Mueller matrix polarimetry for characterization of E-Beam irradiated Uhmwpe

Abstract

Along with existing spectroscopic methods for polymer characterization, continuous efforts are in progress to have more sensitive and simple method for accurate determination of polymer characteristics before and after its modification with the use of various techniques. As an example the chemical and physical changes in biocompatible materials are usually probed with FTIR spectroscopy which uses totally un-polarized light and sophisticated proper aliened optics. It is therefore, for aforementioned objective, a more sensitive, better, and a simple experimental technique was proposed that mainly utilize the polarized light and simple Mueller Marix calculus for inquiring oxidation degradation and degree of cross-linking of irradiated UHMWPE. Mueller Matrix calculus was used for extracting the Depolarization Indices of 30, 65, and 100 kGy irradiated compressed sheets of UHMWPE. The effect of absorbed dose on depolarization index (DI) was monitored over the optical spectral range i.e. from 400 nm to 800 nm. A significant increase i.e. from 0.5 to 0.8 in DI values was observed in lower wavelength regions, however; slight increase was there in higher wavelength region. Radiation induced chemical changes including C=O, C=C unsaturation and voids within the UHMWPE structure along with scattering events because of increase in % crystallinity were attributed for the behavior in lower wavelength region. Scattering events due to increase in degradation because of oxidation or radiation induced defects were the reason for behavior in longer wavelength regime. In addition to this, integrated area under the DI curve and oxidation index of each sample had linear relation with each other. The results reported in this study suggested that the degradation/modification in UHMWPE can be probed with more sensitive physical quantity of light i.e. its polarization state.