Page 349 - Engineering Plastics Handbook

306 Engineering Plastics

into the polymer. This behavior causes small crazes in the surface of the
polymer. If many crazes are formed, then the stress within the polymer
is reduced and cracking is prevented or delayed. If only a small number
of crazes form upon exposure to an aggressive solvent, they grow and prop-
agate into large cracks that can cause catastrophic failure of a finished
article.
It is possible to improve the ESCR of polysulfones through the use of
glass-fiber reinforcement or other fibrous reinforcement such as carbon
fiber. This approach is quite successful as long as the solvent in ques-
tion does not aggressively swell or dissolve the polymer.
In contrast to their response to some organic environments, polysul-
fones offer outstanding resistance to hydrolysis by hot aqueous envi-
ronments such as boiling water. Resistance is also excellent toward
mineral acids and alkalies, and salt solutions. This capability is often
a key reason behind the selection of polysulfones over other engineer-
ing polymers such as polycarbonates, polyesters, polyamides, and poly-
etherimides [17].

Solubility
An understanding of the solubility of polysulfones is important for appli-
cations in which the polymer must be dissolved, such as in coatings and
membrane applications. Solubility of the three commercial polysulfones
follows the order PSF > PES > PPSF. All three polysulfones can be dissolved
in a small number of highly polar solvents to form stable solutions at room
temperature. NMP, DMAc, pyridine, and aniline are suitable solvents
for polysulfones. Also 1,1,2-trichlorethane and 1,1,2,2-tetrachloroethane
are suitable but are unattractive for health reasons. Because of the lower
solubility parameter of PSF, it can also be dissolved in several less polar
solvents such as tetrahydrofuran (THF), 1,4-dioxane, chloroform,
dichloromethane, and chlorobenzene. Solvent choices for PES and PPSF
are fewer because these polymers have a propensity to undergo solvent-
induced crystallization in many solvents.

Radiation resistance
Polysulfones are resistant to many forms of electromagnetic radiation fre-
quencies including microwave, visible, and infrared. They also show good
resistance to X-rays, electron beams [18], and gamma rays [19, 20] under
practical application conditions. Polysulfones have demonstrated an excel-
lent fit in the area of microwave cookware due to microwave transparency
and hydrolytic stability.
Polysulfones exhibit poor resistance to ultraviolet (UV) light, as do
most aromatic polymers. The resins absorb heavily in the UV region,
which causes degradation of the polymer chains on and directly beneath