Effect of Colloidal Silica on Adhesion of Glass Fibres to Polypropylene

Colloidal silica was used to treat glass fibres to improve their adhesion to polypropylene resin (PP). The glass fibres were also treated with a coupling agent and maleic anhydride modified polypropylene emulsion (MAPP) to enhance their interfacial bonding. The surfaces of the glass fibres were observed 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 composites of glass fibres and PP were fabricated by means of a twin screw extruder and an injection moulding machine. The tensile strength and flexural strength were determined and the fracture surfaces were observed by SEM to establish the contribution of the surface treatment. The test results demonstrate that the tensile strength of the composites reinforced by those glass fibres treated with colloidal silica first and then with coupling agent and MAPP was 73.4% higher than that of composites reinforced with untreated glass fibres, and 24.0% higher than that of composites 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% stronger than materials without colloidal silica but treated with both coupling agent and MAPP.