Crystallization behavior of ultrahigh molecular weight polyethylene as a function of in vacuo gamma-irradiation

A comprehensive investigation was carried out to study the effects of in va cuo gamma -irradiation on the crystallization behavior of ultrahigh molecul ar weight polyethylene (UHMWPE) used in joint replacement prostheses. A wid e variety of experimental techniques, including differential scanning calor imetry (DSC), wide-angle X-ray diffraction (WAXD), synchrotron small-angle X-ray scattering (SAXS), hot stage optical microscopy (HSOM), and depolariz ed light scattering (DLS), was used to access information about lamellar an d supramolecular morphology, degree of crystallization, and crystallization kinetics during different nonisothermal and isothermal procedures. It was found that network formation prevailed over chain scission processes in the in vacuo irradiated samples, lowering the crystallizability of the polymer due to imposed geometrical constrains. In addition, the physical net of st able entanglements accompanied by the extensive cross-linking produced by g amma -irradiation generated quite unique crystallization morphology of UHMW PE. We detected the presence of distinct ordered grains, whose size depende d on the irradiation dose, that did not "melt" even after being subjected t o a high-temperature heating cycle. At lower temperatures, however, progres sive chainlike nucleation proceeded right on the skirt of these domains, ma intaining the constant crystallization rate regardless of the degree of und ercooling.