Performance over a wide range of strain rate of polypropylene reinforced by short alfa fibers

Thermoplastics reinforced with short vegetal fibers are appealing materials for technical applications, for instance in automotive, thanks to high specific modulus and at least partially biosourced origin, in particular. However, a more widespread use of those materials is still hampered by a lack of knowledge about their mechanical behavior under severe loading conditions (e.g., high‐strain‐rate loadings). In addition, mechanical behavior is generally anisotropic due to complex reinforcement properties (distributions of fiber length and orientation, strong variability of fiber geometrical and mechanical properties…). In this paper, plates of maleic‐anhydride‐grafted polypropylene (PP) reinforced with short alfa fibers are processed by injection molding, for fiber content varying from 5 to 15 wt%. The tensile behavior of the composites is studied over a wide range of strain rate and for different angles of loading with respect to injection flow direction. Results demonstrate the potential of alfa fibers for the reinforcement of PP from quasi‐static to dynamic loading conditions (strain rate up to about 5 s⁻¹), and in different loading directions. As expected, composite behavior is sensitive to strain rate and the degree of anisotropy logically increases when increasing fiber content. In all cases, material behavior shows a remarkable reproducibility. POLYM. COMPOS., 40:2850–2862, 2019. © 2018 Society of Plastics Engineers