Phase Behavior and Rheological Properties of Amorphous Polymers Plasticized by Crystalline Solids

Abstract

Many high-Tg thermoplastics are difficult to process because of the close proximity of the glass transition and degradation temperatures. For these polymers only a few degrees of latitude in processing temperature are available to the fabricator, causing a high rate of rejection of the finished parts. Common problems include short shots and weak welds because of low temperatures, or splash and poor color because of excessively high temperatures. To increase the processability of high performance polymers, processing aids can be added. These include plasticizers, which lower melt viscosity but also adversely affect the high temperature performance of the resin. Because of the close relationship between melt viscosity and glass transition -- as described, for example, by the WLF relationship -- it seems evident that true plasticizers are not desirable as processing aids unless they can be removed from the polymer after fabrication. Removal of the plasticizer might be, conceivably, by its polymerization, vaporization, or solidification as a separate phase. The latter was chosen as the subject of this work.