Influence of fiber length on the mechanical properties of wood-fiber/polypropylene prepreg sheets

Natural fiber based composites have the potential to improve the mechanical properties of plastics while reducing the cost and weight. This study shows a practical method of blending natural-fiber with polypropylene to form a mat and then consolidated into a sheet by hot pressing. The natural fibers assessed were Pinus radiata and Eucalyptus regnan high temperature thermomechanical pulps and sisal (Agave sisalana) fibers. The tensile strength was shown to decrease with an increase in fiber content, while the tensile modulus was shown to increase. Tensile and flexural modulus were positively influenced by fiber length. The water performance tests of the sheets generally showed approximately 20% weight gain and approximately 3% thickness swell at 30% fiber content. The natural fiber surface chemical composition was determined by X-ray photoelectron spectroscopy and shown to be primarily covered with hydrophobic material such as lignin and extractives, while polypropylene was shown to be partially oxidized. Received: 18 September 2000 / Reviewed and accepted: 20 September 2000