DEPENDENCE OF THE MECHANICAL-PROPERTIES OF WOODFLOUR-POLYMER COMPOSITES ON THE MOISTURE-CONTENT

Woodflour of Eucaliptus saligna with two different chemical treatments (mercerization and esterification with maleic anhydride) was used as filler of an unsaturated polyester matrix. Woodflour was treated to in crease the interfacial adhesion with the matrix, to improve the disper sion of the particles, and to decrease the water sorption properties o f the final composite. The objective of this study was to determine th e influence of the moisture content and the woodflour chemical modific ation on the physical and mechanical properties of the different compo sites. Results indicated that mechanical properties (compression and b ending tests) were severely affected by moisture and chemical modifica tions. In wet conditions, the composites made from treated woodflour h ad the lowest flexural modulus and ultimate stress. It was found that this was a reversible effect, because the original values of the compr ession properties were recovered after drying. Temperature scans in dy namic mechanical tests showed that an irreversible change occurred dur ing exposure to humid environments, probably due to the hydrolysis of the polyester matrix. Essentially, the same behavior was observed for matrix and composites; however, a wood-related transition overlapped t he main transition in the case of wet composites. (C) 1998 John Wiley & Sons, Inc.