Fracture energies of styrene-butadiene-styrene block copolymers

Specimens of SBS block copolymers were prepared by solution casting using different solvents. Measurements of fracture energies of SBS specimens were carried out at various temperatures and rates using two methods, i.e. a conventional tear test and a recently developed cutting test. Effect of casting solvent on the fracture energy was investigated and correlated with morphology. Results show that SBS block copolymers possess relatively high tear strength, about 10 kJ/m² at room temperature. Effect of temperature on tear strength is more pronounced than that of tearing rate. Moreover, the strength is virtually zero at the temperatures higher than the glass transition temperature of PS phase, ca. 95 °C. A small amount of dicumyl peroxides (DCP) was incorporated to slightly crosslink the copolymers to improve the tear strength at high temperatures. Effect of crosslinking density on fracture energy was investigated as well. It's been found that specimens of SBS cured with 0.01 phr DCP still possess relatively large tear strength at room temperature, when compared with uncrosslinked SBS samples. Moreover, the tear strength at high temperature has been effectively enhanced to be about 100 J/m².