FINAL REPORT
A STUDY to EVALUATE TECHNIQUES of ASSESSING
AIR POLLUTION DAMAGE to PAINTS
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FINAL REPORT
on
A Study to Evaluate Techniques of Assessing
Air Pollution Damage to Paints
to
Division of Ecological Research
Materials Branch
Environmental Protection'Agency
Contract No. 68-02-0030
May, 1972
by
G. G. Campbell, G. G. Schurr and
D. E. Slawikowski
The Sherwin-Williams Company
Research Center
10909 Cottage Grove Avenue
Chicago, Illinois 60628
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FOREWORD
This report was prepared by The Sherwin-Williams Company under Contract No.
68-02-0030 "A Study to Evaluate Techniques of Assessing Air Pollution Damage
to Paints" for the Environmental Protection Agency, Division of Ecological
Research, Materials Branch, Research Triangle Park, North Carolina with
Mr. J. W. Spence as Project Officer.
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ABSTRACT
Erosion rate studies supported by ATR measurements and SEM analyses provide a
definitive technique for determining the effect of atmospheric pollutants on
the performance of exterior coatings- This technique is based on the use of a
gas controlled, Xenon Arc type Weather-Ometer. The other methods of testing
that were investigated - tensile strength, gloss or sheen and surface roughness -
provided considerably less consistent trends in data for either the "short term"
exterior exposure or the Weather-Ometer studies.
Atmospheric pollutants at levels representative of a highly polluted in-
dustrial site (1.0 ppm S02 or 03) were shown in Weather-Ometer studies to
exert a significant adverse effect on the performance of specific coatings
compared to the zero pollutant condition. In general, 1.0 ppm S02 as compared
to the zero pollutant level caused a considerable effect on the oil house paint,
a moderate effect on the latex and coil coatings, but no effect on the alkyd
industrial maintenance paint and the automotive refinish. Based on the com-
parison of erosion rates, S02 at the 1 ppm level affected these coatings to
a greater extent in either the shaded or unshaded condition than exposure to
1 ppm 03. Graphs of the erosion rates with accompaning 95 percent confidence
limits versus pollutant level (zero, 0.1 and 1 ppm S02 or 03) supports the a priori
hypothesis that erosion rates are linearly related to pollutant concentration.
In addition, the ranking of a coating in terms of erosion rates was also shown
to be virtually independent of exposure to a pollutant type or level.
The erosion rates for coatings exposed at the Chicago and Valparaiso exterior
testing sites were higher than at the Los Angeles and North Dakota locations.
This trend in data is explained by the higher S02 level at the two former
exposure sites. ATR measurements and SEM photomicrographs also support this
contention. In addition, the ranking in terms of mils loss was virtually
the same as the erosion rates generated in the Weather-Ometer studies regard-
less of exposure location (both north and south).
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TABLE OF CONTENTS
Page
List of Tables IV
List of Figures VI
I. Introduction 1
II. Project Description 2
A. Objective 2
B. Scope of Research 2
III. Materials and Experimental Procedure 2
A. Coatings - 2
B. Test Methods for Determining Film Damage 3
C. The Review of Existing Exterior Exposure Records (Task l) .... 5
D. Panel Preparation for Field and Laboratory Exposures 6
E. Exposure Studies 8
IV. Experimental Results and Discussion 11
A. Task I - The Review of Existing Exterior Exposure Records .... 11
B. Task II - Short Term Exterior Exposure Ik
C. Task III - Accelerated Laboratory Exposures 3^
V. Summary and Conclusions 82
VI. Recommendations for Further Research 8U
VII. List of References 85
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IV
LIST OF TABLES
Table Page
1 Location of Exterior Test Fences 7
2 Application Parameters for the Five Selected Coatings 7
3 Service Life for Acrylic Latex House Paint Exposed at Five
Exterior Exposure Sites 12
k Service Life Data for L/T/Z Oil Base House Paint Exposed at
Five Exterior Exposure Sites 12
5 Service Life Data for the Alkyd Industrial Maintenance Coating
Exposed at Five Exterior Exposure Sites * 1J
6 Service Life Data for Nitrocellulose Acrylic Automobile
Finish Exposed at Four Exterior Exposure Sites „ 13
7 Service Life in Years from Erosion Rate Data Versus Visual
ratings for the Coil Coating, Acrylic Latex and Oil Paint ... 1J
8 Erosion Data (Mils Loss) of the Selected Coatings after 7
months Exposure at Four Exterior Locations (Both North and
South 15
9 Gloss Measurements (60°) of the Selected Coatings after 3 and
7 Months of Exposure at the Four Exterior Locations 17
10 Sheen Measurements (85 ) of the Selected Coatings after 3 and
7 Months of Exposure at the Four Exterior Locations 18
11 Surface Roughness (Percent Change with Respect to Unexposed
Control) of the Selected Coatings after 7 Months Exposure 20
12 Ranking of Percent Change in Surface Roughness for the Five
Selected Coatings Exposed for 7 Months at the Four Exterior
Locations , 21
13 Tensile Strength Determinations (PSl) of the Selected
Coatings After J and 7 Months Exposure at Four Exterior
Locations (Both North and South) 23
Ik Slope of Erosion Data Accompanied by a T-Test Probability
("jo) that a Statistical Difference Exists Between the
Respective Slope for a Given Pollutant Type and Level
Versus the Zero Pollutant Level 36
15 Gloss Measurements (60°) of Panels Exposed to the Various
Pollutant Conditions in the Weather-Ometer 1*3
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LIST OF TABLES (continued)
Table Page
16 Surface Roughness (Percent Change with Respect to
Control) of Weather-Ometer Panels After 1,000
Hours Exposure at Various Pollutant Levels 37
17 Ranking of Percent Change in Surface Roughness of Films
Exposed in Weather-Quieter at Various Pollutant Levels .... kQ
18 Tensile Strength Determination (PSl) of Films Exposed
in Weather-Ometer at Various Pollutant Levels 57
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VI
LIST OF FIGURES
Figure Page
1 Scanning Electron Photomicrograph - Automotive Refinish -
Unexposed Contro 1 - 700X*. - 25
2 Scanning Electron Photomicrograph - Automotive Refinish -
1 Months at Leeds, North Dakota - 700X „ 25
3 Scanning Electron Photomicrograph - Automotive Refinish
- 7 Months at Research Center, Chicago - 700X 25
k Scanning Electron Photomicrograph - Latex House Paint - Unexposed
Control - 700X 27
5 Scanning Electron Photomicrograph - Latex House Paint - 7
Months at Leeds, North Dakota - 700X 27
6 Scanning Electron Photomicrograph - Latex House Paint -
7 Months at Leeds, North Dakota - 7000X 27
7 Scanning Electron Photomicrograph - Latex House Paint -
7 Months at Research Center, Chicago - 700X , 27
8 Scanning Electron Photomicrograph - Latex House Paint - 7
Months at Research Center, Chicago - 7000X 27
9 Scanning Electron Photomicrograph - Coil Coating - Unexposed
Control - 700X , 29
10 Scanning Electron Photomicrograph - Coil Coating - 7 Months
at Leeds, North Dakota - 700X , 29
11 Scanning Electron Photomicrograph - Coil Coating - 7 Months
at Research Center, Chicago - 700X 29
12 Scanning Electron Photomicrograph - Industrial Maintenance
Coating - Unexposed Control - 700X 31
IJ Scanning Electron Photomicrograph - Industrial Maintenance
Coating - 7 Months at Leeds, North Dakota - 700X 3!
Ik Scanning Electron Photomicrograph - Industrial Maintenance
Coating - 7 Months at Leeds, North Dakota - 7000X 3!
15 Scanning Electron Photomicrograph - Industrial Maintenance
Coating - 7 Months at Research Center, Chicago - 700X 31
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VII
LIST OF FIGURES (continued)
Figure Page
16 Scanning Electron Photomicrograph - Industrial Maintenance
Coating - 7 Months at Research Center, Chicago - 7000X 31
17 Scanning Electron Photomicrograph - Oil House Paint -
Unexposed Control - 700X 33
18 Scanning Electron Photomicrograph - Oil House Paint - 7
Months at Leeds, North Dakota - 700X 33
19 Scanning Electron Photomicrograph - Oil House Faint -
7 Months at Leeds, North Dakota - 7000X 33
20 Scanning Electron Photomicrograph - Oil House Paint -
7 Months at Research Center, Chicago - 700X 33
21 Scanning Electron Photomicrograph - Oil House Paint - 7 Months
at Research Center, Chicago - 7000X 33
22 Slopes of Erosion Data Versus Pollutant Level for the Coating
Exposed to S02 in the Weather-Ometer - Shaded Condition 38
23 Slopes of Erosion Data Versus Pollutant Level for the
Coating Exposed to S02 in the Weather-Ometer - Unshaded
Condition 39
2k Slopes of Erosion Data Versus Pollutant Level for the Coatings
Exposed to 03 in the Weather-Ometer - Shaded Condition kO
25 Slopes of the Erosion Data Versus Pollutant Level for the
Coatings Exposed to 03 in the Weather-Ometer (Unshaded
Condition) kl
26 Gloss Versus ppm S02 or 03 After 1000 Hours Exposure in the
Weather-Ometer - Shaded Condition, kk
27 Gloss Versus ppm S02 or 03 After 1000 Hours Exposure in
the Weather-Ometer - Unshaded Condition k$
28 Sorption-Desorption of Weather-Ometer Panels - Unexposed
Controls 50
29 Sorption-Desorption of Weather-Ometer Panels Exposed for a
1,000 Hours to "0" Pollutants - Shaded Condition 51
30 Sorption-Desorption of Weather-Ometer Panels Exposed for a
1,000 Hours to "0" Pollutants - Unshaded Condition 52
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VTII
LIST OF FIGURES (continued)
Figure Page
31 Sorption-Desorption of Weather-Ometer Panels Exposed
for a 1,000 Hours to 1.0 ppm 03. - Shaded Condition ....... 53
32 Sorption-Desorption of Weather-Ometer Panels Exposed
for 1,000 Hours to 1.0 ppm 03 - Unshaded Codition ......... 5^
33 Sorption-Desorption of Weather-Ometer Panels Exposed
for 1,000 Hours to 1.0 ppm S02 - Shaded Condition ......... 55
jit- Sorption-Desorption of Weather-Ometer Panels Exposed for
a 1,000 Hours to 1>0 ppm S02 - Unshaded Condition ......... 56
35 Scanning Electron Photomicrograph - Latex House Paint -
Unexposed Control TOOK > . .................. . ............... 6l
36 Scanning Electron Photomicrograph - Latex House Faint -
Unexposed Control - 7000X ................................. 6l
37 Scanning Electron Photomicrograph - Latex House Paint
- 1000 Hours Exposure to "0" Pollutant - Unshaded Condition
- 700X ................ . ................................... 61
38 Scanning Electron Photomicrograph - Latex House Paint -
1,000 Hours Exposure to "0" Pollutant - Unshaded Condition -
7000X . . ............. „ ..................................... 61
39 Scanning Electron Photomicrograph - Latex House Paint -
1,000 Hours Exposure to 1.0 ppm 03 - Unshaded Condition -
700X [[[ 63
kO Scanning Electron Photomicrograph - Latex House Paint -
1,000 Hours Exposure to 1.0 ppm 03 - Unshaded Condition -
7000X [[[ 63
ill Scanning Electron Photomicrograph - Latex House Faint -
1,000 Hours Exposure to 1.0 ppm S02 - Unshaded Condition -
700X ...................................... . ............... 63
42 Scanning Electron Photomicrograph - Latex House Paint -
1,000 Hours Exposure to 1.0 ppm S02 - Unshaded Condition -
7000X ..... . ............................... . ............... 63
4-3 Scanning Electron Photomicrograph - Coil Coating - Un-
exposed Contro 1 - 700X .... ................................ 65
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IX
LIST OF FIGURES (continued)
Figure Page
45 Scanning Electron Photomicrograph - Coil Coating -
1,000 Hours Exposure to "0" Pollutant - Unshaded Condition
- TOOX ..., 65
46 Scanning Electron Photomicrograph - Coil Coating - 1,000
Hours Exposure to "0" Pollutant - Unshaded Condition -
7000X 65
47 Scanning Electron Photomicrograph - Coil Coating - 1,000
Hours Exposure to 1.0 ppm 03 - Unshaded Conditio - 700X •••• 67
48 Scanning Electron Photomicrograph - Coil Coating - 1,000
Hours Exposure to 1=0 ppm 03 - Unshaded Condition -
7000X 67
49 Scanning Electron Photomicrograph - Coil Coating - 1,000
1 Hours Exposure to 1.0 ppm S02 - Unshaded Condition - 700X ... 67
50 Scanning Electron Photomicrograph - Coil Coating -
1,000 Hours Exposure to 1.0 ppm S02 - Unshaded Condition -
7000X 67
51 Scanning Electron Photomicrograph - Oil House Paint -
Unexposed Control - 700X 69
52 Scanning Electron Photomicrograph - Oil House Paint -
1,000 Hours Exposure to "0" Pollutant - Unshaded Condition -
700X ,.. 69
53 Scanning Electron Photomicrograph - Oil House Paint - 1,000
Hours Exposure to "0" Pollutant - Unshaded Condition -
7000X 69
54 Scanning Electron Photomicrograph - Oil House Paint -
1,000 Hours Exposure to 1.0 ppm 03 - Unshaded Condition -
700X . ,. ,, .., ... „ 71
55 Scanning Electron Photomicrograph - Oil House Paint - 1,000
Hours Exposure to 1.0 ppm 03 - Unshaded Condition -
7000X , 71
56 Scanning Electron Photomicrograph - Oil House Paint -
1,000 Hours Exposure to 1.0 ppm S02 - Unshaded Condition -
700X 71
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LIST OF FIGURES (continued)
Figure Page
57 Scanning Electron Photomicrograph - Oil House Paint - 1,000 ...
Hours Exposure to 1.0 ppm S02 - Unshaded Condition - 7000X 71
58 Light Microscopy Photograph - Oil House Paint - 1,000 Hours
Exposure to 1.0 ppm S02 - Unshaded Condition - l^OX 73
59 Scanning Electron Photomicrograph - Industrial Maintenance
Coating - Unexposed Control - 700X 75
60 Scanning Electron Photomicrograph - Industrial Maintenance
Coating - 1,000 Hours Exposure to "0" Pollutant - 700X 75
6l Scanning Electron Photomicrograph - Industrial Maintenance
Coating - 1,000 Hours Exposure to "0" Pollutant - 7000X 75
62 Scanning Electron Photomicrograph - Industrial Maintenance
Coating - 1,000 Hours Exposure to 1.0 ppm 03 - Unshaded
Condition - 700X 77
63 Scanning Electron Photomicrograph - Industrial Maintenance
Coating - 1,000 Hours Exposure to 1.0 ppm 03 - Unshaded
Condition - 7000X „ 77
6k Scanning Electron Photomicrograph -Industrial Maintenance
Coating - 1,000 Hours Exposure to 1.0 ppm S02 - Unshaded
Condition - 700X 77
65 Scanning Electron Photomicrograph Industrial Maintenance
Coating - L>000 Hours Exposure to 1.0 ppm S02 - Unshaded
Condition - 7000X 77
66 Scanning Electron Photomicrograph - Automotive Re finish - Un-
exposed Control - 700X 79
67 Scanning Electron Photomicrograph - Automotive Refinish -
Unexposed Control - 7000X 79
68 Scanning Electron Photomicrograph - Automotive Refinish -
1000 Hours Exposure to "0" Pollutant - Unshaded Condition -
700X 79
69 Scanning Electron Photomicrograph - Automotive Refinish - 1000
Hours Exposure to "0" Pollutants - Unshaded Condition - 7000X .. 79
70 Scanning Electron Photomicrograph - Automotive Refinish -
1,000 Hours Exposure to 0.1 ppm 03 - Unshaded Condition - 7000X. 8l
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XI
LIST OF FIGURES (continued)
Figure Page
71 Scanning Electron Photomicrograph - Automotive Refinish -
1,000 Hours Exposure to 1.0 ppm 03 - Unshaded Condition -
700X 81
72 Scanning Electron Photomicrograph - Automotive Refinish -
1,000 Hours Exposure to 1.0 ppm S02 - Unshaded Condition - 700X. 8l
73 Scanning Electron Photomicrograph - Automotive Refinish -
1,000 Hours Exposure to 1.0 ppm S02 - Unshaded Condition -
7000X 81
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T. Introduction
Only during recent years has there been any serious attention focused on the
potential adverse effects that various air pollutants (particularly ozone
and oxides of sulfur) may have on polymeric materials.1 Most published studies
of a fundamental nature have been concentrated in the areas of rubber,
textiles,3 and plastics.2'4 Very few of these investigations have concerned
the influence of air pollutants on the performance of exterior coatings,5'6
and these were conducted at excessively high pollutant levels compared to
normal exterior conditions. They showed that pollutants, specifically S02,
exert a detrimental effect on coating properties and components.
Evaluation programs of coating products designated for exterior use typically
involve environmental exposure at a number of locations. Attempts to pin-
point the reason (s) behind unusual performance behavior and particularly,
ascribing these effects to atmospheric pollutants are obviously difficult
because so many factors are involved simultaneously during exterior weathering.
However, there have been several instances where air pollutants were suspected
of promoting premature film failure, notably "hazing" or "frosting" and inter-
coat peeling. The former problem has been observed on the surface of specific
coatings (readily detectable with colored systems) exposed in polluted environ-
ments particularly containing moderately high levels of S02. The objectionable
surface deposits noted especially under eaves where moisture condensation is
apt to occur would normally require repainting by the customer. If the repaint
surface is not cleaned properly, intercoat peeling could result.
A severe problem of intercoat peeling in protected areas under the eaves
also has been related to the formation of water sensitive materials from zinc
oxide containing repaint surfaces.7 It is interesting to note that a I960
survey conducted in approximately 160 areas in the United States showed that
the most consistent reports of severe intercoat peeling came from the Great
Lakes region. The generally recognized high S02 level associated with this
industrially oriented area could cause formation of the water soluble zinc
sulphate and subsequent adhesion problems.
A study concerning the corrosion of steel provided relatively conclusive
evidence that pollutants, namely S02, adversely affect coating performance.8
It was shown that coating performance on prerusted metal substrates was
dependent in part upon the time of the year in which the panels were exposed
for existing. A more rapid failure was observed with coatings applied to
the rusted bare metal panels recalled during the month of December (higher
S02 level) as opposed to June (lower S02 level). The experiments showed
good correlation with the amount of ferrous sulphate formed on the bare
metal surface and the subsequent performance of the coating system.
The above cited examples involving primarily actual field exposures suggest
that pollutants may indeed exert an experimentally detectable adverse effect
on coating performance. Fundamental studies involving the interaction of
specific pollutants at controlled, realistic levels with coatings should
provide the requisite knowledge to resolve the uncertainty regarding the
role of pollutants as a degradatLve parameter.
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II. Project Description
A. Objective
The purpose of this experimental program was to develop laboratory test
methods capable of detecting the initial degradation of selected exterior
coatings exposed to various pollutant containing environments. Ultimately,
the techniques developed in this study will be employed by the Environmental
Protection Agency in their laboratory facilities to generate the required
additional dose-response and service life data to assess the economic loss
attributable to pollutant damage of exterior coatings.
B. Scope of Research
This experimental study involved accomplishing three tasks:
(l) Review of existing exterior exposure records to establish the
service life of selected classes of commercially important coatings ex-
posed in a number of locations varying in the general type and level of
pollution.
(2) Short term exposure of the selected coatings at four exterior
locations (both north and south exposure) which differ in the general type
and level of pollution. Attempts will be made to correlate the detectable
initial damage from "short-term" outdoor exposure with existing service life
data collected in Task I and with the accelerated laboratory results generated
in Task III.
(3) Simulate the detectable initial film damage under more controlled,
but accelerated weathering conditons in laboratory exposure studies-
III. Materials and Experimental Procedure
A. Coatings
The five coating systems selected for examination in the above three tasks
are listed under the following four commercially important paint classes.
(l) House Paints
Lead/titanium/zinc extender in oil with 100$ rutile Ti02.
Titanium/extender in acrylic latex with 100$ rutile TiOa.
(2) Industrial Maintenance Coatings
Titanium in alkyd with 100$ rutile TL02.
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(3) Coil Coating Finishes
Titanium/extender in urea-alkyd with 75$ rutile and 25$ anatase Ti02.
(4) Automotive Refinish
Titanium in nitrocellulose/acrylic with 100$ rutile Ti02.
Although the finishes selected for the industrial maintenance, coil coating
and automotive areas are considered somewhat less durable than others in
these classifications, they, nevertheless, possess the following desirable
characteristics for a study of this nature:
(l) They represent large volume products and, therefore, are considered
commercially important.
(2) Extensive histories exist for at least four different geographical
locations which differ in environmental conditions.
(3) A considerable amount of performance data versus exterior exposure
time has been collected on these coatings over the years.
The relatively short time element for completing Phases II and III
of the project necessitated selecting less durable coatings which would be
more susceptible to attack by pollutant containing environments.
B. Test Methods for Determining Film Damage
(l) Gravimetric Erosion Studies
This method of testing was employed as the main criterion for assessing the
performance of selected coatings (except for the automotive refinish) ex-
posed in Tasks II and III. It is our contention that coatings classified as
commercially important have been tested and reformulated sufficiently to
avoid the relatively undesirable types of failure such as cracking, de lamination,
etc. and therefore, "fail" by the relatively desirable mechanism of gradual
erosion. In addition, our considerable experience with erosion studies shows that
the exterior and Weather-Ometer erosion rates of the selected coatings are
normally linear after 9 months and ^00 hours of exposure respectively. Con-
sequently, early erosion rates can be used effectively to predict long term
durability as well as correlating the results of Task II with those generated
in Task III.
For erosion measurements, the weight loss or gain by the control panels
maintained in the controlled environment room (77. jr 1° F and ^5 + 2$ RH)
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was used to adjust the weight loss of the respective exposed coatings at
each examination period. This corrected weight determined to the nearest
0.0001 gram was then converted to "dry volume" through a calculated den-
sity constant for each coating. The latter value divided by the measured
area of coating for each panel gives the film thickness lost in mils resulting
from exposure.
The success in generating accurate erosion data is dependent on the
periodic removal of accumulated chalk from the coated panel surface.i0'11
During each examination period, the respective coated metal panels were
washed using a cotton swab saturated with distilled water containing 5$
Tide prior to equilibration and weighing to the nearest 0.001 gram in the
controlled environment room*
(2) Infrared Analysis
Attenuated Total Reflectance (ATR) measurements were made on films using
a Perkins-Elmer Model l)-57 infrared spectrophotometer equipped with a Wilke
Model 12 double beam internal reflection attachment. The ATR reflection
process allows penetration of the infrared beam into the sample at a
depth approximately etjual to one-third of the analytical wavelength.
The absorption bands of particular interest in this phase of the study
included: (l) The C-H region near 3.5*1 (2860 cm'i), (2) The carboxyl re-
gion near 5.8)1 (1730 cm ^), (3) The extender region near 9n (1100 cm"i) and
(k) The Ti02 region near lOn (550 cnfi). The penetration into the film at
these four points would be 1.2, 1-9; 3 and 6 microns, respectively. Care was
exercised to achieve optimum contact between the coating and the ATR plate
in order to maximize spectra resolution.
(3) Gloss and Sheen Measurements
Gloss (60°) and sheen (85°) measurements were made on all coatings using a
Gardner Multi-Angle Glossmeter. All panels were washed with distilled water
containing 5$ Tide prior to the measurements. These properties are, how-
ever, considered of primary importance only for the automotive finish since in
the latter case, loss of gloss rather than erosion is the normal mode of failure,
(k) Surface Roughness Measurements
A Talysurf k instrument was used to determine the change in topography
(micro inch scale) of the control specimens and the five coatings at various
exposure conditions. These measurements were performed on panels which had
previously received the standard washing procedure.
(5) Instron Determinations
In prior work by the Paint Research Department,12 tensile strength versus
exposure time has been shown to correlate well with the known exterior
durability of three of the five selected coatings. The automotive refinish
and coil coating are relatively brittle and, therefore, present problems
in obtaining reproducible tensile strength results.
The films designated for analysis by stress-strain were sized to 3/V1 x 3" with
a Precision Sample Cutter*, amalgamated by floating the test sample film side
up in a bath of mercury and then conditioned in a controlled environment
room for 72 hours before testing with an Instron Mechanical Testing Machine.**
* Produced by Thwing-Albert Instrument Company
**Produced by Instron Engineering Corporation
Mention of any instrument by product name does not indicate endorsement by
the Environmental Protection Agency.
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All coatings, excluding the automotive reflnLsh and the latex paint, were
tested at a strain rate of 10$/roinute. The fragile automotive refinish re-
quired a lower test rate of 1^/minute. The latex films, with their lower modulus,
were examined at a rate of 100$/minute,
(6) Scanning Electron Microscope Analysis
All five coatings were examined with a Scanning Electron Microscope after
selected exposure in either Task II or HI to provide a visual record of
the topography changes which might be attributable to a given test location
or to the aggressive environment in the laboratory exposure study, Two levels
of magnification (jOOX and JOOOX) were employed to fascilitate comparison
of the physical change that occurred at the coating surface during the ex-
posure condition,
(7) Sorption-Pesorptiott Measurements
Moisture sorption/desorption measurements were incorporated to determine the
effect of pollutants on the performance of coatings exposed to laboratory
environments. This technique, a simple gravimetric test, has been recently
used to evaluate film performance."1'3
The test assembly consists of a four place analytical balance mounted on top
of a Plexiglas® chamber maintained at constant relative humidity (92 + 1$) and
temperature (77.+ 1° F). A long rod replacing the pan of the balance extended
into the chamber so that weighings could be performed without removing the coated
panels from the constant sorption atmosphere. An Aminco air unit appropriately
attached to the test chamber for proper air flow was used to maintain the
desired relative humidity. The entire test assembly was' located in a controlled
environment room (77° F and kyf> Rtt).
The experiments were performed on the same coated stainless panels used for
the erosion rate study. All of the panels possessing an equal area of coating
were weighed periodically in the chamber during the 2^-hour sorption phase,
followed by similar weighings at controlled room conditions for a 2k hour
desorption period. This time period was sufficient for the coating to achieve
equilibrium (constant weight) in respect to the specified sorption or desorp-
tion conditions. The weight gain or loss ('milligrams) by the coatings was
standardized by dividing with the respective film thickness previously cal-
culated in the erosion study.
C. The Review of Existing Exterior Exposure Records (Task l)
Visual erosion ratings and experimental erosion rate data were used in this
phase of study as the main criteria for assessing the service life in years
of the five coatings (excluding the automotive refinish) exposed in at least
four of our multiple exterior testing locations. (See Table 1.)
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A visual erosion rating of J, based on a scale of 0 (complete failure) to
10 (no failure), was*considered as the minimum value that a coating can reach
and still be acceptable in appearance. A coating with a rating below 7 would
not have sufficient film thickness to prevent substrate show-through.
In the case of the automotive refinish, the normal mode of failure is not
erosion, but rather loss of gloss. Therefore, panels of automotive refinishes
are seldom left on exposure for sufficient time (>5 years) to exhibit visible
evidence of erosion. For this finish, the service life in years is equated
to the point in time in which the gloss after washing reached k-0.
The service life results for some of the coatings were calculated from experi-
mental erosion rate data (mils loss of coating versus exposure time in months).
For this conversion, a special set of laboratory panels sprayed with the
respective coatings at varying film thicknesses was prepared to establish a
graph of visual erosion ratings (9, 8, *\, etc.) versus film thickness. From
the latter plots, the film thickness required to give a visual erosion rating
of 7 for a given coating was determined. The service life of a coating was
then established by entering the difference between the film thickness at its
recommended spreading rate and the film thickness equivalent to a visual
erosion rating of 7 (from the above plot) in a second graph of experimental
film thickness versus exposure time in months.
D. Panel Preparation for Field and Laboratory Exposures
Stainless steel panels (Type 3 with a 2B finish), measuring 6 inches by 10.5
inches for the field exposure study and 3 inches by 9 inches for the laboratory
exposure study, minimize the effect of corrosion on the test results. Five
3/8 inch holes were drilled in each field panel (one at each corner plus one
centered along an edge for weighing purposes) for subsequent mounting on 1
foot by 3 foot plywood panels. Only one hole was drilled at the top of each
laboratory panel for weighing purposes. The metal panels were then appropri-
ately coded for reference, cleaned in a perchloroethylene vapor degreasing
chamber and weighed to the nearest 0.0001 gram with an analytical balance.
A taping operation was subsequently performed to confine the area of coating
to 6 inches by 9-5 inches for the field panels and 3 inches by 6 inches for
the laboratory panels. Care was exercised during handling of the panel to
avoid contamination of the surface before the coating operation. The five
coatings were then applied directly to the respective panels at controlled
uniform film thickness according to the recommended spreading rates (See
Tables.) with a Spraymation automatic spraying unit. Preliminary Weather-
Ometer exposure studies showed that all of the coatings would maintain
satisfactory adhesion to the unprimed substrates during extended exposure.
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TABLE 1
Location of Exterior Test Fences
Valparaiso, Indiana*
Detroit, Michigan
Cleveland, Ohio
Dayton, Ohio
Gibbsboro, New Jersey
Atlantic City, New Jersey
Miami, Florida*
New Orleans, Louisiana*
Coffeyville, Kansas*
Los Angeles, California
Oakland, California
Garland, Texas
Montreal, Canada
* Major test sites
TABLE 2
Application Parameters for the Five
Selected Coatings
Automotive Refinish
Latex Coating
Coil Coating
Industrial Maintenance
Oil House Paint
Spreading
Rate (fta/gal.)
300
500
7^0
,e UOO
500
Desired
Film (Mils)
1-5
1-5
1.0
2.1
2-5
Mils
Achieved*
1.5 + .1
1.4+ .1
1.1 + .1
2.0 + .1
2.6 + .1
* Averages of 23 panels for each coating
-------
-0-
*
Coatings designated specifically for tensile strength determinations were
prepared with a threaded drawdown bar to achieve a minimum 2 mil dry film
thickness on tin foil over glass plates. Prior to characterization, the
films were removed from their tin foil substrates by amalgamation. This pro-
cedure as specified in ASTM D-2570 precludes damage to the coating caused by
stripping from a glass plate or contamination when employing release agents.
All coated panels and films were then aged for at least two weeks in a con-
trolled environment room (77 _+ 1 F and k$ ± 2% Relative Humidity) to pro-
vide adequate cure before determining the initial properties. Finally,
the coated metal panels were appropriately cleaned and weighed to the
nearest 0.0001 gram. Panels for field exposure including the respective
films taped to aluminum panels were mounted with plastic bolts and spacers
on coded plywood panels for distribution to the designated exterior testing
sites.
E. Exposure Studies
The exposure of the five coatings to field (Task II) and laboratory en-
vironments (Task III) enabled the selection of valid test methods for assessing
loss in film performance. The successful development of a technique is
dependent on generating consistent trends in data for the coatings exposed
in both the field and laboratory studies. If correlation in trends exists,
then exposure studies employing controlled laboratory environments accompanied
by suitable techniques can be used effectively in projecting the economic
loss attributable to pollutant damage of coatings exposed in exterior conditions.
(l) Field Exposure Study (Task ll)
Four exterior locations known to possess different types of pollutants were
selected as exposure sites for the five coatings. The location of the sites
and the dominant pollutant levels are shown below:
Pollution Level
1970 Annual Average
Location Environment (S02 g/M3) Oxidant a- g/M3
North Central, North Dakota clean, rural site low low
Los Angeles, California high oxidant low ~^k
Chicago, Illinois high sulfur dioxide 97 low
Valparaiso, Indiana moderate sulfur dioxide 22 low
Although the exterior test sites for this portion of the study have been selected
to represent a "clean" rural environment, a high S02 environment, and a high
oxidant environment plus a moderate S02 environment, it is recognized that these
sites also vary in temperature, relative humidity and ultraviolet light radiation.
Since the latter three factors interact simultaneously with the coating, it may
-------
-9-
be difficult to discern the effect of pollutant type or level on service life.
without elaborate monitoring and data collection instrumentation. .Apparatn
of this nature was considered beyond the scope of the study. However, in
spite of this apparent difficulty, the results of each test method can be
examined for unusual effects that might be attributable to the pollutant con-
ditions within test locations.
The experimental design, which allows for statistical treatment of the raw
data, is shown below:
Experimental Design for Field Exposure Studies
Test Method Number of Panels Required
Erosion, Gloss, Sheen, Surface 2 replicates x h exposure periods 320
Roughness x 5 paints x h- locations x 2 types
of exposures (north and south)
Infrared,* Scanning Electron 6 exposure periods x 5 paints x k- 2kO
Microscope,** Tensile Strength locations x 2 types of exposure
Controls retained in the con- 2 replicates x 5 paints x 2
trolled environment room substrates 20
Total 580
*Not to be replicated
**To be done on 10 films only
A total of 580 panels were prepared (both stainless steel and tin foil substrates)
for this exposure study. Twenty of the total number of panels were retained
in the controlled environment room for the initial tests and as unexposed con-
trols- The remaining 560 were mounted on exterior test fences located at the
four selected locations. This latter number of panels includes an extra two
sets of coated metal panels and k extra sets of films for each exposure
location (both north and south). The additional material was incorporated
into the experimental design both for extended exposure beyond the one year
contract requirements and as a safety factor in case some panels became damaged.
Separate sets of panels were used for each exposure period to avoid the delay
in exposure that would be incurred during shipping and testing.
Property evaluation was performed at zero, 3 an^ 7 months of exposure. Two
replicates were used for erosion rate determinations because of the emphasis
on this technique. Gloss, sheen and surface roughness measurements were
also made on the same set of coated metal panels. The remaining three tests
were conducted on the appropriate films. After the analyses were completed
for a respective exposure period, the panels were returned to their designated
test fence for continued exterior exposure.
-------
-10-
(2) Laboratory Exposure Study (Task III)
A Xenon light, Dew Cycle Weather-Ometer equipped with automatic control and
monitoring devices for S02, 03, UV light, humidity and temperature was used
to generate data under controlled, but accelerated weathering conditions.
The environmental variables chosen for this phase of study are shown below:
Pollutant Level (ppm)
Clean Normal High
Sulfur Dioxide 0 0.1 1.0
Ozone 0 0.1 1.0
The zero pollutant level represents the control (clean air) with the 0.1 ppm
of each pollutant type considered representative of the levels frequently
reached in polluted cities. The 1.0 ppm level represents a "highly" polluted
(industrial) site.
The experimental design for the laboratory exposure study which allows for
statistical treatment of the raw data is shown below:
Test Method Number of Panels Required
Erosion, Gloss, Sheen, Surface 2 replicates x 5 paints x 5 100
Roughness conditions x 2 types of exposure
(shaded and unshaded)
Tensile Strength, Infrared,* 5 paints x 5 conditions x 2 150
Scanning Electron Microscope** types of exposure x 3 analyses
(amounts to eight 6 inch x 12
inch films per paint)
Control retained in the controlled 2 replicates x 5 paints x 2 20
environment room substrates
Total 270
* Initial, 1 ppm S02, 1 ppm 03
** To be done on 10 films only
A total of 270 panels (both coated stainless steel and films mounted on
aluminum substrates) were prepared for Task III. Erosion rate determinations
were made on two replicates in the case of either 0.1 ppm S02 or 03 exposures
(both north or south) and three or four replicates for the zero pollutant,
1.0 ppm S02 or 03 conditions (north or south). Similarly to Task II, the
non-destructive gloss, sheen and surface roughness measurements were performed
on the same coated metal panels used for the erosion rate determinations. In
most instances, triplicate determinations were made for the tensile strength
studies. The 20 panels retained in the controlled environment room were used
for determining zero hour (initial) tests and as unexposed controls.
-------
-ll-
The basic Weather-Ometer schedule selected for all five of the environmental
conditions involved one hour of Xenon light at about 70$ relative humidity
and 150 F black panel temperature, followed by one hour of darkness during
which dew was condensed on the coated panel or film surface (100$ relative
humidity and 120° F in the chamber). In addition, one-half of the specimens
were shaded from UV light during each environmental condition by the use of
a specially designed stainless steel shield.
The Weather-Ometer was calibrated each day of the week to insure that the
specified conditions (pollution level, relative humidity, temperature,
etc.) were being properly maintained in the chamber. Continuous monitoring
of the pollutant level and UV light intensity (maintained constant at
nanometers with a special filter) was provided by strip chart recorders.
Property characterization was performed on the appropriate panels and films
at zero, UOO, JOO and 1000 hours for each environmental condition. The time
required for washing, equilibration and property analyses necessitated
intermittent exposure from one set of panels to another to insure that all
panels eventually received 1000 hours of exposure to the designated pollutant
condition during the one year contract period.
IV- Experimental Results and Discussion
A. Task I - The Review of Existing Exterior Exposure Records
(l) Introduction
As discussed previously under the Mathods and Experimental Procedure section,
both visual erosion ratings and gravimetric erosion rate data were used to
assess the service life of the selected coatings (excluding the automotive
refinish). It was recognized at the onset of this phase of study that suf-
ficient exposure data was available in our files to set the service life for
each coating exposed in at least four locations, but not necessarily the same
sites in all cases. Greater confidence can be placed on the service life
estimates determined by the gravimetric erosion rate studies compared to the
visual erosion rate method since many of the variables normally involved
in exterior exposure programs and the subjectivity of visual ratings are
eliminated.
(2) Results and Discussion
The service life data for the five coatings exposed in at least four different
exterior locations (except for the coil coating) are presented in Tables 3
through 7- Comparison of the overall average service life in years between
coatings indicates that the acrylic latex house paint is the most durable
(6.^1 years - visual ratings); the oil house paint is second in durability
(5•l8 years - visual ratings); the coil coating is third in durability (4.86
years - converted erosion rate data); the alkyd industrial maintenance coating
is unexpectedly fourth in durability (k.28 years - visual ratings); and the
automotive refinish system is the poorest in durability (2.27 years - based
on a gloss after washing of kO). It is also noted that within each of the five
-------
-12-
paint systems the range Ln average years required to reach an erosion rating
of seven or a gloss after washing of kO is approximately two to three years.
Further examination of Tables 3 through 7 shows that the width of ranges in
months required to reach an erosion rating of- seven or a gloss after washing
of hO is fairly large for the two house paints and the alkyd industrial paint
exposed in Valparaiso, Indiana and for the automobile coating exposed in
Miami, Florida. However, the magnitude of the ranges is not entirely unreason-
able when considering all of the potential variables entering into the visual
erosion rating (influence of substrate type, primer differences, film thick-
ness variations, different evaluators, etc.)
TABLE 3
gervice Life for Acrylic Latex House Paint Exposed at Five Exterior Exposure Sites
Location
Vertical South
Valparaiso, Tnd.
Miami, Fla,
Wilmington, Del.
Newton, Pa.
Palmerton, Pa.
Overall Average
Ave . Yrs. to
Erosion Rating of 7
Ave . Mos . to Range
Erosion Rating of 7 in Mos.
7.
6,
5.
5-
75
17
16
08
7-92
93
7^
62
61
95
60-136
5^-85
U8-86
70-107
No. of
Panels
20
6
6
1
3
TABLE k
Service Life Data for L/T/Z Oil Base House Paint Exposed at Five Exterior Expos. Si'es
Location
Vertical South
Valparaiso, Ind.
Miami, Fla.
Wilmington, Del.
Concord, Calif.
Palmerton, Pa.
Ave. Yrs. to
Erosion Rating of 7
.83
.00
.17
.1*2
6-5
Ave. Mos. to Range
Erosion Rating of 7 in Mos
70
hB
50
65
78
28-60
U5-60
63-66
No. of
Panels
29
9
5
2
1
Overall Average
5-18
-------
-13-
TABLE 5
Service Life Data for the Alkyd Industrial Maintenance
Coating Exposed at Five Exterior Exposure Sites
Location
Vertical South
Valparaiso, Ind.
Miami, Fla.
Oakland, Calif.
Atlantic City, N.J.
Garland, Texas
Overall Average
A\e. Yrs. to
Erosion Rating of 7
Ave. Mos. to Range No. of
Erosion Rating of 7 in Mos. Panels
4,
4,
3
3
5
58
66
16
25
75
55 02
56 42-60 5
38 - l
39 - l
69 - l
TABLE 6
Service Life Data for Nitrocellulose Acrylic Automobile
Finish Exposed at Four Exterior Exposure Sites
Location
45° South
Valparaiso, Ind.
Miami, Florida
Wilmington, Delaware
Memphis, Tenn.
Overall Average
Ave. Yrs. to
40 Gloss
2-33
2.67
2-33
1.83
Ave. Mos . to
40 Gloss
28
32
28
22
Range
in Months
13-65
22-36
Number
of Panels
1
58
5
1
2.29
TABLE 7
Service Life in Years from Erosion Rate Data versus Visual Ratings
for the Coil Coating, Acrylic Latex and Oil Paint
Paint
Coating
(45 South)
Acrylic Latex
(856 South)
L/T/Z Oil
Base Paint
(85° South)
Erosion Rate Data*
Valparaiso Miami
5-42 yr. 4.31 yr.
(Unprimed) (Unprimed)
(Overall average 4.86)
5-90 yr.
(Unprimed)
5-75
(Dark primer)
8.84 yr.
(Unprimed)
6.83 yr.
(Dark primer)
Visual Ratings**
Valparaiso Miami
7-75
5-83 yr.
6.17 yr.
4.00 yr.
* Determined from experimental erosion rate data (mils loss versus exposure time)
**Previous data presented in Tables 3 and 4
-------
-u-
B. Task II - Short Term Exterior Exposure
(l) Introduction
Only two data points (three and seven months) for each test method were collected
during Task II. Consequently, the limited data essentially precludes statis-
tical trear^ntand necessitates only the reporting of apparent trends which may
conceivably change consequent to additional exterior exposure.
(2) Results and Discussion
(a) Gravimetric Erosion Studies
The discussion of erosion studies for Task II will be centered on the J months
results since the latter time period is nearly equivalent to the point where
the erosion rate becomes linear. Consequently, greater confidence can be placed
on the existing trends in data.
Examination of the data presented in Table 6 shows the expected consistency
in the level of erosion (mils loss) being greater particularly for the exposed
alkyd industrial and oil house paint panels (south location) compared to the
specimens on the unexposed or north side of the test fencea It is also
apparent, particularly for the exposed panels, that the mils loss of coating
is higher at Chicago and Valparaiso than at the Los Angeles and North Dakota
locations. These results may be explained by the higher S02 levels at the
former two exposure sites. As will be revealed during the discussion in
Task III, this trend is consistent with the Weather-Ometer studies which
show that S02 at concentrations representative of a highly polluted indus-
trial site (l ppm) produced a greater adverse effect on the level of erosion
than 03 at similar levels for specific coatings. Rainfall, sunlight, UV
light intensity, and pollutant type and level were not monitored at the
various test sites to confirm the proposed effect of pollutants on exterior
erosion levels. It is also significant from the standpoint of correlation
that the ranking in terms of mils loss (magnitude of erosion) for the
coatings in Table 8 is virtually the same as in the accelerated studies regard-
less of exposure location (both north and south).
-------
TABLE 8
ErosLon Data (Mils Loss)of the Selected Coatings after 7 Months
Exposure at Four Exterior Locations (Both North and South)
Exposure Site Location
Research Valparaiso, Los Angeles, Leeds,
Center Indiana California North Dakota
Coatings £°£^!l South North South' North South North South
Automotive Refirish .01 .01 .01 .02 .01 .01 .01 .02
Coil Coating .Oh .06 .06 .06 -Ok .05 .01 .02
Latex Coating .06 -07 .07 .07 .Oh .Oh .06 .06
Industrial Maintenance .07 ,11 .09 .11 .06 .08 .06 .07
Oil House Paint .10 .16 .12 .13 .10 .13 .07 .10
(b) Infrared Analysis
Attenuated Total Reflectance (ATR) measurements were performed on films of
the selected coatings exposed for 3 and 7 months only at the Chicago (Research
Center) location (both north and south exposures). Emphasis will be placed
on the spectra for the 7 month exposed samples since they were very similar
to those for the 3 month exposure except for the expected greater binder
degradation. This degradation was even mote pronounced for the coatings ex-
posed on the south position of the test fence. The extent of binder break-
down was determined by the reduction in intensity of the ester carbonyl and
C-H bands relative to pigment absorption, specifically Ti02.
The oil and alkyd systems (oil house paint, industrial maintenance, coil
coating) were degraded to a greater extent than the two acrylic coatings
(latex, automotive refinish) consequent to the weathering conditions at the
Chicago test site. In addition, the former three coatings showed a con-
siderable increase in metallic soap content. Concentration of driers at the
surface during weathering or formation of metallic soaps of fatty acids and/
or degradation products could account for this observation.
The oil house paint and coil coating which contain a moderate amount of
CaC03 extender exhibited a considerable decrease in carbonate content
accompanied by the formation of sulphite and/or sulfate compounds. This
formation was detected irrespective of north or south exposure and despite
the fact that the samples were washed to remove any accumulated chalk or
dirt prior to ATR analysis. The sjTpbite or sulfate compound could be formed
by the reaction of the dissociated inert cation (in this case, Ca ) with
sulfurous acid (absorbed S02 + H20) and/or sulfuric acid (S03 z H20) that is
present in the paint film.
-------
-16-
The results of this phase of study provided the initial evidence that S02 at
moderate to high concentrations exerts a detectable adverse effect on coatings
particularly containing inerts susceptible to dissolution in acidic media.
The disapperance of the inert through formation of water soluble compounds
would be reflected in high apparent erosion levels which, in part, supports
the contention that the higher erosion encountered at Chicago and Valparaiso
versus Los Angeles and North Dakota may be attributable to the S02 level.
(c) Gloss and Sheen Measurements
Gloss (60 ) and Sheen (85 ) measurements of the selected coatings were made
after 3 and 7 months exposure at the four test sites (both north and south
positions) using a Gardner Multi-Angle Glossmeter. All panels had been
washed as a standard procedure and weighed for the erosion studies prior to
characterization by gloss and sheen. These methods of testing are, however,
considered of primary importance particularly for the automobile refinish
since in the latter case, loss of gloss rather than erosion is the normal
mode of failure. The service life for the latter coating is equated to the
point in time in which the gloss after washing reaches ^0.
Gloss measurements provided more consistent trends than sheen particularly
for the automotive refinish and the industrial maintenance coating which
exhibit a high initial gloss and/or a gradual decrease in gloss during
exposure.. As shown in Table 9, the gloss for the former two coatings is
higher (as expected) for the north side position at all four locations. It is
also noted that the automotive refinish is retaining a relatively high gloss
level. In addition, the level of gloss for the industrial maintenance coating
is lower at Valparaiso and Chicago versus Los Angeles and North Dakota. The
latter trend suggesting greatercoating degradation is consistent with the
erosion and ATR results previously presented. The other three coatings (oil,
latex and coil) exhibit a relatively low gloss irrespective of exposure
location.
The results of the sheen determinations presented in Table 10 do not at this
time correlate with the trends discernible from the gloss data after 7 months
exposure. However, detectable differences specific to a test site may
develop with additional exposure since the sheen of four coatings is presently
at a reasonable level.
-------
-IT-
TABLE 9
Gloss Measurements (60 ) of the Selected Coatings after 3
and 7 months of Exposure at the Four Exterior Locations
Exterior Test Site Location
Valparaiso, Indiana
Automotive Refinish
Industrial Maintenance
Oil House Paint
Coil Coating
Latex Coating
Automotive Refinish
Industrial Maintenance
Oil House Paint
Latex Coating
Coil Coating
Automotive Refinish
Industrial Maintenance
Oil House Paint
Latex Coating
Coil Coating
Automotive Refinish
Industrial Maintenance
Oil House Paint
Latex Coating
Coil Coating
Initial
89
37
12
5
5
Initial
89
37
12
5
5
Initial
89
37
12
5
5
Initial
89
37
12
5
5
North
3 months 7
82 '
30
6
h
3
Research
North
3 months 7
89
37
9
3
5
months
82
26
5
3
3
Center,
South
3 months 7
82
30
10
k
3
Chicago
months
81
22
5
3
3
South
months
89
25
5
3
^
3 months 7
87
31
7
3"
5
months
87
20
h
3
3
Los Angeles, California
North
5 months (
92
32
8
3
months
90
30
3
3
South
•5 months I
85
35
5
3
IS
8k
25
3
3
Leeds, North Dakota
North
3 months 7
89
33
12
3
5
months
88
32
5
3
5
South
3 months 7
87
26
10
3
5
months
86
oli
Ji
3
5
-------
-15-
TABLE 10
Sheen Measurements (85°) of the Selected Coatings After 3
and 7 Months Exposure at the Four Exterior Locations
Exterior Test Site Location
Valparaiso, Indiana
»T _ ._»_
Coatings
Automotive Refinish
Industrial Maintenance
Oil House Paint
Coil Coating
Latex Coating
Automotive Refinish
Industrial Maintenance
Oil House Paint
Coil Coating
Latex Coating
Automotive Refinish
Industrial Maintenance
Oil House Paint
Coil Coating
Latex Coating
Automotive Refinish
Industrial Maintenance
Oil House Paint
Coil Coating
Latex Coating
Initial
82
42
31
17
4
Initial
82
42
31
17
4
Initial
82
42
31
17
4
Initial
82
42
33
17
4
North
3 months 7
74
36
24
11
4
months
74
32
18
11
4
- South
3 months 7
74
36
29
12
3
months
74
35
18
12
3
Research Center, Chicago
North
3 months 7
73
39
31
10
3
months
73
39
21
10
3
Los Angela Sj,
North
3 months 7
78
40
30
12
3
Leeds
North
months
75
40
10
10
3
, North
3 months 7 months
76
41
33
15
fc
76
40
30
15
3
-~ South
3 months 7
72
40
24
12
3
California
South.
3 months 7
76
40
30
10
3
Dakota
Soutth
--
months
72
40
12
12
3
months
70
40
10
10
3
3 months 7 months
75
37
29
12
4
74
35
22
12
3
-------
-19-
(d) Surface Roughness Measurements
A Talysurf k instrument was used to determine the change in topography
(microinch scale) of the unexposed controls and the five coatings exposed
only for 7 months at the four exterior test sites. These measurements were
performed on the erosion panels which had been washed with a 5$ Tide solution
to minimize the influence of dirt accumulation on the test results.
The data collected on the exposed coatings (both north and south) were con-
verted initially to a percent change in surface roughness (S.R.) with respect
to the unexposed control values (% change = S.R. exposed - S.R. control).
S. R. control
A positive value reflects an increase in surface roughness resulting from
exposure whereas as a zero or negative percent change indicates no change or
decreased surface roughness respectively, compared to the unexposed, control
value. Subsequently, the data for a given coating in Table 11 were ranked on
a scale from 1 (highest % change in surface roughness) to 5 (lowest % change),
both within and between test sites. These data are presented in Table 12.
Coatings with equivalent change in surface roughness were given identical
rankings. Summation of the individual rankings in columns (within location)
provides five numbers for subsequent comparison of the magnitude of change
in surface roughness specific to a given coating irrespective of test site.
Similarly, summation of the rankings in rows (between location) facilitates
establishing the effect of the test site on the level of surface roughness
independent of a coating type. The trends in data either within or between
test sites are then determined by comparing the magnitude of the summations.
A low value indicates a high percentage change in surface roughness whereas
a high summation connotes a low change in roughness.
Examination of the results presented in Table 12 for ranking within test
site shows that the automotive refinish exhibited the greatest change in
surface roughness followed by the oil house paint, industrial maintenance,
coil coating and latex paint, respectively. This trend is apparent regardless
of panel position (shaded or unshaded) on the test fence. Comparison between
locations illustrates that the Valparaiso and Los Angeles test sites effected
a higher percentage change in surface roughness for the five coatings than
exposure at the Research Center and Leeds, North Dakota locations (both north
and south).
Consideration of the results presented for the erosion (Table 8) and surface
roughness techniques, shows limited consistency wLth respect to the ranking
in level of property for the five coatings. The inconsistency is particularly
dramatic for the automotive refinish which exhibited the highest percentage
change in surface roughness but yet high gloss retention and the lowest level
of ersoion.
It is apparent, however, that agreement in trends exists from the standpoint
of extremes in exposure location. The Valparaiso test site produced the
greatest change in both erosion and surface roughness whereas Leeds, North
Dakota showed the least effect.
-------
-20-
TABLE 11
Surface Roughness (Percent Change with Respect to Unexposed
Control) jf the Selected Coatings After 7 Months Exposure
Coatings
Automotive Refinish
Oil House Paint
Industrial Maintenance
Coil Coating
Latex Paint
Automotive Refinish
Oil House Paint
Industrial Maintenance
Coil Coating
Latex Paint
Automotive Refinish
Oil House Paint
Industrial Maintenance
Coil Coating
Latex Paint
Automotive Refinish
Oil House Paint
Industrial Maintenance
Coil Coating
Latex Paint
Exposure Test Site Location
Valparaiso, Indiana
North South
53
17
6
k6
31
21
1.1
Research Center, Chicago
North South
46 46
29 26
12 9-3
0.0 9.7
3-3 3-3
Los Angeles, California
North South
69 61
52 57
9.3 9.3
17 17
3-3 l.l
Leeds, North Dakota
North
5-2
4.6
0
0
-------
-21-
TABLE 12
Ranking of Percent Change in Surface Roughness for the Five
Selected Coatings Exposed for 7 Months at the .Four Exterior Locations
COATINGS
Ranking Within Location - Shaded
Exposure Test Automotive Latex Coil Industrial Oil House
Site Location Refinish Coating Coating Maintenance Paint
Valparaiso,Ind. 15^3 2
Research Cen.,Chgo. 1^53 2
Los Angeles, Calif. 1 5 3 k 2
Leeds, North Dakota !_ jfj? k-5 % 2
Summation k 18-5 16-5 13 8
Ranking Within Location - Unshaded
Automotive Latex Coil Industrial Oil House
Refinish Coating Coating Maintenance Paint
Valparaiso,Ind. 1^53 2
Research Cen.,Chgo. 153^ 2
Los Angeles, Calif. 1 5 3 k 2
Leeds, North Dakota _1 J5 J* _£ 2
Summation k- 19 15 1^ 8
Ranking Between Location - Shaded
Automotive Latex Coil Industrial Oil House
Refinish Coating Coating Maintenance Paint Summation
Valparaiso, Ind. 211-51 2 - 7-5
Research Cen.,Chgo. 3-5 2-5 3-52 3 = lU-5
Los Angeles, Calif. 1 2-5 1-53 1 - 9-0
Leeds, North Dakota 3.5 1*. 3.5 k k - 19
Ranking Between Location - Unshaded
Automotive Latex Coil Industrial Oil House
Refinish Coating Coating Maintenance Paint Summation
Valparaiso, Ind. 123-51 2 = 9-5
Research Cen.,Chgo. 312 2-5 3 = 11-5
Los Angeles, Calif. 331 2-5 1 = 10-5
Leeds, North Dakota 3 ^ 3.5 k k 18.5
-------
-22-
(e) Stress-Strain Determinations
Both tensile strength and elongation were determined during the analysis of
free films with the Instron Testing Machine. Major emphasis is placed on the
property of tensile strength since it exhibits an inversion or inflection
point with exposure time indicating that the process of chain-scissioning
commences to predominate over cross linking. Elongation is a less desirable
property due to the gradual exponential decrease during weathering. Coatings
with good to excellent durability typically show a gradual positive slope
before and a negative slope aEter the inversion point in tensile strength.
Conversely, poorer performing coatings exhibit a rather abrupt transition in
tensile strength versus exposure time. Consequently, this approach to
property characterization can be used to assess the service life of a wide
variety of coatings.3 Relatively brittle coatings represent an exception since
they tend to give non-reproducible tensile strength results.
Examination of the tensile strength results for the latex, oil and alkyd
industrial maintenance coatings presented in Table 1J show an expected
increase in tensile strength with exposure time for both the north and
south positions. The brittle automotive refinish and coil coatings are
exhibiting erratic tensile strength behavior for all exposure sites. Addi-
tional exposure time will be required for generation of sufficient tensile
strength data to establish the effect of test location and to provide service
life projections-
(f) Scanning Electron Photomicrographs
The coatings exposed for 7 months on the south position only of the Research
Center and Leeds, North Dakota test sites were selected for examination by
scanning electron microscopy. As previously noted these locations represent
the extremes in the level of SO^ and produced the greatest difference in the
results generated by the erosion study. Unexposed controls were also included
in the series for comparison.
Figures 1 through 21 are arranged according to a coating type depicting the
unexposed control, Leeds, North Dakota and Research Center photomicrographs for
the automotive refinish, latex house paint, coil coating, alkyd industrial
maintenance coating and oil house paint, respectively. It is readily apparent
that the Research Center location caused a greater topographical change for the
coil and industrial maintenance coating than exposure to Leeds, North Dakota.
The automotive refinish appears unaffected by exposure to either location.
Examination of the latex paint at 7000X (Figures 6 and 8) shows essentially no
difference in the amount of surface degradation between the two exposure sites.
These observations are generally consistent with the trends in results reported
for the erosion studies and the surface roughness measurements. An apparent
deviation specifically with the erosion data (Table 8) exists for the oil house
paint. As shown in Figures 19 and 21 (jOOOx), a greater quantity of exposed
pigment suggesting more extensive binder degradation is evident on the Leeds,
North Dakota samples despite the fact that the Research Center location produced
the highest level of erosion.
-------
-23-
TABLE 13
Tensile Strength Determinations (PSl) of the Selected
Coatings after 3 and 7 Months Exposure at Four Ex-
terior Locations (Both North and South)
Exterior Test Site Location
Coatings
Automotive Refinish
Coil Coating
Latex Coating
Industrial Maintenance
Oil House Faint
Automotive Refinish
Coil Coating
Latex Coating
Industrial Maintenance
Oil House Faint
Automotive Refinish
Coil Coating
Latex Coating
Industrial Maintenance
Oil House Faint
Automotive Refinish
Coil Coating
Latex Coating
Industrial Maintenance
Oil House Paint
Initial
2800*
1600
850
500
Initial
2800
1600
850
500
400
Initial
2800
1600
850
500
400
Initial
2800
1600
850
500
400
Valparaiso,
North
3 months 7 months
Indiana
South
3 months 7 months
2400 2100 2800 1050
2750 2050 2800 2200
1200 1650 1400 1650
750 1150 800 1150
800 1200 1000 1400
Research Center., Chicago
North
3 months 7 months
3300 2300
2500 2950
1300 1500
700 i 100
900 1100
Los Angeles,
North
3 months 7 months
2500 1000
1950 2300
1300 1500
850 1300
1000 1200
Jeeds, North
North
3 months 7 months
3550 2000
2100 2000
1350 1450
800 1300
, 600 950
South
3 months 7 months
2600 2300
2100 2450
1400 1650
700 1200
900 1450
California
South
3 months 7 months
3150 2300
2650 2250
1350 1650
700 900
1000 1200
Dakota
South
3 months 7 months
2200 2250
2200 2250
1350 1600
850 900
900 1350
* Tensile strength rounded to nearest 50 PSI
-------
-2k-
-------
AUTOMOTIVE REFINISH
Figure 1 - Unexposed Control 700X
Figure 2-7 Months at Leeds, North Dakota 700X
Figure 3 - " " " Research Center, Chicago 7000X
-------
-25-
Ftg- 1
Fig 2
Hg 3
-------
-26-
-------
IATEX HOUSE PAINT
Figure k - Unexposed Control 700X
Figure 5 - 7 Months at Leeds, North Dakota 700X
Figure 6 - " » " " " " 7000X
Figure 7 - " " " Research Center, Chicago 700X
Figure 8 - " " " " " " 7000X
-------
-27-
Fig k
Fig- 5
Fig. 6
Fig- 7
Fig. 8
-------
-28-
-------
COIL COATING
Figure 9 - Unexposed Control 700X
Figure 10-7 Months at Leeds, North Dakota TOOK
Figure 11 - " " " Research Center, Chicago 7000X
-------
-29-
Fig. 9
~
•m
:* I
•Ml
•
•'*
Fig. 10
Fig. 11
-------
-30-
-------
INDUSTRIAL MAINTENANCE COATINGS
Figure 12 - Unexposed Control 700X
Figure 1J - 7 Months at Leeds, North Dakota 700X
Figure 14 - " " " " " " 7000X
Figure 15 - " " " Research Center, Chicago 700X
Figure 16 - " " " " " " 7000X
-------
Fig. 12
Fig. IJ
Fig.
Fig. 15
Fie. 16
-------
-32-
-------
OIL HOUSE PAINT
Figure 17 - Unexposed Control 700X
Figure 18 - 7 Months at Leeds, North Dakota 700X
Figure 19 - " " " " " " 7000X
Figure 20 - " " " Research Center, Chicago 700X
Figure 21 - " " " " " " 7000X
-------
-37-
by the binder on the apparent rate of degradation (erosion). Both of these
processes are logically occurring simultaneously during exposure in the
Weather-Ometer. The weight gain contribution due to adsorption of pollutant
by the binder would ultimately reflect a lower level of erosion. At .the
0.1 ppm S02 or 03 levels, there is apparently sufficient adsorption of
pollutant to produce a level of erosion lower than the respective zero
pollutant condition. In the case of the 1.0 ppm S02 or 03 exposures, the
degradation process almost completely predominates compared to adsorption,
resulting in significantly higher rates of erosion than the zero pollutant
condition. However, it should be re-emphasized that the adsorption phenomenon
would be most likely to occur during exposure to 03 regardless of the pollutant
level. This condition would tend to magnify any differences that exist
between the level of erosion produced by S02 versus 03.
In view of the above conflicting trend in data, major emphasis during the
subsequent discussion will be placed on the comparisons between the .rates
of erosion for the zero and 1.0 ppm S02 or 03 pollutant levels. Examination
of the probabilities for the 1.0 ppm S02 pollutant level (within either the
shaded or unshaded condition) shows that S02 caused a statistically signifi-
cant effect on the oil house paint, latex paint and the urea/alkyd coil
coating, but no effect on the alkyd industrial maintenance and nitrocellulose/
acrylic coatings. It is an important point to note that the latter two •
paints which were unaffected by exposure to S02 are essentially free of
metallic silicate or calcium carbonate extenders. The other three paints
that exhibited significant effects from S0a all contain aluminum or magnesium
silicate or calcium carbonate or combinations of these inerts-
In contrast to the trend in data for the 1.0 ppm S0a exposure, 03 at the
1.0 ppm level affected all coatings (excluding the nitrocellulose/acrylic)
in the unshaded condition. Furthermore, the alkyd industrial maintenance
coating was significantly affected by 03 regardless of exposure in the
shaded or unshaded condition. In view of the results for both S02 and 03
exposures, the attack by S02 appears to be mainly on the extender component
(absent in the industrial maintenance and automotive refinish whereas P3
almost exclusively attacks the binder through a chain scissioning process.
However, because of the general similarity of the oil vehicle with respect
to the alkyd, it is not entirely clear why the oil house paint was unaffected
by 1.0 ppm 03 in the shaded condition.
The slopes of the five coatings with accompanying 95 percent confidence
levels plotted versus pollutant level (zero, 0.1 ppm S02 or 03, and 1.0 ppm
S02 or 03) provide easy comparison of the composite data in a few graphs.
The plots presented in Figures 22 through 25 demonstrate that the previously
discussed anomalies associated with exposure of the coatings to 0.1 ppm
S02 or 03 do not for the most part negate the a priori hypothesis of erosion
rates or mils loss being linearly related to pollutant concentration. Con-
sequently, these curves along with similar exterior erosion data collected
over an extended exposure period (2 years minimum) can be used as a method for
predicting the effect of any level of pollutant on coating durability.
-------
t-60
Figure 22 - Slopes of Erosion Data Versus Pollutant
Level for the Coating Exposed to S02 in the Weather-
Ometer-Ometer (Shaded Condition'
-t20
0
t-20
0
-, -2C
ID
'o
i 1
x 0
CO
(—I
5-20
D
a
o
Oil House Paint
Alkvd Industrial Maintenance Coating
Latex House Paint
Coil Coating
-20
+20
Automotive Refinish
i" "
0
0.1
1.0
Concentration of S02 ppm,
-------
Fig
Fig. 18
Fig. 19
Fig. 20
Fig- 21
-------
C. Task III - Acceleratej Labprajory Exposures
1. Introduction
This phase of the study provided the most meaningful results due to the self-
contained experiments permitted with Weather-Ometer exposures coupled with
accurately controlled environments and frequent examination periods. It is
recognized, however, that the high relative humidity (70-100$) that was main-
tained in the Weather-Ometer cabinet could conceivably cause higher rates of
degradation of specific coatings, particularly when S02 is present. In this
latter case, sulfurous acid formed from the reaction of S02 and water on or
within the film will continuously be in contact with the coating because the
concentration of S02 was maintained essentially constant at 0.1 or 1.0 ppm
during the entire exposure period. The latter condition may be too accelerated
compared to exterior exposure where the coatings are intermittently subjected
to a relatively low level of sulfurous acid- It is possible, however, that
the above contention could be premature since the pH of the water droplets
formed on the panel surface during the dew cycle and those present during the
initial portion of the "light on" phase was 5 for both the shaded and unshaded
condition (0,1 and 1.0 ppm SOp exposures). Also the dew on the panels located
at the Research Center test site showed a pH of 5- The limited time for this
study did not permit a repeat experiment to determine whether the detectable
effects of pollutants such as S02 on coatings properties is still real under
identical environmental conditions except for a lower relative humidity during
the light-on phase of the cycle.
2. Results and Discussion
(a) Grayimetrij: jSrosioni_Studigj_
Linear regression analyses were performed on the erosion data (mils loss)
for the five coatings exposed in the Weather-Ometer for 1000 hours to either
the zero pollutant, the 0.1 or 1.0 ppm S02 and the 0.1 or 1.0 ppm 03 levels
(shaded and unshaded conditions)- Only the data points collected at 400,
TOO and 1000 hours of exposure were used in determining the slope (rate of
erosion) since the curves for most of the coatings (excluding the oil base,
shaded condition, 1.0 ppm S02 and 1.0 ppm 03, and unshaded 0.1 ppm 03 and
1.0 ppm 03; latex, unshaded, 0,1 ppm S02) are linear during this exposure
period for both the shaded and unshaded conditions. The zero hour data point
was excluded from the analysis because the slope of virtually all erosion
rate curves during the zero to 400 hour period is somewhat greater than the
latter part (400-1000 hours) due primarily to the removal of water soluble
materials. In essence, the contribution o£ the weight loss or mils loss
attributable to the removal of the water sensitive materials is eliminated from
consideration. Consequently, meaningful conclusions concerning the erosion
due mainly to loss of binder and pigment can be made by simply comparing
slopes. The intercept of the curve will be ignored in the discussion of
-------
-35-
results since the magnitude of the intercept is dependent on the extent of
water soluble loss.
It is apparent from the above discussion that erroneous conclusions may result
if based solely on erosion values (mils loss) after a given exposure period.
For example, two coatings may show different mils loss but equal rates of
erosion after 1000 hours exposure in a Weather-Ometer. Providing the dif-
ference in the magnitude of erosion was caused by loss of water soluble
materials, both coatings should exhibit equivalent service life within the
environment under consideration.
The slopes and 95$ confidence limits for the erosion data (mils loss)
collected after kOO, 700 and 1000 hours exposure are presented in Table 14.
It is readily apparent that the confidence limits for the slopes of a number
of coatings are relatively wide. This situation is commonly encountered with
a limited number of data points. Consequently, T-Test probabilities were
calculated to facilitate discerning whether there is a statistically signi-
ficant difference between the slope (rate of erosion) of a given coating ex-
posed to any pollutant type or level versus the slope for the respective
zero pollutant exposure. Comparisons can also be made between the effect of
pollutant types or levels on a given coating within an exposure condition
(shaded or unshaded) because all probabilities were based on the respective
zero pollutant level slope.
The criterion of statistical significance is often arbitrarily set at 95
percent confidence. On a practical basis, however, reasonable confidence
can be expressed when there is an 80 percent probability that a difference
exists between two estimates derived from relatively limited data. Increasing
the number of data points would normally narrow the confidence limits for a
given statistic providing justification for comparing at a high level of
confidence such as 95 percent.
A further clarification should be made concerning statistical versus practical
significance. It is noted in Table 1^ that there is a 95 percent probability
that 1.0 ppm S02 (unshaded condition) affected the automotive refinish com-
pared to the zero pollutant level. Despite the statistical significance, the
automotive re finish lost only 0.02 mils and 0.0} mils after exposure in the
unshaded condition to the zero pollutant and 1.0 ppm S02 level respectively.
Consequently, there is no practical difference in terms of mils loss for the
coating in question. Similar reasoning can also be applied for the automotive
refinish regardless of the pollutant type or level in either the shaded or
unshaded conditions-
The majority of coatings exposed to 0.1 ppm 03 and to a lesser extent with
0.1 ppm S02 (both shaded and unshaded conditions) exhibited a slope (Table Ik)
lower than the respective zero pollutant slope. This trend in data contradicts
the expected behavior of increasing rates of erosion upon exposure to higher
levels of pollutant for both S02 or 03. The deviation from the expected trend
can be reasonably explained by considering the influence of adsorption of 03
-------
-36-
TABLE 111-
Slope of Erosion Data Accompanied byia T-Test Probability (%) that
a Statistical Difference Exists Between the Respective Slope
for a Given Pollutant Type and Level Versus the Zero Pollutant level
SHADED
S02 S02 03 03
Coating 0 0.1 ppm 1.0 ppm 0.1 ppm 1.0 ppm
oil 9.5+6.4 9.4+4.3 47.0+10.6 8.3+6.8 10.6+ 3.0
01.2$ 99f 25$ 30$
Industrial Maintenance 10.9+4.6 8.4+9-4 12.6+2-9 6.1+8.8 21.1+15
75# 87^
Coil 2.5+1.9 3-l«-+5-^ 19.4+10.5 0.8+6.1 4.1+4.2
9$ 70# 55^
Latex 0.24+1-76 2.0+2-2 7-8+2-0 2-2+ 4-4 2-5+1.6
72% 95%
Automobile Refinish 1.1+1.3 1.4+2-2 2-9+1-4 0-9+2-3 3-0+1.4
95^ 15% 96$
UNSHADED
SOo SOo Oo Oo
W^J MW^ J J
Coating 0 0.1 ppm 1.0 ppm 0.1 ppm 1.0 ppm
Oil 20.1+7.2 22+2.0 141.0+19-0 22.2+17-2 44.7+10.5
99^5
Industrial Maintenance 18.6+5-1 12.0+3-3 22.4+7-0 9-6+14.1 28.1+14.0
97$ 66#~ 87^ .
Coil 11-9+2-3 8.5+1.7 34.1+4.7 5-5+3-3 14.9+2-5
99*
Latex 3-5+1-5 2.7+13.4 11.1+1.0 2-4+0.3 8.5+5.9
'"99* 9<# 9$
Automotive Refinish 1.8+0.8 3.9+5.0 3-1+2.6 1.6+1-7 5.1+1.3
-------
+ 100
-1-30
+-60
+-UO
-(-20
N
as
o+-20
x
CO
Figure 23 - Slopes of Erosion Data Versus Pollutant
Level for the Coating Exposed to SOP in the Weather
Ometer (Unshaded Condition)
Oil House Paint
•!••*••
-+-20
Latex House Paint
0)
ex
o
-20
+-20
Coil Coating
+-10
0
Automotive Re finish
0
0.1
Concentration - S02
170
-------
Figure '2k - Slopes of Erosion Data Versus Pollutant
Level for the Coatings Exposed to 03 in the Weather-
Ometer (.Shaded Condition)
Oil House Paint
x'":-'vW!"'-"-!v!v'.!^
-20
Alkyd Industrial Maintenance Coating
+20
0
in
« 420
Latex House Paint
£ °
o
i—i
CO
-20
+20
Coil Coating
-20
+20
Automotive Refinish
UM
i
£
-2C
1
0
0.1
Concentration 03 ippm)
1.0
-------
-20
Figure 25 - Slopes of the Erosion Data Versus Pollutant
Level for the Coatings Exposed to 0-> in the Weather-
Ometer Unshaded Condition)
Oil House Paint
Alkyd Industrial Maintenance Coating
+•20
.:::::::.:.:•:.:.:•:.:•:•:•:•:•:•:•:•:•:•:•:•:•:•:&
o
.—i
X
Latex House Paint
:*
r
0
-20
+20
0
-20
+-20
Coil Coating
•:•:•:**&:£:•:•:•:£:£& fi'i:ffi:i:':'!?ifffi:i'i:'^
lA^ASWiMAyJwMAiAWwS&MM
Automotive Refinish
0.1
Concentration -
1.0
-------
.1,2-
It is interesting to note that despite the high statistical significance for
the coatings affected by either S02 or 03, the slope for the majority of
coatings exposed to S02 at the 1.0 ppm level are generally greater than the
slopes for the respective 03 exposed coatings- This trend in results not
only supports the contention that the greater erosion encountezed at Chicago
and Valparaiso versus Los Angeles and North Dakota is attributable to the
S02 level but demonstrates conclusively that atmospheric pollutants under
the given environmental conditon in the Weather-Ometer exert an adverse
effect on the performance of specific coatings. It is also significant from
the standpoint of correlation that the ranking in terms of erosion rates
(slope) for the five coatings exposed in the Weather-Ometer was virtually the
same as the ranking in terms of mils loss reported for the exterior studies.
This consistency in trends in data indicate that exposure studies employing
laboratory controlled environments can be used effectively in projecting
pollutant damage of coatings exposed in exterior conditions.
(b) Infrared Analysis
ATR (Attenuated Total Reflectance) infrared measurements were conducted on
the selected coatings after 1000 hours of exposure to the zero pollutant,
1 ppm S02 and 1 ppm 03 levels. The results of this study showed that the oil
house paint, the coil coating and the industrial maintenance coating degrade
much more readily than the two acrylic systems (latex paint and automobile
refinish) when exposed to 1 ppm S02 for 1000 hours in the Weather-Ometer.
In the presence of ultraviolet light (unshaded condition), the oil/coating
showed severe breakdowns of the binder, followed by the alkyd, urea/alkyd,
acrylic latex and nitrocellulose/acrylic coatings, respectively. The shaded
coatings exhibited a similar trend but with less binder degradation.
Examination of the 1.0 ppm 03 samples after 1000 hours exposure showed spectra
similar to the zero pollutant results but with slightly greater binder
degradation. The extent of degradation was greater for the unshaded exposure
(as expected) than for the shaded condition with the difference considerably
less than that for the S02 exposed coatings (excluding the automotive refinish).
In the case of the latter finish, the organic portion was considerably degraded
by 03 compared to the zero pollutant sample. In general, the above results
are consistent with the trends reported for the exterior and Weather-Ometer
erosion data (mils loss).
(c) Gloss and Sheen Measurements
All coatings were characterized by gloss and sheen during each examination
period (1*00, 700 and 1000 hours) for the five pollutant conditions. However,
only the gloss data is presented due to the inconsistencies exhibited by the
sheen results. The cumulative gloss data presented in Table 15 show that only
the automotive refinish and the industrial maintenance coating exhibit dis-
cernible trends between pollutant type and level. The graphs of gloss versus
ppm S02 or 03 levels for the latter two coatings presented in Figures 26 and
27 show that 03 at the 0.1 ppm level for both shaded and unshaded conditions
produced a considerable reduction in gloss particularly for the automotive
refinish compared to S02. Consistently lower gloss was caused by exposure to
-------
-43-
TABLE 15
Gloss Measurements (60°) of Panels Exposed to the
Various Pollutant Conditions in the Weather-Ometer
SHADED EXPOSURE
Zero 0.1 ppm 1.0 ppm 0.1 ppm 1.0 ppm
Pollutant S03 S0g Oj 03
Con- 400 700 1000 400 700 1000 400 TOO 1000 WO 700 1000 WO 700 1000
trols Hr. Hr. Hr. Hr. Hr. Hr. Hr. Hr. Hr. Hr. Hr. Hr. Hr. Hr. Hr.
Automotive
Refinish 90 73 82 ?8 8l 76 75 68 63 62 78 31 31 84 71 71
Industrial
Maintenance 37 23 19 l8 26 20 15 19 13 11 22 20 20 21 9 8
Oil House
Paint 13 7 5 33556 5343 364 3
Latex House
Paint 3 3 2 23333 3332 233 3
Coil Coating 5 3 3 24323 3333 222 2
UNSHADED EXPOSURE
Automotive
Refinish 90 71 8l 77 8l 70 65 74 70 68 72 21 21 74 53 35
Industrial
Maintenance 37 11 14 14 26 20 15 10 14 12 11 5 6 11 12 10
Oil House
Paint 13 6 3 35553-5 Fated 43 33 33
Latex House
Paint 3 3 2 23223 2232 22 22
Coil Coating 3 2 2 33332 2332 22 22
-------
Automotive Refinish 0
Industrial Maintenance "V
0.1
PPM SOS OR 03
-------
100
Figure 27 - Gloss Versus PPM S0a or 03
After 1000 Hours Exposure in the
Weather-Ometer Unshaded Condition
Automotive Refinish O
Industrial Maintenance
PPM S02 or 03
-------
03 at either ppm level in the unshaded condition. A similar but less pro-
nounced trend is apparent for the alkyd industrial maintenance coating
exposed in the unshaded condition.
As will be revealed later, the drastic drop in gloss of the automotive
refinish is attributable to the considerable formation of water insoluble
surface deposits of unknown composition on the panel surface. It is con-
ceivable that the binder of the automotive refinish was degraded as indicated
by the AIR spectra coincident to the formation of the surface deposits. These
counterbalancing effects would reflect only a small but misleading weight loss.
The latter contention would explain the apparent negligible effect of 03 (0.1
or 1.0 ppm levels) on the erosion data (mils 'loss) for this coating. The above
discussion illustrates the important point that more than one test method is
required to accurately determine the effect of aggressive environments on
coating performance. Also, the crystalline deposits noted on the 03 exposed
panels tends to obscure the validity of the gloss level being lower than the
acceptable service life limit of 40.
(d) Surface Roughness Measurements
The surface roughness data collected on the coatings exposed to all five
pollutant conditions in the Weather-Ometer (both north and south conditions)
were assembled in tabular form (Table 16) and then ranked similarly in procedure
as discussed under this section in Task II.
Table 17 presents the results of the rankings both within and between pollutant
conditions (shaded and unshaded) for the respective coatings* Examination of
the magnitude of the summation in columns shows that the oil house paint ex-
hibited the greatest percentage change in surface roughness (low total value)
with respect to the unexposed control, followed by the automotive refinish,
coil coating, alkyd industrial maintenance and latex coating in descending
order of severity. The above trends exist for both shaded or unshaded conditions
irrespective of the pollutant type or level.
The effect of pollutant type and level is determined by summing the ranked
value in rows. As before, a low summation is indicative of a large percentage
change in surface roughness. The tabulated results for the shaded condition
show that the zero pollutant exposure caused the least change in surface
roughness with th 0.1 S02, LO ppm S02, 0.1 ppm 03 and 1.0 ppm 03 producing
increasing percentage change in roughness, respectively. A similar analysis
for the unshaded coatings is precluded' because of the failure of the coatings
exposed to 1.0 ppm S02.
The trends in rankings are again inconsistent with the erosion results collected
in Task II and III in that high surface roughness is not equated with high
erosion. However, ozone at either the 0.1 or 1.0 ppm level produced the greatest
effect on surface roughness as well as the previously discussed detrimental effect
on gloss.
-------
-vr-
TABLE 16
Surface Roughness (Percent Change with Respect to Control) of Weather-
Ometer Panels After 1,000 Hours Exposure at Various Pollutant Levels
Shaded Unshaded
"0" 0.1 1 .1 1 "0" 0.1 1 .1 1
Pol- ppm ppm ppm ppm Pol- ppm ppm ppm ppm
lutant SOg SOg 03 03 lutant SOg SOg
Oil
House Paint 58 39 55 60 71 53 jk - k2 58
Automotive
Refinish 23 15 31 23 130 23 15 31 23 92
Coil
Coating 0 2k 1? 29 17 -12 17 -^.8 17 -1^
Industrial
Maintenance -9-3 -^.6 -2-3 6-9 ^-6 30 -25 -12 6-9 -6-9
Latex
House Paint -13 3A -U-5 3-^ 6-7 -25 1.1 1-1 0 3.^
-------
-1)8-
TABLE 17
Ranking of Percent Change in Surface Roughness of Films
Exposed in Weather-Ometer at Various Pollut antieve1s
Polutant
Level
"0" Pollutant
0.1 ppm S02
1.0 ppm S02
0.1 ppm 03
1.0 ppm 03
Summation
"0" Pollutant
0.1 ppm S02
1.0 ppm S02
0.1 ppm 03
1.0 ppm 03
Summation
COATINGS
Ranking Within Pollutants - Shaded
Automotive
Refinish
2
3
2
3
l
11
Latex
Coating
5
k
5
5
ij-
23
Coil
Coating
3
2
3
2
1
13
Industrial
Maintenance
5
k
k
5
22
Oil House
Paint
1
1
1
1
2
Ranking Within Pollutants - Unshaded
Automotive
Refinish
3
3
2
2
I
11
Latex
Coating
5
k
3
5
20
Coil
Coating
2
^
3
Industrial
Maintenance
2
5
5
20
Oil House
Paint
1
1
1
1
2
Ranking Between Pollutants - Shaded
"0" Pollutant
0.1 ppm S02
1.0 ppm S02
0.1 ppm 03
1.0 ppm 03
Automotive
Refinish
3-5
5
2
3-5
1
Latex
Coating
5
2-5
4
2-5
l
Coil
Coating
5
2
3-5
1
3-5
Industrial Oil House
Maintanance Paint
3
l
2
3
5
fc
2
1
Sum.
21-5
18.5
16-5
10.0
8-5
Ranking Between Pollutants - Unshaded
"0" Pollutanl
0.1 ppm S02
1.0 ppm S02
0.1 ppm 03
1.0 ppm 03
Automotive
Refinish
3-5
5
2
3-5
l
Latex
Coating
5
2-5
2-5
Coil Industrial Oil House
Coating Maintenance Paint Sum.
1-5
3
1-5
5
l
5
2
3
Failed
3
1
15-5
18.0
Ik
11
-------
(e) Instron Determinations
Stress-strain analyses performed on free films of the selected coatings after
zero, ^00 and 1000 hours of exposure to the various pollutant conditions
generally yielded inconclusive results. As shown in. Table l8 virtually all
coatings (excluding the latex paint) exhibited inconsistent trends in peaks
in tensile strength within and between the shaded arici unshaded conditions.
Some of these abnormalities may have been resolved through additional data
points. However, this latter limitation may not be of practical significance
since the automotive refinish, coil coating and oil house paint became relatively
brittle (approximately 2% or less elongation) after kOQ hours of exposure (shaded
and unshaded conditions). As noted previously, tensile strength measurements
of brittle coatings are difficult to reproduce with good precision. Consequently,
any apparent trends in results for these coatings would be fortuitous. In the
case of the flexible latex coating, it is noted that an inflection point in
tensile strength occurred only at 1.0 ppm S02 (shaded condition). All other
exposures caused an expected increase in tensile strength with the level being
higher in the unshaded condition.
(f ) Sorption-Desorption Measurements
The coatings exposed for 1000 hours to the zero, 1.0 ppm S02 and 1.0 ppm 03
pollutant levels in the Weather-Ometer (both shaded and unshaded) along with
the appropriate unexposed controls were characterized in terms of their sorption-
desorption properties. One objective of this auxiliary project was to determine
whether sorption-desorption measurements of the unexposed control coatings could
be used to predict the susceptibility to attack particularly by S02 during sub-
sequent exposure in the Weather-Ometer studies. It was reasoned'that coatings
which retain a moderate to high level of moisture following exposure to a
specified desorption condition would be more readily affected by exposure to
S02 containing environments- The greater coating degradation (erosion) ex-
pected would result from longer exposure to the hydrolytic action of dilute sul-
furous acid formed from absorbed S02 and the water within the film. In addition
to the above objective, it was desired to determine the magnitude of change in
sorption-desorption properties with respect to those of the unexposed control
that might occur during exposure to the various pollutant conditions (zero,
1 ppm S02 or 03) in the Weather-Ometer.
Figures 28 through 3 ^ show graphs of the normalized weight gain (sorption) or
weight loss (desorption) in milligrams versus the respective periodic weighing.
Essentially all of the coatings irrespective of the pollutant type or level
achieved equilibrium sorption or desorption (constant weight) within a 2-6
hour period. The rapid equilibration of the unexposed control paints (Figure
28) during the desorption period nullifies the hypothesis of predicting the
susceptibility of attack by S02 through initial sorption-desorption measurements.
Examination of the data for the exposed coatings in Figures 29~3^ shows that
pollutants irrespective of the type or level effected an insignificant change
(2-k milligrams) in the equilibrium sorption level for any given coating. Only
the latex paint exhibited a marked decrease in sorption level compared- to the
unexposed control results (Figure 23. The relationship of sorption and erosion
-------
Figure128 - Sorption - Desorption of
Unexposed Controls
13-0,-
-1.0
Automotive Re finish
Latex Coating
Coil Coating
Industrial Maintenance
Oil House Paint
o
A
X
V
D
h 6 10
Sorption
20 Sh 25 26 28
Time (Hours)
Desorption
-------
13-0
12-0
11.0
10.0
Figure 29 - Sorption-Desorption of Weather-Ometer
Panels Exposed to 1,000 Hours "0" Pollutants.
Shaded
-1.
Automotive Re finish
Latex Coating
Coil Coating
Industrial Maintenance
Oil House Paint
O
A
X
V
I
I I I
I
I
k 6 10
Sorption
20
24 25 26 28 30
1*0
Desorption
Time (Hours)
-------
13-0
12.0
11.0
10.0
Figure -30 - Sorption-Desorption of Weather-
Ometer Panels Exposed for a 1,000 Hours
to "0" Pollutants. Unshaded
-1.0
Automotive Refinish
Latex Coating
Coil Coating
Industrial Maint.
Oil House Paint
o
A
x
V
D
r
i i i
3 2 1* 6
1
10
1
20
1 1 1
2k 2526 2
1 1
8 30
1
40
1
. 1
Time vHours)
-------
12.0
11.0
10.0
9-0
r
Figure 31 T Sorption-Desorption of Weather-
Ometer Panels Exposed for 1000 Hours to
1.0 ppm 0^. Shaded-
•H
8.0
-1.0
Automotive Refinish
Latex Coating
Coil Coating A
Industrial Maintenance T/
Oil House Paint |_J
VJl
I I
10
Sorption
20
242526 28 JO
Desorption
Time (Hours)
-------
r
12.0
11.0
10.0
9-0
Figure 32-- Sorption-Desorption of Weather-
Ometer Panels Exposed for 1000 hours to
1 ppm 0-3. Unshaded.
Automotive Refinish
Latex Coating
Coil Coating
Industrial Maintenance
Oil House Paint
X
v
v/i
• i
0 2 h 6 10
|* Sorption
20
2k 2526 28 30
Time (Hours)
Desorption
U8
•I
-------
13 •Or-
12'0-
Figure 33- Sorption-Desorption of
Weather-Quieter Panels Exposed
for a 1,000 Hours to 1.0 ppm
S02 Shaded
o
Automotive Re finish
Latex Coating
Coil Coating X
Industrial Maint. V
Oil House Paint
i
20
?-\ 2T. 26
-I-
26
•= O
4 O
rime Hours.
Desorption
48
"I
-------
12.1
11.0
10.0-
Figure $4 - Sorption-Desorption of Weather-Ometer
Panels Exposed for a 1.000 Hours to 1.0 ppm
S02- Unshpded
Automotive Refinish
Latex Coating
Coil Coating
Industrial Maint.
Oil House Paint
o
A
X
V
D
1 1 1
) 2 k
\
6
1
10
l
20
1
2h
.»!
1
25
1
26
1
26
1 1
30 14.0
|
J
Time 'Hours)
-------
-57-
TABLE 18
Tensile Strength Determinations (PSl) of Films Exposed in
Weather-Ometer at Various Pollutant Levels
SHADED
"0" 0.1 ppm 1 ppm 0.1 ppm 1 ppm
Con- Pollutant SOg S03 03 Oa
trols WO 1,000 1|00 1,000 kOO1,000 400 1000 kOO
THT-) (Hr.) (Hr.) (Hr.) (Hr.) (Hr.) (Hr.) (Hr.) (Hr.) (Hr.)
Automotive
Refinish 2800 3050 2850 3150 2kOO 2800 2550 3^0 2950 3200 1350
Latex
Coating 850 1500 1650 1300 1700 1550 ikOO 1700 2050 1300 1900
Coil
Coating 1670 1650 2000 l800 2550 2300 2050 1700 1700 1750 2050
Industrial
Maintenance 500 IkOO 1650 1200 1950 1600 1250 1700 3000 1150 1700
Oil House
Paint ^00 1150 900 1250 1950 900 1000 1150 1^50 1300 1350
UNSHADED
Automotive
Refinish 2800 3500 3200 2900 1250 1750 1600 3150 2850 3200 1250
Latex
Coating 850 2000 2200 1750 2100 1300 2100 1800 2500 2050 2250
Coil
Coating 1670 2600 1900 1950 3150 1250 1600 2200 2150 1650 2200
Industrial
Maintenance 500 1950 1750 1850 2050 ikOO 2200 1600 2^00 1550 1100
Oil House
Paint lj.00 1150 1050 1550 UOO 800 1200 1550 1150 1050 900
Tensile Strength rounded to nearest 50 PSI.
-------
-•53-
is consistent only for the automotive refinish which shows the least sensi-
tivity to moisture and the lowest level of erosion.
The above discussion reveals that the technique of sorption-desorption is not
a totally reliable indicator of the effect of aggressive environments on coating
performance.
(g) Scanning Electron Photomicrographs
Films of the five coatings exposed to the zero pollutant, 1.0 ppm S02 or 1.0
ppm 03 conditions (unshaded only) in the Weather-Ometer were examined with
the scanning electron microscope. Unexposed controls were also included in the
series for comparison.
The photomicrographs presented in Figures *o through 73 are arranged according
to a coating type to facilitate discerning the extent of surface degradation
caused by the three pollutant conditions. Two levels of magnification (?00x, fOOOx)
were employed to enable a critical analysis of the topographical changes which
occurred at the coating surface.
Examination of the unexposed controls in Figures >')-.> 4jj, 5l,' 59 an<^ 69 show
a layer of binder which obscures the underlying pigment morphology. Only the
latex house paint and the coil coating exhibit a significant degree of initial
surface roughness-
The level of degradation caused by exposure to the three pollutant conditions
is discerned through examining the surface texture at jOOx magnification and
the pigment (TiOs and/or extender) binder matrix at the 7000x level. Holes
appearing in the coating surface indicate the loss of agglomerated pigment
consisting of combinations of Ti02, inert and/or binder. Large depressions or
crevices between the relatively massive extender particles also suggest a
greater degree of surface degradation.
In view of the above degradative features, it is apparent that Che latex house
paint, the coil coating and the oil house paint (Figures 3 " to \2, "kj to ' ")
and 51 to 57 respectively) show the greatest amount of physical change in
respect to the unexposed control during exposures to the three pollutant con-
ditions. Exposures to 1 ppm S02 appears to have effected the greatest degrada-
tion which diminishes on exposure to 1 ppm 03 and the zero pollutant levels,
respectively. Dramatic differences in surface topography are evident between
the 1 ppm S02 and the zero pollutant levels for the latex coating and the oil
house paint. The surface of the latter two coatings (7000x) exposed to the
zero pollutant condition show a considerable amount of apparently unaffected
binder.
Although the film of the oil house paint (Figure ^7 7000x) exposed to the 1.0
ppm S02 condition exhibited major surface modification as evidenced by the
deep fissures between the massive extender particle?, even greater degradation
on a macroscopic level occurred during similar exposure of the coated metal
panels. Extensive microchecks developed randomly over the latter coating
surface between kOO and 700 hours of exposure. The reflected light micrograph
-------
-59-
presented in Figure 58 (I30x) shows a portion of the failure which extends
almost to the metal substrate.
Examination of the alkyd industrial maintenance coating at fOOx. magnification
(Figures 59 and 65) shows a random development of holes in the surface of all
exposed samples. However, the surface topography revealed in the lOOOx photo-
graphs is relatively uniform with no apparent difference in pigment packing
irrespective of the three pollutant conditions.
The,relatively non-descript surface of the automotive refinish (Figures 66
and 73) indicate that this coating was the least affected in respect to
binder degradation during exposure to the three pollutant conditions. Ex-
posure to 1.0 ppm S02 has apparently caused slightly greater surface roughness
than exposure to the zero pollutant level. However, this observed topography
change attributable to binder-pigment loss exerted an inconsequential effect
on the erosion rate (Table li(). The crystal formation evident on the surface
of both the 0.1 ppm and 1.0 ppm 03 exposed samples presented in Figure 70 and
71 (700x) explains the respective drastic reduction in gloss level noted in
Table 15 and the increased surface roughness apparent in Table 16. These
deposits of unknown composition are more pronounced on the 0.1 ppm Q3 sample
(Figure 70).
The above discussion clearly shows that SEM analyses provide a useful quali-
tative technique in characterizing the degradation of coatings exposed to
aggressive environments. The photomicrographs show trends consistent with
the erosion rate data (Table ik) in respect to the greater degradation caused
by S02 versus 03 or the zero pollutant conditions- Comparison can readily
be made between coatings showing extremes in degradation. However, diffi-
culties are encountered in ranking the durabilities of coatings such as the
latex house paint, coil coating and the oil house paint which contain extenders
as part of the pigment composition and exhibit major apparent surface roughness
due to exposure.
The scanning electron photomicrographs are consistent with the surface roughnss
data (Table 16) only for the automotive refinish, the oLl house paint and
possibly the latex paint. The coil coating shows decreased surface roughness
irrespective of the three pollutant conditions but considerable surface degrada-
tion (holes indicating loss of agglomerates) according to the photomicrographs
(Figures ^5, kj, k-9)• The general increase in apparent roughness of the ex-
posed industrial maintenance coating versus the unexposed control (Figures
60, 62, 6^, and 59 respectively) is also contrary to the surface roughness
measurements•
-------
-60-
-------
LATEX HOUSE PAINT
Figure 35 - Unexposed Control • 700X
Figure 36 - " " 7000X
Figure 37 - 1000 Hours Exposure to Zero Pollutant - Unshaded 700X
Figure 38 - " " " " " » " 7000X
-------
-61-
Fig. 35
Fig. 36
Fig- 37
Fig. 38
-------
-62-
-------
LATEX HOUSE PAINT
Figure 39 - 1000 Hours Exposure to 1.0 ppm 03 - Unshaded 700X
Figure ^0 - " " » » " " 03 - " 7000X
Figure 1»1 - " " " " " " S02 - " 700X
Figure k2 - " " " " " " S02 - " 7000X
-------
-63-
•
Fig. 39
Fig. UO
Fig. kl
Fig.
-------
-6k-
-------
COIL COATING
Figure ^3 - Unexposed Control TOOK
Figure h-k - " " 7000X
Figure k$ - 1000 Hours Exposure to Zero Pollutant - Unshaded 700X
Figure K6 - 1000 " " " " " " 7000X
-------
-65-
Fig.
Fig.
;*
Fig 45
Fig.
-------
-66-
-------
COIL COATING
Figure kj - 1000 Hours Exposure to 1.0 ppm 03 - Unshaded 700X
Figure W - " " " " " " " - " TOOOX
Figure U9 - " " " " " " S02 - " ?OOX
Figure 50 - " " " " " " " - " JOOOX
-------
-67-
Fig.
Fig. 48
'-T
Fig.
Fig. 50
-------
OIL HOUSE PAINT
Figure 51 - Unexposed Control 700X
Figure 52 - 1000 Hours Exposure to Zero Pollutant - Unshaded 700X
Figure 53 - " " " " " " " 7000X
-------
-68-
-------
Fig. 51
i
Fig- 52
Fig- 55
-------
-TO-
-------
OIL HOUSE PAINT
Figure 5^ - 1000 Hours Exposure to 1.0 ppm 03 Unshaded JOOX
Figure 55 - 1000 " " " » " " " JOOOX
Figure 56 - 1000 " " " " " S02 " TOOX
Figure 57 - 1000 " " " " " " " 7000X
-------
-71-
Fig.
Fig. 55
Fig. 56
Fig- 57
-------
-72-
-------
OIL HOUSE PAINT
Figure 58 - 1000 Hours Exposure to 1.0 ppm S02 Shaded IjOX
-------
-73-
Fig. 58
-------
-------
INDUSTRIAL MAINTENANCE COATING
Figure 59 - Unexposed Control 700X
Figure 60 - 1000 Hours Exposure to Zero Pollutant 700X
Figure 6l - " " " " " " 7000X
-------
-75-
Fig. 59
Fig. 60
Fig. 61
-------
-76-
-------
INDUSTRIAL MAINTENANCE COATING
Figure 62 - 1000 Hours Exposure to 1.0 ppm 03 Unshaded 700X
Figure 63 - " " " " " " " " 7000X
Figure 64 - " " " " " " S02 " TOOK
Figure 65 - " " " " " " " " 7000X
-------
-77-
; -ii
Fig. 62
Fig. 6j
Fig.
Fig. 65
-------
-78-
-------
AUTOMDTIVE REFINISH
Figure 66 - Unexposed Control 700X
Figure 6? - " " 7000X
Figure 68 - 1000 Hours Exposure to Zero Pollutant - Unshaded 700X
Figure 69 - " " " " " " " TOOOX
-------
-79-
Fig. 66
Fig. 67
Fig.
Fig. 69
-------
-80-
-------
AUTOMOTIVE REFINISH
Figure 70 - 1000 Hours Exposure to 0.1 ppm 03 - Unshaded - 700X
Figure 71 - " " " " 1.0 » » " - 700X
Figure 72 " " " " 1.0 " S02 " - 700X
Figure 73 " " " " 1.0 " " " - 7000X
-------
-81-
Fig. 70
Fig. 71
Fig- 72
Fig- 73
-------
-82-
SUMMARY AND CONCLUSIONS
In this study, research was concerned primarily with the development of test
methods that are sufficiently sensitive to detect the initial degradation
of selected exterior coatings exposed to various pollutant containing environ-
ments. The test methods employed in generating dose response data included
erosion rates, attentuated total reflectance (ATR), gloss and sheen, surface
roughness, tensile strength and scanning election microscopy. Five commerically
important paint systems were selected for characterization including an oil
house paint, latex coating, an alkyd industrial maintenance coating, a coil
coating and an automotive refinish lacquer. The properties of the coating
systems were determined periodically consequent to "short term" exposure at
four exterior locations and to various pollutant containing environments under
controlled, but accelerated conditions in a Xeonon light, Dew Cycle Weather-
Ometer, The test sites for the former "short term" exterior study were located
at Leeds (north central), North Dakota; Los Angeles, California; Chicago (Research
Center), Illinois and Valparaiso, Indiana. These sites represent a "clean" rural
environment, a high 03 environment, a high S02 environment, and a relatively
high 03 environment plus a moderate S02 environment, respectively. In the
accelerated laboratory exposure study, five environmental pollutant conditions
were employed in the Weather-Ometer including a zero pollutant, 0.1 ppm and
1.0 ppm S02 and 0.1 ppm or 1,0 ppm 03 level. The zero pollutant condition re-
presents the control (clean air) with 0.1 ppm of each pollutant type considered
representative of the levels frequently reached in polluted cities. The 1.0
ppm levels represent a highly polluted (industrial) site.
Concurrent to implementing the above two phases of the experimental program,
a limited effort was devoted to reviewing existing exterior exposure records
to establish the service life for each coating exposed in at least four
locations, but not necessarily the same sites in all cases. The data from the
latter study coupled with the results generated in the other two phases would
potentially provide the required information for determining the reliability
of any given test method to predict the service life of the selected coatings
at each of the exposure sites, Unfortunately, the limited time element of
this research contract did not permit the development of sufficient data for
this extrapolation. It is also recognized, although not a specific requirement
in satisfying the project objectives, that erosion rate curves established from
the Weather-Ometer studies along with similar erosion data collected over an
extended exterior exposure period (? years minimum) can be used to provide an
assessment of the economic loss attributable to the damage caused by atmospheric
pollutants on coatings.
Conclusions from this investigation are:
(l) Erosion rate studies provide a definitive technique for determining
the effect of atmospheric pollutants on the performance of exterior coatings.
Consistent trends in erosion data were observed between the ''short term" and
Weather-Ometer exposure studies- ATR measurements on the coatings correlate
well with the results of the erosion studies despite the generally mediocre
spectra produced from the massive infrared absorption by the prime pigments.
In addition, ATR analyses provide meaningful information concerning the
chemical changes which occur in the film that would not normally be detected
-------
-85-
with erosion scudies. Scanning electron micrographs lend credence to erosion
data and provide a permanent record of the topography changes which occur
during exposure to aggre-sive environments.
The remaining three test methods employed Ln coating characterization pro-
vided only moderately useful information. Tensile strength measurements
performed on the coatings exposed in the Weather-Ometer were virtually
meaningless due to the rapid development of costing embnttlement, However,
the tensile strength of coatings in the less severe exterior environment
are following expected trends. Surface roughness analyses were even less
definitive in differentiating between the effect of pollutant type and level
on coating performance than tensile strength measurements. Gloss and sheen
determinations are relevant only for the coating? which exhibit a high initial
gloss level and/or a gradual decrease In gloss during exposure. The latter
method of testing was capable of differentiating generally between the extremes
in exterior exposure conditions.
(2) A significant conclusion derived particularly from the erosion, ATR
and SEM analyses of the Weather-Ometer exposed panels is that atmospheric
pollutants at levels encountered in polluted (industrial) sites (1.0 ppm
S02 or 03) and under the environmental conditions employed (temperature,
relative humidity) exert a definite adverse effect on the performance of
specific coatings compared to the zero pollutant condition. In general 1.0
ppm S02 as compared to the eero pollutant level casused a considerable effect
on the oil house paint, a moderate effect on the latex and coil coating, but
essentially no effect on the alkyd industrial maintenance coating and auto-
motive refinish. Based on the comparison of erosion rates (slope), S02 at the
1 ppm affected the majority of coatings to a greater extent in either the
shaded or unshaded condition than exposure to 1 ppm Oo, In addition, the
ranking of a coating in terms of erosion rates (mil* loss) is virtually in-
dependent of exposure to a pollutant type or level.
(3) Graphs of the slope of erosion rate with accompanying 95 percent
confidence limits versus pollutant level (zero, 0.1 and 1 ppm S02 or 03) for
the Weather-Ometer exposed coatings support the a priori hypothesis that
erosion rates are linearly related to pollutant concentration. Consequently,
these curves along with exterior erosion data collected over an extended
exposure period (two years minimum) provide the basis for assessing the
economic loss of damage caused by atmospheric pollutants on coatings.
(M The trends in erosion data for the ''short term" exterior study after
7 months of exposure show that the mils loss of coating is higher at Chicago
and Valaraiso than at the Los Angeles and North Dakota locations. These
results were explained by the higher S02 levels at the former two exposure
sites •< ATR measurements and the SEM micrographs also supported this con-
tention. It is also significant from the standpoint of correlation that the
ranking in terms of mils loss for the exterior exposed coatings was virtually
the same as the erosion rates generated in the accelerated studies regardless
of exposure location (both north or south).
-------
RECOMMENDAT:IONS FOR FURTHER RESEARCH
In view of the results generated in this experimental program and, considering
that other forms of atmospheric pollutants, in addition to gaseous, may also
exert a detectable adverse effect on coating performance, the following areas
for investigation are proposed:
(l) Continuation of the "short term" exposure of selected coatings at
the four exterior locations to confirm existing trends in detectable Initial
film damage data. Our considerable work with erosion studies shows that the
exterior erosion rates of the selected coatings become linear after 9 months
of exposure. Consequently, early erosion rates can be used effectively to
predict long term durability as well as to provide a correlation factor for
the linear erosion rates generated in Weather-Ometer exposures.
(2) Repeat of the accelerated laboratory exposure study to simulate
the detectable initial film damage encountered in exterior exposures using
identical pollutant levels (i.e.j zero, 0.1 and 1 ppm S02 or 03), but at a
lower relative humidity than in the present study. This effort would show
whether the observed effect of the pollutants such as SQS or 03 are moisture
dependent -
(3) Conduct a feasibility study concerned with determining the effect
of atmospheric particulate matter on coating performance. This proposed
area of study would be difficult to handle on an accelerated basis in the
laboratory since there is no standard type of particulate matter nor well
developed methods for controling the level of particulates. However, this
research effort could be accomplished by constructing a modified test fence
at one of the four exterior test sites. Equipment is available for providing
accelerated exposure but under exterior weather conditions typical for the
given test site.
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-85-
LIST OF REFERENCES
1. Jellinek, H. H. G- 196?. "Fundamental Degradation Process Relevant to
Outdoor Exposure of Polymers." Applied Polymer Symposia, 4_: kl-59-
2. Jellinek, H. H. G-, F. Flajsman and'F. J. Kryman, 1969, "Reaction
of S02 and N02 with Polymers,1' Journal of Applied Polymer Science, l^ (l):
107-116.
3- Beloin, N. J., 1970 "Fading of Dyed Fabrics by Air Pollution: A
Field Study." A report prepared by the Division (of Economics Effects Research,
Environmental Protection Agency. Raleigh, North^ Carolina.
k. Jellinek, H. H. G. and F. J. Kryman, 1969- "Reaction of S0a with
Polymer," Journal of Applied Polymer Science, 1% (2): 50^-2505-
5- Holbrow, G. L. 1962. "Atmospheric Pollution: Its Measurement and
Some Effects on Paint." Journal of the Oil and Colour Chemists Association
t£ (10): 701-718.
6. Gutfreund, K. 1966. "De termination of the Susceptibility of .Paint
Films to Deterioration." Journal of Paint Technology 38 (•503)": 732.- 7-39-
7- Schurr, G. G. and M. Van Loo. 1967- "Undereave Peeling of:.flouse
Paints." Journal of Paint Technology 39 (506) : 128-133-
8. Mayne, J. E. 0. 1957- "Current Views on How Paint Films Prevent
Corrosion." Journal of the Oil and Colour Chemists Association jj-0 (3):
183-199.
9- Berg, C. J., W. R. Jarosz, and G- F. Salathae. 1967- "Performance
of Polymers in Pigmented Systems." Journal of Paint Technology 39 (510): 436-^53.
10. Stieg, F. B. 1966. "Accelerating the Accelerated Weathering Test,"
Journal of Paint Technology 38 (U92): 29- 36.
11. Stieg, F. B. 1971. "Weathering and Titanium Dioxide," Journal of
Paint Technology V3 (555): 83-89.
12- Schurr, G. G-, T. K. Hay, and M. Van Loo. 1966. "Possibility of
Predicting Exterior Durability by Stress/Strain Measuremnts ." Journal of
Paint Technology 38 (501): 591-599
13. Hay, T. K. and G. G. Schurr. 1971. "Moisture Diffusion Phenomena in
Practical Paint Systems." Journal of Paint Technology 4-3 (566): 63-72.
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