Insert injection molding of polypropylene single-polymer composites

A process for making polypropylene (PP) single-polymer composites (SPCs) by insert injection molding was investigated. PP SPCs with relatively good tensile and interfacial properties were prepared with a relatively short cycle time. Melt-spun PP fibers from the same resin as the matrix were treated in heated silicone oil, with and without tension, to study the changes of fiber properties upon exposure to high temperature. PP SPCs containing 36 wt% lab-made fabric achieved a tensile strength of 70 MPa, 2.3 times that of neat PP. Polarized light microscopy of PP SPCs with uniaxial fibers indicated that different crystalline regions formed from partial melting of fibers along the fiber surface. Differential scanning calorimetry results showed that most fibers could maintain the thermal properties after molding. Voids were not observed in the scanning electron microscopy images of the fracture surface after tensile failure indicating good bonding between the matrix and fibers.