Quasi-static and dynamic nanoindentation studies on highly crosslinked ultra-high-molecular-weight polyethylene

In four separate studies, the effect of three methods used to highly crosslink ultra-high-molecular-weight polyethylene (UHMWPE) (gamma irradiation, electron beam irradiation, and peroxide treatment) on the polymer's stiffness was investigated using quasi-static and dynamic nanoindentation. From the quasi-static studies, it was found that (a) the highest value of the elastic modulus, E (2240 +/- 157 MPa) was obtained from specimens prepared from direct compression molded UHMWPE crosslinked using gamma irradiation, with a dosage of 7.5 Mrad; (b) the value of E for specimens formed from direct compression molded UHMWPE was higher (1950 +/- 255 MPa) compared to results obtained from specimens formed from ram extruded UHMWPE (1583 +/- 140 MPa); and (c) the magnitude of the decrease in the value of E as a result of subjecting a highly crosslinked UHMWPE specimen to uniaxial tensile forces depends on the method used for the crosslinking. From the dynamic study, (d) it was found that the extent of the change in both the storage modulus and the loss modulus, as a result of subjecting a highly crosslinked UHMWPE specimen to uniaxial tension forces, depends on the method used for the crosslinking.