Effect of gamma irradiation on the optical properties of UHMWPE (Ultra-high-molecular-weight-polyethylene) polymer

The UV-Visible absorption spectra of virgin and high dose gamma irradiated (up to 2000 kGy) UHMWPE polymer have been studied by using UV-Visible spectrophotometer (JASCO, V-570). The existence of the peaks, their shifting and broadening as a result of gamma irradiation has been observed. In the present work the Urbach energy is calculated by using Urbach edge method. Also the direct and indirect energy band gap in virgin and gamma irradiated UHMWPE polymer has been calculated. The values of indirect energy band gap have been found to be lower than the corresponding values of direct energy band gap. A decrease in the optical energy band gap with increasing gamma irradiation has been discussed on the basis of gamma-irradiation-induced modification in the UHMWPE polymer. The correlation between optical energy band gap and the number of carbon atoms in a cluster with modified Tauc's equation has been discussed in this polymer. We have also observed the color formation which became more and more prominent with increasing dose and at the highest dose the fully transparent sample became completely opaque. Looking at the trend of the absorption curve this polymer can be used as a very good dosimeter for the gamma ray irradiation. (C) 2011 Elsevier B.V. All rights reserved.