Characterizing water sorption and diffusion properties of wood/plastic composites as a function of formulation design

In this study, the water sorption and diffusion properties of wood/plastic composites (WPCs) as a function of formulation design were investigated. Composites with different amounts of wood, coupling agent and high density polyethylene (HDPE) were produced by profile extrusion method. The time required to reach saturation point, moisture contents at saturation point, diffusion coefficients and thickness swelling were measured for all composites. The results showed that the response of WPCs towards water exposure is heavily dependent on formulation design. The time required to reach saturation point varied between four weeks and 84 weeks. Such a big difference reflected magnitude of formulation design on water resistance of WPCs. Composites with large particles demonstrated weak performance towards water. Any increase in wood content led to an increase in water absorption. Coupling agent reduced water absorption. Diffusion coefficients and thickness swelling were also affected by wood and coupling agent contents, and wood particle size. The highest diffusion coefficients and thickness swelling were found in composites with high wood contents and large particles. Studying the water sorption process in WPCs showed that the process follows kinetics and mechanisms described by Fick's law. (C) 2017 Elsevier Ltd. All rights reserved.