Effect of the temperature on the tensile mechanical behavior of irradiated linear polyethylene

Abstract

The mechanical behavior of two γ-irradiated linear polyethylenes was determined at 75 and 105 °C under tensile stress. Each polymer was crystallized from the melt after different thermal histories so that samples would be obtained with various degrees of crystallinity. Subsequently, they were irradiated in vacuo and at room temperature to total doses ranging from 20 to 200 kGy. The initial crystallinity, dose level, and test temperature determined whether the samples displayed ductile, brittle, or transitional behavior. The yield stress decreased as the temperature increased. The value of the yield stress at a given temperature showed a tendency to increase with dose; this became more evident as the initial crystallinity increased. The extensibility of ductile samples, estimated from the draw ratio after break, decreased with the gel content. For ductile samples, the temperature affected the values of this property when the gel fraction that developed in the samples was relatively low. The effect of temperature became less noticeable when the gel reached values larger than 60%. The ultimate stress, normalized with the crosslinking density, correlated with the draw ratio after break in a way that resembled the type of relationship observed in other crosslinked systems.