Interface/morphology/property relationships in polyamide-6/ABS blends

Optimization of the compatibilizer concentration in polymer blends has gene rally been achieved through an indirect correlation with property improveme nts. In this article the evolution in particle size with percent interfacia l modifier (emulsification curve) is used to quantitatively assess the stat e of the interface under a wide range of processing conditions in ABS/polya mide-6 (nylon-6) blends. This type of dependence can yield important inform ation concerning the state of the interface of a given blend, including the concentration of compatibilizer necessary for interfacial saturation. To i llustrate the applicability of an emulsification curve to polymer processin g equipment, a comparison is made between the twin-screw extruder and the s ingle-screw extruder. In order to simulate a wide processing performance ra nge no additional mixing devices were used to enhance mixing on the single- screw extruder. The twin-screw extruder therefore represents the case of go od mixing and the single-screw extruder represents that of poor mixing. Fin ally, for the good mixing case, the impact strength has been analyzed in or der to observe its behavior at the critical concentration for interfacial s aturation as well as the effect of dispersed phase composition. The size of the dispersed domains reveals important differences between the compounding effects of the single-screw as compared to the twin-screw extr uder. A compatibilizing agent renders such a blend more homogeneous by redu cing the particle size of the dispersed phase. It was also found for the si ngle-screw extruder that the interface is not saturated and the phase size equilibrium value is not obtained even at high levels of interfacial modifi er. The higher efficacy of the twin-screw extruder in migrating the modifie r to the interface is clearly demonstrated through the use of the emulsific ation curve. The impact strength of material prepared by twin-screw/injection molding sh ows a significant increase at a modifier concentration, which correlates we ll with the critical concentration for interfacial saturation of interfacia l modifier from the emulsification study. The impact strength of an optimal ly compatibilized system as a function of dispersed phase composition displ ays a maximum impact strength around 50% ABS in the co-continuous morpholog y region. (C) 1999 John Wiley & Sons, Inc.