Thermal and Mechanical Properties of Polypropylene/Wood-Flour Composites

In this research, polypropylene/wood-flour composites (WPCs) were blended with different contents of wood and/or maleated polypropylene (MAPP) and clay. We found that the addition of MAPP or clay in the formulation greatly improved the dispersion of the wood fibers in the composite; this suggested that MAPP or clay may have played the role of an adhesion promoter in the WPCs. The results obtained with clay indicate that it also acted as a flame retardant. The thermal tests carried out with the produced samples showed an increased crystallization temperature (T-c), crystallinity, and melting temperature (T-m) with wood loading. The increase of the two former parameters was explained by the incorporation of wood flour, which played the role of nucleating agent and induced the crystallization of the matrix polymer. On the other hand, the T-m increase was ascribed to the insulating properties of wood, which hindered the movement of heat conduction. The effects of UV irradiation on T-m and T-c were also examined. T-c increased with UV exposure time; this implied that UV degradation generated short chains with low molecular weight that could move easily in the bulk of the sample and, thus, catalyze early crystallization. The flexural strength and modulus increased with increasing wood-flour content. In contrast, the impact strength and tensile strength and strain decreased with increasing wood-flour content. All of these changes were related to the level of dispersion of the wood flour in the polymeric matrix. (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 119: 3321-3328, 2011