Morphological Characterization of Irradiated Ultra High Molecular Weight Polyethylene (UHMWPE)

Effects of radiation (gamma and proton) on Ultra High Molecular Weight Polyethylene (UHMWPE) is studied for prosthetic joints and for radiation shielding for manned space missions. The first section of the dissertation will cover gamma radiation effects on UHMWPE by means of solubility, hardness, three-phase model, crystallite thickness, and molecular mobility studies. The second part will cover proton radiation effects on UHMWPE by means of solubility, three-phase crystallite model, and crystallite thickness study. The combined studies of the gamma irradiated samples shows that chain scission occurs on the surface and crosslinking in the center. The combined studies of the proton irradiated samples show that crosslinking occurs in the amorphous region and breaking of the tie chains and loops causes the growth of the already existing crystals. A new method has been developed to analyze DSC data based on crystallite thickness that generates crystallite thicknesses (number-average, weight-average, and z-average) and the lamella thickness polydispersity index, PDI (l_w/l_n and l_z/l_n). This new analysis method agrees with all other experiments conducted on the samples (solubility, molecular mobility, and three-phase model analysis).