To improve the performance of bamboo and increase its utilization value, this study aimed at investigating the effects of impregnation pretreatment and thermal treatment on the structural changes of bamboo. The samples were pretreated in sodium hydroxide or zinc chloride solution, and then treated at 160 °C. The pretreated and control samples were characterized by X-ray diffraction (XRD), thermogravimetric analysis (TG), and Fourier transform infrared spectroscopy (FTIR). The results showed that the cellulose crystallinity and intensity of samples pretreated by ZnCl₂ could be reduced, but the crystal structure remained the same. As for samples pretreated in NaOH, the crystal structure of fiber was destroyed and the crystallinity was increased significantly. High temperature treatment has little effect on the thermal stability of bamboo. However, after treatment with NaOH and ZnCl₂, the thermal degradation temperature changed obviously and moved to a lower temperature. ZnCl₂ pretreatment had influence on the chemical structure of bamboo, while NaOH pretreatment had greater influence on the chemical structure of bamboo.

This work investigated the physicochemical properties of Chinese fir after ultrasound-assisted pretreatments with borax and sodium hydroxide additives in an aqueous solution. TGA, FTIR, and XRD were used to analyze the thermal degradation processes, changes in chemical structures, and crystallinity of the treated samples, respectively. Additionally, the release of volatiles from wood pyrolysis was measured on-line by the TG-FTIR apparatus. In thermal analysis, all samples showed main degradation stages at 220-500 °C, and alkaline compounds could efficiently shift the process to lower temperatures with lower maximum weight loss rate (MWLR) and more residues. From TG-FTIR, it was observed that CO2 was the primary gas product from pyrolysis in the alkaline-treated samples, while there were more carbonyl compounds released in the control and deionized water groups. Due to the destruction and removal of hemicellulose and lignin after alkaline treatments, the related peaks changed greatly. Changes in the ester groups caused by saponification also accounted for one of the most significant differences between samples. Moreover, except for the deionized water group without sonication, the crystallinity of the samples increased from 6.34% to 11.29%. Overall, comparing the samples treated with or without ultrasound, the results showed that the ultrasound treatment did influence the samples' physicochemical properties, and its' effects varied by the basicity of the solution. This in-depth investigation offers a better understanding of ultrasound-assisted and alkaline pretreatments of wood materials.

The hygroexpansion and anisotropy of wood limit its application in construction and wood products industry. Zinc chloride–silicone oil was use to decrease the hygroscopicity and improve the dimensional stability of wood at 80 °C, 140 °C, 160 °C and 180 °C. The effects of the treatment on the dimensional stability, chemical structure, thermal degradation, morphology of wood were evaluated, and the mechanism was determined. Results indicated that the zinc chloride–silicone oil treatment at 80 °C improved the dimensional stability and decreased the hygroscopicity of wood. The tangential, radial, and volumetric swelling coefficients of the treated wood decreased by 9.7%, 33.5%, and 18.2%, respectively, relative to those of the untreated wood. Zinc chloride–silicone oil treatment also changed the chemical structure of wood by degrading the wood components and decreasing the moisture absorption groups. Moreover, zinc chloride–silicone oil treatment significantly influenced the thermal degradation of wood, as samples treated with zinc chloride–silicone oil at 140 °C, 160 °C and 180 °C presented sharp peaks around 511 °C, 501 °C and 473 °C. The control group exhibited a more common derivative thermogravimetric curve with a sharp peak at 375 °C. In addition, the silicone oil could impregnate wood, occlude moisture passage, and prevent the movement of moisture in wood. This method can be applied in building and wood industries to expand the applications of wood products.

In recent years, China is increasingly dependent on imported wood. Afrormosia and Newtonia are some of the imported species with good utilization potential. However, both of them also have problems with poor dimensional stability. In order to make better use of these two types of wood, the influence of heat treatment under air and palm oil conditions on the color, dimensional stability, and hygroscopicity of Afrormosia and Newtonia was investigated. The Afrormosia and Newtonia wood samples were heated in air or palm oil medium for two hours at 160 °C, 180 °C and 200 °C, respectively. Then, the color, weight changes, swelling, moisture absorption and chemical structure were evaluated for each case. As results, the heat treatments with air or palm oil increased the dark color of Newtonia and Afrormosia wood and this increase was proportional to the treatment temperature. The tangential and radial swelling coefficient for air heat treatment of Afrormosia wood at 200 °C were, respectively, reduced by 24.59% and 19.58%, while this reduction for Newtonia was 21.32% and 14.80%. The heat treatment in palm oil further improved the stability and hygroscopicity of the wood, showing that the Afrormosia samples treated by palm oil at 200 °C underwent a decrease of its tangential and radial swelling coefficient, respectively, by 49.34% and 45.88%, whereas the tangential and radial swelling coefficient of Newtonia treated under the same conditions were reduced by 42.85% and 33.63%, respectively. The heat treatments of Afrormosia and Newtonia samples under air at 200 °C diminished the water absorption by 21.67% and 22.12%. The water absorption of Afrormosia and Newtonia heat-treated under palm oil at 200 °C was reduced, respectively, by 39.40% and 37.49%. Moreover, the FTIR analysis showed the decrease of hydroxyl groups in proportion to the wood treatment temperature.

Cavitation intensity is affected by ultrasonic intensity (UI) and is a key parameter to describe experimental results during ultrasonic treatment. The relationship between the UI and physicochemical properties of Chinese fir was investigated. In this study, four frequencies (25, 28, 40, and 59 kHz) were used at the same intensity of 240 W and the same duration of 35 min. The UI during the ultrasonic treatment was determined, and the chemical components were determined. The chemical structure, crystallinity, morphology, and extractives of wood were respectively analyzed by Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), and gas chromatography-mass spectrometry (GC-MS). The results showed that higher crystallinity was associated with a larger integrated area under the curve of the ultrasonic intensity (UIA). The largest UIA was observed at 25 kHz, followed by those at 40, 59, and 28 kHz. The relative content of hemicellulose was strongly affected by the ultrasonic treatment. No chemical reactions were observed in the wood, whereas the ultrasonic treatment affected the torus of the bordered pits and facilitated the migration of extractives. In general, the higher the UIA, the stronger the effect of the cavitation was. The most significant changes in the physicochemical properties were observed at 25 kHz. The instantaneous ultrasonic intensity (IUI) changed over time, and the UIA was closely associated with changes in the physicochemical properties of the wood. The results of this study demonstrate that UI has a significant influence on the physicochemical properties of wood.

Acidic aluminum sulfate hydrolysis solutions can be used to catalyze the thermal degradation of wood in a mild temperature environment, and thus reduce the temperature required for heat treatment process. To improve the dimensional and thermal stability of Chinese fir during heat treatment at 120 °C, 140 °C and 160 °C, this study investigated the effects of soaking pretreatment with 5%, 10% and 15% aluminum sulfate on the chemical and structural changes of the heat-treated Chinese fir. The results indicated that the samples treated at 15% aluminum sulfate concentration and 160 °C heat treatment achieved the best dimensional and thermal stability. Chemical analyses by Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD) indicated that the catalysis of aluminum sulfate resulted in degradation of hemicelluloses during the heat treatment, and an increase in the soaking concentration and heat treatment temperature also affected the thermal degradation of celluloses. The scanning electron microscope (SEM) and mass changes test results proved that the hydrolyzed aluminum flocs mainly adhered to the inner wall of the wood tracheid as spherical precipitates, and when the soaking concentration reached 10% and 15%, a uniform soaking effect could be achieved. The thermogravimetric (TG) analysis revealed the soaking pretreatment effectively improved the thermal stability of the heat-treated wood by physically wrapping and promoting the formation of a carbon layer on the wood surface during heat treatment. Thus, aluminum sulfate soaking pretreatment exerted a great effect on the dimensional and thermal stability of wood, allowing heat treatment to be performed at a lower temperature.