INTERACTION OF PROCESS VARIABLES WITH THE FRACTURE-BEHAVIOR OF AMORPHOUS POLYSTYRENE DURING ATTRITION

This study investigates the fracture of oriented general-purpose polys tyrene. Specimen microstructure was controlled using an extrusion-shee ting technique where draw ratio, polymer melt temperature, cooling roi l temperature, and nip roll pressure changed according to a designed e xperiment. Sharp-notched tension results display a 4X difference in lo ngitudinal vs. transverse specimen values. Shrinkage measurements show contraction in the machine direction amplifies with increasing draw r atio. Craze formation is visible only in those specimens tested in the longitudinal direction. Fracture mechanisms have strong orientation d ependence and the extrusion-sheeting process produces an ideal system to study the effects on attrition. Comminution studies illustrate draw ratio has an effect on the final median particle size and width distr ibution of the powder. Increasing the draw ratio reduces the volume me dian particle size and minimizes the formation of fine particles. A mo notonic fracture mechanism was initially considered but rejected in fa vor of a low cycle fatigue model based on estimates of fracture streng th.