The influence of electron beam irradiation conducted in air on the thermal, chemical, structural and surface properties of medical grade polyurethane

It is well known that polyurethane (PU) provides good irradiation resistance; however, extremely high irradiation doses can alter the structure and/or function of macromolecules, resulting in oxidation, chain scission and crosslinking. In this present study, modifications to the material characteristics resulting from irradiation were extensively examined through a broad array of analytical techniques. Fourier transform infrared spectroscopy (FTIR) revealed that there were a number of changes to the chemical structure after electron beam irradiation while dynamic frequency sweeps identified an occurrence of crosslinking particularly in the higher irradiation doses. The degree of crosslinking was further analysed by implementing the crosslink density experiment, which illustrated a high level of crosslinking at 200 kGy only. X-ray diffraction (XRD) and differential scanning calorimetry (DSC) identified an increase in phase segregation and as a consequence it could lead to soft segment mobility. This increase in mobility could be responsible for an increase in the degree of chain orientation. Surface morphology of the electron beam irradiated material was determined using scanning electron microscope (SEM) imagery and this provided evidence that the surface of the material had clearly transformed with the development of additional ridges. The influence of such modifications initiated a significant reduction in the contact angle at the upper irradiation dose regime. Overall, this study demonstrated that the medical grade PU was highly affected by radiation exposure, particularly at high irradiation doses.