POLYSTYRENE HIGH-DENSITY POLYETHYLENE BLENDS COMPATIBILIZED BY A TRI-BLOCK COPOLYMER I - PROPERTIES AND MORPHOLOGY

The compatibilization of polystyrene (PS)/high density polyethylene (H DPE) blends was achieved by using a (styrene-ethylene/butylene-styrene ) tri-block copolymer (SEBS) as a compatibilizer. The blends were prep ared by a twin-screw extruder. The mechanical properties of the blends were greatly improved after addition of SEES, suggesting the compatib ilizing role of the tri-block copolymer in the immiscible PS/HDPE syst em. The morphology of the blends was observed by scanning electron mic roscopy (SEM). It was found that the copolymer is very efficient in re ducing the size of the dispersed phase, and that a co-continuous two-p hase structure appears as the content of SEES increases to 4 wt%. The results of a SEM study of the fracture surfaces of the tensile bars sh owed that the unmodified and modified blends exhibited different fract ure characteristics. The melt rheology of the blends was investigated by capillary rheometry. The melt viscosity of the blends increases aft er the addition of 4 wt% SEES. The thermal properties of these blends were measured by a differential scanning calorimeter (DSC). The SEES c ontent does not affect the glass transition temperature of the polysty rene phase and the melting point of the polyethylene phase in the blen ds.