Impact modification of hybrid polypropylene composites with poly(vinyl alcohol) fibers

Polypropylene (PP) hybrid composites were prepared by the combination of three reinforcing (carbon, glass, and wood) and a synthetic (PVA) fiber. Tensile and impact testing, acoustic emission measurements, and scanning electron microscopy (SEM) were used for the characterization of the composites as well as to follow deformation and failure processes. The results obtained prove that the novel concept of using synthetic fibers for impact modification can be applied successfully also with PVA fibers. The extent of improvement in impact strength depends on fiber type and content, but also on interfacial adhesion which strongly influences the local deformation processes occurring around the fibers during fracture. Both the reinforcing and the synthetic fibers take part in these processes and contribute to energy consumption. Debonding and the subsequent plastic deformation of the matrix consumes energy the most efficiently, but the fracture of the PVA fibers also requires energy; thus, PVA fibers improve impact resistance both at poor and good adhesion. This approach allows the design of materials for structural applications; the combination of a stiffness of 4–6 GPa and an impact resistance of 20–25 kJ/m ² exceeds the properties of most PP composites available on the market.