ANALYSIS OF THERMAL-PROPERTIES OF POLYMERIC BIOMATERIALS - I - ULTRAHIGH-MOLECULAR-WEIGHT POLYETHYLENE

The effects of sample size and heating and cooling rates on thermal tr ansitions of ultrahigh-molecular-weight polyethylene (UHMWPE) were inv estigated. The thermal parameters were studied using differential scan ning calorimetry (DSC) and thermogravimetric analysis (TGA). While hea ting rates and sample size had strong effects on thermal properties, t he influences of cooling rates were minor. For DSC, broad melting tran sitions were obtained at faster heating and/or slower cooling rates an d larger sample sizes. Higher melting temperatures were obtained when heating rates and sample size were increased. Slower cooling rates als o produced higher melting and crystallization temperatures. Faster coo ling rates yielded lower heats of fusion during melting and also lower heats of crystallization. The dependence of peak melting and crystall ization temperatures on the heating and cooling rates are illustrated by two empirical formulas. For TGA, it is found that faster heating ra tes and larger sample sizes produced higher decomposition temperatures . This detailed analysis may explain the large variations in the repor ted data on thermal properties and crystallinity of UHMWPE and provide solutions to the current clinical problems associated with polymeric biomaterials. (C) 1998 John Wiley & Sons, Inc.