EFFECTS OF MOLECULAR-WEIGHTS AND COMPATIBILIZING AGENTS ON THE MORPHOLOGY AND PROPERTIES OF BLENDS CONTAINING POLYPROPYLENE AND NYLON-8

Polymer blends containing nylon-6 of different molecular weights (MW) and polypropylene (PP) were prepared by using a twin screw extrudes in order to examine the effects of molecular weights of nylon and the in fluences of different types of compatibilizing agents on the phase mor phology and the properties. The morphology of the resulting blends was characterized by using both scanning electron microscope (SEM) and op tical microscope and the properties measured included Izod impact stre ngth, melt flow index (MI), flexural modulus, and heat distortion temp erature (HDT). It was found that the molecular weights of the nylon ma trix had a significant effect on the phase morphology. The fracture su rface of the low MW nylon blend demonstrated a uniformed phase morphol ogy with the dispersed PP particles of dimensions in the range of 1 mu m in diameter embedded in the nylon matrix, suggesting an improved co mpatibility as compared with the high MW nylon system, even though the se two constituents were incompatible in nature. Three different types of compatibilizers, including maleic anhydride modified PP (MA-g-PP), acrylic acid modified PP (AA-g-PP), and ethylene glycidyl methacrylat e copolymer (EGMA), were used to examine their effects. It seemed that blends compatibilized with MA-g-PP exhibited the most homogeneous pha se morphology and superior mechanical properties among the three. In t he blends containing low MW nylon as the matrix phase, the Izod impact strength was shown to have increased by about 40% as compared with th e noncompatibilized blend, while a 20% increase of the impact strength was measured in the high MW nylon system. The effects of nylon's mole cular weights and the compatibilizers were also studied in systems of PP/nylon blends reinforced with silane-treated glass fibers. It was sh own that the properties of the composites relied on the phase morpholo gy which, in turn, was affected by both the molecular weight of nylon and the compatibilizing agents. (C) 1995 John Wiley and Sons, Inc.