Effect of colloidal silica on adhesion of glass fibres to polypropylene

Colloidal silica was used to treat glass fibres to improve their adhesion t o polypropylene resin (PP). The glass fibres were also treated with a coupl ing agent and maleic anhydride modified polypropylene emulsion (MAPP) to en hance their interfacial bonding. The surfaces of the glass fibres were obse rved by scanning electron microscopy (SEM). Because colloidal silica made the surfaces of the glass fibres rougher, PP could anchor on the surface of glass fibres to improve the fibre/PP bonding . These results were proved by using a microbonding pull-out test. The comp osites of glass fibres and PP were fabricated by means of a twin screw extr uder and an injection moulding machine. The tensile strength and flexural s trength were determined and the fracture surfaces were observed by SEM to e stablish the contribution of the surface treatment. The test results demonstrate that the tensile strength of the composites re inforced by those glass fibres treated with colloidal silica first and then with coupling agent and MAPP was 73.4% higher than that of composites rein forced with untreated glass fibres, and 24.0% higher than that of composite s without colloidal silica but still treated with coupling agent and MAPP. As for the flexural strength, the colloidal silica, coupling agent and MAPP -treated composite was 75.9% stronger than the untreated ones and 22.3% str onger than materials without colloidal silica but treated with both couplin g agent and MAPP.