A review of wood thermal pretreatments to improve wood composite properties

Abstract

The objective of this paper is to review the published literature on improving properties of wood composites through thermal pretreatment of wood. Thermal pretreatment has been conducted in moist environments using hot water or steam at temperatures up to 180 and 230°C, respectively, or in dry environments using inert gases at temperatures up to 240°C. In these conditions, hemicelluloses are removed, crystallinity index of cellulose is increased, and cellulose degree of polymerization is reduced, while lignin is not considerably affected. Thermally modified wood has been used to manufacture wood-plastic composites, particleboard, oriented strand board, binderless panels, fiberboard, waferboard, and flakeboard. Thermal pretreatment considerably reduced water absorption and thickness swelling of wood composites, which has been attributed mainly to the removal of M. R. Pelaez-Samaniego

Effect of torrefaction temperature on properties of Patula pine

“…Torrefaction is a mild thermochemical process conducted in oxygen-free environments at temperatures ranging from 200 to 300 °C (Bridgeman et al 2010, Chen and Kuo 2010, Ibrahim et al 2013, Phanphanich and Mani 2011, Xue et al 2014. In this range of temperatures, in addition to moisture and volatiles release, degradation of hemicelluloses occurs, while cellulose is subjected to dehydration and both cellulose and lignin are subjected to partial depolymerization (da Silva Grassmann et al 2016, Pelaez-Samaniego et al 2013.…”

Review of energy potential of the wood biomass of orchards and vineyards in the Czech Republic

“…When drying fresh wood to the desired moisture content, its weight is reduced by 30-40% (Maga et al 2008;Pelaez-Samaniego et al 2013;Simpson 2013). Also, Sims (2002) states that reducing wood moisture from 50% to 20% represents a weight loss of 37.5%.…”

Impulse-cyclone Drying Treatment of Poplar Wood Fibers and its Effect on Composite Material’s Properties

“…Thus the natural fibers must be dry-treated, in advance, to a moisture content of 1% to 5% (Huang et al 2006). After drying, the natural fibers can be prone to agglomeration, due to the formation of hydrogen bonds between cellulose molecules that contain many hydroxyl groups and thus cause uneven dispersion during mixing (Ndiaye et al 2013;Pelaez-Samaniego et al 2013;Effah et al 2015). Moreover, the majority of polar (hydrophilic) natural fibers are not compatible with non-polar (hydrophobic) substances, due to the existence of many hydroxyl groups on the cellulose and hemicellulose of natural fibers.…”