Design Guide - Solvay Plastics

Environmental Resistance
As previously mentioned, the performance of polymeric
materials may be reduced by environmental factors.
This section discusses the effects of environmental
factors, such as chemical exposure, conditions
likely to promote hydrolysis, exposure to gamma
and/or ultraviolet radiation, on the performance of
Amodel resins. When appropriate, the effects of
these environmental factors on the performance
of competitive resins is included for comparison.
Chemical Resistance
Amodel resins are semi-crystalline polyphthalamides,
and like other members of the semi-crystalline
polyamide family, they exhibit excellent chemical
resistance to common organic solvents. However, the
chemical structure of Amodel resins is highly aromatic
— imparting an even greater degree of chemical
resistance to an even broader range of chemicals.
It is difficult to predict the exact effect of chemical
exposure on a polymeric component because the
reagent, the concentration of the reagent, the exposure
time, the temperature of the reagent, the temperature
of the polymeric component, and the stress on the
component all affect the extent of attack and any
change in performance. While the only reliable method
for evaluating the effect of chemical attack on the
performance of a polymeric component is prototype
testing, screening tests are often performed to provide
general guidance and compare materials.
Screening chemical resistance testing was performed
by immersing ASTM D638 Type I tensile bars in
various chemicals for 30 days at the indicated test
temperatures. The Amodel resin used was the 33%
fiber glass reinforced grade — Amodel AS-1133 HS.
Data on 33% glass reinforced PA 6,6 and 30% glass
reinforced polyethylene terephthalate (PET) is provided
for comparison.
Table 39: Key to Chemical Resistance Ratings
% Reduction in
Symbol
Rating
Tensile Strength
E Excellent ≤ 10
A Acceptable ≤ 50 but ≥ 10
U Unacceptable > 50
The material performance was rated as shown in Table 39.
In addition to the performance rating, data on the percent
change in tensile strength, length, and weight are reported.
The chemicals used for the screening tests were
classified into three groups:
• Organic solvents (Table 40)
• Aqueous solutions (Table 41)
• Automotive fluids (Table 42)
The screening evaluation using aqueous solutions at
elevated temperatures showed a loss in tensile strength
for all three of the resins tested. This phenomenon is
common to all glass reinforced thermoplastics. The loss of
tensile strength for Amodel AS-1133 HS resin in deionized
water at 93°C (200°F) is initially rapid due to loss of
interfacial adhesion between the glass fibers and the
resin matrix, and then slows to a gradual rate reflecting
hydrolytic attack. Aqueous solutions of antifreeze or
zinc chloride produce a similar effect. PA 6,6 is severely
attacked by the zinc chloride solution. PET is severely
attacked by the antifreeze solution and even badly
hydrolyzed by distilled water at elevated temperatures.
58 Amodel ® PPA Design Guide
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