PHASE MORPHOLOGY AND PROPERTIES OF INJECTION-MOLDED POLYPROPYLENE ETHYLENE-VINYL ALCOHOL COPOLYMER BLENDS

The phase morphology of injection molded blends of polypropylene and e thylene vinyl alcohol copolymer (EVOH) changes dramatically throughout the sample and especially across the sample thickness. The developmen t of laminar structure was evaluated by image analysis of scanning ele ctron micrographs. The results indicate that laminar morphology is mos t likely to develop in the shear zone, as maxima in particle size and aspect ratio are observed in directions parallel and transverse to flo w in this region of the sample. The laminar structure is more pronounc ed at high concentrations of the EVOH minor phase, and at low maleatio n levels of the matrix resin, as well as for low molding thickness. Th e influence of processing conditions such as injection speed and mold and melt temperatures appears to be small. Intensive preblending of th e components in a twin screw extruder hinders the development of the l aminar structure. Toluene permeability measurements show that the pres ence of laminar phase morphology in injection molded samples produces substantial improvements of the barrier characteristics in the materia ls. However, impact tests indicate that there is need to optimize the conditions employed in producing the laminar morphology, in order to a void deterioration of mechanical properties. (C) 1996 John Wiley & Son s, Inc.