Mechanical properties of wood‐fiber/toughened isotactic polypropylene composites

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Abstract
This study investigates the mechanical properties of wood‐fiber/toughened PP composite modified by physical blending with an EPDM rubber to improve impact toughness. Wood‐fiber thermoplastic composites were prepared with a modified PP matrix resin, employing high shear thermokinetic compounding aided with maleated PP for the fiber dispersion. The addition of EPDM improved the impact toughness, while it reduced stiffness and strength properties. To compensate the non‐plane strain fracture toughness, the specimen strength ratio (Rsb) was adopted as a comparative measure of fracture toughness. The strength ratio increased with the addition of EPDM, while it decreased with increasing wood‐fiber concentration. The work of fracture increased with EPDM level except at large wood‐fiber concentration. The effectiveness of the impact modification was assessed with the balance between tensile modulus and unnotched impact energy as a function of wood‐fiber concentration. EPDM rubber modification was moderately effective for wood‐fiber PP composites. The examination of fracture surfaces showed twisted fibers, fiber breakage, and fiber pull‐out from the matrix resin.