Steam-exploded residual softwood-filled polypropylene composites

Residual softwood sawdust was pretreated by a steam-explosion technique. It was used as a natural filler in polypropylene (PP)-based composites. Dynam ic mechanical analysis and tensile properties of these materials were studi ed. The influence of filler loading, steam-explosion severity, and coating the fiber with a functionalized compatibilizer, such as maleic anhydryde po lypropylene (MAPP), on the mechanical behavior of the composite was evaluat ed. The results were analyzed in relation with scanning electron microscopy observations, and surface energy (dispersive and polar components) and app arent specific area measurements. Experimental data indicate a better compa tibility between MAPP-coated fiber and PP with respect to the untreated one . The coating treatment of the softwood fiber was found to promote interfac ial adhesion between both components, and to enhance the tensile properties of the resulting composite. This reinforcing effect was well predicted fro m theoretical calculations based on a mean field approach (Halpin-Kardos mo del). The steam-explosion pretreatment severity increased the surface energ y and apparent specific surface, and resulted in a loss of the fiber entire ty. The sorption behavior of these composite materials was also performed. It was found that the composites absorb more water, as the filler content i s higher. MAPP coating provided protection from water uptake in the interph ase region. (C) 1999 John Wiley & Sons, Inc.