The Impact Properties of Bulk Compatibilized PS/LDPE Blends

The impact properties of bulk compatibilized PS/LDPE blends have been studied. Polystyrenc-block-poly (ethylene-butylene) – block- polystyrene (SEBS) triblock copolymer with number average molecular weights (M[subscript n]) of 250,000 and 55,000 were employed as compatibilizers. The PS/LDPE blends with various concentrations of SEBS were prepared by melt mixing using a mini twin screw extruder at a mixing temperature of 180 and a screw speed of 60 rpm. The bulk morphology of the blends was studied using optical (OM), electron (SEM) and atomic force (AFM) microscopy. From these techniques the size and size distribution of the rubbery phase were obtained. Clear evidence of droplet type morphology was found in most samples. The SEBS copolymers have the effect of reducing the interfacial tension between the homopolymers, as indicated by the smaller dispersed phase dimensions when small amounts of the SEBS copolymers were added to the blends. The low molecular weight copolymer was found to be superior to the high molecular weight one in terms of emulsifying effect. The mechanical properties (impact strength) of the blends were studied using a standard charpy impact instrument. Little increase in impact strengths of the blends was observed in the uncompatibilized blends. A further increase in impact strength was obtained in the SEBS compatibilized blends. However, the marginal increase in the impact strengths of the both the uncompatibilized and compatibilized blends indicated the LDPE has low potential in toughening PS.