(59g) Effect of Compatibilizer on Strength and Toughness of Glass Fiber Mat Reinforced Polypropylene Composites

High performance glass fiber mat reinforced polypropylene composites were prepared by double steel press melting impregnation method. The effect of maleic anhydride grafting polypropylene (MPP) as compatibilizer on the mechanical properties of composites was investigated. It was found that both the tensile and flexural strength were efficiently improved with the certain amount of MPP contained in the matrix. On the other hand, the impact strength decreased slightly then sharply and then kept invariability with the increasing of MPP content in the matrix. It was interesting and salutary to note that there was an appropriate MPP content to balance the strength and toughness of materials. Based on the composites without MPP, the tensile and flexural strength were increased about 38.6% and 60.2% respectively with different MPP fraction, the former the 7% and the latter the 5%, meanwhile the impact strength decreased about 43.0%. However, the changing trend of mechanical properties versus the MPP content revealed that there was some concession on strength for toughness. This compromise was reached near the MPP content about 1%. In this case, though the tensile and flexural strength were increased only about 26.4% (96MPa) and 25.9% (146MPa), the impact strength kept 94.5% (108.95KJ/m2) compared with the composites without MPP.

The dramatically improved mechanical properties could be attributed to the simultaneously appropriate enhanced interfacial adhesion and homogenous micro crystals in both matrix and interfacial area under the condition of suitable MPP content. For clarity, The DSC cooling and second heating scan curves of the composites were determined. It was showed that the increasing of MPP content led to lower crystallization temperature Tc than that of composites with MPP loading of 1%, which was almost the same as without MPP ones, indicating reduced nucleation. This was verified by the in-situ polarized optical micrographs for composites samples during isothermal crystallization at 140°C. The detailed isothermal crystallization illustrated that nucleation ability was not decreased until the introduced MPP loading exceeding 1%, and this was consistent with lower Tc. Also, it was claimed that, with increasing MPP content, the diameter of crystal spherulite increased, typically more MPP anchored on the surface of glass fiber led to the formation of transcrystalline, which play a vital role on the improved strength but the deteriorated toughness because of the excessive interfacial adhesion and larger spherulite. Excitingly, in the condition of MPP content about 1% in matrix, the appropriate interfacial microstructure and the favourable nucleation yielding lower diameter crystal and higher crystallinity balanced the strength and toughness of composites.

A schematic mechanism of this strength and toughness with lower MPP content is depicted, in which the appropriate interfacial microstructure combined with the favourable micro crystal structure in matrix, and the longer glass fiber pulled absorbing more energy when failure occurred were considered as key factors. These were confirmed by polarized optical micrographs, also verified with the SEM and optical graphs of fracture surface morphology.