Effect of hemicellulose extraction on water absorption and mold susceptibility of wood–plastic composites

The hygroscopicity of woody materials results in moisture absorption into wood-based composites, including wood–plastic composites (WPC). The objective of this research was to improve the water resistance and mold resistance of WPC by extraction of hemicelluloses from the wood raw material. The treatment may also eliminate extractives such as free sugars, starches, and lipids that can serve as food for fungi. Liquid hot water extraction was performed on southern yellow pine flakes under different temperatures (140, 155, and 170 °C) and over a period of 60 min. Wood flour from extracted or control flakes was compounded with isotactic polypropylene in an extruder, both with and without a coupling agent. Injection molding was used to make tensile test samples. Wood–plastic composite samples were immersed for 5, 10, and 15 wk in water and the water absorption and tensile properties of the samples were measured. The susceptibility of the WPCs to mold was evaluated also. The water absorption of samples decreased after extraction; this resulted in higher mechanical properties of WPCs from extracted wood flour after different periods of soaking in water. Extraction also resulted in improvement in mold resistance of the WPC. ► Liquid hot water extraction was used for extraction of hemicellulose. ► Extraction resulted in decreased water absorption of wood–plastic composites. ► Extraction increased resistance to water-induced mechanical property loss. ► Mold resistance of wood–plastic composites improved after extraction.