Effect of mechanical restraint on the properties of heat-treated Pinus koraiensis and Paulownia tomentosa woods

Abstract

The objective of this study was to improve the properties of Korean white pine (Pinus koraiensis Sieb. & Zucc.) and royal paulownia (Paulownia tomentosa (Thunb.) Siebold & Zucc. ex Steud.) via heat treatment. The woods were treated at 160 °C, 180 °C, 200 °C, and 220 °C for 2 h. The effect of mechanical restraint through clamping during heat treatment on the dimensional stability, physical, and mechanical properties was evaluated. The results showed that increased temperature increased the weight loss and volume shrinkage, while equilibrium moisture content and wettability decreased. Royal paulownia showed higher weight loss, but lower shrinkage and equilibrium moisture content, when compared to Korean white pine. The samples with clamps in both woods had lower weight loss and volume shrinkage after heat treatment. The modulus of elasticity and modulus of rupture decreased with increased temperature followed by a noticeable decrease obtained after heat treatment at 200 °C and 220 °C. Clamping minimized strength reduction in both woods. Consequently, it was suggested that mechanical restraint was a useful method to maintain the wood properties during heat treatment.

Elevating Timber Sustainability: Exploring Non-Chemical Wood Modification via Air Heat Treatment for Diverse Applications

“…Lee et al [25] clarified that during heat treatment, a rise in temperature might impact the density of the wood by causing hemicellulose and extractive compounds to degrade. Polymer depolymerization in wood may be the cause the density at higher temperatures [26]. In addition, the reduction in wood density subsequent to heat treatment may also affect the material's strength and structural soundness [24].…”

“…Boonstra et al [51] clarified that the drop in moisture content in wood was brought about by less water being absorbed by the cell walls as a result of heat treatment, which altered the chemical composition of the wood by reducing the amount of hydroxyl groups. Heat-treated wood will degrade hemicellulose and have lower moisture content in the cell walls [26,52]. A wood that has not been heated or treated as control has a moisture content of 15% EMC.…”

“…In the meantime, when the treatment temperature rose, the amount of wood treated with AHT at 190℃ and 210℃ dramatically dropped. According to Hidayat et al [26], low moisture content and the release of extractive chemicals are caused by higher heat treatment temperatures. At ˃ 170℃, heat treatment evaporates extractive chemicals and changes the moisture content of the wood, among other things [26].…”

“…Heat treatment can also increase the hydrophobic properties of wood and the color of the wood can become darker [26,27]. There are several types of heat treatment methods for wood, namely heat treatment with air (Air Heat Treatment), steam (Thermowood Treatment), and a combination of air and steam (Plato Wood Treatment), and heat treatment using oil [22].…”

Effects of Temperature during Oil Heat Treatment on the Quality Improvement of Mindi (Melia azedarach) and Sengon (Falcataria moluccana) Woods

“…Suri et al (2022) also reported that OHT heat modified Paulownia tomentosa and Korean white pine wood showed the highest density value at 180 °C and then decreased slightly at 200 °C and 220 °C. The decrease in the density of OHT-produced wood at temperatures of more than 180 °C is related to the evaporation of extractive substances and the degradation of the chemical compositions contained in the wood such as holocellulose (hemicellulose and cellulose) due to high temperatures (Hidayat et al, 2017b;Razak et al, 2012). The density of the two control wood species was in accordance with the standard measurements of Martawijaya et al (1989) and PKKI (1961) as well as increasing wood density changed the strength class of sengon wood from class V to class IV and mindi from class III to class II.…”