Biaxial self-reinforcement of isotactic polypropylene prepared in uniaxialoscillating stress field by injection molding. I. Processing conditions and mechanical properties

This research explores the longitudinal and latitudinal mechanical properti es of injection-molded isotactic polypropylene (iPP) prepared in a uniaxial oscillating stress field by oscillating packing injection molding (OPIM). The methods, processing conditions, and mechanical test results for iPP by conventional injection molding (CIM) and OPIM are described. The mechanical properties in the flow direction (MD) and transverse direction (TD) of the OPIM moldings indicate three types of self-reinforced iPP moldings. The pr onounced biaxially self-reinforced iPP specimens exhibit a 55-70% increase of the tensile strength and more than a fourfold increase of the impact str ength in the MD, together with more than a 40% increase of the tensile stre ngth and a 30-40% increase of the impact strength in the TD. The OPIM moldi ngs show different stress-strain behavior in the MD and TD. (C) 2000 John W iley & Sons, Inc.