Effect of gamma irradiation on tensile properties of low molecular weight polyethylene samples

Three high density polyethylene (PE) samples of different origins, with weight average molar masses ranging from 38 to 63 kg mol−1 and displaying a semi-ductile behavior with strain at break εR values of the order of 100-140%, were gamma irradiated under nitrogen for doses up to 33.3 kGy. Steric exclusion chromatography and rheometry allowed to quantify the crosslink density X. This later reached values ranging from 4.6 to 9.0×10−3 mol kg−1, i.e. situated below the gelation point. Differential calorimetry, density measurement and small angle X-rays scattering showed the absence of significant changes in the crystalline morphology, especially lamellar dimensions. Tensile testing revealed an unexpected trend towards brittle regime of fracture while yield stress increases significantly at low doses. It appeared that branching disfavors cavitation during yielding, but this effect is not favorable to ductility.