Microstructural evolution in the processing of auxetic microporous polymers

Microstructural formation in auxetic microporous UHMWPE has been studied in detail using extensive mapping of the microstructure during its processing. To ease sectioning for microstructural examination, a sintering and extrusion route was used. The fibrillar microstructure was found to occur in both the radial and longitudinal directions. Fibril generation was also seen to occur prior to extrusion with enough fibrils of sufficient size to lead to auxetic behaviour. A mechanism for fibril generation is proposed which is based on surface melting of the particles and drawing out of the interparticle contact points by particle movement, which is not necessarily the result of extrusion through a die. These findings will aid in the understanding of processing of auxetic microporous polymers and in the drive to extending the range available to include other polymeric materials and different processing routes. (C) 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.