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) blends were studied. The blends were obtained by simultaneous compounding of maleated styrene-ethylene-butylene-styrene block copolymers (SEBS) containing different amounts of MA, with nylon and PP. The microstructures were examined using cross-polarized transmission optical microscopy (TOM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Both tensile and fracture properties of the maleated blends were reported and discussed in terms of the morphological features uncovered by these microscopic techniques. Tensile strength increased with MA-grafted SEBS content in the 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 of the functionalized styrenic block copolymers from the PP phase to the dispersed nylon domains in the 50/50 nylon 6,6/PP blends. An optimized morphology was found when SEBS grafted with 0.74 wt% MA was blended with 75/25 nylon 6,6/PP. At this composition, SEBS inclusions were dispersed uniformly in the continuous nylon matrix and thin layers of SEBS molecules also existed at the nylon-PP interface. The latter gave a morphology similar to a core-shell rubber modified structure (i.e. SEBS shell and PP core) and imparted the highest fracture toughness to this blend with an optimal combination of tensile strength and ductility.