Project Details:

Structure, Processing and Performance of Ultra-High Molecular Weight Polyethylene

Project No.:2010-019-1-400
Start date:2010-05-01
End date:0000-00-00
Division:Polymer Division
Objective:

To develop improved methods for characterizing UHMWPE mouldings, and hence improve quality assurance procedures for hip and knee prostheses. Team members will address problems of monitoring changes in molecular weight, crystallinity, crystal morphology, interfacial reptation and entanglement during moulding, and the effects of these changes on strength and wear resistance.

Description:

Compression mouldings made from UHMWPE (Mw > 1 MDa) are widely used in replacement hip and knee joints. In a minority of cases, their service lifetimes are drastically shortened by micro-cracking and wear. Problems are exacerbated by osteoclast cells, which remove bone debris, but not PE. Instead, they summon reinforcements, which attack living bone and cause arthritis. Good quality control is necessary to avoid these problems, but is difficult to achieve. Reactor powder has high crystallinity (~70%) and is intrinsically rigid and strong, but adverse changes occur during moulding. Ideally, processing should produce strong, void-free interfaces, with minimum loss of stiffness and strength. However, ultra-high molecular weights limit reptation and the formation of entanglement across interfaces, and heat treatment reduces crystallinity, thereby impairing mechanical properties. There are major problems in characterizing UHMWPE at different stages of processing, and hence in relating structure to performance, because standard methods cannot be used for measuring MWt or observing flow behaviour.

To address these problems, IUPAC Subcommittee on Structure and Properties of Commercial Polymers has formed a well-balanced project team consisting of industrial and academic members with expertise ranging from molecular weight determination and electron microscopy to micro-cracking and wear of joints. Several team members already have strong backgrounds in research on UHMWPE, and the participation of a major manufacturer is an added strength. Ticona will supply three HMWPE grades, with approximate MWts of 0.4, 5 and 9 MDa, as both powder and standardized mouldings. Other participants will develop methods for observing and quantifying the changes that occur during processing, especially those affecting fracture and wear resistance, which will also be evaluated.

Progress:

July 2010 - project announcement published in Chem. Int. Jul-Aug, p. 20

Chairman: