BLOCK-COPOLYMERS AS COMPATIBILIZERS FOR BLENDS OF LINEAR LOW-DENSITY POLYETHYLENE AND POLYSTYRENE

Compatibilization of blends of linear low-density polyethylene (LLDPE) and polystyrene (PS) with block copolymers of styrene (S) and butadie ne (B) or hydrogenated butadiene (EB) has been studied. The morphology of the LLDPE/PS (50/50) composition typically with 5% copolymer was c haracterized primarily by scanning electron microscopy (SEM). The SEB and SEBS copolymers were effective in reducing the PS domain size, whi le the SB and SBS copolymers were less effective. The noncrystalline c opolymers lowered the tensile modulus of the blend by as much as 50%. Modulus calculations based on a core-shell. model, with the rubbery co polymer coating the PS particle, predicted that 50% of the rubbery SEB S copolymer was located at the interface compared to only 5-15% of the SB and SBS copolymers. The modulus of blends compatibilized with crys talline, nonrubbery SEB and SEBS copolymers approached Hashin's upper modulus bound. An interconnected interface model was proposed in which the blocks selectively penetrated the LLDPE and PS phases to provide good adhesion and improved stress and strain transfer between the phas es. (C) 1995 John Wiley & Sons, Inc.