Page 345 - Engineering Plastics Handbook

302 Engineering Plastics

The data mentioned previously in Table 13.4 give short-term mechan-
ical properties under very simple loading conditions. These values are
typical of commercially available PSF, PES, and PPSF of practical molec-
ular weight. When one is considering a polymer for a particular end-use
application, it is very important to also consider other service life fac-
tors such as creep and fatigue properties as well as temperature and
other environmental factors.

Thermal properties
As mentioned previously, polysulfones offer excellent thermal stability
and resistance to oxidation during manufacture and melt processing as
well as in the end use. Polysulfones can be melt-processed at temperatures
up to 400°C. Their excellent thermal stability is evidenced by their behav-
ior during thermogravimetric analysis (TGA) in air. Figure 13.1 shows
that all three commercial polysulfones must approach temperatures of
500°C prior to the occurrence of significant weight loss. Polysulfones are
therefore very forgiving during melt processing. Outstanding thermal sta-
bility also allows for polysulfones to be used in a number of thermally
aggressive environments such as those found in medical sterilization,
food service, and electronics. The glass transition temperature of poly-
sulfones produced via nucleophilic polycondensation can be tailored by the
choice of the bisphenol, as shown in Table 13.2. The high glass transition
temperature T is attributed to the rigid phenyl rings in the backbone.
g

110
100
90
80
Weight retained, % 60
70

50
40
30
20
10
0
0 100 200 300 400 500 600 700 800 900
Temperature, °C
Figure 13.1 Thermogravimetric analysis curves in air for (▫) PSF, ( ) PES, and ( )PPSF.
TGA in nitrogen is at a heating rate of 10°C/min [17].