 5.
For example, every
contain 0.23 kg of
and carcasses requ
pound of rubber used
carbon black; tubes
re only slightly les
in tire treads may
require even more,
s.
In the preparation of colored stocks, a sufficient quantity
of a background pigment with high hiding power (e.g.,
titanium pigments) and organic dye are added to give the
desired color. .For preparation of less bright shades,
inorganic pigments such as iron oxide, antimony sulfide,
chromium sulfide, chromium oxide, cadmium selenide and
ultramarine blue are used. Basic requirements for colored
pigments depend on their stability during product cure and
the requirements of the final product itself. Other pigments
that may be used for specific purposes include: fibrous
asbestos, for its stiffening effect and heat resistance;
cotton or other textile fibers for the same purpose at less
heat resistance; graphite to produce lower friction coeffi-
cient; ground cork for compounds needing low density; glue
as a stiffener; litharge or other lead pigments where high
23
-------
Table 5. PIGMENTS USED IN RUBBER COMPOUNDING1'1
Pigment
Grade or trademark
and company
Average
particle
diameter, nm
Carbon black
CC
10-20
S301(MPC)
25-30
S300(EPC)
30-33
N440 (FF)
36
N6 01(HMF)
50-60
N7 7 0(SRF)
70-90
N880(FT)
150-200
N9 9 0(MT)
250-500
Acetylene
43
Whiting
Witco AA (Witco Chemical
Co., Inc.)
3 , 900
Micronized (The Glidden
Co. )
1,500
Witcarb R-12 (Witco
Chemical Co., Inc.)
14 5
Witcarb R (Witco Chemical
Co., Inc.)
50
Purecal V (Wyandotte
Chemicals Corp.)
40
Purecal M (Wyandotte
Chemicals Corp.)
1, 500
Atomite (Thompson, Weinman)
1,500
Calcene TM (PPG Industries).
100
Clay
Catalpo (Freeport Kaolin)
800
Dixie (R. T. VanderbiIt
Co., Inc.)
1, 0 00
Siiica
Hi-Sil (PPG Industries)
25
Calcium silicate
Silene EF (PPG Industries)
30
24
-------
density is required for opacity to x-rays; and stiffening
resins such as polyvinyl chloride, phenolformaldehyde resins
polystyrene, or high-styrene/'low-butadiene copolymer resins.
(3) Softeners, extenders and plasticizers - A wide variety
of oils, tars, resins, pitches, and synthetic organic
materials are used as softeners in rubber compounding. Thes
compounds do not necessarily have any relation to the soft-
ness of the compounded material. The softeners are used to:
decrease the material viscosity for .improved workability,
reduce mixing temperature, increase tack and stickiness,
aid in disperison of pigments, reduce shrinkage, provide
lubrication, and improve the following extrusion or molding
and the like. The term extender is applied to materials
that replace a portion of the rubber, usually with some
processing advantage. Both of these materials can also be
used as diluents.
Plasticizers are primarily used to lower the viscosity of
the uncured stock. Usually, they are used in a very low
concentration and their effect is a lower f'tooney viscosity
of the rubber on milling. They should not affect the rate c
vulcanization or properties of cured rubber. The ease of
plasticization corresponds with the ease of oxidation, whiclr
is in the following order: natural rubber > polyisoprene >
polybutadiene > polystyrene > polychloroprene > nitrile
rubber. The concentration of plasticizers applied to
natural and synthetic rubbers may range from 0.2 5 parts to
_l.5 parts/100 parts of rubber material. The plasticizers
are effective in natural rubber, polyisoprene, and SBR.
The other synthetic rubbers are less affected by the pre-
sence of a plasticizer.
25
-------
The best softeners are those which are cjooc! solvents for the
rubber. Table 6 lists some softeners and plasticizers used
in the processing of natural and synthetic rubber.
(4) Vulcanization and acceleration agents - When rubber is
mixed with sulfur and heated, vulcanization (cure) occurs.
The terms cure and vulcanization are interchangeable, and
may be defined as the chemical reaction which combines the
polymer molecules of rubber by cross.link.ing into larger
molecules, restricting their further movement. Vulcanization
changes the rubber to a strong elastic substance which is
tack free, abrasion resistant, and not readily soluble in
common solvents. Sulfur is the vulcanization agent that has
been used during the whole period of rubber's existence.
Regardless of how little or how much suLfur is used in
vulcanizing, some sulfur remains unconibined, and is known as
free sulfur. High sulfur materials that liberate sulfur at
vulcanizing temperatures, such as organic polysulfides, may
substitute for sulfur. Examples of these compounds are:
tetramethylthiuram disulfide (Methyl Tuads), tetraethylthiuram
disulfide (Ethyl Tuads), dipentamethylencthiuram tetrasulfide
(Tetrone A), 4,4'-dithiodimorpholine (Sulfasan R), selenium
diethyldithiocarbonate (Selenac), aliphatic polysulfide
polymer (Thiokol VA-7), and alkylphenol disulfides (Vultac
2,3).
Because some rubbers contain no unsaturation the vulcaniza-
tion must be done using different chemicals and techniques
such as peroxides or radiation. Another class of curing
agents is found among the organic peroxides, such as di-
tcrt-(designated herein as tert) butyl and dicumyl peroxides
for SBR and silicone rubbers. Terpolvmers containing a
known nonconjugated diene were developed and can use sulfur
for vulcanization. Neoprene rubber is vulcanized using
26
-------
Table 6. TYPICAL SOFTENERS AND PLASTICIZERS USED
IN P,'J BEER COMPOUNDING1 u
Rubber type
Softener/Plastici?;er
Natural rubber {SEE)
All petroleum, fractions
Pine tars and resins
Coal tar fractions
Pentachlorothiophenol (RPA-6,
Renacit VI) and its activated
zinc salt (Endor)
¦
T nioxyle nols (Pitt-Consol u 40)
2, 2'-Dioensamidooi phenyldisu Lf ide
(Pepton 22)
Zinc 2-benza;nidoLhiophenoxide
(Pepton 65)
Neoprene (CP.)
Kaphthenic petroleum fraction
Coal tar fractions
Esters
Dxoctyl sebacate
Butyl oleate
Monoir.eric polvether
Triethylene glycol caprylatecaprate
Trioctyl phosphate
Nitrilss (Buna N)
Coal tar fractions
'Monomer.ic esters
Adipates
Sebacates
Tributoxyethyl phosphate monomeric
fatty acid ester (Synthetics L-l)
Di (butoxyethoxyethyl)adipate (TP-95)
Triglycol ester of vegetable oil
fatty acid (Plasticizer SC)
Coumarone - indene resins
Rosins
Modified phenolics
Te trahydronaphthalene
Dibutyl phthalate
Dibutyl sebacate
Butyl rubber (IIPO
Mineral oils
Paraffin wax
Petrola turn
Paraffinic and naphthenic oils
27
-------
zinc oxide and magnesium oxide. Butyl rubber may be vulcan-
ized using alkylphenolformaldehyde resins. Oxides of certain
metals such as lead and zinc are used to accelerate the
vulcanization.
Depending on the difficulty of obtaining rubber, the amount
of sulfur used may range from 1/2 part to 60 parts. Use of
elemental sulfur as the vulcanizing agent requires the addi-
tion of auxiliary materials to supply the desired properties.
The organic accelerator is the most important of these
materials. The accelerator has a strong influence on pro-
cessing safety, the rate of vulcanization, and the physical
properties of sulfur vulcanized rubber. Accelerators are
listed in Table 7.
(5) An tlozonan ts - As their name suggests, antiozonants are
used to protect rubber from the effects of ozone. Ozone can
cause severe cracking in rubber articles, particularly under
stress. For example, rubber insulation used around electri-
cal equipment, UV lamps, and neon lights must contain anti-
ozonants because of the high ozone concentrations present.
As a result of ozone attack on rubber there is a loss of
double bonds. Consequently, highly unsaturated rubbers
(natural and styrene-butadiene) are most easily attacked.
The antiozonants appear to work by forming a protective film
between the rubber and the ozone atmosphere. Commercial
antiozonants used for rubber protection are listed in Table 8.
(6) Other rubber chemicals -
(a) Reclaiming agents - Reclaiming agents are used in
converting the rubber scrap to plastic processable material.
28
-------
Table 7. COMMERCIAL ACCELERATORS1"
Chemical name
Trade names or trade-
marked names
Aldehyde-amine
reaction products
Ace talde'nyde/ammonia
Acetaldehyde Ammonia, Aldehyde
Ammonia
Formaldehyde/e thyl
chloride/ammonia
Trimene Base
Butyraldehyde/butylamine
Accelerator 8 33
Butyraldehyde/aniline
Accelerator 808, A-32, Beutene,
Goodrite Pullman
Butyraldehyde/ace taldehyde/
aniline
A-100
Formaldehyde/p-toluidine
Accelerator 8
Acetaldehyde/aniline
Ethylidene Aniline
Heptaldehyde/aniline
Hepteen Base
2-Ethyl-2-hexenal/aniline
Phenex
Hexamethylene tetramine
Aceto 1-IHT, Methenamine NF
Arylguanidines
Diphenylguanidi ne
DPG
Di-o-tolylguanidine
DOTG
Triphenylguanidine
Triphenylguanidine
Mixed diarylguanidines
Accelerator 4 9
Diphenylguanidine phthalate
Guantal
Di-o-tolylguanidine salt of
dicatechol borate
Permalux
Dithiocarbamates
Copper dimethyl-
Cumate
Lead dimethyl-
Ledate
Bismuth dimethyl-
Bismate
Zinc dimethyl-
Methy 1 Z ima te , Me thyl Z .iram,
Methazate, Accelerator L,
Eptac 1, Aceto ZDMD,
Vulcacure ZM
Selenium dimethyl-
Methyl Selenac
29
-------
Table 7 (continued). COMMERCIAL ACCELERATORS1'1
Trade names or trade-
Chemical name marked named
Di thiocarbamates (con tinued)
Zinc diethyl-
Zinc dibutyl-
Zinc aibenzyl-
Selenium diethyl-
Tellurium diethyl-
Piperidinium penta-
methylene-
Potassium pentamethyl
Zinc pentamethylene-
Caclmium diethyl-
Sodium dibutyl-
Tetramethylthiuram raono-
sulfide
Tetrabutylthiurarn mono-
sulfide
Tetramethylthiuram di-
sul£ ide
Tetraethylthiuram disulfide
Dipentamethylenethiuram
te trasulfide
Dime thyId iphenylthiuram
disulfide
Ethyl Zimate, Ace to ZDED,
Cyzate E, Ethazate, Ethyl
Z iram
Butyl Zimate, Dutazate, Butyl
Ziram, Cyzate B, 7\ceto ZDBD
Arazate
Ethyl Selenac, Ethyl Seleram
Tellurac
Accelerator 552
Thione.x, Ace to TMTM, Cyuram MS,
Unads, Monex, Mono Thiurad,
TMTM-Menley
Pentex
Aceto TMTD, Cyuram DS, Methyl
Thirarn, Methyl Tuads,
Thiurad, Thiuram M, Tuex,
Vulcacure TMD, Royal TMTD
Aceto TETD, Ethyl Thiram,
Ethyl Thiurad, Ethyl Tuads,
Ethyl Tuex, Thiuram E
Tetrone A, Sulfads
Accelerator J
ene- Accelerator 89
ZPD-I-Ienley
Ethyl Caclmate
Butyl Mamate, Pennac SDB,
Tepidone, Vulcacure NB
Thiuram sulfides
30
-------
Table 7 (continued). COMMERCIAL ACCELERATORS11'
Chemical name
Trade names or trade-
marked names
Thiazoles
2-Mercaptobenzoth iazole
MBT, Captax, Rotax, Mertax,
Royal MBT, Thiotax, Akron MBT
Zinc benzothiazolyl
mercap tide
Zetax, ZMBT, Pennac ZT,
Vulcacure ZT, O-X-A-F, Bantex,
Zeni te
2,2'-Dithiobis(benzo-
thiazole)
MBTS, Altax, Thiofide, Royal
MBTS, Akron MBTS
2-Benzothiazyl-N,N-die thy 1-
thiocarbamyl sulfide
Ethylac
Sulfenamides
N-t-Butyl-2-benzoth.iazole-
Santocure MS
N-Cyclohexy1-2-benzo-
thiazole-
Cydac, Comae S, Santocure,
Delac S, Durax, Royal CBTS
N,N-Diisopropyl-2-benzo-
thazole-
DIBS, Dipac
N-oxydiethylene-2-benzo-
thiazole
AMAX, NOBS Special, Santocure
MOR
N- (2,6-dimethylmorpholine)-
2-benzothiazole-
Santocure 26
N-d iethyl-2-benzothiazole-
Accelerator AZ
Misce
llaneous
Trimethy1thiourea
Thiate E
Trialky1thiourea
Thiate G
1,3-Die thylthiourea
Pennzone E
1,3-Bis(2-benzothiazolyl-
mercaptomethy1)urea
El-Sixty
2-Mercaptothiazoline
2-jMT
31
-------
Table 8. COMMERCIAL ANTIOZONANTS1h
Chemical name
Trade names or trade-
marked names
Symmetrical diamines
N, N 1-di-sec-butyl-p-
phenylened iamine
N, N 1-dime thy1-N,N1-bis
(1-methylpropyl)-p-
phenylenediamine
N,N'-bis(1-ethy1-e-methyl-
pentyl)-p-phenylene-
diamine
N, N 1-bis(1-methylheptyl)-
p-phenylened iamine
Mixture of dialkylary1-p-
phenylened iamines
N, N'-bis(1,4-d imethyl-
pentvl)-p-phenylene-
diamine
Eastozone 2, Gasoline AO-22
Eastozone 32
Eastozone 31, UOP 8S
2, Santoflex 17
Antoz i te
Eastozone 30, UOP 288,
flex 217, Antozite 1
Santo-
Wingstay 100, Wingstay 200
Eastozone 33, Antozite MPD,
Santoflex 7 7
Unsymmetrical diamines
N-isopropyl-W'-phenyl-p-
phenylenediamine
N-phenyl-N'-cyclohexy1-p-
phenylenediamine
N-phenvl-N'-sec-butyl-p-
phenylenediamine
N-phenyl-N'-(1,3-dime thyl-
butyl)-p-phenylenediamine
N-phenyl-N1-sec-octy1-p-
pnenylenediamine
Fle.xzone 3-C, Santoflex 36,
Cyzone IP, Eastozone 34,
Nonox ZA, A.0. 4 010 NA
Flexzone 6-H, Santoflex 66,
A.0. 4010
Flexzone 5-L
Antozite 67, Flexzone 7-L
Santoflex 13, UOP 588,
Wingstay 30 0
UOP 68 8
Other types
1,2-Dihydro-2,2,4-trimethyl- Santoflex AW, Polyflex
6-e thoxyquinoline
Nickel dibutyIdithiocar- NBC
bainate
Nickel isopropylxanthate "KPNI
Waxes
32
-------
In this process, the depolymerization of: vulcanized rubber-
occurs in-the presence of reclaiming agents and at elevated
temperature. Sodium hydroxide and calcium and zinc
chlorides are used as the defibering agents, pine oils and
plasticizers are used as swelling agents. Many cher.iicals
similar to plasticizers are also good reclaiming ageivcs;
e.g., di- and tr la Iky lphenol sulfides anc! disulfides, thiols,
amine compounds, and unsaturated compounds. Preferred
amines include aliphatic long-chain, C1()-Ci.'(, and primary
amines.
(b) Blowing agents - Blowing agents are used to
produce cellular rubber (foam): They must be finely dis-
persed and of fine size to give uniform pore product. The
cellular structure is formed by gases which are generated
within the compound during vulcanization, or dissolved in
a compound under pressure. Examples of blowing agents
include sodium bicarbonate, sodium carbonate, ammonium
bicarbonate, and ammonium carbonate. Some organic materials
which release nitrogen are also in use and are summarized
in Table 9.
(c) Organic activators - In some cases even the
addition of an accelerator results in a slow rate of rubber
cure. This rate can be increased by incorporation of or-
ganic activators. Examples of these compounds are given in
Table 10.
(d) Retarders - Prevention of premature cure during
the processing of rubber stock is important if fast accel-
erators are used to prevent rubber scorching. Some of the
retarding agents are listed in Table 11.
33
-------
Table 9. BLOWING AGENTS WHICH RELEASE NITROGEN1"
Chemical name
Formula
Trade name
Azodicarbonamide
0 0
II II
H 2NCN=NCNH2
Celogen AZ; Genitron AC,
Keraoore R-125, Porofor K-1074
Azoisobutyronitrile
CH i CH -I
! 1
NCC-N=N-CCN
1 1
ch3 ch3
Genitron AZDN, Porofor N,
Accto AZIB, Warecel 7 0
Diazoaminobenzene
c6h 5nhn=ncgh 5
Porofor D3, diazoaminobenzene
Azocyclohexylnitrile
C5Hi o (CN)N=N(CN)CSHJo
Genitron CHDM
M,N1-dinitrosopentamechylene-
tetramine
CH2 N C H 2
1 1 1
ONN CH2 NNO
i 1 1
CH y_~N CH2
Unicel ND, DNPT, Opex,
Vulcacel
N,N'-dimethyl-N,N1 -
din itrosoterephthalamide
C.sH1; (CON (NO) CH3) 2
Nitrosan
Benzenesulfonyl hydrazide
C6H5S02NHNH2
Genitron BSH, Porofor 3SH
3enzene-l,3-disulfonyl
hydrazide
CgHu (S02NHNH2)2
Porofor B-13
p,P'-Oxybis(benzenesulfonyl
hydraz ide)
0 (C6H,1S02MHNH2 ) 2
Celogen, Genitron OB, Porofor
DO-4 4
Diphenylsulfon-3,3" disulfony1
hydrazide
so2 (c6h1;so,niinh2 ) ,
Porofor D-33
4,4'-Diphenyldisulfonyl azide
(CGHi,S02N3 ) 2
Nitropore CL-100
-------
Table 10. ORGANIC ACTIVATORS 1
Composition
Trade name
Primary fatty amines
Alamine 7,46
Mono- and ciibenzylamines
DBA
Dipheny Icjuanidine
Guantal
phthala tc
Zinc salts of a mixture
Laurex
of fatty acids
Mixture of organic and
MODX
inorganic acetates
Dibutyl ammonium oleatc
Ba rak
Normal lead salicylate
Norma sal
Fatty acids and metal soaps
Table 11. COMMONLY USED RETARDERS1u
"
Chemxcal name
Trade name
Phtalic anhydride
Retarder E-S-E-N
Benzoic acid
Salicylic acid
i-laleic acid
Maleic anhydride
Terpene-resin acid blend
Turcujn S
N-mi trosodiphenylamine
Goodrite Vultrol,
Retarder J, Redax
-------
2.
Fabr ica tion111
The basic techniques applied to rubber and rubber latex in
the fabrication of rubber products are described in this
section. - The large number of products made of rubber and
rubber late:-: required the development of many specific
approaches to shape the product (hose, belt, molded goods),
combine it with other materials (fabric, wire), or produce
proper rubber consistency (hard rubber, foam, sponge). These
approaches vary based on product specifications. In general,
however, all rubber product fabrication processes consist
of (1") ' preparation of a rubber or latex compound, (2) forming
the compound into the desired shape (calendering, molding,
extrusion, dipping), and (3) product vulcanization or curing.
Additional auxiliary operations may include cutting, flash
removal, spraying, and product quality control.
Since the tire and inner tube industry is the major in-
dustry of this source (see Table 1) processing 66% of the
total rubber in the United States, a more detailed descrip-
tion of individual processing steps is given in Section
III.E.3. A process diagram is also shown for the production
of molded goods that consume 9.8% of the total rubber
produced annually. The rest of the rubber processing indus-
try consists of many other types of production, each con-
suming not more than 45 of the total rubber. Process
diagrams are not given for these production categories, but
they can be easily constructed based on inEormation presented
in tliis section.
a. Rubber Fabrication Techniques - Once the recipe is
selected for a given product type, the individual components
must be compounded or weighed, mixed, formed, and vulcanized.
As a plastic material, rubber rhay be spread, calendered,
36
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extruded, molded, cemented, caulked, puttied or wrapped into
virtually any shape; coated on cloth, plastic or metal;
sandwiched; or forced into cracks. Rubber is an extremely-
tough material and heavy machinery is needed to work it.
Working the rubber generates large amounts of heat which
must be properly controlled and dissipated. Rubber fabri-
cation steps include mastication, mixing and forming.
(1) Mastica tion - Mastication is a preliminary step used in
working natural rubber to lower its viscosity prior to the
compounding operation. The combination of heat and work on
crude natural rubber produces a physical and chemical change.
Highly masticated or soft rubber is used in friction com-
pounds, sponge stocks, and rubber solutions or cements.
Medium soft rubber is used in calendering compounds, while
lightly masticated rubber is used for stiff stocks.
Mastication is carried out at temperatures either below 55°C
or higher than 132°C. The intermediate temperatures influ-
ence rubber very little. Mastication is performed on a roll
mill (low temperature region), internal mixers or screw
plasticators (high temperature region of 150°C to 176°C).
The roll mill consists of two parallel horizontal rolls
rotating in opposite directions at slightly different speeds.
The rubber is worked by being pulled through the nip. The
temperature in the roll mill is controlled by passing cold
or hot water, steam, or hot oil through the hollow rolls.
The nip width is adjustable. Rubber comes out of the roll
mill as a sheet which is cut to proper size before further-
use .
The internal mixer such as the Banbury is a
device for rubber mastication. It consists
enclosed mixing chamber in which two spiral
more effective
of a completely
shaped rotors
-------
operate, as illustrated in Figure 1.
(•;-o
*17;'^
r;i
V-r.sj
>-•: -i. j-1
/ r1
I
'p)"-" 1/
/-/' !*•(... nn ^ bviDt-JC k»ic
fi i/'v::-:-. '
|(H3- ?) (o) )';>$
. \ /
' v
Figure 1. Cross section of a-Banbury internal
mixer mounted over a rubber mill1-'
Rubber is fed through a hopper. The two rotors rotate
in opposite directions at slightly different speeds and
are hollow to allow circulation of water or steam for
temperature control. The product mix from the internal
mixer is discharged into a two roll mill, producing rubber
sheets.
15McPher son, A. T., and Klemin.,- A. Engineering Uses of
Rubber, New York, Reinhold Publishing Corporation, Chap-
man £ Hall, Ltd, London, 1956. 490 p.
38
-------
h plasticator is actually an extruding machine feci by a hop-
per, with a largo screw carrying the material through the
machine and extruding it in the form o£ a cylinder. The
rubber cylinder is then cut and opened up to give a continu-
ous ribbon. Rubber sheets of desirable size can then be cut
from this ribbon for further processing. The plasticator
screw is hollow for circulation of water or steam to allow
temperature control. The plasticator cylinder is ^jacketed
for the same purpose.
Since plasticizers function best at elevated temperatures
such as those developed in the internal mixer and the plasti-
cator, a chemical plasticizer may be added during the masti-
cation step.
(2) Compounding - One of the most important stages in
rubber processing is compounding (mixing). It governs the
quality of the final product since all the process steps
that follow depend on an adequate and uniform mix. Mixing
must provide (1) a uniform blend of all the constituents of
the mix; (2) an adequate dispersion of the pigments; and (3)
uniformity in consecutive batches for smooth further pro-
cessing. Mixing can be carried out on a two-roll mixer or
an internal mixer such as the Banbury, Intermix, or Boiling
mixer. All of these mixers are designed for batch operation.
The batch size processed on a mill can vary depending on
mixing equipment capacity. Mills are available in sizes
ranging from 0.35 m to 1.07 m with . the smaller sizes being
more popular due to the better batch control they provide.
Mixing equipment capacity is 68 kg to 136 kg for a 2.13-m
mill and 4 54 kg or more for the largest internal mixers.
39
-------
To obtain good mixing, carefully selected individual ingre-
dients must be added in a specific order because some
materials mix with rubber better than do others.
After the raw rubber has been passed between the heated mill
rolls a few times it becomes sufficiently soft to adhere to
the front, slower moving roll. The distance between rolls
is then adjusted so that there is a "bank" of rubber in the
"bite" of the rolls. When the rubber is sufficiently soft,
additional compounding ingredients arc spread on the rubber
on the bank. The rubber is cut and covered over to aid in
dispersing the individual materials throughout the batch.
Intermix and Boiling mixers are very similar to the Banbury
mixer described previously. In the Intermix mixer the shear-
ing action takes place between the rotors rather than between
the rotors and the chamber wall. In the operation of the
Boiling mixer, the ram pushes the preweighed charge of
material down into the mixing chamber where it is forced
between helically Cluted rotors. Shearing action occurs
between the rotors and the chamber walls as in the Banbury.
A battery of roll mills is usually placed on the floor below
the internal mixers so that the .mixed compound may be discharged
by gravity to the mills on which it is sheeted.
Internal mixers can handle large batches in relatively short
periods of time. However, they are not suitable for the
addition of sulfur because their high operating temperature
could cause premature vulcanization or scorching. Conse-
quently, even though most of the compound ingredients are
added to the internal mixer, the sulfur is added in a subse-
quent operation on a roll mill.
4 0
-------
(3) Forming - The rubber slabs obtained from the mixing
mills may be immediately cut into disks or rectangular pieces
suitable for charging into a mold. The consistency of the
compound often determines how the rubber will be processed
and what -equipment can be used for building or making up
rubber articles. Host of the mixed rubber must be processed
into a form suitable for further fabrication. Processes
utilized here include calendering, extrusion, frictioning,
spreading, slabbing, and cutting.
A calender usually consists of three hollow revolving rolls
placed one above the other in such a way that the spacing
between them can be accurately adjusted. The temperature
on the rolls can be controlled by circulation of steam or
cold or hot water through the hollow rolls. The rolls can
be driven either at the same or different speeds. A calender
which takes the rubber passed through a mill is schematically
shown in Figure 2.
£ai ("~o.'Q COOllNO DPUMS
i
Figure 2. Diagram of the calendering process15
41
-------
The purpose of calendering is to form smooth sheets of
rubber compound of accurate thickness; it can also be used
to coat or imprecjnate fabric. Coating operations are per-
formed in either three or four roll calenders. The three
roll calender applies a coat to one side of the fabric and
the four roll calender coats both sides of the fabric.
When the use of fabric is required for reinforcement, as in
hose belting, fabric-inserted diaphragms, tires and footwear,
the fabric is usually rubberized by passing it through a
friction calender along with the rubber compound. In fabric
frictioning the center roll' of the calender is run hotter
and faster than the top and bottom rolls. This forces the
rubber into the mesh of the fabric.
Fabric rubberizing is sometimes accomplished by spreading
on the fabric surface a heavy dough prepared by blending a
suitable rubber compound with gasoline or other solvent.
The fabric is stretched and the dough is applied in a thin,
uniform layer by means of a knife mounted perpendicular to
the fabric. When the spreading is completed the fabric is
passed slowly over heating coils to evaporate the solvent.
The spreading process is applicable to cases in which either
the fabric or the compound is not adaptable to the friction
process.
Rubber compound obtained from calendering may be used in a
variety of applications in many different shapes. Calendered
rubber may be automatically cut into strips as it comes
from the cooling drums, die-cut to any desired shape by
means of a clicking machine, or cut to desired lengths by
means of a water-lubricated circular cutter.
42
-------
The process of extrusion involves forcing the rubber com-
pound through an extrusion machine. These machines operate
with either a cold or a warm rubber feed. Cold feed extruders
are longer than the warm feed type in order to permit suffi-
cient breakdown of the rubber compounds for smooth extrusion.
Basically, s. power driver, screw forces the rubber through a
cylinder to the front of the machine where it is forced
through a die. The extrusion cylinder as wall as the screw
may be equipped with cooling water or steam Eor temperature
control. Any number of dies are available to provj.de the
desired extruded shapes. Since the rubber expands after
being pushed through the die, the die must be smaller in size
than the resulting exurutied article, The axtruder nay be fed
by hand or by a force-feed system consisting of two feed
rollers. Hewer extruders operate under vacuum to eliminate
trapped air and moisture.
Extrusion is a very economical and widely used method of
processing rubber, both for making blanks for ir.old.ing an3 for
forcing rods, cubes, strips, channels, and gaskets in. a 'wide
variety of sizes and shapes. The operation sequence in the
extrusion process is shown in Figure 3.
Figure 3. Extrusion processeslj
-------
When it is intended to employ a compound as insulation or
jacket on a wire, or as a cover on a previously prepared
hose carcass, a side delivery head is used on an extrusion
machine. In this case a wire or a hose carcass is fed
through the. head in a direction perpendicular to the axis
of the extruder screw. The head is designed so that the
compound is deflected 1.57 radians (90°) and completely
surrounds the wire or hose carcass.
Some rubber articles may be produced directly by cutting
the milled rubber stock; e.g., if large pieces of heavy
gauge rubber stock are needed as blanks for molded rubber
articles, they are cut from mixing mill stock (made into
a slab of the proper thickness) by means of a knife and a
template. Similarly, tubed or extruded compound is cut as
needed using cutting machines which may be synchronized with
the extruder.
b. Fabrication of Rubber Goods from Latex - The first
requirement in production of rubber articles from latex
is to bring the rubber latex and all the compounding ingre-
dients into solution or dispersion form. Solution is used
when all of the ingredients are water soluble. Frequently,
the ingredients are not water soluble and it is necessary
to emulsify the liquid ingredients and disperse the solid
materials in water.
Dispersions are generally prepared from a coarse slurry of
powder with water containing small amounts of dispersing
agents and stabilizer. The slurry is then ground on a
suitable mill to give the desired particle size. The function
of the dispersing agent is to keep the particles suspended.
Typical dispersing agents are sodium 2-naphthylene sulfonate
and formaldehyde, and an alky 1*.'metal salt of sulfonated
44
-------
lignin. The amounts of dispe.
experimentally. To produce a
wetting agent is usually used
1% by weight.
rs.ing agents must be determined
satisfactory dispersion a
in concentrations less than
Dispersions are prepared using grinding equipment such as
colloid mills -which break aggregates but do not change the
particle size. Colloid mills are used for clay, precipi-
tated whiting, zinc oxide, etc. Grinding equipment that
reduces ultimate size and breaks agglomerates is used for
solids such as sulfur, antioxidants, and accelerators. Ball
and pebble mills, ultrasonic mills and attrition mills are
used for this purpose. Typical recipes and directions for
antioxidant such as Aminox and ultra accelerator such as
zinc dime thy Id i th iocarbona te (Methazate) are given in
Tables 12 and 13.
Emulsions are prepared by first making a coarse suspension
of ingredient droplets in water and then exposing this
mixture to an intense shearing in a colloid or ultrasonic
mill or a honogenizer (a machine that forces the emulsion
.through a fine orifice under high pressure). Emulsions can
be simply prepared by adding the material to a soap solution.
Soap can also be prepared quickly in the machine by adding
fatty acid or anionic parts such as stearic, oleic, or
rosin acid to a solution of potassium hydroxide or an amine
in water. Examples of emulsion recipes are presented in
Tables 14 and 15.
The preparation of the latex compound is a very simple opera-
tion consisting of weighing and mixing the proper amounts of
various solutions, emulsions, and dispersions. This is done
in a large tank with a mechanical agitator.
45
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Table 12. PREPARATION OF A DISPERSION OF AMINOX
SUITABLE FOR LATEX COMPOUNDING11'
Material
Weight
Procedure
A.
Water
O
CO
Add A to ball mill
B.
Water
22 . 8
Make up B separately and
add to mill
/vmmonia (28% N1-1,)
1.0
Add C and D to mill
Blancol
4 . 0
Ball mill 4 days - keep
cooling water on to
• • b
Dowicide A
avoid sintering Amino:-:
0.2
Case in
2.0
C.
KWK bentonite
2 . 0
D.
¦Amino:-:
TOTAL °
100. 0
200 . 0
3Trademark of GAF Corporation.
^Trademark of Dow Chemical Company.
CTotal solids, 54. 2",; active solids, 505.
Table 13. PREPARATION OF A DISPERSION OF METHAZATE SUITABLE
FOR LATEX COMPOUNDING 1 'l
Material
Weight
Procedure
A.
Water
70.0
Add A to ball mill
B.
Ammonia (28% NJ-h)
1.0
Make up B and add to ball
mill
Blancol
4 . 0
Add C to ball mill
Dowicide A
2 . 0
Ball mill 4 8 hr
Casein
2.0
Water
22.8
C.
Me thazate
TOTAL3
10 0 . 0
200 . 0
c\otal- solids, 53%'; active solids, 50%.
4 6
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Table 14. PREPARATION OF A NAUGAWHITE EMULSION SUITABLE
FOR LATEX COMPOUNDING1'4
Material
Dry
parts
We t
par ts
Procedure
Water (hot)
19. 0
Add Nopco 14 4 4Ba to hot water
with high-speed stirring
Nopco 14 4 4B
5. 4
6.0
Naugawhite
75 . 0
75 . 0
Add Naugawhite slowly, allowing
a few minutes between
addi tions
After all the Naugawhite has
been stirred in, continue
stirring for 15 min
TOTAL
1
1 o
CO
100. 0
3Nopco 1444B .is a highly sulfonated castor oil produced by
Nopco Chemical Company.
Table 15. PREPARATION OF AN OIL EMULSION SUITABLE
FOR LATEX COMPOUNDING1 '*
Material
Parts
Procedure
A. Mineral oil
70
Add A to B using an agitator
such as the Eppenbach
Homo-mixer
Oleic acid
1.5
B. Potassium hydroxide
1.5
Put emulsion through a
homogenizer to obtain
a very small particle
size and a high
emulsion stability
Water
27 . 0
TOTAL
100. 0
4 7
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Fabrication of rubber articles using compounded latex can be
done by a variety of methods. One of the simplest techniques
is to dip a form into the latex, and dry the thin film formed
on the foam at room temperature or in warm air at 4 9°C to
60 °C whil-e rotating the form to ensure a uniform film thick-
ness. Thicker films are made by multiple dipping.
Another technique for fabricating rubber articles uses
porous formers, or porous molds, made of plaster of paris
or unglazed porcelain with smaller pore size than the small-
est rubber latex particles. The rubber particles are
filtered out by this material and latex coagulates due to
the presence of calcium ions in the plaster to form a film.
The molds are dried in an oven at 60°C for one hour. This
can be repeated for 30 minutes after the articles are re-
moved from the mold. For example, dolls and squeeze toys
are manufactured using this technique.
Since the rubber particles in latex are negatively charged,
electrodeposition has been used to coagulate rubber and
make rubber articles. Evolution of oxygen' on the anode
produced oxidation of the product and caused porosity in the
article. Electrodeposition was therefore abandoned but
essentially the same coagulation can be attained by using
chemical coagulants.
A thin layer of a chemical coagulant is produced by dipping
the former in the coagulant solution and evaporating the
solvent, preferably alcohol. The thin layer of coagulant
can be produced either directly on a clean former or on a
former that is coated with a very thin layer of the latex.
The former is then dipped in the latex. When the film
attains the desired thickness it is washed m hot water at
60°C to 71°C for about an hour'to remove the coagulant and
4 8
-------
all other water soluble ingredients. The film is then dried
in air at room temperature, and the article is cured in a
66°C oven.
Typical coagulants are calcium chloride or calcium nitrate
in solution of denatured ethyl alcohol. They are used in
mixture with a nonionic surfactant and a release agent (a
fine, insoluble powder such as talc, clay or diatomaceous
earth) which is suspended in the coagulant. The surfactant
and release agent are used to aid in wetting the former and
releasing the article from the former, respectively.
Another variety of this process uses a gelling agent (elec-
trolyte with a weak coagulating effect such as ammonium
salts and sodium fluorosilicate) in metal molds. This
method offers the advantage that latex sets to the gel with
no change in volume and without distortion.
Some rubber products may be made by extrusion of the latex.
For example, latex thread is produced by extrusion of the
latex compound through fine orifices into a coagulant bath
which gels the thread. The thread is then toughened, washed,
dried and cured. A dilute acetic acid is usually used as
the coagulant bath.
The broadest application for both latexes, natural and
synthetic, is foam sponge. There are two basic processes
available, the Dunlop and the Talalay process, applied in
different variations. In the Dunlop process, which is the
most commonly used, the latex is whipped to a froth by the
mechanical incorporation of air into the latex. The Talalav
u
process produces the froth by chemical rather than mechanical
means. Hydrogen peroxide and an enzymic decomposition
catalyst are used for this pur-pose. Oxygen produced by the
4 9
-------
decompositon of the peroxide foams the latex mix. The
foam is chilled ana CO? is introduced to gel the latex.
Further treatment is the same as in the Dunlop process.
The frothed structure must be set using a coagulant or a
gelling agent. Sodium silicofluoride (Na^SiF^) is widely
used in this application. Zinc oxide is also believed to
take an active part in the process. Sodium silicofluoride
decomposes and forms sodium fluoride (NaF), silicon tetra-
hydroxide (Si(Oil)i,), and hydrofluoric acid (HF). Zinc
apparently reacts with the fatty acid latex stabilizers
forming a soluble soap. This destabilizes the latex parti-
cles, causing them to coalesce and form a gel. The Si (OH) t(
may also form very fine particles which could adsorb
stabilizer and further enhance gelation. In very stable
latexes, some secondary gelling agents may be utilized to
induce gelation. Cationic soaps, other salts and amines
are used for this purpose.
Whipping can be done either continuously or in a batch pro-
cess. After the gelling agents are added the foam is poured
into molds and cured. Additional curing is done after the
product is removed from the mold.
Ammonium acetate or ammonium sulEate, in combination with
zinc oxide, are employed as the gelling agents in the pro-
duction of foam backings for various fabrics such as carpets,
scatter mats, and upholstery fabrics. Ammonium hydroxide
is the product of the reaction. Once gelation occurs the
foam is spread directly on the fabric, or it is spread on
a belt and transferred wet, to the fabric. The gelling is
carried out at elevated temperatures usually by means of
infrared lamps.
50
-------
Latexes are also applied to the undersides of carpets, rugs,
and upholstery fabrics. This is done after a film forming
adhesive is applied to the underside of the fibrous mater-
ial. Low-cost latexes that can accept a high loading of
pigment and provide desirable anchorage for the fibers are
used in this application; e.g., medium styrene-butadiene
latexes and self-curing carboxy modified SBR latexes. Pig-
ments utilized here include whiting and soft clays plus
some titanium oxi.de for opacity.
Nitrile latexes and medium styrene-butadiene mixed v/ith
beaten paper pulp arc used to coat paper and provide ex-
cellent strength, elongation, bursting strength, internal
bond, and tear strength. Similar application on asbestos
fibers produces excellent materials for gaskets, linoleum
bases, etc. The pulp coating may also be accomplished by-
passing the paper web through a latex bath. The amount of
coating is controlled by the speed through the bath and by
the concentration of the latex bath. Vinyl and acrylic
latexes may be applied to paper as a decorative coating to
provide a high gloss paper stock. Latexes are also used as
adhesives for highly pigmented clay coating and pigment
binders applied to paper and paperboard.
c. Vulcanization - Vulcanization of rubber products is
done at elevated temperatures and can be carried out under
numerous conditions. Some articles are cured in their
manufacturing step if sufficient heat is generated in the
process (e.g., molded products); other afticles require a
separate curing step (e.g., latex products and tires).
51
-------
(1) Mold curing - Molded rubber parts are formed and vulcan-
ized in a single operation by the simultaneous application
of pressure and heat. Compression is the oldest type of
molding and consists of placing preshaped rubber into a mold
and closi-ng the mold under pressure, allowing the rubber to
fill out the mold cavity. The heat from the heated platens
of the p.ress in conducted through the mold and vulcanizes
the rubber. The platens arc usually heated by circulating
steam through holes drilled in them. Occasionally, electri-
city or gas burners are used for this purpose.
The rubber overflow or flash must be removed from the
article. This operation is labor demanding and expensive
because it requires hand labor. If possible the rubber
parts are dipped in dry ice where the thin rubber flash
becomes brittle and breaks off. This method can be used
only if the main body of the part is large enough not to
become cool and inflexible and if the rubber is not freeze
resistan t.
In transfer molding the uncured rubber stock is transferred
from one place to another within the mold, allowing the
manufacture of complex shapes and articles containing metal
inserts. Transfer molding permits closer dimensional
control and generally reduces flash. Normally the rubber
is placed in a transfer cavity which is fitted with a ram
or piston. The force applied to the ram or piston and the
heat from the mold cause the rubber to be softened and
spread in. the molding cavity and cured at the same time.
Injection molding is the same as transfer molding except
that the soft rubber compound is injected into the molds.
A screw mechanism is utilized to force unvulcanized rubber
into a tightly closed mold. Forcing the rubber through
52
-------
small passages under high pressure increases the temperature
of the injected compound and cures the rubber. In order to
make injection molding profitable, very short cycles are re-
quired, generally in the 4 5 second to 90 second range. Due
to these short times, a curing temperature of 204°C is re-
quired .
In molding thick articles long curing times are needed
because of the low thermal conductivity of the rubber. This
problem is partially overcome by dielectric heating oE the
blank before it is placed in the mold. This heating also
improves the flow of the compound in the mold.
The processing steps involved in the production of molded
goods are shown schematically in Figure 4.
An example of more complicated molding is that of the pneu-
matic tire in which a steel mold shapes the exterior surface
of the tire from bead to bead, and the pressure during cure
is supplied from a flexible bag acting as a diaphragm that
forces the uncured tire against the mold surface. The dia-
phragm, an integral part of the press, is made of a resin
cured butyl stock which lias extremely good heat resistance.
Steam or hot circulating water is introduced to the inside
of the diaphragm to cure the tire from the inside. (Tire
vulcanization is further described in Section III.B.3.)
(2) Curing of other rubber articles - Extruded and some
molded articles may require additional curing. The most
common method of vulcanizing these articles is to place
them in pans that arc set on a truck and rolled into a
large steam chamber or- heater for vulcanization. Varnish
or lacquer may be applied before vulcanization to produce a
smooth, glossy product finish.
53
-------
Figure 4. Processing steps in the production of molded goods
-------
Rubber articles that would sag or flatten under their own
weight before they could completely set up must be supported
during vulcanization. In most cases such articles are em-
bedded in talc or powdered soaps tone. Gum rubber tubing is
placed on a mandrel or rod and wcapped with fabric which is
subsequently removed. Hose and insulated wires and cables
may be supported during vulcanization by means of a lead
sheath that is extruded over them. The vulcanization step
takes about 30 minutes at 140°C to 150°C.
The continuous vulcanization of insulated wire represents a
special case in which the wire is rubber covered while
passing through an extruder (as described in Section III.B.2.
a(3)), then run directly into a tube containing steam at
1.3 8 MPa to 1.7 2 MPa. Such a tube may be 3 0.5 m to 61 m long
and the wire resides in it for approximately 15 seconds.
Large cables are usually processed in vertical machines but
horizontal and catenary types are also available.
Hose cured in lead is another special case, involving a
combined mold and hydrolytic cure. In this process, 'the
prepared construction is surrounded with a lead wall ex-
truded through a die. The inside surface of the lead
casing gives the desired design (usually ribbed). Long
lengths of the leaded hose are wound on drums, and fittings
are applied to the two ends to permit circulation of heated
water under pressure. The drum is then placed in a steam
autoclave and steam is applied externally. Thus, the lead
casing is in effect the mold, and the hose is forced firmly
against the mold by hot water circulating through the in-
side under pressure. After cure, the lead jacket is split
and removed.
55
-------
Continuous curing is utilized in the production of belting
or floor matting. A continuous length of belt is made
without splices or overlapping and cured in a "Roto-Cure."
This press consists of a rotating vulcanizing drum about
1.5 mi in .diameter. A belt of highly polished steel is
pressed tightly against this curing drum around a large
portion of its circumference. The compound is fed into the
space between the curing drum and the belt and vulcanizes
during its trip around the drum.
Sponge rug underlay and sheet sponge are made by placing
a compound containing a chemical blowing agent between two
mesh or cloth belts that travel between two long platens.
The blowing agent decomposes before the curing progresses
significantly and expansion takes place to the desired
thickness, governed by the spacing between the platens. At
the end of the platens, the cure has been completed and the
sponge is rolled up.
Continuous curing in a liquid is utilized in the production
of both solid and cellular extruded goods. In this case,
the uncured stock passes directly from the extruder into a
liquid heat transfer medium which is maintained at tempera-
tures from 204°C to 316°C. Eutectic mixtures of metals
(e.g., 53% bismuth - 42% tin) or salts and heat stable
organic liquids such as polyalkylene glycol are used in
these applications. Some techniques utilize a fluidized
bed for the heat transfer medium. For travel through the
curing tank the product either passes through a series of
driven rollers or is submerged in a lighter density organic
liquid and floated on the bottom layer of molten metal.
The latter method is satisfactory for solid extrusions.
Hollow sponge extrusions float on the organic liquid and
these have to be driven throug'h the curing bath.
56
-------
If curing at elevated pressure is desired, water is used in
place of steam. Rubber lined vessels are steam cured unless
they are too large to fit in a steam autoclave. Boiling
water is used in such cases.
7\ir is sometimes preferred over steam in the vulcanization
step, especially when moisture must be avoided, or staining
or water spotting must be prevented. Hot air at either
atmospheric or elevated pressure, 103.4 kPa to 27 5.8 kPa, is
usually used, but ammonia gas is sometimes applied to pro-
duce a glossy surface on footwear. The air is circulated
at a rapid rate to provide even heating of the article and
avoid bad spots in the vulcanizates. Waterproof goods, boots
and shoes are vulcanized in hot air ovens.
Articles made from rubber latexes are vulcanized using the
same principle as those for dry rubber compounds. Lov;
temperature curing is completed at about 104°C whereas hard
rubber latex compounds require about 14 9°C. Hot air, steam
or hot water cures are most frequently used.
3. Tire Manufacture
As shown in Table 1, the tire industry processes 66% of
the total rubber processed in the U.S. and is the most impor-
tant industry of the rubber processing source discussed in
this document.
Tires are built from several parts as illustrated in Figure
5. There are three variations in tire construction: con-
ventional, belted bias, and radial ply tires, as shown in
Figure 6. Different rubber compounds are used in making
the several tire parts because each part performs a different
function. The carcass (made o-f body fabric or cord plies),
57
-------
the impact plies (which are placed between the body plies
and the tread to provide extra impact resistance), the bead
assembly, the tread, and the tire wall are all made from
different rubber compounds. Tire manufacturers use both
synthetic and natural rubber, the latter mainly for steel
belted and large size tires. The basic recipes for rubber
compounds are generally very similar except that synthetic
compounds require different black loadings, somewhat more
softener, less sulfur, and more accelerator.
Figure 5. Cross s.ection of a Lire'5
-------
COMVEHTiONALTIBE
(2 or4 pSics]
v"1
A< -vXKtftj
v-T'' v-. \t'i
' ' \ w"v>
i t /
r _ r
W'S '
t».s
<-\
Body ply l- j
cords run at bias anyiu
•BELTED SiAS TIRE
p::-a*r.i; ,1
* *. '
1^5
\iS/ /i ) j^Tread
! ..^'stabilizer
; ^ belts
Body (i!y cords
run at bins anyle
RADIAL
ply
\ %s '
\/^;. '•'
/\
-------
The basic steps involved in tire manufacturing are schematic-
ally shown in Figure 7. Recipes for each specific part of
the tire are selected and the compounds are prepared using
roll mills and Banbury mixers. Table 16 lists typical
compositions of the rubber compounds for different tire parts.
All ingredients except sulfur and the accelerator are added
to the rubber in a Banbury mixer. The batch is then dumped
on a roll mill, shown earlier in Figure 1, located below the
mixer for addition of the curing ingredients. Compounded
rubber is made into standard sheets whic!i» are then used to
manufacture the individual tire parts.
Carcass plies are made of cord fabric insulated with rubber
compounds. A variety of carcass materials are available to
the tire manufacturer including cotton, rayon, nylon, poly-
ester, steel wire, and glass fiber; the last two materials
are used in radial tires. Today, very little cotton cord
is used in pneumatic tires. Cotton has been replaced by
rayon and more recently by nylon. The increasing popularity
of radial tires has increased the use of steel wiring and
glass fiber in tire manufacture. Selection of the cord
fabric depends primarily on cost because tire cords repre-
sent a large portion of the cost of tires.
Rubber compound used to manufacture tire plies must adhere
to the cord fabric and have enough tack to hold together
while the green (unvulcanized) tire is being assembled and
cured. Impact plies are built somewhat tougher than inner
plies since they must remain intact to divert road shocks
and bind the rigid carcass of the tire to the tire tread.
Both sides of cord plies for the tire carcass are coated at
once on a four roll calender.
60
-------
RUBBER,
CARBON BLACK,
FINISHED PRODUCT
Figure 7. Tire plant process flow diagram
-------
Table 16. TYPICAL COMPOUND COMPOSITIONS FOR
TIRE PARTS15
Parts by
Tire part
Component
weigh t
Inner carcass or body
Natural rubber
100
plies (truck tires)
SRF black
25
Zinc oxide
3
Stearic acid
2
Sof tener
5
Antioxidan t
1
Sulfur
2.8
Primary accelerator
0 . 75
Secondary accelerator
0. 15
Outer carcass or body
Natural rubber
100
plies (truck tires)
SRF black
15
EPC black
20
Zinc oxide
3
Stearic acid
2
Sof tener
5
Antioxidant
1
Sulfur
2.3
Primary accelerator
0 .75
Secondary accelerator
0.15
Impact plies
Natural rubber
100
EPC black
40
Zinc oxide
.J
Stearic acid
2
So ftener
5
Antioxidant
1
Sulfur
2 . 80
Primary accelerator
0.80
Secondary accelerator
0 . 20
62
-------
Table 16 (continued). TYPICAL COMPOUND COMPOSITIONS
FOR TIRE PARTS15
Tire part
Component
Parts by
weight
Beads
Natural rubber
100
SRF black
120
Zinc oxide
8
Precipitated whiting
15
So £ tener
11
Stearic acid
5
Sulfur
3
Accelerator
].. 5
Treads
Natural rubber
100
EPC black
4 5
Zinc oxide
3
Stearic acid
2
Softener
3
Antioxidant
1. 50
Sulfur
2 .75
Accelerator
0.90
Inner tubes
Natural rubber smoked sheets
100
Peptizer
1
Zinc oxide
4
Fine thermal carbon black
40
An tioxidant
2
Para ffin
1
Sulfur
1.5
Primary accelerator
1.4
Secondary accelerator
0.2
63
-------
Its relatively rough surface texture allowed natural rubber
stocks to be applied directly to cotton cord. This is not
quite feasible with rayon and nylon cords which must be
coated with an adhesive before the cord fabric can be coated
with rubber compound in the calender . Medium styrene-buta-
diene and butadiene-styrene vinyl pyridiene latexes are
usually used in this application. Vinyl pyridine latexes
are universally used for nylon tire cord. A typical tire
cord dip solution is given in Tabic 17.
Table 17. TYPICAL TIRE CORD DIP SOLUTION11'
Ma terial
Dry parts
Wet parts
SBR type 2 00 0 latex at 4 0%
80
200
VinvIpyridine latex, at 4 7%
20
43
Stabilizer (20"; Dresinate 731)
1
5
Water to 2 05, solids
78
Resin solution (6.5%)
17 . 3
266
Total
118 . 3
592
Resin solution formula
Water to 6.5%
238 . 5
NaOH
0 . 3
0 . 3
Resorcinol
11.0
o
r—1
«—1
Formaldehyde (37%)
6 . 0
16 . 2
Total
17 . 3
266.0
In the normal sequence of operations, ply fabric is passed
through the adhesive dip solution, the excess dip is removed
the coated fabric is dried to a moisture level less than 1%,
the rubber compound is calendered on both sides of the cord
fabric, and rubber cement is applied to the carcass. The
last step is necessary only Co'-r carcass plies with a high
6 4
-------
percentage of synthetic rubber compounds because the tack
of synthetic rubber is insufficient to stick properly to
the vulcanized rubber. Finally, the fabric is cut to a
specific angle and the required, width on a bias cutting
machine.
Wire bead, made of several strings of high carbon steel is
used to keep the tire on the rim. Each strand is coated
with rubber compound while passing through an extruder.
Several strands are passed simultaneously through the die
of the extruder, then rolled together to make the bead.
The bead is wrapped with rubberized square woven fabric,
then rewrapped with the same fabric, the edges of which
extend upward into the sidewall where they can be anchored
into the lower sidewall of the tire.
The tread and sidewall of the tire are formed by extrusion
through dies. The extruded profile is designed to provide
sufficient rubber to fill in the tread and sidewall pattern
in the mold.
Tire tread is made of two sections: the cap, which contacts
the road; and the base, the section next to the carcass.
Since the two sections are made of different rubber com-
pounds, dual extruding units have been developed. Good
adhesion between the cap and the base is important, and in
dual extrusion these two parts are plied together hot. Some
extruding machines produce the cap and base already joined.
Passage through a water bath cools and shrinks the continuous
tread slab, which is then cut to the correct length for tire
assembly.
Tires are assembled on rotating drums of a diameter slightly
larger than that of the tire. \ Individual tire parts are
65
-------
supplied to the builder in a form that allows the fastest
assembly of the tire. Carcass plies are cut to the proper
angle, width, and length, and may be delivered in rolls
that allow unreeling of the fabric without strain (to avoid
angle distortion), or in bands of two to four plies. The
treads and sidewalls are also delivered precut to length.
Synthetic rubber tread is.delivered with crude rubber cement
on its underside and ends to ensure proper adhesion to the
tire carcass.
Four to eight cord plies are applied to the drum without
stretching; each is tied under and over the bead in a
manner which securely locks the bead. Natural rubber plies
should have enough tackiness to adhere to themselves. Syn-
thetic rubber plies are coated with a rubber cement to
provide sufficient tackiness. If impact plies are used,
they are added next, followed by the sidewall and tread
sections. At this point the assembled tire is cylindrical
in shape.
Usually, the whole tire is assembled on the drum by one man,
but machines have been developed that automatically rotate
the drum through several stations for addition of the
successive parts. The drum is then collapsed to release
the tire, which gains its final shape during vulcanization
in the mold. The inside contour of the tire is formed by a
caring bag placed inside the tire. The bag fulfills two
functions: it gives the tire the proper shape and it pro-,
vides a container into which heat and pressure can be applied
to vulcanize the inside of the tire. Heat and pressure are
supplied by various combinations of steam, air, and water.
Tire shaping and curing equipment have undergone several
developments. The curing bladder is an integral part of a
66
-------
new curing press. This combines the forming and curing
operations in a single machine and eliminates the labor of
inserting and removing the curing bag. Because the bladder
is a part of the press and also is thinner than the separate
bags, more effective use of internal heat in curing the tire
and a significant reduction in curing time are achieved.
Tires are vulcanized at 100°C to 200°C for 20 to 60 minutes.
Longer times are required to cure large truck tires.
C. GEOGRAPHICAL DISTRIBUTION
Two states, Ohio and California, contain over 25% of the
1500 rubber product plants in the United States. In contrast,
33 other states account for 255; of the total, while the re-
maining 50% of the plants are found in 15 states -with 25 to
85 plants per state. The largest number of tire and inner
tube plants are found in cities such as Akron, Ohio and
Los Angeles, California (with population densities exceeding
50 0 persons/km2).
Table 13 is a summary of the product type and number of
rubber producing plants in the United States, by state.
Figure 8 is a graphic representation of the total number of
plants on a state by state basis.
Rubber product plants are located in the population and
manufacturing centers of the country, particularly in the
East North Central (Great Lakes) region. In individual
categories, states with 2 5 or more total plants per state
contain approximately 7 5% of the plants in the category
rubber products, N.E.C. Nine states (Ohio, California,
Tennessee, Alabama, Pennsylvania, Illinois, Texas, North
Carolina, and Oklahoma) contain 50"o of the tire and inner
tube manufacturing plants.
67
-------
Table 13. SUMMARY OF RUBBER PRODUCING PLANTS 31' PRODUCT TYPE1"5
n
Fabricated
/
Ruteer and
Rubber ar.c!
rubber
,
Tires and
plas tics
plastic hose
products
Reclaimed ¦
State
inner tubes
footwear
and belting
" N . E . C . a
rubber ^
Total
Aiaoama
J 1C
.!
3
3
1
2 5
Ala ska
C
0
1
1 2
0
T
Arizona
1
0
i
2
0
4
Arkansas
5
2
1
¦c-
1
14
Cali rcrnia
15
3
5
14 4
2
169
Co T: o r ado
1
e
2
2
0
COliT^CZlCLZ
3
£
-------
Table 13 (continued). SUMMARY OF RUBBER PRODUCING PLANTS BY PRODUCT TYPE1-5
Fabrica ted
Rubber and
Rubber and
rubber
Tires and
plas tics
plastic hose
products
Reclaimed
State
inner tubes
footwear
and belting
N.E.C.a
rubber
To tal
Nebraska
1
0
1
7
0
g
Nevada
3
0
1
2
0
6
Ncw Hampshire
2
5
2
10
0
19
New Jersey
3
7
2
63
0
80
New Mexico
1
0
1
2
0
4
New York
4
7
4
67
1
83
North Carolina
7
2
2
17
1
29
North Dakota
1
0
0
5
0
6
Ohio
27
5
12
169
4
217
Oklahoma
7
2
1
7
1
18
Oregon
3
2
1
4
0
10
Pennsylvania
8
9
4
48
1
70
Rhode Island
1
3
1
5
0
10
South Carolina
4
1
1
14
0
20
South Dakota
1
0
0
5
0
6
Tennessee
11
4
2
13
1
31
Texas
7
2
2
36
1
48
Utah
1
0
1
2
0
d
Vermont
2
5
2
10
0
.19
Virginia
5
2
1
17
1
26
Washington
4
2
1
4
0
11
West Virginia
2
1
1
11
0
15
Wisconsin
4
1
2
35
1
43
Wyoming
1
0
1
2
_0
4
TOTALS
202
106
90
110 3
21
1522
aMot elsewhere classified.
^Es'cimate .
-------
Figure 8. Geographic distribution
>
V.
\J
product plants i
in
the U . S
-------
Table 19 gives a summary of production capacities by state
for three categories: tires and tubes, rubber and plastics
footwear, and rubber and plastic hose and belting. Seventv-
five percent of the tire ana tube production is located in
13 states: Ohio, California, Tennessee, Pennsylvania,
Michigan, Alabama, Mississippi, Massachusetts, Iowa, V7iscon-
sin, Texas, Illinois and Kansas.
71
-------
Table 19. STATE BY STATE PRODUCTION OF RUBBER GOODS1'-'11'9
S tate
Tire and tube
production,
millions
of units/yr
Rubber and a
plastics footwear,
millions of
units/yr
Rubber and
plastic hose
and bel,ting,c
Gg/yr
Alabama
31
11
12
Alaska
--
--
4
Arizona
--
—
4
Arkansas
4
6
4
Californ ia
33
2
20
Colorado
2
--
4
Connecticut
6
11
4
De lav/are
--
--
--
Florida
--
5
4
Georgia
6
3
4
Hawai i
—
--
—
Idaho
--
--
1
Illinois
10
4
14
Indiana
7
3
1
Iov/a
15
--
11
Kansas
11
--
11
Kentucky
8
3
4
Louisana
1
6
4
Maine
1
17
S
Maryland
9
3
4
Ma ssachnsetts
15
14
8
Michigan
23
2
14
Minnesota
--
—
5
Mississippi
15
J
4
Missouri
—
2
11
Montana
--
--
4
Nebraska
5
aEs timates .
-------
Table 19 (continued). STATE BY STATE PRODUCTION OF RUBBER GOODS
Tire and tube
Rubber and
Rubber and
produc tion,
plastics footwear,3
plastic hose
millions
millions of
and belting,
S ta te
of units/yr
units/yr
Gg/yr
Nevada
_ —
2
New Hampshire
--
14
8
New Jersey
1
7
8
New Mexico
--
—
4
Nov/ York
1
7
16
North Carolina
6
6
8
North Dakota
--
--
--
Oh io
53
5
87
Oklahoma
2
6
5
Oregon
1
--
4
Pennsylvania
24
10
16
Rhode Island
--
8
4
South Carolina
2
3
4
South Dakota
--
--
Tennessee
24
: :
8
Texas
12
6
9
Utah
--
--
2
Vermont
--
14
8
Virgin ia
4
5
4
Washington
1
1
4
(vest Virginia
--
3
4
Wisconsin
12
1
7
Wyoming
—
—
2
TOTALS
340
200
390
aEstimates.
-------
SECTION IV
EMISSIONS
A. LOCATIONS AND DESCRIPTIONS
Emissions from rubber processing plants are a function of
the unit operations performed and the chemical substances
used during processing. The materials omitted include
particulates (carbon black, zinc oxide, soapstone, oil iiusts,
etc.) and hydrocarbons (volatilized rubber chemicals, rubber
impurities, ere.). These materials are emitted from the
following unit operations: compounding, forming, building,
and curing. The emissions from each of the unit operations,
specifically for tire manufacturing are discussed below.
1. Compounding
The blending of ingredients used in rubber processing is
performed in batchwise operations using rubber mills or
internal (Banbury) mixers.16 These units typically handle
68 kg to 136 kg per hour of blended rubber stock. The
ingredients which are compounded (blended) in this operation
are:1&
1 5 Daniel son, J. 7\. Air Pollution Engineering Manual, 2nd
Edition. Air Pollution Control District, County of Los
Angeles. U.S. Environmental Protection Agency, May 1973.
7 4
-------
Base polymer or blend
Vulcanizing acjents; e . cj. , sulfur, sulfur monochlor icle ,
selenium, tellurium
Vulcanizing accelerators; e.g., aldehyde amines,
cjuanidines, and thiuram sulfides
Accelerator modifiers; e.g., activators and retarders
Ant.idegradants; e.g., antioxidants, an tiozonants,
protective waxes, inhibitors of metal-catalyzed
oxidation
Reinforcing fillers; e.g., carbon blacks, minerals
Processing aids; e.g., chemical peptisers for poly-
mers, softeners, plasticizcrs, dispersing aids,
tackifiers, Factice'^, and lubricants
Coloring agents, both organic and inorganic
Diluents; e.g., inert mineral fillers, organic
materials, extending oils
Specific additives; e.g., blowing agents, fungicides,
fibrous materials
Reclaimed or vulcanized rubber
In the compounding operation, the various materials must be
added in a specified order to provide the desired rubber
stock physical properties. The rubber is added to the mixer
first, followed by accelerators, plas ticizers, reinforcing
pigments, antioxidants, and any inert fillers or coloring
agents. The vulcanizing agent is always added last to
prevent vulcanization of the rubber during compounding. The
order of addition of materials to the compounding unit de-
termines the order in which materials are emitted.16
Emissions from compounding consist of particulates and
hydrocarbons. The particulates are solids (carbon black,
zinc oxide, soapstone, etc.) and liquid aerosols (organic
additives).16 The hydrocarbon vapors oriciinate from im-
purities in the rubber and from the organic additives.
Particulate emissions occur when the additives are intro-
duces into the batch. The resultant cloud has an opacity
75
-------
gf 53 to 50% (per EPA Method No. 9). This cloud persists
for a few seconds to several minutes and the particulates
have diameters less than 15 :im. Hydrocarbon emissions occur
as a result of the heat generated during the mechanical mix-
ing of the batch.1°
Compounding units are equipped v;ith exhaust hoods that
remove the heat generated by the mining action. They also
remove particulate and hydrocarbon emissions from the work
area. Bag filters are employed to recover the solid par-
ticulates for recycle within the plant. ] 6 , ,j[r ^
2. Curing
Curing (vulcanization) is a batch process for molded pro-
ducts (tires, mechanical goods, etc.) and can be a continuous
process for extruded goods (sheets, strips, etc.). Curing
temperatures typically range from 10G°C to 200°C but may be
as low as 25°C or as high as 30C,oC for specialized stocks
and processes. Curing times typically range from 20 minutes
to 6 0 minutes but can be several days. The time required
for vulcanization is a function of temperature and stock
thickness.17
Vulcanization temperatures (100°C to 200°C)_result_in_the_
emission of organic materials from the rubber stock. Theo-
retically, these emissions can occur via two distinct
mechani sins, which are: (1) the volatilization of species
present in the stock; and (2) the formation of new com-
17Rappaport/ S, m. The Identification of Effluents from
Rub-ocr Vulcanization. University of North Carolina.
Chapel Hill. Ph.D. Thesis. '1274.
76
-------
pounds by chemical reactions. In the case of tire manu-
facturing, it has been shown that the discharges are the
result of volatilization rather than chemical reaction
products.17 In addition, the emission of low boiling com-
pounds .(G5 to C8) has been shown to be one to two orders of
magnitude greater than the discharge of high boiling compounds
(C]o and above) ') The materials volatilized, the source of
each material in the stock, and the relative concentrations
of the materials emitted are presented in Table 20. The
raw data used to generate the relative concentrations for
six of the compounds are presented in Tabic 21.
The available literature indicates that emissions occur
primarily among ingredients which are either .liquids at
room temperature or solids with melting points at or below-
curing temperatures. On this basis, the possible species
emitted can be determined as indicated below.17
(a) Polymer or Blend Vola tiles - General purpose polymers
do not decompose until pyrolysis temperatures (300°C to
400°C) are reached. Depolymerization reactions have been
indicated only upon continued heating at 175°C to 225°C for
several hours. Curing operations of much shorter duration
result in little or no breakdown. Hence, polymer emissions
will be the result of residual monomer and impurities from
the manufacturing process ana should represent less than 1 %
of total polymer by weight. However, monomers are suffi-
ciently volatile that appreciable amounts may be lost in
procuring operations such as milling and calendering. Typi-
cal boiling points are 1-'15°C for styrcne, 78°C for acryloni-
trilc, and 59.4°C for chloroprene.
(b) Antioxidants and Antlozonants - In most cases, emissions
of phenolic compounds are higher than those of amines. Total
77
-------
Table 20. MATERIALS EMITTED DURING RUBBER VULCANIZATION17
Material emitted
Source in rubber stock
Relative , .
¦ &, b
concentra cj.on ,
ppb by
volume
Toluene
Polybutadiene rubber
1, 120
4-Viny1-1-cyclohexene
Polybutadiene rubber
71
Et hy1 ben zene
Aromatic oil extender
78
m-Xylene
Aromatic oil extender
(35)
p-Xylene
Aromatic oil extender
(35}
S t y r e n e
Stvrene-butadiene rubber
84
t-Butylisothiocyanate
(90)
1,5-Cyclooctadiene
Polybutadiene rubber
6 . 3
Benzothiazole
Accelerator
(30)
N-sec-butylaniline
An tiozonan t
(30)
1.5 j 9-O'c lodoaeca-riene
" j i
Polybutadiene rubber
15 . 3
Methyl naphthalenes
Aromatic oil extender
<9z-:
Butadiene trimer
Polybutadiene rubber
(15)
Ethyl naphthalene
Aromatic oil extender
(10)
D i me t h y1 naphthalene
Aromatic oil extender
(10)
Diphenyl guanidine
Accelerator
(100)
aRelative concentrations were obtained by sampling the atmosphere within
the curing room. The values reported indicate concentrations of the
individual compounds within the curing room.
^Parentheses around data indicate estimates of concentrations made by
Monsanto Research Corporation from Rappaport's published raw data.
-------
Tab
j 2 1 CuS
r.-G c:c-.cl
:.Tr_\Tio:.s
OF Sr".CCTr
a,! 7
D CC'PW ;v.
ConC_-riL I 1 Otl
5 ior Odch T.-lJisu: cr
ioncr o;_b b
^olu.TiC
Co-.;*ou:v'i
1
2
3
4
5
s
7
3
9
•"'jc.n
doviotior
.rtor, 1
Tol ii'^nc
1,500
1,290
1, 190
SS7
99?
] , 530
1 , M0
832
660
1, 120
301
20.7
•'.-Vinyl -1-c,. ;loh--=^a
G'S.5
97 . 7
66 L
56.0
70.G
77 .7
71.6
60.6
71 0
8.-.2
9. 1
tthy] hcir.^nC'
SI.6
1 2b
gs.o
53.-1
82.3
90.0
"6.5
60 5
53.3
73. 2
22.7
22.3
SLyrcno
56. 3
130
7Q.-;
61.5
83.22
86.7
95.6
67.5
61. 6
8-J. 6
21 _>
19.5
1, 5-Cyc loo? lad l
8.19
7.7 1
5.95
4 . Gl3
7 .CR
6.39
7.37
-1.61
¦; :?
3 27
l.-M
17.7
1,5, 9-CycLodco..-:a:riL"j
3. 68
0.6-*.
5. 63
5. S6
3.37
7 . 13
9. 2i
5.61
5 70
7 . 2 i
1.52
16.2
°Ali '-de :ol! jcl
eci n cen
or of t:h^ p
."iSS-acjCi* Lire con:1
area.
-------
emissions are greater in black stocks than in gum. The
total emissions from curing molds may range as high as 5%
to 20 a for thin stocks and the more volatile antidegradants.
However, normal vaporization losses amount to only 0.5% to
1.0% byv/eight of the ant.idegradant present in the stock.
The melting points of the common antioxidants are given in
Table 22.
Table 22. MELTING POINTS OF COMMON ANTIOXIDANTS
Antioxidan t
type
Compound
m. p . , ° C
Phenol
2,6-Di-t-butyl-4-methylphenol
6 9 to 7 0
11
2 , 4 -Di- t-amylp'nenol
Liquid
n
3 -t-Euty1-4 -hydroxyanisole
Liquid
it
2,2'-Methylene-bis(4-methyl-
125 to 13 0
6-t-butyl phenol)
Amine
Phenyl-3-naph thylamine
105 to 10 6
11
N-N'-diphenyl-p-phcnylenediamine
14 4 to 15 2
11
N-N'-diphenylethylenediamine
60 to 6 5
(c) Accelerators - As with the antidegradants, the common
accelerators have melting points between 7 0°C and 200°C.
Hence, emissions of these components are to be expected at
normal curing temperatures. Average total emissions of
0.5% to 1.0% by weight of accelerator present can be anti-
cipated.18 The melting points of the common accelerators
are given in Table 23.
-8/\ngert, I. G., et al. Volatilization of Phenyl-2-Naphthv-
lamine from Rubberr Rubber Chemistry and Technology,
3_4_:307, July-September 1961.
80
-------
Table 23. MELTING POINTS OF COMMON ACCELERATORS
Accelerator type
Compound
m.
P- r
°C
Di thiocarbarnate
Zinc diethyldithiocarbamate
171
to
ISO
II
Zinc dibutyldithiocarbarnate
98
to
103
11
Sodium dibutyldithiocarbamate
liqui
.d
11
Selen .ium dime thy ldi thioca rbamate
140
to
172
Thiuram
Tctramethylthiuram monosulfide
103
to
108
11
Tetramethy11hiuram disulfide
140
to
148
11
Tetraethylthiuram disulfide
62
to
75
Sulfonamide
N,N-d iethy1-2-benzothiazy1sui fenamide
liqu
d
T1
N-cyclohexyl-2-benzothiazylsulfenamide
93
to
103
11
N-oxvdie thylene-2-benzothiazylsulfenamide
70
to
90
Thiazole
2-Mercaptobenzothiazole
164
to"
176
11
Benzotniazyl di sulfide
160
to
176
II
2 -B e n z o t h i a z y1-N,N-d i e t h y11 hioc a rbam.ylsulfide
69
Guanidine
Diphenylguanid ine
14 5
to
147
II
Di-o-tolylguanidine
167
to
173
-------
(d) Processing Aids, Diluents - Processing aids are
generally in the form of oils, usually paraffinic, and
function as lubricants,, plasticizers, and softeners. Dilu-
ents are primarily aromatic extender oils used to improve
overall performance of synthetic rubbers. Volatilization
from these mixtures is expected to vary considerably depend-
ing on their composition. Available data show that the
total emissions in 3 hours at 167 °C range from O.OS's to
1. 0 o by weight. 1 Cj
(e) Miscellaneous Compounding Ingredients - The materials
in this category which are most likely to be volatilized
are the vulcanizing agents and retarders. These substances
include amines, esters, and organic__acids , most of which are
either liquids at room temperature or solids with melting
points between 70°C and 200°C. Emissions of the order of
1% by weight can be expected.
In nearly all Ccises, the materials used in rubber blends are
of technical grade. Hence, the purity of the principal
component is low (60% to 95%), and some of the impurities
will be sufficiently volatile to be emitted during curing^
The wide melting point ranges of many of the compounds given
above are indicative of high impurity levels. Gas chromato-
graphic analysis of commercial antioxidants has confirmed the
high impurity levels in these compounds.20 As a result, there
are hundreds of compounds which may be emitted in trace
amounts during the curing operation.
igDuke, J. , et al. Oil Types in the Program for Oil
Extended Rubber. Industrial and Engmeerina Chemistry.
4_7:107 7, May 1955.
-°Cacta, 1,. J., et n.L. Antioxidant Analysis. Rubber
Age. 101: t\ 7 , March 19 67.
8 2
-------
(f) Volatilized Components - The volatilization of components
from rubber stock during cure has been shown to follow the
theoretical equation:18
C = Cq (l-e~mt/R) (1)
where C = amount of component lost in time t, percent
by weight of rubber
Cq = initial weight percent of component
m = a constant which depends on the diffusion
coefficient of the species at the curing
temperature
R = thickness of rubber stock
t = time
Thus, physical losses of particular ingredients are related
exponentially to the temperature and duration of cure, stock
thickness, and individual diffusion coefficients.
G. G. Winspear used Equation 1 to estimate the loss of
various components from two typical _tread stocks, black
sidewalls, and white sidewalls.15 The formulations for
each of the tire parts used to calculate the loss of
materials from typical tires are given in Tables 24, 25
and 2 6 (tire tread, black sidewall and white sidewall,
respectively). Table 27 defines the commercial ingredients
of the various formulations. The estimated emission factors
using Equation 1 and Tables 24-26 are presented in Table
28 which lists the emission factors by material emitted
for each tire part with the source of the material identi-
fied by ingredient.
Table 28 shows that the total amount of volatile material
released is between 5 g/kg and 7 g/kg, or 0-5% to 0.7% by
Weight,, or 50 to_70_grams per tire. Of this amountt 90Z
S~o "•
I
¦
' , r
-------
Table 24. PASSENGER TIRE TREAD FORMULATIONS18
Rubber
type
Natural rubber
SBR/ci s-
Polybu tadiene
Ingredient
Par ts
by weight
Weight,
o
"O
Parts
by weight
height
o
c
Smoked sheet
100
44.8
-
-
SBR 1712
-
-
103 .1
66 . 3
c is-Polybutadiene
-
-
25
16.1
REOGEN
2
0.9
-
-
K-STAY G
-
-
5
3 . 2
Stearic acid
2 . 5
1.1
2
1.3
Zinc oxide
3 . 5
1. 6
3
1. 9
AGERITE RESIN D
1.5
0.7
1.5
1.0
AGERITE HP
0.5
0.2
• 0.5
0 . 3
ANTOZITE 67 S
4
1.8
4
2 . 6
Microcrystalline wax
1
0.5
1
0.6
Philrich 5
5
2 . 2
7
4 . 5
HAF
50
22 . 4
-
-
ISAF
50
22.4
-
-
Sulfur
2 . 5
1.2
1.8
1.2
AMAX NO. 1
-
-
1. 5
1.0
RED AX
0.5
0.2
-
-
Totals
223 . 0
100. 0
155.4
100 . 0
84
-------
Tabic 25. PASSENGER TIRE FORMULATIONS FOR BLACK SIDEWALLS18
Rubber
type
Natural rubber
SBR
Ingredient
Parts
by weight
We ight,
q.
'o
Parts
by weight
Weight,
o.
o
Smoked sheet
100
55.6
-
-
SBR 1500
-
-
50
25 . 8
SBR 1712
-
_ i
50
25.8
REOGEN
1
0.6
i
0.5
Stearic acid
Jj
1. 7
1.5
0.8
Zinc oxide
5
2 . 3
3
1.6
ANTOZITE 6 7 S
4
2 . 2
4
2 . 1
Microcrystalline wax
1.8
o
I—1
2
1. 0
AGERITE SUPERFLEX
SOLID
2
1.1
2
1. 0
Philrich 5
-
-
12
6.2
THERMAX
10
5. 6
-
-
GPF Black
5 C
27.7
65
33.6
Sulfur
2 . 5
1. A
2 . 1
1 1" 1
AMAX
0 . 5
0 . 3
i—1
I—I
0.5
Totals
179 . 8
100 . 0
193 . 7
100.0
35
-------
Table 26. PASSENGER TIRE FORMULATIONS FOR WHITE SIDEWALLS18
Rubber type
Natural rubber/
neoprene/hvpalon
Natural rubber/
SBR
Ingredient
Parts
by weight
Weight,
o.
*b
Parts
by weight
Weight
0.
High modulus crepe
4 0
20 . 1
1
70
37 . 7
Neoprene W
40
20 .1
-
-
Hypalon 2 0
20
10 . 0
-
-
SBR 1502
-
-
30
16 . 1
Stearic acid
1
0 . 5
1.5
0.8
Zinc oxide
35
17 . 6
20
10.8
AGERITE SUPERLITE
1. 5
0.8
1.5
0 . 8
Titanium dioxide
40
20 . 1
37
19 . 9
Whiting (ppt)
7 . 5
-
7 . 5
-
McNamee clay
4
2 . 0
20
10 . 8
Light process oil
15
7 . 5
1
0.5
Ultramarine blue
0.3
0 .1
0 . 3
0 . 2
Sulfur
1.3
0 . 7
2 . 8
1. 5
ALT AX
0. 9
0.4
1.5
0 . 8
METHYL TUADS
0 . 3
0.1
-
-
Diphenyl guanidine
-
-
" 0.2
0 .1
Totals
199.3
100 . 0
185.3
100.0
1
86
-------
Table 27. DEFINITIONS OF COMMERCIAL INGREDIENTS18
Inciredien I
REOGEN
Definition
K-STAY G
AGERITE RESIN D
AGERITE IIP
ANTOZITE 67 S
HAF
ISAF
AMAX
AMAX NO. 1
RED AX
Philrich 5
AGERITE SUPER-
FLEX SOLID
THERMAX
ALT AX
METHYL TUADS
A mixture of an oil soluble sulfonic acid
of high molecular weight with a high boiling
alcohol and a paraffin oil. Used as a
peptizing agent and strong plasticizer for
all elastomers. Functions as a scorch
re tarder.
Mixtures of an oil soluble sulfonic acid of
high molecular weight and selected petrol-
eum base oils.
Polymerized 1, 2-di.hydro-2 , 2 , 4-tetramethyl-
quinolme antioxidant, melting point = 74 °C
minimum.
A blend of approximately 65 parts phenyl-
B-naphthylamine and approximately 3 5 parts
of diphenyl-p-phenylenediamine antioxidants,
melting range = 89-96°C.
N- (1, 3-dimethylbutyl) -N ' -p'neny 1-p-phenylene-
diamine antiozonant, 50"s active, semi-liquid
High abrasion furnace black.
Furnace black.
N-oxydiethylene benzothiazole-2-sulfenamide
accelerator, melting range = 70-80°C.
AMAX plus a percentage of benzothiazyl
disulfide (MBTS).
N-nitrosodiphenylamine retarder, melting-
range = 63-68°C.
Aromatic petroleum oil, extender and
plasticizer.
A diphenylamine-acetone reaction
product, 7 5% active antitoxidant.
Medium thermal carbon.
Benzothiazyl disulfide (MBTS), melting
range = 159-170°C.
Tetramethylthiuram disulfide (TMTD),
melting range = 142-156°C.
87
-------
Tab1e 2o . ESTIMATED EMISSIONS OF VOLATILE COMPOUNDS FROM i-YPOTKETICAI. PASSENGER TIRE WITil
10 kg COMBINED WEIGHT OF TREAD AND SIDE1.'.'ALL STOCKS13
Tread = 9 kg; Sidcwalls = 1 kg
Emission factors.
g/kg
Tire trasu
V:hite side
wall.
Black' s id e'.-.'fl 11
ingradient
Natural
rubber
SBR/cis-
Polybutadiene
Natural rubber/
neoprcne/h yp.fi Ion
Natural
rubber/SBR
Ma t ural
rubber
S3E
Polyrr.er
Smoked sheet
SBR 1712
High ~-cculus crops
Folybutad iene
Neoprcne W
Hypalon 20
SBR 1500
S3R 1502
5 . ID
. 12
.1.0 2
0.19
0. 19
0 . 01
0 - 36
0.16
0.55
0 . 26
0 . 26
An tidegradant
AGEPITE ?ESI>; D
AGEP.I7E HP
AGERITE SUPERLITE
AGEPITE S.S.
AKTOZITE 67 S
0 . OS
0.03
0 . 21
0. 06
0.02
0.16
0. 00 5
0. 003
0 . 01
€ . 02
0 . 01
0 . 02
Accelerator
amax ;-:o. l
AMAX
ALT
METHYL TUADS
D?G
0 . 03
0.06
0 . 004
0 . 001
0 . 008
0.001
0. 002
0.005
Oil
Phil rich 5
Light process
0 . 26
0.29
0 . 07
0 . 005
0 . 06
Mi sco1laneous
REOGEE
K-STAV-G
REDAX
0 . 11
0 . 03
0.21
0 . 006
0.005
Tote; Is
5. 9 ='•
5 . 9 -i
0 .
-------
is derived from the polymer blend. Antidegradants contribute
appr_oxima te_ly_5 d to the losses and accelerators..roughly 1%.
Note that synthetic rubbers discharge approximately three
times as much accelerator as does natural rubber. The
remaining 3% of the emissions stem from a mixture of oils
and special additive ingredients.17
To appreciate the number of emitted materials represented
by this 50 to 70 grams per tire, the following assessment
might be helpful. Each of the two stocks per tire considered
are assumed to contain an average of 10 ingredients which
could be volatilized. Rappaport states that since technical
grade ingredients are used, there are as many as 1000
different compounds which may conceivably be released.17
Since rubber vulcanization is performed over a range of
processing temperatures, Rappaport measured the total loss
of hydrocarbons from tread stock during vulcanization. His
experiments were performed on 6.4 mm thick tread stock at
curing temperatures ranging from 160°C to 200°C and a
curing time 6f 20 minutes. Table 29 summarizes the tire
formulation used in Rappaport's research. Table 30
summarizes the results he obtained and the empirical
correlation presented below shows the loss of volatile
hydrocarbons as a function of temperature:17
C = 0.00212 T - 0.1532S (2)
where C = amount of total hydrocarbon lost, weight
fraction of rubber
T = curing temperature, °C
89
-------
Table 29. TREAD STOCK FORMULATION USED BY RAPPAPORT17
Ingredien t
Weight percent
(approximate)
Polymer
Styrene-butadiene rubber (1)
25
Styrene-butadiene rubber (2)
25
Polybutadiene(cis) rubber
10
/vntidegradan t
N-pheny1-N-sec-butyl-p-
0.5
phenylenad ianune
Accelerator
N-t-bu ty1-2-bcnzothiozole
0 . 5
sulfenamides
Diphenyl guanidine
0 .1
Carbon black
Furnace black
30
011 a
Aromatic
20
Miscellaneous
Sulfur
0 . 5
Activated zinc oxide
0 . 5
Stearic acid
0 . 5
Sunproof wax
0.5
Total
113
Since some oil is used to extend styrene-butadiene rubbers,
the figures shown here are the total weight percent for all
oils; this brings the total to 113%.
90
-------
Table 30. VOLATILIZATION OF GREEN TREAD STOCK DURING
VULCANIZATION AT TEMPERATURES BETWEEN
16 0 ° C and 200°C17
Vulcanization
temperature, °C
Weight
loss, %
Total hydrocarbon
emission factor,a
g/kg
160
0.189
1. 89
170
0. 196
1.96
160
0. 176
1.76
180
0.268
2 . 68
190
0. 259
2 . 59
190
0 . 232
2 . 32
170
0. 201
2. or
160
0. 195
1.95
200
0. 261
2 .61
180
0 .235
2 . 35
170
0. 202
2 . 02
170
0.2 04
2 . 04
200
0.273
2 .73
180
0 .231
2 . 31
' , , , ,
Statistical analysis of total hydrocarbon emission factors
for temperatures ranging from 160°C to 200°C:
mean = 2.2 3 g/kg
standard deviation = 0.3 2 g/kg
relative error = 0.19 g/kg or 8.41%
91
-------
3 . Under Tread Cementing
Under tread cementing, which is one o£ the forming operations,
is a spreading operation used to apply a glue or cement to
the underside of a tire tread to facilitate its application
to the green tire. Solvent is used as the vehicle for
application of the glue. The_solyents_.used__ev_apcrate .and
become hydrocarbon emissions within_the tire plant.21
Van Lierop and Kolika have published data on the measurement
of hydrocarbons from an under cementing operation:21 ' The
solvent used as the vehicle in these studies was Texol©, a
low-boiling naphtha type of solvent. The amount of solvent
(as Cs) which evaporates from under tread cementing was
measured as 83 g/nv2 . This amounts to 23 g/tire assuming
that the average tire tread has a cemented surface area of
0.28 m'- . A total of 8 tests was performed to obtain this
"emission factor which has a standard deviation of 7.8 g/m2.
These data can be manipulated to yield an emission factor of
1.88 g/kg by assuming that the average tire weighs 12.25 kg.
4. Green Tire Spraying
Green tire spraying, which is one of the building operations,
utilizes two distinct solvent based sprays (one internally
and one externally) to act as mold release agents and rubber
flow promoters during cure.21 The solvents used in this
operation evaporate both inside and outside of the spray
booth used.
21 Van .LieropG e t al. Measurement oE Hydrocarbon Emissions
'and Process Ventilation Requirements at a Tire Plant. Arm-
strong Rubber Co. (Paper presented at the 68th /Annual
Meeting of the Air Pollution Control Association, Boston.
June 15-20, 197-5.) 23 p.
92
-------
Van Lierop and Kalika published emissions data on the solvent
evaporation from green tire spray operations. The solvent
used was Texol, a low-boiling naphtha. The amount of sol-
vent (as C5) which evaporates from green tire spraying
was found to be 0.14 kg/tire which- corresponds to 11.1 g/kg ,
assuming the average tire weighs 12.25 kg. Average solvent
consumption is 0.15 kg/tire which shows that SS°o of the sol-
vent applied to green tires evaporates [roi'i the tire. The
fugitive emissions (i.e., those to the workroom) accounted
for 27% to 3 5% of the total hydrocarbon emissions.
5. Other Processing Emission Points
Other emission points within the tire plant that result
from rubber processing are calendering and extrusion opera-
tions. The mechanical work performed on' the rubber compound
in these operations generates a considerable amount of heat.
The materials emitted during such operations are similiar to
the hydrocarbons from compounding operations.2-
B. EMISSION FACTORS
The quantities of materials emitted per unit of rubber
processed have been reported by several authors as dis-
cussed in Section IV.A. Table 31 is a compilation of the
information gathered from the literature and contains infor-
mation from only those articles that present emission factors
or data.that could be used to calculate emission factors.
(Blanks in Table 31 indicate that the particular data are
not reported in the cited references, while dashes indicate
no emissions of the criteria pollutant for the operation.)
The emission factors presented in Tables 3 2 and 33 were
obtained by sampling a representative tire manufacturing
93
-------
Table 31. SUMMARY OF EMISSIONS DATA REPORTED IN THE LITERATURE FOR RUBBER PROCESSING
Criteria pollutant emission factor,3 g/kgt
Processing step
Particulates
Sulfur
oxides
Nitrogen
oxides
Hydrocarbons
Carbon
monoxide
Compounding
-
-
-
Curing
-
-
-
7 . 05
-
Calendering
-
-
-
-
Extrusion
-
-
-
Under tread cementing
-
_
_
h-1
CO
CO
-
Green tire spraying
_
•
-
11 . 4
-
Whole incineration
Totals
aBlanks in the above table indicate that specific data are not reported in the cited
references; dashes (-) indicate no emissions of the criteria pollutant for the
processing step.
-------
Table 32. EMISSION FACTORS FOR COMPOUNDING IN A TIRE PLANT
Material emitted
Emission factors,
kg/tire g/kgcl
Particulates
Carbon black
Zinc oxide
Sulfur
Others
Hydrocarbons
Toluene
•I -Vinyl-l-cyclohexene
Ethyl benzene
Stvrene
1, 5-Cyclooctadiene
1,5,9-Cyclododecatriene
m-Xylene
p-Xylene
t-Buty1isothiocyanate
Benzothiazole
N-sec-bu tylaniline
Methyl naphthalenes
Butadiene trimer
Ethyl naphthalene
1
Dimethyl naphthalene
Dipheny.'L quanidine
Others
Assuming the average tire weighs 12.2 5
95
-------
Table 33. EMISSION FACTORS FOR CURING IN A TIRE PLANT
Material emitted
Hydrocarbon s
Toluene
4-Viny1-1-cyclohexene
Ethyl benzene
Styrene
1,5-Cyc]ooctadiene
1,5,9-Cyclododecatriene
rn-Xylenc
p-Xylene
j:-Buty lisothiocvanate
Benzothiazole
N-sec-butylaniline
Methyl naphthalenes
Butadiene trimer
Ethyl naphthalene
Dimethyl naphthalene
Diphenyl guanidine
Others
Emission factors,
kg/tire g/kg
96
-------
plant. These data were used to calculate the cround level
concentrations, mass emissions, and affected population in
Section IV.D.
C- DEFINITION OF A REPRESENTATIVE SOURCE
In order to determine the source severity, which is described
in Section IV.D., a representative source for rubber pro-
cessing was defined as fellows:
1) The representative source is 3.imited to the
»anufacture of tires since this area of rubber
processing constitutes 66" cf the industry. The
emissions from o'ther branches of the industry
will be the same in materials emitted and
approximately the same in mass of emissions because
the emissions are a function of the rate of
volatilization of ingredients used in the rubber
(Sec tion IV.A.) .
2) The plant capacity for this rspresar.tative source
is "he 3]3Ein production capacity of all tire
plants, which is 1.7 million units per year.
(See Section III.C.) Assuming that the average
tire weighs 12.25 kg, the mean plant capacity
also equals 20.1 Gg.
3) The composition of the representative tire is
given in Tables 24, 25 and 26.
4) The representative source is located in the
state with the largest number of plants; i.e.,
Ohio (Section III.C.).
97
-------
Table 34. MAXIMUM GROUND LEVEL CONCENTRATIONS OF DIFFERENT EMISSIONS
FROM RUBBER PROCESSING8
Material emitted
Mass emission
rate, g/sec
y ,
'^rnax
jjg/m3
TLV,
mg/m3
j Ambient
air quality
standard, mg/m3
Criteria pollutants
Particulates
10
0.26
Hydrocarbons
1. 36
3.10
NA
o.i6c ,
Sulfur oxides
13
0.365
Nitrogen oxides
9
0 . le
Carbon monoxide
55
4 0 f
Chemical substances
Carbon black
3 . 5
NA9
Soapstone
6 . 7
NA
Z'inc oxide
5
NA
Toluene
0.39
88
375
NA
4 - V i n y 1 -1 - c y c 1 o h e x e n e
0 . 02
4 . 5
NA
NA
Ethyl benzene
0 . 03
6 . 8
435
NA
Styrene
0 . 03
6 . 8
420
NA
1,5-Cyclooctadiene
0.002
0.45
N A
NA
1,5,9-Cyclocodecatriene
0 . 003
0 . 68
NA
MA
Naphtha
0 . 89
200
400
NA
Others
.
^Calculations based on estimated emission.
24-Hour average.
53-Hour average,
a,,, „
24-hour average.
®Annual average.
' 1-Hour averace.
0
"NA - not aoplicable.
-------
where Q,n = mass emission rate, g/sec
u = average wind speed = 4.5 m/scc.
II = average height of emissions = 15.2 in
e = 2.72
m = 3.14159
2 . Severity Factor
To obtain an indication of the health hazard potential of
the emission source, a severity factor, S, was defined as:
S = ^ (4)
where x = time-averaged maximum ground level
max , ,
concentration
F = hazard factor; equal to the primary air
quality standard for particulate, sulfur
oxides, nitrogen oxides, carbon monoxide
and hydrocarbons, and equal to TLV x S/'2 4
1/100 for ali chemical substances
This severity factor represents the ratio of the time-
averaged maximum ground level exposure to the potential
hazard level of exposure for an emitted material.
v was calculated using the formula:
•'max J
_ I ^ \°" 1 1
W= ^maxi^fj (5)
where t =3 minutes
max
ti = appropriate averaging time, minutes
The appropriate averaging time was 24 hours for all other
pollutants.
100
-------
For particulate, sulfur oxides, nitrogen oxides, carbon
monoxide and hydrocarbons, the averaging times are the same
as those used in the primary ambient air quality standards.
v and 'severity factors for each material emitted from
max J
the representative rubber processing plant are presented in
Table 35. [These calculations were based on emission factors
obtained from the literature and do not necessarily represent
the values that might be obtained from a sampling program.]
3. Contribution to Total Air Emissions
The contribution of rubber processing to statewide and
nationwide air emissions was measured by the ratio of mass
emissions from this source to the total emissions from all
sources.
The mass emissions of hydrocarbons and particulates resulting
from rubber processing were calculated by multiplying the
emission factors by the total processing done in the state.
The mass emission for each pollutant is shown in Table 3 6
for the states where rubber processing is performed, along
with the nationwide emissions. [There are no figures for
sulfur oxides, carbon monoxide, and nitrogen oxides in Table
36 because the emission of these from rubber processing is
presently unknown.]
Table 37 gives the ratios of hydrocarbon and particulate
emissions resulting from rubber processing to the total
emissions of these materials in each corresponding state
and the nation. The total pollutant emissions for each
state were obtained from the 197 2 National Emission Report.
On a nationwide basis, the emissions from rubber processing
constitute 0.3% or more of the' total hydrocarbon emissions.
101
-------
Table 35. TIME-AVERAGED MAXIMUM GRODD LEVEL CONCENTRATIONS
AND SEVERITY FACTORS FOR EMISSIONS
FROM RUBBER PROCESSING
V
Ama k '
Material emitted
}j g/m3
Severity factor, S
Criteria pollutants
Particulates
Hydrocarbon s
190
1. 2
Sulfur oxides
Nitrogen oxides
Carbon monoxide- ¦
Chemical substances
,
Carbon black
Soapstone
Zinc oxide
1
Toluene
| 31
0 . 087
A - V i n y 1 -1 - c y c ?i c h e x e n e
1.6
Indeterminate
Ethyl benzene
2.4
0.00058
S tyrene
1 2 . 4
0.00060
1,5-Cyclooctadiene
! 0 . .1G
Indetermina te
1,5,9-Cyclododecatrisne
0.24
Indeterminate
Naphtha
! 7 0
0 .018
Others
1
I
a..
Indeterminate, since TLV for species has not been establishec
102
-------
Table 36. TOTAL EMISSIONS OF HYDROCARBONS AND
PARTICULATES RESULTING FROM RUBBER
PROCESSING OPERATIONS BY STATE
Hydrocarbons,
Particulates,
State
Gg/yr
Mg/yr
Alabama
7.7
Alaska
-
Arizona
-
Arkansas
1.0
California
8 . 2
Colorado
0. 5
Connecticut
1.5
De lav/are
-
Florida
-
Georgia
1. 5
I-lavjaii
-
Idaho
-
I1linois
2.5
Indiana
1.7
Iowa
3 . 7
Kansas
2 . 7
Kentucky
2 . 0
Louisiana
0 . 25
Maine
0 .25
Maryland
2 . 2
Massachusetts
3 . 7
Michigan
5.7
Minnesota
-
Mississippi
3 . 7
Missouri
-
Montana
-
Nebraska
-
Nevada
-
Nev; Hampshire
-
103
-------
Table 36 (continued). TOTAL EMISSIONS OF HYDROCARBONS AMD
PARTICULATES RESULTING FROM RUBBER
PROCESSING OPERATIONS BY STATE
S tate
Hydrocarbons,
Gg/yr
Particulates,
Mg/yr
New Jersey
0.25
Mew Mexico
-
New York
0.25
North Carolina
1.5
North Dakota
-
Ohio
13 . 0
Oklahoma
0. 5
Oregon
0 . 25
Pennsylvania
6. 0
Rhode Island
-
South Carolina
0.5
South Dakota
-
Tennessee
6 . 0
Texas
3 . 0
Utah
-
Vermont
-
Virginia
1.0
Washington
0 . 25
West Virginia
-
Wisconsin
3 . 0
Wyoming
-
U.S. Totals
84 . 3
104
-------
PERCENT CONTRIBUTION OF EMISSIONS OF
HYDROCARBONS AND PARTICULATES FROM RUBBER
PROCESSING TO CORRESPONDING STATE
EMISSIONS FROM POINT SOURCES
Sta te
Hydrocarbons
Particulates
Alabama
1.2
Alaska
-
Arizona
-
Arkansas
0.51
California
0. 38
Colorado
0.26
Connecticub
O.SS
De lav/are
-
Florida
-
Georgia
0 .33
Hawa i i
-
Idaho
-
Illinois
0.14
Indiana
0. 12
Iov;a
1.2
Kansas
0 .37
Kentucky
0.61
Lo u i s i a n a
r—1
O
o
Maine
p. 20
Maryland
0.74 |
Massachusetts
0.34
Michigan
0.79
'Minnesota
-
M i s s i s s ipp i
CO
O
Missouri
-
Montana
-
Nebraska
-
Nevada
-
Nev: Hampshire
-
105
-------
Table 37 (continued). PERCENT CONTRIBUTION OF EMISSIONS OF
HYDROCARBON'S AND PARTICULATES FROM RUBBER
PROCESSING TO CORRESPONDING STATE
EMISSIONS FROM POINT SOURCES
State j
Hydrocarbons
Particulates
New Jersey
0.03
New Mexico
-
New York
0.02
North Carolina
0. 34
North Dakota
-
Ohio
1. 13
Oklahoma
0 . 15
Oregon
0. 11
Pennsylvania
0 . 67
Rhode Island
-
South Carolina
0. 06
South Dakota
-
Tennessee
1. 65
Texas
0 . 14
Utah
-
Vermont
-
Virginia
0. 27
Washington
0 . 07
West Virginia
-
Wisconsin
0 . 57
Wyoming
-
U.S. Totals
0 . 34
i
106
-------
4. Population Exposed to High Pollutant Concentrations
To obtain a quantitative evaluation of the population in-
fluenced by a high concentration of emissions resulting from
a typical- rubber processing plant, the areas exposed to the
time-averaged ground level concentration, v, for which
x/F > 1 and x/F > 0-1 were obtained by determining the
area within the isopleth for \r an<3 the number of people
within the exposed area was then calculated by using a
proper population density.
The representative population density used in the calculation
of affected population was the average state population den-
sity, weighted by the amount of rubber processing in each
state. For each of the pollutants with a severity factor
greater than or equal to 1, the area and population exposed
to a time-averaged ground level concentration for which
x/F > 1 and v/F > 0.1 are shown in Table 38. For each of
the pollutants with 0.1 < S < 1, numbers are shown only for
x/F >0.1. In addition to the average exposed population,
two extreme cases were also examined and these are listed
in the same table.
It can be seen from Table 3 8 that for the average case, the
population influenced by high ground level concentration is
for the pollutants with S > 0.1. [However, it should
be noted again that there may be some other compounds
emitted but not reported in the literature.]
107
-------
Table 38. AREA AMD POPULATION EXPOSED TO POLLUTANTS FOR V:HlCil
X/f - l ahd x/'r - 0-1'1
Pol] utar.t
Affected
2
area, .-cir,
Exposed population
Best case Worst case
.Average
X/F ^ 1
1
y/F - 0.1
1
XI
f7l
IV
)—
X/F ^ 0.1 | X/F - 1
,0.1
Hydroca rbons
Par ticultiLes
[
C
Others
i
o
CO
I
-------
SECTION V
CONTROL TECHNOLOGY
Emissions from the rubber processing
hydrocarbons and particulates. Each
technology.
A. HYDROCARBONS
1. Adsorption
Adsorption is the process for removing molecules from a
fluid by contacting them with a solid. Gases, liquids, or
solids can be selectively removed from airstreams with
materials known as adsorbents. .The material which adheres
to the adsorbent is called the adsorbate.22
The mechanism by which components are adsorbed is complex,
and although adsorption occurs at all solid interfaces, it
is minimal unless the adsorbent has a large surface area,
is porous, and possesses capillaries. The important character-
istics of solid adsorbents are their large surf ace-to-vol. ume
ratio and preferential affinity for individual components.22
22Ilughes, T. W., et al. Source Assessment: Prioritization
of Air Pollution for Industrial Surface Coating Operations.
EIYA- 6 5 0 / 2 - 7 5 - Q19 - a , Contract No. 63-02-1320 "ask 1A) .
February 197 5.
industry consist of
type has its own control
109
-------
The adsorption process includes three steps. The adsorbent
is first contacted with the fluid, and adsorption results.
Second, the unadsorbcd portion of the fluid is separated from
the adsorbent. For cjases, this operation is completed
when the gases leave the adsorbent bed. Third, the adsorbent
is regenerated by removal of the adsorbate. Low pressure
steam is used to regenerate the adsorbent, and the condensed
vapors are separated from the water by dccantation, dis-
tillation, or both.'2
Activated carbon is capable of adsorbing 95£ to 931 of the
organic vapor from air at ambient temperature in the presence
of water in the gas stream.23 Because the adsorbed compounds
have low vapor pressure at ambient temperatures, the re-
covery of organic materials present in air in small concen-
trations is low. The adsorption system can be operated
without hazard because the vapor concentration is below the
flammable range. 2 ¦-
When an organic vapor in air mixture starts to pass over
activated carbon complete adsorption of the organic vapor
takes place. As the adsorptive capacity of the activated
carbon is approached, traces of vapor appear in the exit
air, indicating that the breakpoint of the activated carbon
has been reached. As the air flow is continued, and al-
though additional amounts of organic materials are adsorbed,
the concentration of organic vapor .in the exit air continues
to increase until it equals that in the inlet air. The
adsorbent is saturated under these operating conditions.22
23liydrocarbon Pollutant Systems Study. Vol. I. Stationary
Sources, Effects, and Control. MSA Research Corporation.
(PB-219 073.) October 1972.
110
-------
The adsorption of a mixture of adsorbabie organic vapors in
air is not uniform, and the more easily adsorbed components
are those with the higher boiling points. 'When air containing
a mixture of organic vapors is passed over activated carbon,
the vapors are equally adsorbed at the start. however, as
the amount of the higher boiling component in the adsorbent
increases, the more volatile component revaporizes. The
exit vapor consists primarily of the more volatile component
after the breakpoint has been reached. This process con-
tinues for each organic mixture component, until the highest
boiling component is present in the exit gas. 1st the control
of organic vapor mixtures, the adsorption cycle should be
stopped when the first breakpoint occurs as determined by
detection of vapors in. the exit gas. Many theories have
been advanced to explain the selective adsorption of certain
vapors or gases. These theories are presented in Perry and
Chilton21' and will not be discussed here.
The quantities of organic vapors adsorbed by activated
carbon are a function of the particular vapor in question,
the adsorbent, the adsorbent temperature, and the vapor
concentration. Removal of gaseous vapors by physical ad-
sorption is practical for gases-with molecular weight over
45. 2'' Each type of activated carbon has its own adsorbent
properties for a given vapor and the quantity of vapor
adsorbed for a particular vapor concentration in the gas
and at a particular temperature .is best determined experi-
ment ally. The quantity of vapor adsorbed increases when the
vapor concentration increases and the adsorbent temperature
deer eases . 2
2'¦ Percy, J. H., and C. H. Chilton. Chemical Engineers'
Handbook. New York, McGraw-Hill, 1973.
Ill
-------
After breakthrough has occurred, the adsorbent is regenerated
by heating the solids until the adsorbate has bear, removed.
A carrier cas is use also he used to remove the va.pors released.
Lov.--pressure saturated steam is used as the heat source for
cncrcri a also as tbs carrier :as. 5uMr-
heated steam at 3 5 0°C may be necessary to remove high boiling
compounds ar.c return the carbon to its original condition
when high boiling compounds have reduced the carbon capacity
to the point where complete regeneration is necessary.2?
Steam requirements for regeneration are a function of ex-
ternal heat losses and the nature of the organic material.
The amount of steam adsorbed per kilogram of adsorbate, as
a function of elapsed tiir.e, passes through a itiirisua. The
carbon should be regenerated for this length of tire to
permit the mir.irnur.i use of stean.After regeneration, the
carbon is hot and saturated with water. Cooling and drying
are done bv blowing organic-dree air i h j: c u r r i h 3 carocn as d .
Evaporation of the writer r.ids cooling oC the carbon. If
high temperature stean has been used, other means of cooling
the carbon are required.
Fixed bed adsorbers arrayed iji two or more parallel bed
a rr a rig em sr. t s are used fco re-rove organic w >ors from air
!£aa rigrre Chess are fcatch-typs -am gaiierr^.. vhEie
bed is used until breakthrough occurs, arid is then regenera-
ted. The simplest adsorber design of this type is a two
bed system where one carbon bed is being regenerated as
the other is adsorbing organic vapors. In a three bed
arrangement a greater quantity of materia:, crm fco adsorbed
par LUiit of carbon because the effluent passes through tv.'o
beds in series v;hiie the third bed is being regenerated. This
perr.its the activated carbon to be used after breakthrough
since the second bed in the scries removes organic vapors
112
-------
in the exit gas from first bed- When the first bed is
saturated, it rs removed from the stream for regeneration;
the bed which was vised to remove the final traces cf organic
vapors from the effluent then becomes the new first bed; and
the bed'which has been regenerated becomes the new second
_ ^ ^
oeo . ~ -1
Heat is released in the adsorption process, which causes
the temperature of the adsorbent to increase. If the con-
centration of organic vapors is not high, as in the case of
room ventilators, the temperature rise is typically 10°C.22'25
The pressure drop through a carbon bed is a function of the
gas velocity, bed depth, and carbon particle size. Activated
carbon manufacturers supply empirical correlations for
pressure drop in terras of these quantities. These correlations
usually include pressure drop resulting from directional
change of the gas stream at inlet and outlet. 2?-
Activated carbon adsorption sys tems installed in rubber
processing plants have been reported__i21_.the._litera.tur.e-
One system was installed in a latex based operation for the
manufacture of gloves. The gloves were dried in a_dry.ing
room to remove traces of solvent and the air from the drying
room 'was vented into a solvent recovery system operated on
1-hour adsorbency cycles. The efficiency of the system was
72% to 73%, including collection of the vapor-laden air.25
25Air Pollution engineering Manual, Second Edition. U.S.
Environmental Protection Agency, Research Triangle Pari..
Publication No. AP-4 0. May 1973. 987 p.
26Solvent Recovery System Proves a Speedy Payout. Rubber
World. .1GJ5 (5) -.44 / February 1372.
113
-------
EXHAUST
COOLING
WATER
ORGANIC WASTE
STREAM WATER
figure 9. Carbon¦adsorption system23
114
-------
2.
Absorption
Absorption is the process by which one or more soluble com-
ponents are removed from a gas micture by dissolution in a
liquid. 'The absorption process may consist of dissolving
the component in a liquid followed by reaction with a reagen
or of solution without reaction.22
The equipment used for continuous absorption can be a tower
filled with a solid packing material, an enclosure through
which the gas flows and into which the liquid is sprayed, or
a tower which contains a number of bubblc-cap, sieve, or
valve-type plates. Absorption operations are carried out
in a wetted-wall column (a tubular column in which the gas
flows vertically through the tube and the liquid flows
down over the column wall), a stirred vessel, or other type
of equipment.22
The design of absorbers has been discussed by Treyball27
and Perry and Chilton.24 The problems which arise in de-
signing absorbers can be attributed to variation cf solu-
bilities because of non-isothermal operating conditions,
semi-ideal liquid solutions, and the change in the gas and
liquid flow rates caused by transfer of the solute from the
gas phase to the liquid phase.
3. Incineration
a. Thermal Incineration - Direct-flame afterburners
depend upon flame contact and high temperatures to burn
•^'Treybal, R. E. Mass Transfer Operations. New York,
McGraw-Hill, 1968. 666 p.
115
-------
the combustible material in gaseous effluents to form
carbon dioxide and v;a ter.2 3 The combustible materials may
be gases, vapors, or entrained particulate matter which
contributes opacity, odor, irritants, photochemical reacti-
vity, and: toxicity to the effluent. Direct-flame afterburners
consist of a refractory-lined chamber, one or more burner
temperature indicator-controllers, safety equipment, and,
sometimes, heat rocovery equipment.--8
The afterburner chamber consists of a mixing section and a
combustion section. The mixing section provides contact
between the contaminated gases and the burner flame. Good
mixing is provided by high velocity flow which creates
turbulence. The combustion section is designed to provide a
retention time of 0.3 sec to 0.5 sec Eor completion of the
combustion process. Afterburner discharge temperatures
range from 540°C to 800°C, depending on the air pollution •
problem. Higher temperatures result in higher afterburner
efficiencies.2 3
The gas burners used in afterburners are of the nozzle-
mixing, premixing, miltiport, or mixing plates type. Burner
placement varies depending on burner type and on the design
objective of providing intimate contact of the contaminated
air with the burner flames. When all the contaminated air
passes through the burner, maximum afterburner efficiency
is obtained.2 8
Nozzle-mixing and premixing burners are arranged to fire
tangentically into a cylindrical afterburner. Several
2GRolke, R. W., et al. Afterburner Systems Study. Shell
Development Company, (PB-212 5G0). August 1972.
116
-------
burners or nozzles are required to ensure complete flame
coverage, and additional burners or nozzles may be arranged
to fire along the length of the burner. Air for fuel com-
bustion is taken from the outside air or from the contaminated
air stream, which is introduced tangentially or along the
major axis of the cylinders.7-0
Hultiport burners are installed across a section of the
afterburner separate from the main chamber. Although all
air for combustion is taken from the contaminated air stream,
miltiport burners are not capable of handling all of the
contaminated air stream. Contaminated air in excess of
that used for fuel combustion must be passed around the
burner and mixed with the burner flames in a restricted and
baffled area. 8
Mixing plate burners were developed for afterburner appli-
cations, and arc placed across the inlet section of the
afterburner. The contaminated air and the burner flames
are mixed by profile plates installed around the burner
between the burner and afterburner walls. The high veloci-
ties (1 m/sec) provided by the burner and profile plate
design ensure mixing of the burner flames and the contaminated
air not flowing through the burner. The contaminated air
stream provides air for fuel combustion.26
The efficiency of an afterburner is a function of retention
time, operating temperatures, flame contact, and gas
velocity. No quantitative mathematical relationship
between these variables exists because the kinetics of the
combustion process are complex and flow inside afterburners
is not defined. However, for good design, the following
ovscrvations can be made with .respect to afterburner
ef f iciency 8
117
-------
Efficiency increases with increasing afterburner
operating temperature.
Efficiency decreases if the contaminated gases entering
the afterburner are excessively preheated.
Efficiency increases with increasing contact between
the~contaminated gases and the burner flame.
Efficiency increases with increasing retention time
for retention times less than one second.
Efficiency is a function of the afterburner design
and the inlet concentration of organic materials.
Ninety percent afterburner efficiency is difficult
to reach below a 700°C operating temperature if the
generation of carbon monoxide in the afterburner is
included.
An example of the application of direct-flame incineration
to a rubber processing plant is reported in the literature.2^
B. F. Goodrich Sponge Products operated a curing oven which
was exhausted to the atmosphere. The exhaust stream
contained an oil aerosol and also presented an odor problem.
A direct-flame incinerator \n th heat recovery equipment was
installed. The incinerator used Mo. 2 fuel oil as a supple-
mentary Eucl. At a system flow of 14 Mg/hr and an incinera-
tion temperature of 600°C, total hydrocarbons were reduced
from 1,305 ppm (by weight) to 207 ppm, an efficiency of
84%. Allowing for the contribution of fuel oil, the
efficiency becomes 89o. In another run at a temperature
of 640°C, total hydrocarbons were reduced from 1,055 ppm
(by weight), to 89 ppm for an efficiency of 92%. Again
allowing for the contribution of the fuel oil, the efficiency-
becomes 91Z.
1S? nclomir sky, A. G., et al. Fume Control in Rubber Pro-
cessing by Direct-Flame Incineration. Journal of the Air
Poj-lucion Control Association. 16 (12) :673-676 , December 1966.
118
-------
b. Catalytic Incineration - A catalytic afterburner con-
tains a preheat burner section, a chamber containing a
catalyst, temperature indicators, and controllers, safety
equipment, and heat recovery equipment. The catalyst in
such an.afterburner promotes combustion by increasing the
rate of the oxidation reactions without itself appearing to
change chemically.22 (See Figure 10).
PREHEAT
BUHNER
CATALYST
ELEMENT
FUME STREAM
20°C - 200°C
300°C - 500°C
400°C - 600°C
COMBUSTION/MIXING
CHAMBER
OPTIONAL
HEAT RECOVERY
(REGENERATIVE OR
RECYCLE SYSTEM)
CLt.Ai\j GAS
TO STACK
Figure 10. Catalytic afterburner
t-2 3
The contaminated air entering a catalytic afterburner is
heated to the temperature necessary for carrying out the
catalytic combustion. The preheat zone temperature, in the
range of 34 0°C to 600°C, varies with the combustion and type
of contaminants. Because of thermal incineration in the
preheat zone, the preheat burner can contribute to the
efficiency of a catalytic a fterburner .
Catalysts used for catalytic afterburners may be platinum-
family metals supported on met'al or matrix elements made of
119
-------
ceramic honeycombs. Catalyst supports should have hich
geoiretric surface area, lov: pressure drop, scrucrural rnteg-
rity and durability, and should perir.it uniform distribution
of the fiov? of the ¦¦¦fcste stream through -he catalyst.
Catalyses can be pc J. s o ned by p ho s p n o r u s r b i sam th , a r s a r. i c
antimony. mercury, I s ad, sine, and rir;j which are thought to
form alloys with -he in3to 1 catalyst. . Catalysis arc deacti-
vated by materrals ¦¦¦.'hich forir. coatings on there, $ucn as
particulate material, resins, and carbon formed during
organic ir.aterial breakdown. High temperatures will also
deactivate catalysts. Because the combustion reaction is
exothermic, the catalyst bed temperature is above the inlet
renperature. The temperature increase depends on the con-
centration or organic ma-aerial burned and the heat of
coipbustion of: that naterxal. Co.f psnsatior: for decreased
catalyst activity can be in^de by: [1] initial overde s i c n
in specifying the quantity of catalyst required to attain
required perforuiar.ee; increasing prehear ten pec ate. re
?-= cr.srirri activity decrease-; l;) regenerate."- "q t e
a a d !-^h' re r= 1 a c j. - n l'ho .or. talv sr.. ¦-r:
The quantity of catalyst reeuirsd for 05c to 05% conversion
of Hydrocarbons ranges from 0.5 iri^ to 2 r.i-5 of catalyst per
ICOvJ n3/x::hi of waste stream. Although the catalyse ranpera-
ture depends c-:i the hydrocarbon burned and the condition of
me catalyst, the operating tempers tyre of catalytic after-
burners ranges fron 2 50°C to 54C3C.23
L- 1 po r Co nd a n s a t i o n
Organic ccrjpour.d s can be ren.oved trcRi an air stream by con-
densation. A vapor will condense v?hen, at civen temperature,
the partial pressure of the compound is equal to or greater
than its vEpcr pressure. Si;r._larly r if the tempers-ure of
120
-------
a gaseous mixture is reduced to the saturation temperature
(i.e., the temperature at which the vapor pressure equals
ths partial prassure of ens c~ the censti ;u3^-$] j uhe
material will ccoSsr.se. Thus, eiuher increasing ~he system
pressure-or lowering the temperature can cause condensation.
In nest air pollution control applications, decreased tempera-
ture; is used. to condense organic material-?, since increased
pressure is usually impractical - 3c
The equilibrium partial pressure limits the control of
orcar.ic emissions by condensation. as condensation, occurs,
the partial pressure of material remaining ir. the gas de-
creases rapidly, preventing complete condensation. For
example, at 0°C and atmospheric pressure, a gas stream
saturated with toluene would still contain £;bout 8,000 ppm
of that gas. Thus, a condenser must usually be followed
by a secondary air pollution control cevise such as an
af rorburr.er . 3 3
B. PARTICULATE
1. Wet Scrubbing
Wet scrubbers use a liquid (e.g., water] either to remove
particulate matter directly fron the gas stream, by contact
or to improve collection efficiency by preventing: re-
encrain.Tient. The mechanisms for particle removal are: (1)
fine particles -are conditioned to increase their effective
srzo, enab-ing then ~o be collected more easily; ar.d (.2) rhe
3 'Control Tachnirpjes Ear lycrcpe r!:on = an; Cr^anic Solverst
Eriissi-cns from luuticnrry Ecurces. U.S. Department of
Health, Education, and Welfare. AP-68, March 1370.
12 L
-------
collected particles arc trapped in a licjuid film and
washed away, reducing rcentrainment.31
The effective particle size may be increased in two ways.
First, fine particles can act as condensation nuclei when
the vapor passes through its dew point. Condensation can
remove only a relatively small amount of dust, since the
amount of condensation required to remove nigh concentrations
is usually prohibitive. Second, particles can be trapped on
liquid droplets by impact using inertia', forces. 'Die follow-
ing six mechanisms bring particulate matter into contact
with liquid droplets:31
Interception occurs when particles are carried by a
gas in streamlines around an obstacle at distances
which are less than the radius of the particles.
Gravitational force causes a particle, as it passes
an obstacle, to fall from the streamline and settle
on the surface of the obstacle.
Impingement: occurs when an object, placed in the path
of a particle containing gas stream causes the gas to
flow around it. The larger particles tend to continue
in a straight path because of inertia and may impinge
on the obstacle and be collected.
Diffusion results from molecular collisions and, hence,
plays little part in the separation of particles
from a gas stream.
Electrostatic forces occur when particles and liquid
droplets become electrically charged.
Thermal gradients are important to the removal of
matter from a particle containing gas stream because
particulate matter will move from a hot area to a
cold area. This motion is caused by unequal gas
molecular collision energy on the hot and cold sur-
faces of the particles and is directly proportional
to the temperature gradient.
31 Control Techniques for Particulate Air Pollutants. U.S.
Department of Health, Education, and Welfare, (PB 190 253).
January 1969.
122
-------
Wet scrubber efficiencies are compared on the bases of
contacting power and transfer units. Contacting power is
the useful energy expended ir. producing contact of the
particulate natter v,-ith the scrubbing liquid. The contacting
power represents pressure head loss across the scrubber,
head loss of the scrubbing liquid, sonic energy or energy
supplied by a mechanical rotor. The transfer unit the
numerical value of the natural logarithm of the reciprocal
of the fraction of the ctubt passing through the scrubber)
is a measure of the difficulty of separation of the particu-
late matter.31
a. Spray Chamber - The simplest type of wet scrubber is
the spray chamber, a round or rectangular chamber into
which water is sprayed either cocurrently, countercurrently,
or crosscurrently to the gas stream. Liquid droplets travel
in the direction of liquid flow until mertial forces are
overcome by air resistance. Large droplets settle under
the influence of gravity, while smaller droplets are swept
along by the gas stream. These droplets and particulate
matter may then be separated from the gas stream by gravi-
tational settling, impaction on baffles, filtration through
shallow packed beds, or by cyclonic action.31
b. Gravi ty s p r ay tower - Another simple type of wet
scrubber is the gravity spray tower in -which iiqutc droplets
fall downward through a countercurrent gas stream containing
particulate matter. To avoid droplet entrainment, the
terminal settling velocity of the droplets is greater than
the velocity of the gas stream. Collection efficiency in-
creases with decreasing droplet size and with increasing
relative velocity between the droplets and air stream.
Sxr.ce those two conditions are. mutually exclusive, there
is an optimum droplet sxse for maximum efficiency: from. SCO uni
to 1, 0 00 ijm. 3 L
123
-------
c. Centrifugal Spray Scrubbers - Ar. improvement on the
gravity spray tower is the centrifugal spray scrubber.
(Figure 11). This type of wet scrubber increases the rela-
tive velocity between the droplets and gas stream by using
the centrifugal force of a spinning gas stream. The
spinning motion may be imparted by tangential entry of either
the liquid or gas streams or by the use of fixed! var.es and
impellers.31
d. Impingement Plate Scrubbers - An impingement plate
scrubber (Figure 12) consists of a tower equipped with one
or .more impingement stages, mist removal baffles r and spray
chambers. The impingement stage consists of a perforated
plate that has from 6,500 to 32r000 holes per square meter
ana a set of impingement baffles arranged so that a baffle
is located above every hole. The perforated plate has a
weir for control of its liquid level. The liquid flows
over the plats ana through a downcomer to a sump or lower
stage. The gas enters in the lower sector of the scrubber
and passes up through a spray zone created by a series of
low pressure sprays. As the gas passes through the impinge-
ment stage, the high gas and particle velocity (2.25 to
3 m/sec) atomizes the liquid at the edges of perforations.
The spray droplets, about 10 in diameter, increase fine
dust collection.31
e. Venturi Scrubbers - High collection efficiency of fine
particles by impingement requires small obstacle diameter
and high relative velocity of the particle as it impinges on
the obstacle. Venturi scrubbers (Figure 13) accomplish this
by introducing the scrubbing liquid at right angles to a
high velocity gas flow in the throat of a venturi where the
velocity of the gas alone causes the disintegration of the
liquid. Another factor which affects the efficiency cf a
12'I
-------
CLEAN GAS
OUT
A
FLUSHING JETS,
DIRECTED
DOWNWARD
SEPARATOR
CLEAN GAS
OUT
WATER
IN
IMPINGEMENT
PLATES
I
WASTE OUT
WATER 0 U i
CYCLONIC SPRAY SCRUBBER.
MULTI-WASH SCRUBBER.
Figure II. Centrifugal spray scrubbers31
-------
IMPINGEMENT
BAFFLE 5TACE
agglomerating
SLOT STAGE
\ .==si;^
V
IM^INGF.'.iEl-.'T J-CR JBBE :
target
plate \
-V
OniFiCE
plath
f] water
3/" level
'\ZZ3
4cix;r:'
3AS F=LO=.
arrangement of "target pL4"Er
!H i;.\Plf)GE'.'.ENT SCRJB3ER
WA.TER DROPLETS MOJAIZEO
AT EDGES OF OKI r ICES
fcSKS^J -•'H€SS3 /:";
K /r-K /-- -
CAS F_OW
DOWNSPOUT TO
LOV.'ER STAGE "
i M P ¦ N G E .'¦ IE !'¦¦' T P L A T E O c r AIL 5
figure 12. Impingo'nent pl=-te scrubber -
126
-------
Figure 13. Venturi scrubber31
127
-------
venturi scrubber is the conditioning of the particles by
condensation. If the yas in the reduced pressure region in
the throat is saturated or supersaturated, the Joule-Thompson
effect will cause condensation. This helps the particle to
grow, and the wetness of the particle surface helps agglomer-
ation and separation.31
f. Packed Ded Scrubbers - Packed bed scrubbers (Figui~e 14)
are similar to the packed bed absorbers discussed previously.
The irrigating liquid serves to wet, dissolve, and/or wash
the entrained particulate matter from the bed. In general,
samller-diameter tower packing gives a higher particle
target efficiency than larger-size packing for a given gas
veloc itv - 3 1
g. Self-Induced Spray Scrubbers - The self-induced spray
scrubber uses a spray curtain for particle collection. The
spray curtain is .induced by gas flow through a partially-
submerged orifice or streamlined baffle. Baffles or swirl
chambers are used to minimize mist carryover.
The chief advantage of the sclf-induced spray scrubber is
its ability to handle high dust concentrations and concen-
trated slurries.31
h. Mechanically Induced Spray Scrubbers - Mechanically
induced spray scrubbers use high velocity sprays generated
at right angles to the direction of gas flow by a partially
submerged rotor. Scrubbing is achieved by impaction of
both high radial droplet velocity and vortical gas velocity.
Advantages are the relatively low liquid requirements, small
space requirements, high scrubbing efficiency, and high dust
load capacity. The rotor, however, is susceptible to erosion
from large particles and abrasive dusts.31
12 8
-------
GAS CUTLET
PACKiNG
SUPPORT
GRID
LIQUID
DISTRIBUTION
HEADERS
U N W E T T E D
SECTION FOR
MIST ELIMINATION
*' P A C KIN' G SUPPORT
GRID
DIRTY
GAS IN
FRONT
CLEANING
SP R AYS
T I n ! i I 1 i I FTTTT
GAS INLET
m
MIST
ELIMINATOR
SECTION
LIQUI D
INLET
'V WEIR
DISTRIBUTOR
PACK ED
SCRUBBING
SECTION
P AC KING
SUPPORT
I I
n1
/
LIQUID
OUTLET
CROSS-FLOW SCRUBBER
COUN TE RCURRENT-FLOW SCRUBBER
Figure 1'). Packed bed scrubbers31
-------
i. Disintegrator Scrubber - A disintegrator scrubber con-
sists of a barred rotor with.a barred stator. Water is
injected axially through the rotor shaft and is separated
into fine droplets by the high relative velocity of rotor
and stator bars. Advantages of this scrubber are high
efficiency for submicron particles and low space require-
ments. The primary disadvantage is its large power require-
ment'. 61
j. Centrifugal Fan Wet Scrubber - This type of scrubber
(Figure 15) consists of a multiple-blade centrifugal blower
Its advantages are low space requirements, moderate power
requirements, low water consumption, and a relatively high
scrubbing efficiency . 3-1
k. Inline Wet Scrubber - In the axial-fan-powered gas
scrubber, a water spray and baffle screen wet the particles
and centrifugal fan action eliminates the wetted particles
through concentric louvers. Advantages are low space
requirements and low installation costs.31
1. Irrigated Wet Filters - Irrigated wet filters consist
of an upper chamber, containing wet filters and spray-
nozzles for cleaning the gas, and a lower chamber for stori
scrubbing liquid. Liquid is recirculated and sprayed into
the surface of the filters on the upstream side of the bed.
Two or more filter stages are used in series.31.
2. Fabric Filtration
Fabric filters use a filter medium to separate particulate
matter from a gas stream. Two types of fabric filters are
130
-------
3890-1
Figure 15. Centrifugal fan wet scrubber31
131
1
-------
in use--high energy cleaned collectors and low energy
cleaned collectors.32
a. High Energy Collectors - High energy collectors use
pulse jet-s to clean the filter medium, a felt fabric which
is kept as clean as possible.32 The principle of the pulse
jet is based oil the use of an air ejector for dislodging
dust from the bags. The ejector produces a short pulse of
compressed air in the direction opposite to that of the gas
being filtered. The jet must accomplish three things.33
Stop the normal filtering flow.
Transmit a burst of air to the filtration medium,
giving it a vibratory shock.
Create enough pressure in the bag to ensure a reversal
of flow from the clean side to the dirty side of the bag.
b. Low Energy Collectors - Low evergy collectors use shaking
or reverse air flow methods of cleaning. The filter base
is a woven cloth that acts as a site on which the true filter
medium, or dust cake can. build up. 32
3. Mist Eliminators
Mists are liquid aerosals (collections of extremely small
liquid particles suspended in an air stream). Incineration,
one of three methods for controlling mists, has already
been discussed Another technique is scrubbing, but unless
32Frey, R. E. Types of Fabric Filter Installations.
Journal of the "Air Pollution Control Association. 2 4:1148-
114 9. December 1974.
33Bakke, E. Optimizing Filter-Parameters. Journal of the
Air Pollution Control Association. 2_4:1150-1154 , December
137 4 .
13 2
-------
high energy scrubbers are used, extremely Line mist will
not be collected. The third method of controlling mists is
with mist eliminators, of which there are four types. 311
a. Wet-Fiber Mist Eliminator - Wet fiber mist eliminators
depend upon two mechanisms, Brownian diffusion and inertial
impaction, to separate mist and dust particles from air
streams. Brownian diffusion dominates when filter beds have
large specific surface areas, gas velocities range from
1.5 to 9.0 m/min, and the mist consists largely of sub-
micron sized particles. A characteristic of such equipment
is that collection efficiency increases with decreasing gas
velocity because of increased filter bed retention time.
Brownian motion is an important factor in particle capture
by direct interception.31
Interial impaction dominates in collection of particles above
3 pm in size at gas velocities in excess of 9 in/sec in coarse
filter beds. Inertial impaction efficiency increases with
increasing gas velocity.31
Wetted filters are available in two designs, low velocity
(1.5 to 9 m/min) and high velocity (9 to 27 m/min). The
low velocity design consists of a packed bed of fibers
between two concentric screens. Mist particles collect on
the surface of the fibers, coalesce to form a liquid that
wets the fibers, and are moved horizontally and downward by
gravity and the drag of the gases. The liquid flows down
the inner screen to the bottom of the element to a collection
3''Farkas, M. D. Mist Abatement from Plastics Processing
Operations. Plastics and Ec'oiogy, Society of Plastics
Engineers, Inc. Cherry Hill. October 27-28, 1970.
3 8 p.
133
-------
•reservoir. Collection efficiencies are greater than 99% for
particles smaller than 3 ym in diameter.31
The high velocity filter consists of a packed fiber bed
between" two parallel screens. Liquid flow patterns are
similar to those of the low velocity filter and removal
efficiencies range from 852 to 90S for 1 cm to 3 urn particle:
b. Impingement Baffle Mist Eliminator - Baffle mist
eliminators are used to control large diameter solid and
liquid particles. Mist removal efficiencies of 95% may be
achieved for 4 0 inn spray droplets up to a maximum gas
velocity of 7.6 m/sec. Higher gas velocities result in
reentrainment of the liquid droplets.-31
c. Vane-Type Mist Eliminators - Vane-type mist eliminators
have an operating range of 3 to 15 m/sec with collection
efficiencies as high as 99% for 11 urn particles. The
principal advantage of the vane-type mist eliminator over
.the baffle type is the wider range of operation at ccmparabl
removal efficiencies.31
d. . Packed Bed Mist Eliminators - Packed beds can also be
used as mist eliminators. Removal efficiencies range up
to 6 5% at gas velocities of 2 to 3 m/sec. Mist reentrain-
ment occurs at higher gas velocities.31
134
-------
SECTION VI
GROWTH AND NATURE OF THE INDUSTRY
A. PRESENT TECHNOLOGY
The five basic steps involved in rubber processing are:
compounding, mixing, forming, building, and vulcanization.
Compounding is the process of determining the proper in-
gredients and proportions to be used in the rubber recipe
in order to obtain the required properties of the end
product. The main objectives of the mixing operation are
to obtain a uniform blend of the ingredients and to achieve
consistent properties from batch to batch. • Mixing is
presently carried out as a batch process using either a tv/o
roll mixer or an internal (Banbury) mixer. Batch size
varies according to mixing equipment capacity, which is
typically from 68 kg to 136 kg. for a 2.13 m mill and 4 54 kg
or more for the largest internal mixers.
Forming operations usually consist of calendering or ex-
trusion. Calendering involves forming the rubber compound
into thin sheets, coating it on a fabric, or wiping it into
a fabric by means of a series of rollers. Thin sheets of
rubber are built up to make the final thickness desired,
e.g., eight to 10 sheets may be used to make a final sheet
135
-------
1.6 fu-Ti thick, tr»si3r is oc;-cxi;s-:ad by a pc*ver -driven
scxev; in a stationary cylinder viiich forces the heated rufcbar
compound through a die to give the desired shape. Other
forming operations used in robber processing include casting,
blov; molding, and irrjcation rr.olciing.
Building operations vary widely according bo ths product
being anar.ufactured. Tor e::air.ple, ir. tire manufac turs, the
e.v£ruced cord pliss ace applied to tVit± assembly drum one at
a time to build up a tv;o, four, six or eiqht ply tiro.
Vulcanization, A'hich imparts elastic characteristic? ~o
rubberj can be carried out usang Polos heated to I38cC £or
ID 3im to 90 min as m rire manufacturing. Alternatively,
rubber products may be cured in ai~i autoclave with steam or
v/ater cepsr-ding on the required temper a ture and pressure.
Hsatcc air< either au atmospheric Or elevated pressure, car;
also be us£d to vulcanise product.5- thf.t are- acversaiv
affected by -"-icisturs. various con'iiir.c.tions of these cores
are also used in order to achieve the desired properties
ir. the product.
2. EMEHGING TECHNOLOGY
Curing the 12 50 's and '550's, ahe ruober industry ex-
perienced a slov- rate of technological advancement. liowever,
recent years have witnessed. an accelerated pace, arid many
nev; innovatioas are nov beginning to alter ths industry. For
era-sr.pl e, ?aany plants nov employ tanks and silos for bulk
storage and handling of rav,r materials such as fillers or
rein.f orcers. The use of large pre.biending systexs tc provide
fliore uniform quality of raw materials is being explored. In
this vein, the "Far eel Company is reportedly developing
technology for blending chopped or crumb rubber to even
236
-------
out batch-to-batch variations.35 In addition, some large
production facilities now employ fully automated, computer
controlled charger-mixer systems.
An improvement in the curing process is the use of cure
rate integrators that employ a special sensor to accurately
monitor the temperature. These devices have reportedly
reduced curing times by 8£.35 Another example of the trend
toward ' increasing automation is in use in radial tire plants.
The last 2 minutes of the 5-minute tire assembly operation
are now said to be automated.J5
An important advance in blending operations, that of con-
tinuous mixing, is being actively developed. The combination
of an internal mixer with some type of screw mixing will
permit increased mixing capacity and reduced mixing times.
At present, however, this technology is considered to be
several years away.35 The increasing demand for exterior
automotive components made of dent-proof rubber and the
steeply rising cost of energy are expected to further
accelerate the development of new manufacturing processes
in the rubber industry.
The new manufacturing techniques should hasten the further
development of new forms of rubber and their acceptance and
use by fabricators. The new forms of rubber include powdered
rubber for continuous mixing, thermoplastic types which allow
the vulcanization stage to be eliminated, and liquid poly-
mers (especially polyurethancs) for use in casting and
injection molding processes. One source estimates that
3r,Survey Results on Machinery, Equipment. Rubber World.
July 19 7 4. p. 57.
137
-------
within the next 5 years, liquid and powdered rubbers will
account for 20^ of the total rubber market in. the united
States.3 6
C- MARKETING STRENGTHS AND WEAKNESSES
I - 'i'ires
The future growth of the rubber industry is closely related
to the automotive industry, since about two-thirds of all
new rubber produced goes into automotive tires. Of this
amount, about 85% on a unit basis (60S on a weight basis)
goes into passenger car tires. Hence, the demand for rubber
will be greatly'affected by the total passenger vehicle
miles driven and by tire design, which affects tread life.
Average passenger car mileage for the past 10 years has
increased steadily from about 15 Min to 16 Mm annually.
However, this figure is expected to remain nearly constant
or even decline somewhat during the next several years due
to increased fuel costs.
Tire tread life is expected to continue to increase due
to the shifts to beited bias ana radial tires and to smaller
lighter weight cars. From 1968 to 1970, new car manufacturers
switched almost completely from bias ply to belted bias tires,
which offer about 25£ better mileage. The switchover in the
replacement tire market is proceeding at a much slower rate
and is expected to scop at 3 Si to 4 OS, because the owner of
3&Status Report on Elastomeric*Materials. Rubber World.
February 1974. 39 p.
133
-------
an older car is less inclined to buy expensive, long-wearing
tires.3 7
/Another factor that may adversly affect the tire market is
the trend to only four tires per car. Development work towar
this objective is under way at all companies.33 In addition
to safety and convenience, the incentives to "eliminate the
spare" include reduced car weight, more trunk space, and
reduced new-car cost.
The above considerations lead to a projected increase in
consumption of rubber for automotive tires from 1.9 5 Tg in
1974 to 2.142 Tg in 1980. The tire industry's percentage
of total rubber consumption is expected to decrease from
645 m 197 4 to 59% in 198 0.37,38
2. Molded and Extruded Products
The strengths and weaknesses of the molded and extruded
rubber products markets vary with the variety of products
falling in this category. Automotive products (especially
those such as bumpers, seals, electrical wiring, etc.,
which are not normally replaced during the car's lifetime)
exhibit a major weakness. These products are suffering most
heavily from the effects of the recession in the automobile
industry. However, the long-term outlook in this area is
much better. The new emphasis on weight reduction of
37Richardson, II. M. Forecasting in the Rubber Industry.
In: Hydrocarbons: The Dilemma in Forecasting, (papers
presented at the joint meeting of the Chemical Marketing
Research Association and the Commercial Development
Association, New York. May 1974.) p. 77.
3 8 Rubber Products: 1974-1975. Rubber World. January
19 7 5. p. 27.
139
-------
automobiles to improve gasoline mileage should result
in the use of many more rubber and plastic parts.
Another area which could show substantial gains is the re-
placement of PVC products by rubber products. Over the past
8 years, vinyl resin products have replaced rubber in such
products as wire and cable, garden hose, foe :v?ear . weather
stripping, sealants, toys and auto mats. However, a trend
back to rubber is developing due to rising costs of vinyl
resins and the lower processing ccsts associated with
thermoplastic elascorners.39 This "rend could be accelerated
because of the health problems recently associated "with vinyl
chloride monomer.
Rubber parts used by the oil industry in wells, platforms,
refineries, and transportation of oil also have a good
outlook for tiie immediate and long term future due to the
renewed emphasis on drilling in the U.S. as well as other
areas of the world.
The Rubber Manufacturers Association's 1975 prediction for
the moldedr extruded and lathe cut sectors of the rubber
business, shown in Figure 1G, indicates a significant in-
crease in dollar volume in each of the three areas. Although
this prediction was made in November 1974 before the sharp
drop in the economy, the general strength in this area
should still remain when economic recovery begins to take
effect. Another indication of the strength of this segment
:Dworkin, D. Changing Markets- and Technology for
Specialty Elastomers. Rubber World. February 1975
p. 43.
14 0
-------
:.v^SA\»
111
illli
.-.ivi-;-.. ' '"
1974
1975
Figure 16. Domestic market estimates and forecasts
molded, extruded, lathe cut products
of the industry is the RMA data on new rubber consumption
shown in Table 39. Although total consumption for 1974 shows a
decline from 1973, the decrease is confined to the tire and
tire products area. The non-tire products show an increase
of about 4 Gg.
141
-------
Table 39. MEW RUBBER CONSUMPTION38
Year
(Tg)
Tires
Won-Tires
Total
1965
1.306
0 . 7 4 9
2 . 055
197 0
1. 578
0 . 899
2.477
1971
1.771
0 . 912
2 . 683
1972
1.919
1. 010
2.929
1973
1.990
1. 09G
3 . 086
1974
1 . 9 5 0 a
1.100Q
3 . 0503
aEstimated by the Rubber Manufacturers
Association. ¦
The long-term strength in the molded and extruded products
sector can also be inferred from the data in Reference 39 on
specialty elastomers. These data suggest strong growth for
all but a few specialty materials over the next 4 years.
Since the use of specialty rubbers is heavy in the molded
and extruded fields, the increases should be reflected in
these areas.
3 . ilose and Belting
The major strengths of the hose and belting sector of the
rubber industry are in equipment for the oii industry and in
automotive replacement parts. The latter 'field should prove
particularly strong if, as expected, many people continue to
defer the purchase of a new car due to high prices. On the
other hand, new automobile parts represent a major weakness
in this sector due to the recession in the automotive in-
dustry.
14 2
-------
The ultimate short-term strength of this segment of the
industry may well depend upon the effect of government
deficits on interest rates. Many plants should be scheduled
for expansion and new plants should be built if industry
is to be "prepared for the nc:-:t round of high level business.
Hov.-ever, high interest rates could cause postponements in
construction with a resultant drop in demand for rubber
hose and belting.
The long-term strength of the hose and belting sector is
indicated by the Rt-iA estimates of the market potential for
these products over the next 5 years as shown in Figure 17.
Figure 17. Market potential for rubber
hose and belting38
14 3
-------
Natural Rubber
The long-term outlook for natural rubber is extremely good
due to the problems of high prices and short supplies of
raw materials for synthetic rubber created by the steep
rise in petroleum prices. One source1'" estimates that the
world market for natural rubber may double by 1980.
Major weaknesses over the short term are associated with
the slumps in the automotive and housing industries. Two-
thirds of all natural rubber is used for tires, while 401-
of the latex produced is used by the carpet industry for
carpet backing. The carpet business is down 303 to 40%,
and many carpet mills are reportedly in danger of folding.35
Another short-term problem facing the natural rubber industry
is the shortage of fertilize::, which could limit the ability
to increase production.
5. Total Mew Rubber Consumption
From 1960 to 1973, total new rubber consumption in the
United States increased at an average annual rate of 5.4?,. 1,1
In 1974, consumption decreased approximately 1% from '1973.
Through 1930, consumption is expected to increase at a more
moderate rate, 2.43 to 3 . 8% , 3 7 r2 primarily due to the
effects of energy conservation programs and the socio-
economic trends in the transportation industry detailed
above. This rate of growth will result in total new rubber
it0 Rubber Age. June 197 4. p. 18.
aiRubber Demand Faces Lower Growth
Engineering News. May 20, 1974.
u2Rubber Consumption to Increase,
p. 83 .
Rate. Chemical and
p. 12.
Rubber World. Kay 197 5.
14 4
-------
consumption of "3.52 Tg to 3.82 Tg in 1980, compared to an
estimated 3.05 Tg in 137 4. Table 4 0 gives a breakdown of
estimated new rubber consumption for 19 3 0 based on an
average annual growth rate of 3% from 1974 through 1980.
The recent history of new rubber consumption is depicted
graphically in Figure 18.
Table 40. RUBBER CONSUMPTION FORECAST FOR 198031
(Tg)
Tires
Non-Tire
Total
Styrenc-butadiene rubber
0.846
0 . 353
1.199
Polybutaaiene rubber
0.32 4
0.03 6
0 .360
Isoprenic rubber
0.832
0.310
1.192
EPDM rubber
0.04 5
0 . 250
0 . 295
Butyl or chlorobutyl rubber
0.045
0 . 100
0.145
Nitrile rubber
-
0 . 086
0.086
All other elastomers
-
0 . 354
0 . 354
2.142
1.489
3 .631
145
-------
(EST)
Figure 18. Total new rubber consumption,
synthetic vs '-natural source
146
-------
SECTION VII
APPENDIX
K-ATIO^ALE FOP. A SAMPLING Pi,AM
Literature-derived omission factors v/ere used in the
preliir.mary assessment of rubber processing m order to
calculate the state and national mass emissions, the maxi-
mum ground level concentration, and, thus, the severity
factor and affected population for each pollutant shown.
Additional information on emission factors from compounding
and curing operations is needed tc assess the environincnLai
impact from these sources.
As described in Section IV.A.l., emissions from compounding
consist of particulates and hydrocarbons. Compounding
generates a cloud of 5% to 50% opacity (per EPA Method No. 9 J
which is removed from the building via an exhaust hoed. The
literature however, does not contain amissicn factors for
either particulate or hydrocarbon emissions from compounding
operations (as evident in Tables 31 and 32). Field sampling
is thus required to obtain this information.
Sirailari ly , Section IV. A. 2. describes curing operations .
Jigs in, the literature does ncn contain enission factors fer-
tile compounds emitted and fie.lc sarr.pJ.ing is necessary to
obtain this information.
-------
SECTION VIII
CONVERSION FACTORS1'3
To convert from
:o
M u1tiply by
degrees
foot
foot3
degree Fahrenheit
inch of water (60°F)
pound (mass)
ton
radian
meter (m)
meter3 (in3)
degree Celsius
pascal (Pa)
kilogram (Kg)
meg ag ram (i-lg)
1.745 v 10"---
3.048 x 10"1
2.832 x 10~2
t°c = (t°F - 32)/1.3
2.488 x 102
4.33 6 x 10
9.072
10
- 1
- i
PREFIXES
Pref ix
Symbol
Multiplication
Factor
Example
tera
T
1012
l
Tg
- 1 x 101
gig a
C,
c^.
o
I—1
l
Gg
- 1 x 10s
mega
M
10 5
l
i'-ic
= 1 x 10s
kilo
k
103
l
km
= 1 x 103
milli
m
10~3
l
mm
= 1 x 10-
micro
u
Uj
1
O
i—{
i
um
= 1 x 10"
nano
n
10" 9
l
mil
I
0
r—!
1 1
II
"3Metric Practice Guide, E 330-74. American Society for
Testing and Materials. Philadelphia, November, 1974.
3 4 p.
14 3
-------
SEC. ION iX
REFERENCES
1. Preliminary Report, 137 2 Census of Manufactures,
Industry Series, Tires and Inner 'J'ubcs, SIC 3011,
U.S. Department of Coserce, Social ar.il Economic
Statistics Administration, Bureau of the Census,
Washington, D.C., March 1974.
2. Preliminary Report, 1972 Census cf Manufactures,
Industry Series, Rubber and Plastics Footwear,
SIC 3021, U.S. Department of Commerce, Social and
Economic Statistics Administration, Bureau cf the
Census, Washington, D.C., March 1974.
3. Preliminary Report. 1972 Census c-f Manufactures,
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