Effects of processing conditions and copolymer molecular weight on the mechanical properties and morphology of compatibilized polymer blends

The mechanical properties and morphology of melt mixed polystyrene (PS)/polyethylene (PE) blends that were modified by the addition of up to 16% of a semicrystalline PS‐b‐hPB (hydrogenated polybutadiene) diblock copolymer with varying molecular weight are reported. As a result of the blocks of the copolymer penetrating the corresponding homopolymers, these diblock copolymers are capable of reinforcing the PS/PE interface significantly. This increase in interfacial strength between the immiscible blend components does not necessarily result in an improvement in the mechanical properties of the blends as measured by Izod or tensile tests. This may be because the effect of the copolymers on the rheological properties of the blends during processing outweighs their emulsifying/reinforcing effects. If found to be universally true for polymer blends, these results suggest that the relationship between the effects of copolymers on interfacial strength, their emulsifying effects, and the mechanical properties of copolymer modified blends are not as simple as suggested by many statements found in the literature.