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Durham University

Department of Engineering

Staff Profile

Publication details for Professor Jun Jie Wu

Wu, J. J., Buckley, C. P. & 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): 423-431.

Author(s) from Durham

Abstract

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.

Notes

A5 Special issue: materials processing.