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Thermally modified timber (TMT) reduces hygroscopicity, increases dimensional stability, and decay resistance. Although there is a substantial amount of research on heat-treated wood, investigations on the sensitivity of cell wall swelling behavior to water variation are limited. Therefore, this study focused on the swelling behavior of TMT from cellular and chemical perspectives. The effects of heat treatment on the hygroscopicity and swelling behavior of the wood cell walls were studied using dynamic vapor sorption and confocal laser scanning microscopy. Changes in the chemical composition and cellulose crystallinity were studied using attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) and X-ray diffraction. The results revealed that the hygroscopic swelling of latewood significantly decreased with increasing treatment temperature, reducing the anisotropy of the wood cell swelling. The hygroscopicity of wood was reduced by heat treatment, and a clear decrease in hysteresis was observed at elevated treatment temperatures. The FTIR spectra indicated that both hemicellulose and lignin were degraded. The crystallinity and lateral size of the cellulose increased after heat treatment. Similar changes in the chemical composition and crystallinity of cellulose were observed in the latewood and earlywood. [ABSTRACT FROM AUTHOR]

The influence of heat treatment severity (resulting from temperature) on the colour and gloss distribution changes of mahogany wood, and the effects of wood density on the responses to heat treatment were evaluated. The wood timbers with different densities were treated at 150°C to 200°C with an interval of 10°C and duration of 4 hours for heat treatment schedules. The colour parameters (lightness L*, red‐green axis value a*, yellow‐blue axis value b*) and gloss (parallel and perpendicular to the grain) values of heat‐treated wood were determined. The distributions of colour and gloss were analyzed using a frequency counts method. Results show that heat treatment resulted in the distinct decrease in L* and b*, while almost no change in a* for mahogany wood. The lower gloss values were obtained in the wood after heat treatment. The colour and gloss uniform on the exposed surface of the wood was improved due to heat treatment. Heat‐treatment induced colour and gloss changes were more effective in the samples with lower density. The effects of density on the colour and gloss variability in the original wood were reduced by heat treatment, and this reduction was more distinct at high heat treatment temperature. The total gloss change was found to be highly correlated with the total colour change of heat‐treated wood. [ABSTRACT FROM AUTHOR]

Mahogany wood (Swietenia macrophylla King) was thermally modified by heating at various temperatures. The wood-water-related parameters of the heat-treated wood, including fiber saturation point, equilibrium moisture content, moisture excluding efficiency, hygroscopic hysteresis, swelling, anti-swelling efficiency, water adsorption, and surface wettability were determined to clarify the mechanism of heat treatment to reduce wood hygroscopicity. The wood treated at a higher temperature demonstrated a more significant decrease in hygroscopicity. The reduction in hygroscopicity of the heat-treated wood was partially diminished as the moisture excluding efficiency decreased in the absorption and desorption processes caused by the changes in environmental temperature and relative humidity. The fiber saturation point (determined by nuclear magnetic resonance spectroscopy), surface free energy, and the surface wettability of wood were reduced by heat treatment, resulting in the decreased hygroscopicity of the heat-treated wood. Mahogany wood became more insensitive to the influence of moisture due to the heat treatment, and this effect was more distinct for wood treated at a high temperature. [ABSTRACT FROM AUTHOR]

• Changes of chromatic values in heat treatment wood are systematically discussed. • Variation of modulus of elasticity and modulus of rupture with heat treatment temperature are explored. • Artificial neural networks are employed to predict mechanical properties based on the chromatic values. In this study, the modulus of elasticity (MOE) and modulus of rupture (MOR) of heat treatment (HT) radiata pine wood were assessed by artificial neural network (ANN) models based on the changes of chromatic values. In the established ANN models, the chromatic values, i.e. L *, a * and b * conjunction with HT temperature were as input variables, the MOE and MOR as output parameters. According to the results, the values of L *, a * and b * had a good consistency with HT intensity. The MOE changed with HT temperature in a fluctuating tendency, whereas the MOR generally deteriorated with increasing HT temperature. As for the established ANN models, the predicted values were in good agreement with the measured ones, the determination coefficient of the prediction model for MOE and MOR were 0.904 and 0.783, respectively. [ABSTRACT FROM AUTHOR]

• Water related properties of heat treatment wood are systematically discussed. • Hygroscopicity swelling ratio at different grain directions is explored. • The mechanism of reduced hygroscopicity by heat treatment is analyzed. • Surface wettability is clearly weakened after heat treatment. Wood is a green and renewable building material, however, the hygroscopicity restrict its use in the field of construction and building. To study the effect of heat treatment (HT) on wood hygroscopicity and other water related properties, radiata pine wood was subjected to HT at four temperature levels of 185, 200, 215 and 230 °C, for the duration of 4 h. Overall, the equilibrium moisture content, moisture adsorption, water absorption and volume swelling ratio were all decreased, while hygroscopic hysteresis was enhanced with increasing HT temperature. The surface wettability was clearly weakened after HT, reflected as the increased contact angle and reduced surface free energy. [ABSTRACT FROM AUTHOR]