Effect of radiation on the structure of ultrahigh molecular weight polyethylene

Radiation sterilization of ultrahigh molecular weight polyethylene (UHMW-PE) was recently found to cause changes in crystallinity, contradicting earlier observations on linear polyethylene of lower molecular weight. In this study, UHMW-PE (Hercules 1900) was gamma-irradiated up to 21 Mrad. Changes in melting and crystallization temperatures, enthalpies of melting and of crystallization, determined by differential scanning calorimetry, are reported. In particular, the temperature at the onset of crystallization provided a clearer view of the radiation damage to the polymer chains. A mechanism based on chain scission is proposed to explain the observed increase in crystallinity in agreement with recent findings. The crystallization temperature may be useful as an indicator of radiation and/or other damage to the UHMW-PE.