Wu, J. J. and Buckley, C. P. and O'Connor, J. J. (2002) 'Processing of ultra-high molecular weight polyethylene : modelling the decay of fusion defects.', Chemical engineering research and design : official journal of the European federation of chemical engineering : part A., 80 (A5). pp. 423-431.
A problem in applications of ultra-high molecular weight polyethylene (UHMWPE) is the tendency for components to contain fusion defects, arising during processing of the as-polymerized powder. These defects have been implicated previously in failures of UHMWPE load-bearing surfaces, in knee and hip prostheses. Recent work of the authors has recognized two forms of defect: voids (Type 1) and particle boundaries deficient in diffusion by reptation (Type 2). To assist process and product design, a method has now been developed for predicting the decay of severity of Type 2 defects during processing, for a component of given shape and process history. A new quantifier was introduced for characterizing the progress of diffusion at Type 2 defects in UHMWPE—the maximum reptated molecular mass M. This was computed using results from reptation theory, embedded within a Finite Element thermal model of the process. The method was illustrated by simulating compression moulding trials already carried out experimentally by the same authors. It was discovered that M never reached the viscosity average molecular mass of the polymer, indicating incomplete boundary diffusion, and explaining the previous observation of Type 2 defects even in fully-compacted, apparently perfect mouldings. The method described has potential as a design tool, especially for optimizing manufacture of UHMWPE prosthesis components.
|Keywords:||UHMWPE, Polyethylene, Reptation, Finite element analysis, Thermal model, Fusion defects, Compression moulding, Powder processing.|
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|Publisher Web site:||http://www.extenza-eps.com/ICE/doi/abs/10.1205/026387602320224003|
|Record Created:||02 Jun 2008|
|Last Modified:||08 Apr 2009 16:21|
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