Effect of rubber functionality on microstructures and fracture toughness of impact-modified nylon 6,6 polypropylene blends: 1. Structure-property relationships

The effects of maleic anhydride (MA) content and its reactive functionality on the phase size and phase morphology of nylon 6,6/ polypropylene (PP) bl ends were studied. The blends were obtained by simultaneous compounding of maleated styrene-ethylene-butylenestyrene block copolymers (SEBS) containin g different amounts of MA, with nylon and PP. The microstructures were exam ined using cross-polarized transmission optical microscopy (TOM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Bath tensile and fracture properties of the maleated blends were reported and di scussed in terms of the morphological features uncovered by these microscop ic techniques. Tensile strength increased with MA-grafted SEES content in t he 75/25 nylon 6,6/PP blends but a reverse trend was observed in the 50/50 nylon 6,6/PP blends. It was thought that this was caused by the migration o f the functionalized styrenic block copolymers from the PP phase to the dis persed nylon domains in the 50/50 nylon 6,6/PP blends. An optimized morphol ogy was found when SEBS grafted with 0.74 wt% MA was blended with 75/25 nyl on 6,6/PP. At this composition, SEES inclusions were dispersed uniformly in the continuous nylon matrix and thin layers of SEES molecules also existed at the nylon-PP interface. The latter gave a morphology similar to a core- shell rubber modified structure (i.e. SEES shell and PP core) and imparted the highest fracture toughness to this blend with an optimal combination of tensile strength and ductility. (C) 1998 Elsevier Science Ltd. All rights reserved.