Simple preparation method for colorless wood via one-pot bleaching at ambient temperature after alcoholysis

Abstract This study presents a mild delignification approach for preparing colorless wood from Japanese cedar ( Cryptomeria japonica ) using a two-step pretreatment involving alcoholysis followed by sodium chlorite (NaClO₂) treatment at ambient temperature (25 °C). Although the alcoholysis step has been extensively optimized, the subsequent NaClO 2 treatment step has received far less attention and has not been sufficiently investigated. Conventional NaClO 2 treatments are typically conducted at elevated temperatures (70–80 °C) and require repeated reagent addition during the reaction to maintain delignification efficiency, resulting in increased energy consumption and operational complexity. To address this deficiency in the present study, after completing the alcoholysis reaction, the samples were treated with NaClO 2 at 25 °C, with the entire reagent dose added at the start, thereby eliminating the need for repeated addition or external heating. Fourier transform infrared spectroscopy (FTIR) and ion chromatography confirmed the effective removal of lignin and hemicellulose, and X-ray diffraction showed that the crystalline structure of the cellulose was largely preserved. Principal component analysis (PCA) of the FTIR spectra further revealed that the samples could be clearly classified into three groups—untreated, partially delignified, and extensively delignified states—reflecting compositional changes with increasing treatment severity. Moreover, FTIR-based PCA served as an effective tool for evaluating treatment severity and delignification extent. Microscopic observations further demonstrated that the overall anatomical structure after prolonged treatment at 25 °C remained comparable to that of the untreated samples and samples processed using conventional high-temperature NaClO₂ methods. Overall, this treatment adaptation achieved delignification performance comparable to that of conventional methods while reducing energy consumption and operational complexity.