THE EFFECT OF THE PROCESSING PARAMETERS ON THE FABRICATION OF AUXETICPOLYETHYLENE .1. THE EFFECT OF COMPACTION CONDITIONS

A novel fibrillated particulate microstructure has been fabricated in ultra high molecular weight polyethylene (UHMWPE) that produces a nega tive Poisson's ratio (auxetic) material. The processing route involves compaction, sintering and extrusion of a UHMWPE fine powder. The firs t, compaction stage is examined in this paper in detail in order to as certain the compaction conditions required to produce, as an end-produ ct, an auxetic polymer and to assess the importance of this stage in t he processing route. It was found that while part of the function of t he compaction stage was to impart structural integrity to the processe d polymers, the conditions for optimizing the production of auxetic UH MWPE were not identical to those for optimum structural integrity of t he compact. Both sets of conditions were examined, with compaction pre ssure and temperature being the most important of the variables examin ed.