Use of preimpregnated sisal yarn in woven reinforced polypropylene sheets: Thermoformability and mechanical properties

Abstract

Thermoplastic composites were made from polypropylene (PP) and long sisal fibers (SF) by using different processing techniques. Four sets of composites specimens were made with a 60/40 (wt/wt) SF/PP ratio: the first set was made by melt-blending PP and SF and compression molding 2-mm-thick flat sheets; a second set was made by melt-blending PP, SF, and maleic anhydride grafted polypropylene (MA-g-PP); the third set was made by compression molding knitted SF yarns, preimpregnated with PP, between PP sheets; the fourth set was also made by compression molding knitted SF yarns, preimpregnated with diluted MA-g-PP, between PP sheets. The bidirectional array of fibers, containing 60% of SF well-impregnated with a small quantity of MA-g-PP, increases the flexural modulus by 600%, the tensile modulus by 475%, and the tensile strength by 300% compared with unfilled PP. The composites sheets were successfully thermoformed with small wall thickness reductions to obtain a three-dimensional (3D) shape with very low forming energy, outstanding mechanical properties, and excellent surface finish. POLYM. ENG. SCI., 45:976–983, 2005. © 2005 Society of Plastics Engineers