Effect of Urea-High-Temperature Combined Treatment on the Dimensional Stability of Densified Fast-Growing Wood

Abstract

Due to the continuous depletion of timber resources and the increasing ecological awareness among people, large-scale fast-growing artificial forests have become a key solution to address the imbalance between timber supply and demand. In recent years, the problem of low density and mechanical strength of fast-growing timber has been addressed through timber densification. However, densified timber still faces issues such as high moisture absorption and poor dimensional stability. Urea molecules can expand the volume of the non-crystalline region of cellulose to protect the cell wall structure of timber from damage during the densification process. In this paper, an effective modification strategy was proposed to prepare lightweight high-strength wood through the synergistic effect of urea vacuum impregnation treatment and high temperature densification, which solved the problem of poor dimensional stability of densified wood. Research results indicate that when the concentration of urea solution is at 50%, the maximum weight gain of the timber samples reaches 17.76%. After densification treatment, the absolute dry density of the test samples increased by more than 0.031g/cm3. Timber treated with a 50% urea solution and processed at 170°C demonstrates good dimensional stability, with a radial swelling rate of only 0.79% under a relative humidity of 65%. Therefore, the joint modification of wood using urea and high-temperature treatment is an effective and environmentally friendly method, presenting broad prospects for development.