Role of delignification in water state changes during water absorption and air drying of wood characterized with LF-NMR

Delignification, recently much used in wood modification and functional material preparation, is closely related to wood-water interactions. To attain more information on the role of delignification in wood, this study characterized the water state changes during water-absorption and air-drying process with LF-NMR. By adjusting delignification time, lignin was removed about 15%, 34%, and 61%, respectively. Water absorption increased after delignification, and free water was generated more and faster than bound water. This was because delignification changed wood-water interaction environments suggested by SEM and FTIR analysis. Specifically, delignification increased hygroscopic polysaccharide percentage and sorption site concentration. New pore generation and enlargement after delignification provided more water exchanging paths and accommodation. Besides, delignified wood had higher and faster moisture decrease, and wood air drying was facilitated because of enriched water exchanging paths and higher initial moisture gradient difference in water-saturated delignified wood. Therein, free water decreased more and faster than bound water. The T2s of bound water and free water were both shortened after delignification, indicating water had tighter intermolecular interaction with delignified wood. The study provided new insight for understanding the role of lignin in water state changes during wood-water interactions and may facilitate better preparation of functional material and wood modification.

Automated summary

This study used LF-NMR to characterize the changes in water state during the delignification process in wood. The results showed that delignified wood had increased water absorption capacity and generated more and faster free water. Scanning electron microscopy and Fourier transform infrared analysis confirmed that delignification altered the wood-water interaction environment, increasing the percentage of hygroscopic polysaccharides and sorption site concentration. The generation of new pores after delignification provided more paths for water exchange and accommodation. Delignified wood also exhibited faster moisture decrease during air-drying, facilitated by enriched water exchange paths and higher initial moisture gradient difference in water-saturated delignified wood. The study provides new insight into the role of lignin in water state changes during wood-water interactions and may aid in the preparation of functional materials and wood modification.