Phase morphological study on SEBS compatibilized PS/LDPE blends

Abstract

The co-continuous phase morphology of polystyrene (PS)/low density polyethylene (LDPE) blends
compatibilized with poly(styrene-block-ethylene/butylene-block-styrene) triblock copolymers (SEBS) with
varying molecular weights has been investigated. The blend samples were prepared in a
mini-twin screw extruder. The barrel length and diameter are 224 and 16 mm, respectively. The diameter of
the capillary die is 1 mm. The concentration of the blends was 70/30 wt% of PS/LDPE while that of the SEBS
used was 5 wt% of the blend. The mixing temperatures used were 180, 250, and 280oC, and a screw speed
of 60 rpm. The morphology of the blends was investigated using an AFM technique. Average droplet
diameters of the blend samples were determined using an OM technique. The co-continuous morphology
has not been obtained in all the blends, although the mixing temperature used is as high as 280oC. The
experimental results indicated that the model prediction of the co-continuous morphology proposed by
Willemse and co-worker was not applicable to the blend systems studied. Only droplet-type dispersion was
observed. This is considered to arise from the processing conditions and the mixing device used. The blend
compatibilized with the high molecular weight SEBS had higher dispersed phase size than that of the blend
compatibilized with the medium and low molecular weight SEBSs. This behaviour is likely to arise from
coalescence during melt processing.