Processing of ultra-high molecular weight polyethylene : modelling the decay of fusion defects

Wu, J.J.; Buckley, C.P.; O'Connor, J.J.

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.

Citation

Wu, J., Buckley, C., & O'Connor, J. (2002). Processing of ultra-high molecular weight polyethylene : modelling the decay of fusion defects. Chemical Engineering Research and Design, 80(A5), 423-431. https://doi.org/10.1205/026387602320224003

• Journal Article Type: Article
• Acceptance Date: Feb 28, 2002
• Publication Date: 2002-07
• Deposit Date: Jun 2, 2008
• Journal: Chemical Engineering Research and Design
• Print ISSN: 0263-8762
• Publisher: Elsevier
• Peer Reviewed: Peer Reviewed
• Volume: 80
• Issue: A5
• Pages: 423-431
• DOI: https://doi.org/10.1205/026387602320224003
• Keywords: UHMWPE, Polyethylene, Reptation, Finite element analysis, Thermal model, Fusion defects, Compression moulding, Powder processing.
• Public URL: https://durham-repository.worktribe.com/output/1558830
• Publisher URL: http://www.extenza-eps.com/ICE/doi/abs/10.1205/026387602320224003