The effect of molecular orientation on gamma-radiation induced crosslinking in high density polyethylene☆

The effects of molecular orientation on γ-radiation induced crosslinking in high density polyethylene is studied using two different polymer grades. It is found that transfer of the initial isotropic semi-crystalline polymer structure to fully oriented fibrillar structure results in a large increase in crosslinking efficiency at relatively low radiation doses. However, in the ultra-oriented samples drawn at high temperatures, crosslinking efficiency approaches that of the undrawn polymer. A similar trend is also found for the decay of the inherent vinyl unsaturation while the elastic modulus of the ultra-oriented polymer initially increases with the radiation dose, followed by a decay period. These results are analysed in view of the morphology of the oriented polymer and the direct and catalytic actions of vinyl unsaturation in the crosslinking process.