MORPHOLOGY AND PROPERTIES OF THERMOSET BLENDS MADE FROM UNSATURATED POLYESTER RESIN, POLY(VINYL ACETATE) AND STYRENE

Blends containing an unsaturated polyester resin, poly(vinyl acetate) (PVAc) and styrene monomer in various proportions were cured using benzoyl peroxide as initiator. The morphology of the cured blends was studied using scanning electron microscopy. Polyester resin formed the matrix at low PVAc concentrations and at low styrene contents. A co-continuous phase morphology was observed in blends containing PVAc concentrations greater-than-or-equal-to 6% and styrene levels greater-than-or-equal-to 40%. Increasing the styrene content over the range 20% to 80% caused a narrowing of the principal dynamic loss peak, and an increase in peak height: peak temperature reached a maximum at 40% styrene. The change from particulate PVAc to co-continuous structure was associated with a sharp drop in G(Ic) and K(Ic). Parallel studies have shown this transition to be important in 'low-profile' behaviour.