Fibre Orientation and Mechanical Properties of Short Glass Fibre Reinforced PP Composites

The fibre orientation and distribution in short glass fibre (SGF) reinforced polypropylene (PP) composites were measured and an orientation function ( f) was introduced to describe the fibre orientation distribution. The fibre orientation distribution in the same level plane depended on the fibre position in an injection-moulded plate. The fibres close to the boundary wall of the injection cavity were parallel to the injection direction and those close to the back wall were perpendicular to the injection direction. A commercial maleic anhydride grafted PP (MAPP) was used as a compatibilizer. With the addition of MAPP, the fibre orientation distribution in PP/SGF/MAPP composites was slightly different from that of PP/SGF, but MAPP improved the interfacial adhesion between SGF and PP and consequently the mechanical properties. The use of SGF increased the tensile strength of the PP composites from 26.5 to 45.9 MPa (73% improvement), and for the PP/MAPP/SGF composite the tensile strength increased further to 55.4 MPa. The effect of SGF on the tensile strength can be expressed by a fibre efficiency factor (λσ). The SGF efficiency factor of PP/MAPP/SGF (0.198) was 45% higher than that of PP/SGF (0.137). The impact strength of PP/MAPP/SGF (64.7 MPa) was not only higher than that of PP/SGF (40.8 MPa) by 59% but also higher than that of PP (48.3 MPa) by 34%.