Tensile deformation mechanisms of polypropylene/elastomer blends reinforced with short glass fiber

Polypropylene hybrid composites reinforced with short glass fiber (SGF) and toughened with styrene-ethylene butylenes-styrene (SEBS) elastomer were prepared using extrusion and injection-molding techniques. Moreover, hybrids compatibilized with SEBS-grafted maleic anhydride (SEBS-g-MA) and hybrid compatibilized with PP grafted with maleic anhydride (PP-g-MA) were also fabricated. The matrix of the latter hybrid was designated as mPP and consisted of 95% PP and 5% PP-g-MA. Tensile dilatometry was carried out to characterize the fracture mechanisms of hybrid composites. Dilatometric responses showed that the elastic deformation was the dominant deformation mechanism for the SGF/SEBs/PP and SGF/SEBS-g-MA/PP hybrids. However, cavitation deformation prevailed over shearing deformation for both hybrids at the higher strain regime. The cavitation strain resulted from the debonding of glass fibers and from the crazing of the matrix in the SGF/SEBS/PP hybrid. In contrast, the cavitation was caused by the debonding of SEBS particles from the matrix of the SGF/SEBS-g-MA/PP hybrid. The use of PP-g-MA resulting in elastic deformation was the main mode of deformation in the low-strain region for the SGF/SEBS/mPP and SEBS/ SEBS-g-MA/mPP hybrids; thereafter, shearing appeared to dominate at the higher strain regime. This was attributed to the MA functional group improving the bonding between the SGF and PP. The correlation between fracture morphology and dilatometric responses also is presented in the article.