A COLLABORATIVE STUDY OF THE STRUCTURE AND RHEOLOGICAL PROPERTIES OF EVOH SMA BLENDS PRODUCED BY REACTIVE EXTRUSION (TECHNICAL REPORT)/

Blends of ethylene-vinyl alcohol copolymer (EVOH) and styrene-maleic a nhydride copolymer (SMA) have been produced by reactive extrusion and characterised in terms of their rheology, phase morphology and the deg ree of covalent bonding interaction tester linkages) between phases, a s determined by FTIR. Strongly synergistic behaviour in terms of visco sity and melt elasticity was seen in all blends, for low frequency dyn amic and low shear rate capillary tests, the largest increases occurri ng in blends containing 50-60% EVOH. Finely dispersed droplet phase mo rphologies were seen in most of the blends, the minor phase forming th e dispersed phase. However the blends containing 50-60% EVOH were co-c ontinuous or partly co-continuous; it was also notable that the blends containing 60% EVOH exhibited a surprisingly low value of Melt Index. Evidence of covalent bonding was apparent in all blends, the highest interaction levels again being seen for the 50-60% EVOH blends, despit e a very low anhydride/alcohol molar ratio (only 0.05). Increased mixe r speed and vacuum venting during processing also improved reaction le vels. These findings suggest that the availability of reactive groups is restricted by the phase morphology of the blend during production. As a result, more reaction occurs at or near co-continuous phase compo sitions, where the surface area is maximised. The synergistic behaviou r in viscosity and elasticity can be seen as consistent with the obser ved increased bonding levels, which causes more efficient stress trans fer into the dispersed phase.