The tear behaviour of some tri-block copolymer elastomers.

Four SBS block copolymers were subjected to extensive chemical examination to determine block molecular weights and styrene fractions.Casting from different solvent systems into sheet form resulted in a range of microstructural formations for the normally dispersed styrene phase. These morphological details were studied using transmission electron microscopy and low angle X-ray scattering.Dynamic mechanical tests, on sheet material cast from different solvent systems, in both shear and tension over a wide temperature range, and static tensile tests at +20°C, revealed significant differences in viscoelastic properties between the materials. These differences were related to changes in morphological detail by the use of a model for composite materials. The large strain behaviour at +20°C is modelled by the inverse Langevin function and a debonding parameter which is related to void growth in the material.The conventional analysis of tear behaviour, developed originally for vulcanised rubbers, whilst ranking SBS block copolymers alongside the most tear resistant vulcanised materials over wide ranges of temperature and tearing rate, was found to be suspect for this class of materials. An alternative interpretation, however, succeeds in relating tear strength to tensile properties for the temperatures and tear rates studied, and also relates the tearing behaviour of these elastomers to that of a wide variety of other materials.