Solid-state processing of thermoplastic polymers

Although compaction and sintering of polymeric powders has been investigated since the early 1970's, this processing method is not widely used, possibly because the fundamental mechanisms which control compaction and sintering have never been fully understood. This study has made significant contributions to our understanding of compaction and sintering of polymers. It was demonstrated that mechanical properties (yield strength, modulus) and physical characteristics (degree of physical aging, glass transition temperature, presence of crystallinity) of the particles, and thus, powder processing, storage, and handling techniques, affect the ability of the polymer to be successfully compacted. The difficulties encountered in sintering polymeric compacts were explained in terms of a loss of configurational entropy of the polymer molecules during compaction, which caused large-scale dimensional recovery in the particles upon heating above T g. Hot compaction (above room temperature, but below Tg) was not found to be useful in eliminating recovery during pressureless sintering. However, consolidation of compacts formed at room temperature (by heating 10-20°C above T g and applying a small pressure (less than 50 kPa» was shown to be a promising processing method.