Influence of ageing on strength properties and morphology of fracture surface of hydroxy terminated polybutadiene rubber

Abstract

Vulcanizates of hydroxy-terminated polybutadiene (HTPB) rubber having a range of crosslinking density have been prepared by varying the amount of curing agent, toluene-di-isocyanate (TDI). The effect of oxidative ageing of these rubbers on the tensile and tear strength has been investigated. Kinetics of ageing of the samples are also reported here. The tensile strength, tear strength, modulus and hardness increase with the increase in the amount of TDI i.e. crosslinks. In general, there is an initial drop in the tensile strength and tear strength of these rubbers with time or temperature of ageing. There is a stiffening effect afterwards, particularly for HTPB rubbers cured with a lower amount of TDI. The activation energy for a fracture calculated from physical properties data is found to be 50–65 kj/mole. The increase of physical properties of HTPB rubbers with increasing crosslinking density is also reflected in the morphology of the fracture surface. More tear lines/tear deviations are observed on the fracture surface of rubbers at higher crosslink density. On ageing, however, the fracture surface becomes comparatively smooth for all cases.