It is well-known that ultrasound has been studied for its cavitation, mechanical and thermal effects. As a pretreatment technology, ultrasonic alkali treatment has attracted much attention in the field of biomass biochemical transformation. In this study, the structural and dynamic changes of wood cell walls during ultrasound-water, alkali, and ultrasound-alkali treatments were investigated by stereoscopic microscopy, confocal Raman microscopy, Fourier-transform infrared spectroscopy, and X-ray diffraction. The results indicated that the ultrasound-water, alkali, and ultrasound-alkali treatments had the effect of removing extractives from conduits. The uniform self-shrinking samples with shrinkage conduits were obtained by the alkali and ultrasound-alkali treatments. All of the treatments affected the relative content, structure and distribution of the chemical components in the wood cell walls. Compared with water-immersion samples, the relative content of hemicellulose of the treated samples reduced from 32.31% to 7.02% for ultrasound-8% NaOH treated samples. For the signal intensity of lignin, ultrasound-water treated and ultrasound-alkali treated samples displayed a more significant reductions than the alkali treated samples in the cell wall region. The crystal zone and amorphous zone of cellulose coexisted before and after the treatment, for all of the treated samples, and particularly for the ultrasound-assisted treated samples, the crystallinity increased from 38.15% for water-immersion samples to 57.42% for ultrasound-8% NaOH treated samples.

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.