United States
Environmental Protection
Agency
Industrial Environmental Research
Laboratory
Research Triangle Park NC 27711
Research and Development
EPA-600/S2-80-209 July 1981
Project Summary
Textile Warp Size Reclamation
Using Thermal Precipitation
W. S. Perkins, R. P. Walker, and L J. Hirth
The report describes a novel method
for reclaiming size based on precipita-
tion of the size material by heating the
desize washwater. The method uses
hydroxypropyl cellulose (HPC) or
hydroxypropyl methylcellulose
(HPMC) which are soluble in cool
water but insoluble in warm water.
Reclaiming size would eliminate most
of the BOD typically resulting from
sizing and desizing. Since maximum
system temperature with HPC is
about 50°C, compared to 95°C for a
conventional system, considerable
energy is conserved. Strength and
elongation of yarns sized with virgin
HPC and with reclaimed HPC were not
significantly different from those of
yarns sized with the conventional size,
polyvinyl alcohol (PVA), at similar
add-on levels. Abrasion resistance of
yarns sized with HPC was lower than
that of yarns sized with PVA at similar
add-on levels. Weaving of HPC-sized
50/50 polyester/cotton yarns in the
laboratory was successful. In produc-
tion weaving of percale sheeting, HPC
accumulated on the shuttle caused
poor weaving efficiency. The capital
investment for reclaiming HPC using
thermal precipitation is much lower
than for reclaiming PVA using ultra-
filtration. Operating costs for recover-
ing HPC by thermal precipitation and
for recovering PVA by ultrafiltration
represent a savings over conventional
sizing and desizing without reclaiming
size.
This Project Summary was develop-
ed by EPA's Industrial Environmental
Research Laboratory, Research Tri-
angle Park, NC, to announce key find-
ings of the research project that is fully
documented in a separate report of the
same title (see Project Report ordering
information at back).
Introduction
Virtually all textile yarns which are to
be woven into the lengthwise direction
(warp) in a fabric are coated with a
protective material, called size, during
the slashing process. The purpose of
this size is to improve the performance
of the yarn in the weaving process. In
most cases the size material is removed
from the woven fabric in the finishing
plant. Published data indicate that 45%
to 75% of the BOD load from a woven
fabrics finishing plant results from this
warp size which is removed from the
fabric.
A process to recover and recycle the
warp size used in textile processes has
the potential to lower the BOD and COD
of textile finishing plant effluents more
than any other single change in textile
processing. Such a process has been
the objective of much development
work in recent years. The following are
specific examples of approaches to size
recovery and recycle:
(1) Recovery of carboxymethyl cellu-
lose by chemical precipitation
from the desize wastewater has
been studied but not commercial-
ized.
(2) Recovery of polyvinyl (PVA) by
chemical precipitation has also
been subject to investigation.
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(3) Studies of recovery of warp size
via solvent sizing and desizing
have been made. A solvent sizing
and solvent desizing system has
been developed by two Italian
machinery companies.
(4) Recovery of polyvinyl alcohol
(PVA)by ultrafiltration of the de-
size wastewater has been subject
to considerable development, and
commercial processes have now
been operating for several years.
The tremendous interest of the U.S.
textile industry in recycle of warp size is
understandable since the economic
outlook for such a development is as
favorable as are the environmental
considerations. The size material adds
no value to the product (fabric), since it
is normally removed in desizing and
disposed of in a wastewater treatment
facility. Therefore, the size material it-
self adds to the cost of fabric production.
A process for recovery and reuse of size
material may prove profitable to the
textile mill through reduced fabric
production cost if a high degree of
recovery of the size material is obtained.
Therefore, a size reclamation process
offers the potential for a modification
from which the mill may realize a direct
return on investment. This approach
should be considerably more attractive
to management than the prospect of
construction of additional treatment
facilities which may become obsolete as
the 1983 Effluent Guidelines are imple-
mented. Further, size recycling will
allow the industry room for expansion
and growth without great capital invest-
ment for wastewater treatment
facilities since recovery and recycle of
warp sizes will allow increases in
production without large increases in
effluent loads.
The size reclamation system which is
the subject of this report uses a size
material selected from a group of
polymers having the unusual property
of being soluble in water at room
temperature but insoluble at some
higher temperature. Hydroxypropyl-
cellulose (HPC) is such a polymer. HPC
is soluble in water at temperatures
below 43°C (109°F) but becomes
almost completely insoluble in water at
temperatures above 45°C (113°F).
Hydroxypropylmethylcellulose (HPMC)
also exhibits this "reverse solubility"
property but at a higher precipitation
temperature than is required for HPC.
Most of the work done in this project
was concerned with HPC rather than
HPMC and except where otherwise
specified the discussions pertain to HPC
rather than HPMC.
Precipitation of HPC or HPMC from
desize wastewater can be accomplished
by heating the desize wastewater. A
schematic diagram of the desizing and
recovery system is shown in Figure 1.
Application of the size material to the
warp yarn in slashing and washing of
the size material from the woven fabric
in desizing is done with water at a
temperature {lower than 43°C. The
desize washwater containing HPC at a
concentration of 0.5 to 1.5% by weight
is filtered to remove insoluble impurities
and heated to above 45°C to precipitate
the HPC. The precipitated HPC is then
separated from most of the water. The
HPC redissolves when cooled to yield a
solution concentrated enough to reuse
in slashing. The recovered water can be
cooled to below 43°C and reused in the
desize washer.
This report describes both laboratory
and in-plant work concerned with the
development of a process utilizing HPC
as the warp size with the objective of
reclaiming the HPC using the thermal
precipitation principle. Work was per-
formed in the following areas:
Fabric in
(1) Utility and performance of HPC as\
a textile warp size.
(2) Design and operation of a thermal
precipitation size reclamation
system.
(3) Economics of size reclamation by
thermal precipitation.
Conclusions
Hydroxypropylcellulose (HPC) is
soluble in water at room temperature
but becomes virtually insoluble in water
at a temperature greater than about
43°C. HPC can be precipitated from
water by heating the water to above the
precipitation temperature. The HPC can
then be separated from most of the
water by settling, filtration, or centrifu-
gation. Therefore, a dilute solution such
as is obtainable in a conventional desize
washer can be concentrated to the
extent required for use of the material in
a conventional slashing process. More
than 90% of the HPC in a 1.0% solution
of desize washwater can be obtained at
up to 25% concentration in the re-
claimed solution using a recovery
system based on settling of the HPC in
warm water. Hydroxypropylmethylcel-|
lulose (HPMC) also exhibitsthistherman
Fabric out
Desize Washwaste
11.0% size)
Desize
water at 40°C
Reclaimed Water
Filter for
fiber and
\insoluble
impurities]
Fresh
Water
\fapprox. 10%
of total)
Cooling
of
reclaimed}
water
Heats to
45°C
Water/
Size
Separator
Reclaimed
Water
Concentrated
size to slasher
(8 - 10%)
Figure 1. Schematic of desize and recovery system.
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precipitation phenomenon, but at about
65°C.
Textile yarns consisting of 100%
cotton or 50% polyester and 50% cotton
can be sized with HPC or HPMC. The
physical properties of yarns sized with
HPC or HPMC are adequate for the
yarns to be woven into fabric. The
tensile strength of yarn sized with HPC
is appreciably higher than that of un-
sized yarn and is not significantly differ-
ent from the tensile strength of yarns
sized with the conventional size,
polyvinyl alcohol (PVA), at the same size
add-on. The abrasion resistence of
yarns sized with HPC is higher than
that of unsized yarns. The magnitude of
the improvement in abrasion resistance
depends on the size add-on level. The
abrasion resistance of yarns sized with
PVA is higher than that of yarns sized
with HPC at the same add-on level.
Clear flexible films are formed upon
evaporation of the water from aqueous
solutions of HPC. Clear films are pro-
duced even when the temperature is
higher than that which causes the HPC
to precipitate from water. The strength
of HPC films is similar to that of conven-
tional sizes such as starch and carboxy-
methylcellulose. The elongation of films
of HPC is intermediate between that of
conventional size, starch, and PVA.
Yarns sized with HPC can be woven
into fabric. On 50-inch wide looms
weaving at 215 filling insertions per
minute, the contact of the shuttle with
the yarn results in an accumulation of
HPC on the shuttle. The accumulation of
HPC on the shuttle is undesirable be-
cause it eventually interferes with the
passage of the shuttle into the yarn shed
causing excessive yarn breaks near the
sides of the loom. The accumulated size
material may also be periodically
stripped away from the shuttle and
become woven into the fabric causing a
fabric defect. This accumulation of HPC
on the shuttle does not occur to a dis-
ruptive degree on 24-inch looms weav-
ing at 175 filling insertions per minute.
Whether this accumulation of size on
the shuttle also occurs with HPMC on
50-inch looms is not known, but the
accumulation of HPMC does not occur
to a disruptive degree on 24-inch looms
weaving at 175 filling insertions per
minute.
HPC reclaimed from woven fabric has
tensile strength and elongation not
appreciably different from that of virgin
HPC. Yarns sized with reclaimed HPC
have abrasion resistance not appreci-
ably different from that of similar yarns
sized with virgin HPC. Pure HPC may be
more flexible than is desirable in a size
material. HPC softens dramatically at
high relative humidity, and its effec-
tiveness as a warp size deteriorates.
Fabrics containing HPC can be rapidly
desized using room-temperature water.
The rate of removal of HPC from a poly-
ester/cotton fabric is as rapid at 25°C
(77°F) as the removal of PVA at 95°C
(203°F). Water used for desizing and
subsequently separated from the HPC in
the recovery system is suitable for reuse
in desizing. The content of impurities in
desize washwater increases with each
reuse cycle. A steady state level of
impurities is reached if a fraction of the
desize washwater is discharged at each
cycle.
Thermally precipitated HPC particles
have a negative zeta potential in water.
Consequently, coagulation and settling
of HPC particles is enhanced by addition
of cations such as Ca+* or Al+++. The
addition of cations does not have an
appreciable effecton the settling rate of
particles of thermally precipitated
HPMC.
Virgin HPC is resistant to biodegrada-
tion and solutions can be stored for long
periods. Reclaimed HPC solutions are
subject to biodegradation because of
the presence of natural impurities
removed from the fabric. Reclaimed
HPC solutions can be preserved with
agents typically used for preservation of
textile chemicals. HPC is stable for long
periods at the temperature necessary
for its reclamation.
The capital investment for reclama-
tion of HPC by thermal precipitation is
about one-third of that for reclamation
of polyvinyl alcohol by ultrafiltration.
The operating costs including size
material costs for a system based on
reclamation of HPC by thermal precipi-
tation is slightly higher than for a
system based on reclamation by PVA by
ultrafiltration. The payback period for a
thermal precipitation system is about
one-third of that for an ultrafiltration
system. Because of the value of the re-
claimed material, size reclamation
systems based on thermal precipitation
and ultrafiltration both operate at lower
costs than a conventional desizing
system not involving size reclamation.
A desize and reclamation system
using HPC operates at a maximum
water temperature of about 50°C
whereas a system using PVA operates
at a temperature of about 95°C. The
result is an energy savings of about
0.655 x 106 Btu per 100 Ib. of fabric
desized.
Recommendations
Size reclamation is an economical
approach to chemical and water con-
servation and will reduce the pollution
load from most woven fabrics finishing
plants. The size reclamation technique
that is most applicable to a particular
mill must be selected based on factors
peculiar to that mill. A critical compari-
son of all size reclamation techniques is
not presently available, but such a
comparison would be useful for
decision makers in the textile industry.
Size reclamation using thermal pre-
cipitation appears to be technically and
economically feasible at present only for
selected types of plants. Those plants
weaving cotton or polyester/cotton on
narrow looms can probably use hydrox-
ypropylcellulose as the warp size. This
size can be recovered by thermal precip-
itation and reused for sizing. HPC may
also be useful in shuttleless weaving.
The possibility of using HPC as a size in
be useful in shuttleless weaving. The
possibility of using HPC as a size in
machines using projectile, rapier and air
jet filling insertion mechanisms should
be investigated. HPC is not recommend-
ed for weaving of 50-inch wide fabrics
at a speed of 215 picks per minute using
shuttle looms at the current stage in its
development as a warp size.
The greatest deficiency of HPC as a
warp size is insufficient hardness. The
possibility of chemical modification of
the material to make this property
suitable for warp sizing purposes should
be investigated. This work would best be
done by a chemical company experi-
enced in evaluation of polymers for
warp sizing.
HPC accumulates on the shuttle
during the weaving of 50-inch wide
fabrics if the shuttle is made of wood or
of laminated cotton fabric composite
materials. Shuttles made of other mate-
rials should be tested to determine if the
accumulation of HPC occurs.
Hot melt sizmg is a developing tech-
nology for the textile industry. The
process applies a molten size to the yarn
and uses no water. The first production
model hot melt sizing machine will be
available in the near future. Since HPC
is a thermoplastic material its applica-
bility as a hot melt size should be inves-
tigated. Conventional recoverable size
materials such as PVA and CMC are not
applicable bythe hot melttechnique and
* U.8. OOVEBHMEHIPRIKTIHO OFFICE «61 -757-012/72Z8
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size materials which have been
developed especially for hot melt sizing
are not recoverable. Therefore, the
availability of the recoverable hot melt
size would be highly desirable.
Warren S. Perkins. Robert P. Walker, and Leo J. Hirth are with Auburn University,
Auburn, AL 36830.
Max Samfield is the EPA Project Officer (see below).
The complete report, entitled "Textile Warp Size Reclamation Using Thermal
Precipitation," (Order No. PB 81-129 041; Cost: $8.00, subject to change) will
be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Industrial Environmental Research Laboratory
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
f
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
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