Retarded stress and morphology relaxation of deformed polymer blends in the presence of a triblock copolymer

Abstract

The effect of linear triblock copolymer compatibilizer (styrene–ethylene/butylene–styrene, SEBS) with strong viscoelasticity on the stress relaxation behavior of polypropylene (PP)/polystyrene (PS) (20/80) blends under various shear deformations has been investigated. With the addition of SEBS, the initial deformation of dispersed droplets under step shear strains was suppressed, and the following stress relaxation was found to be continuously retarded. The strain sensitivity of the stress relaxation modulus became weaker with the addition of SEBS possibly due to the improved viscoelasticity and interfacial adhesion. But the increase of strain led to more pronounced retardation in the stress relaxation of compatibilized blends. These phenomena were discussed in terms of the competitive effect of morphology refinement and the changes in interfacial and viscoelastic properties brought by compatibilization. The dominant factors determining the relaxation behavior were suggested to rely on the SEBS loading.