A MICROCELLULAR PROCESSING STUDY OF POLY(ETHYLENE-TEREPHTHALATE) IN THE AMORPHOUS AND SEMICRYSTALLINE STATES .2. CELL-GROWTH AND PROCESS DESIGN

Microcellular semicrystalline polymers such as poly(ethylene terephtha late) show great promise for engineering applications because of their unique properties, particularly at higher densities. Recent studies h ave shown that some high density microcellular polymers have longer fa tigue lives and/or equivalent strengths relative to the neat polymer. Relatively few microcellular processing studies of semicrystalline pol ymers have been presented. In general, semicrystalline polymers are re latively difficult to microcellular process compared to amorphous poly mers. In this paper, the microcellular processing of poly(ethylene ter ephthalate) in the amorphous and semicrystalline states is studied in order to quantify the processing differences. Particular emphasis is g iven to the cell growth stage of microcellular processing comparing th e processing characteristics of semicrystalline and amorphous PET. Bas ed on the results of this study, a number of critical process paramete rs are identified. Another goal of this analysis is to derive robust m icrocellular process design strategies for the amorphous and semicryst alline materials. Process design strategies are given for both semicry stalline and amorphous PET.