High specific strength hybrid polypropylene composites using carbon fibre and hollow glass microspheres: Development, characterization and comparison with empirical models

Synergistic effect of hollow glass microspheres (HGM) addition on various physical and mechanical properties of short carbon fibre (SCF) reinforced polypropylene (PP) hybrid composites were investigated. Hybrid composite samples were prepared by melt mixing PP, maleic anhydride-grafted-PP (MA-g-PP), SCF and surface-treated HGM. Effect of varying concentration of HGM (0-40 wt%) and SCF (0, 5, 8 wt%) on various physical and mechanical properties was analyzed. HGM showed an impressive positive impact in reducing the overall density of composites with its increasing concentration. Among all the different composite formulations, hybrid composite incorporated with 10 and 8 wt% HGM and SCF showed the highest tensile and flexural strength (up by similar to 110 and similar to 112% over pure PP). Interestingly, the specific tensile strength with only 8 wt% SCF was observed to be significantly high (similar to 100 MPa/g/cm(3)) and similar to commercial PP composites containing much higher (40 wt %) fibre contents. Empirical estimates of tensile modulus evaluated using several available micromechanical models, indicated that a combination of Ishai and Cohen (upper bound) and Halpin-Tsai models which assume a perfect particle- and fibre-matrix interfacial adhesion, are in excellent agreement with results of this investigation. Morphological analysis of cryo-fractured surfaces revealed good dispersion and distribution of both HGM and SCF with very negligible broken HGM fillers.