Structure and properties of fiber-reinforced polypropylene prepared by direct incorporation of aqueous solution of poly(vinyl alcohol)

Poly (vinyl alcohol) (PVA) is immiscible with most conventional plastics and also unsuitable for melt processing owing to its extensive hydrogen bonding. Therefore, there have been few studies concerning the melt-mixing of PVA with standard plastics. The present paper describes a novel technique for producing isotactic polypropylene (PP) composites containing PVA fibers by directly introducing an aqueous solution of PVA into molten PP from an injection nozzle in a twin-screw extruder having a wide venting port. The PVA fibers were found to be dispersed homogeneously in the composites obtained by this method. Furthermore, an injection-molded product made from this composite exhibited an increased modulus, high yield strength, and high heat distortion temperature. These properties are attributed to the significant degree of orientation of both the PP chains and the PVA fibers. The nucleating action of the PVA fibers oriented in the flow direction is responsible for the structure of the composite, which in turn results in attractive properties.