Polypropylene and silica short fibers composites

The mechanical properties of composites strongly depend on the type of filler-polymeric matrix interface. An interface characterized by a strong bond between the filler and the matrix generally results in better mechanical properties. In this work, polypropylene, PP, was used as polymeric matrix and silica short fibers, SF, which are amorphous biogenic silica, were employed as filler. In order to promote a better filler-matrix interfacial adhesion, these fibers were previously modified with vinyltrimethoxysilane. The composites were prepared by extrusion and injection molding processes and their mechanical properties were evaluated according to tensile testing, ASTM D 268, by means a fractional factorial design (25-1). The studied factors included fiber content in the matrix, fiber surface modification, injection flow and testing rate. The composite cryogenic fractured surfaces were investigated by field emission scanning electron microscopy, FESEM. The fiber modification promoted a better fiber-matrix interfacial adhesion, resulting in optimized mechanical properties in relation to the others. In this way, the fiber modification was the most important factor on the mechanical performance of the composites.