A micromechanical model for moisture-induced deterioration in fully biorenewable wood-plastic composites

Biobased wood-plastic composite materials were prepared using wood fibers as reinforcement in a microbial polyester matrix derived from poly(beta-hydroxybutyrate)-co-poly(beta-hydroxyvalerate) (PHBV). This paper discusses the influence of moisture on the morphological and flexural mechanical properties of PHBV/wood flour composites. The effect of two fiber-matrix chemical modifications on enhancing composite durability in wet environments was assessed. Physicochemical changes to the matrix microstructure were further investigated using gel permeation chromatography and differential scanning calorimetry. A micromechanical analytical model is presented that predicts the onset of matrix cracking in wood-plastic composites upon exposure to moisture. The model is based on a hollow cylinder subjected to an internal pressure that is induced by the hydroexpansion of wood fiber reinforcement. Monte Carlo simulations were employed to account for statistical uncertainty in constituent mechanical properties as well as seasonal fiber variability. The model was validated using both optical microscopy techniques and experimental mechanical results. (C) 2013 Elsevier Ltd. All rights reserved.