The effect of cross-linking on the elastic modulus of Polythene

Abstract

Abstract Young’s modulus for Polythene, cross-linked by pile irradiation, has been measured by both static and dynamic means. Below about 115°C (the usual melting-point) the modulus decreases with temperature. Above this temperature it increases again, in agreement with the theory of rubber-like elasticity, except for very high degrees of cross-linking, corresponding to a glass-like structure. The effect of radiation is both to produce cross-linking, and to destroy crystallinity. The latter effect predominates below about 4% cross-linking, and a more flexible material is obtained at room temperature. The observed elastic properties below 115°C are ascribed in part to the attraction of neighbouring chains; the activation energy required to break these attractive forces is estimated at about 0·25 eV.