Design Guide - Solvay Plastics

Thermal Stability
The general term, thermal stability, is used to describe
the ability of a material to resist loss of properties due
to heat. Various methods are used to evaluate this
tendency. In the next section, we will discuss several
of these methods, including thermogravimetric analysis,
and long-term heat aging.
Thermogravimetric Analysis (TGA)
Thermogravimetric analysis is performed by increasing
the temperature of a small sample of the test material
at a constant rate while monitoring its weight. The
atmosphere is controlled and the test can be performed
using air or an inert atmosphere, such as nitrogen.
Figure 65 shows the weight loss of Amodel A-1000
resin as a function of temperature in air at a heating
rate of 10°C/min (18°F/min). The graph shows that
Amodel ® PPA resins are thermally stable beyond the
recommended upper processing temperature limit of
350°C (662°F).
Thermal Aging
Nearly all polymeric materials exhibit some loss
of performance properties after long-term exposure
to elevated temperatures. While some polymers are
more stable than others, the property loss is typically
a function of both exposure time and temperature.
Because the property losses result from both oxidative
attack and thermal degradation, the term "thermal
oxidative stability" is frequently used.
Thermal oxidative stability limits the acceptable longterm
use temperature of some polymers. To evaluate
these long-term effects on the properties of Amodel
polyphthalamide, molded test specimens of Amodel
resins were placed in circulating air ovens at several
elevated temperatures. Specimens were removed
from the oven at regular intervals, then tested at room
temperature for tensile strength and impact resistance.
Typically, these aging tests are run until the property
being monitored has been reduced to one-half its
starting value. The aging tests are conducted at
several aging temperatures and an "Arrhenius Plot" is
prepared. An "Arrhenius plot" plots the heat aging time
required to reduce a property to one-half of its starting
value, sometimes referred to as its half-life, against the
reciprocal of the aging temperature in degrees Kelvin.
The advantage of analyzing the data in this manner is
that the plot is theoretically a straight line and, therefore,
easily extrapolated.
Figure 65: Thermogravimetric Analysis
of A-1000 in Air
Weight, %
100
80
60
40
20
Temperature, °F
500 600 700 800 900 1,000 1,100 1,200
0
250 300 350 400 450 500 550 600 650
Temperature, °C
Figure 66: Thermal Aging Comparison -
Tensile Strength
Time to Tensile Strength Half-life
100,000
10,000
1,000
Temperature, °F
320 340 360 380 400 420 440
100
150 160 170 180 190 200 210 220 230
Temperature, °C
AS-1133 HS
33% GR PA 6,6
Figure 66 shows the plot of tensile strength half lives
of Amodel AS-1133 HS resin and GR PA 6,6 versus
the aging temperature. Amodel ® PPA maintains its
tensile strength longer than PA 6,6 does.
Property Data
Amodel ® PPA Design Guide
47