Effect of the compression ratio on wear properties of slightly cross-linked ultra-high molecular weight polyethylene, crsytallized under uniaxial compression

Makoto Ohta, Suong Hyu Hyon, Yu Bong Kang, Syozo Murakami, Shinzo Kohjiya, Masanori Oka, Sadami Tsutsumi

Research output: Contribution to journalArticlepeer-review

16 Citations (Scopus)

Abstract

To improve wear properties of artificial joints, cross-linked ultra-high molecular weight polyethylene (UHMWPE) was crystallized under compression in a molten state. Slight cross-linking was created by γ-ray irradiation at a 0.5 Mrad dose under reduced pressure at room temperature before the compression. Next, the UHMWPE was melted at 200°C and compressed using two metal plates. The compression ratio (CR) is defined as the ratio of the final thickness to the original thickness of the sample. The molecular chain of the UHMWPE was orientated to the direction of deformation and was crystallized by cooling to room temperature while maintaining the deformation. The (2 0 0) crystalline plane was only oriented parallel to the compression plane in the CR = 2 sample; however, in the case of the CR = 5 sample, both the (2 0 0) and the (1 1 0) crystalline planes were oriented parallel to the compressed surface. The density and melting point of the sample depended on the compression ratio. The physical and the mechanical properties were increased in accordance with their compression ratio. The αc-peak of the loss modulus was shifted to a higher temperature compared with the non-compressed sample. Dimensional stability of the compressed sample by heating near 135°C was not found. It was confirmed that the wear factor also depended on the compression ratio based on the findings of pin-on-disc and pin-on-flat wear tests. The wear factor of the (CR = 2) sample was similar to the non-compressed sample (CR = 1); in contrast, that of the CR = 5 sample was significantly smaller.

Original languageEnglish
Pages (from-to)145-151
Number of pages7
JournalWEAR
Volume250-251
Issue number1-12
DOIs
Publication statusPublished - 2001 Oct
Externally publishedYes

Keywords

  • Artificial joint
  • Compression ratio
  • Dynamic modulus
  • Wear resistance

ASJC Scopus subject areas

  • Condensed Matter Physics
  • Mechanics of Materials
  • Surfaces and Interfaces
  • Surfaces, Coatings and Films
  • Materials Chemistry

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