Improvement of the impact resistance of natural fiber–reinforced polypropylene composites through hybridization

Polypropylene (PP) hybrid composites were prepared by the combination of naturalreinforcements and poly(ethylene terephthalate) (PET) fibers. Wood, flax, and sugarpalm fibers were used to increase stiffness and strength, while PET fibers served toimprove impact resistance. Interfacial adhesion was increased by using a maleated PP(MAPP) coupling agent. The hybrid composites containing 20 wt% of the naturalfibers were homogenized in a twin-screw compounder and then injection moldedinto standard tensile specimens. The amount of PET fibers was changed from 0 to40 wt% in the composites. Tensile and impact testing, acoustic emission measure-ments, and scanning electron microscopy (SEM) were used for the characterizationof the composites as well as to follow deformation and failure processes. The resultsproved that the concept of using PET fibers to improve impact resistance works withall natural fibers. Local deformations, the debonding or pullout of the PET fibers, initi-ate the plastic deformation of the matrix, which consumes considerable energy. Thefracture of PET fibers might also contribute to energy absorption. The type of naturalfiber does not influence the effect; the amount of PET fibers determines fractureresistance. The improvement of interfacial adhesion by coupling increases strengthand slightly improves impact resistance. The overall properties of the hybrid compos-ites prepared are acceptable, sufficiently large stiffness and impact resistance beingachieved for a large number of structural applications