ISSN:
0098-1273
Keywords:
Physics
;
Polymer and Materials Science
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
,
Physics
Notes:
Cryogenic pulverization of polymers in liquid nitrogen results in a variety of physical and chemical changes, of which crystallographic transformations are among the earliest. These have been investigated in detail for isotactic polystyrene using x-ray and calorimetric techniques. Amorphization was found to occur rapidly, but with concomitant decreases in crystallite sizes of only a limited extent. These changes can to a large degree be reversed upon annealing at high temperature. Similar behavior is seen also in other polymers possessing stronger intermolecular cohesion, such as polyesters and polyamides. In polymers susceptible to mechanically induced phase transformations, cryogenic pulverization causes polymorphic changes en route to amorphization: these include formation of the monoclinic phase in polyethylene and of the β phase in poly(vinylidene fluoride). Based on these results, a model is proposed for the mechanism of pulverization that incorporates both thermal and mechanical effects; this model suggests a two-phase structure of the pulverized, particles, consisting of an amorphous skin that surrounds a damaged crystalline core.
Additional Material:
13 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/pol.1985.180230708
