Cocontinuous morphologies in polystyrene/ethylene-vinyl acetate blends: The influence of the processing temperature

The influence of the compression-molding temperature on the range of cocontinuity in polystyrene (PS)/ethylene-vinyl acetate (EVA) copolymer blends was studied. The blends presented a broad range of cocontinuity when compression-molded at 160degreesC, and they became narrower when compression-molded at higher temperatures. A coarsening effect was observed in PS/EVA (60:40 vol %) blends upon compression molding at higher temperature with an increase in the phase size of the cocontinuous structure. Concerning PS/EVA (40:60 vol %) blends, an increase in the mixing and molding temperatures resulted in a change from a cocontinuous morphology to a droplet-matrix morphology. This effect was observed by selective extraction experiments and scanning electron microscopy. The changes in the morphology with the molding conditions affected the storage modulus. An increase in the storage modulus in blends compression-molded at 160degreesC was observed as a result of dual-phase continuity. An EVA copolymer with a higher vinyl acetate content (28 wt %) and a higher melt-flow index resulted in blends with a broader range of cocontinuity. This effect was more pronounced in blends with lower amounts of PS, that is, when EVA formed the matrix. (C) 2003 Wiley Periodicals, Inc.