Influence of temperature and vacuum level on the drying rate, moisture content distribution, wood color and drying stress of rubberwood in vacuum drying
Lin Yang, Xuanjiang Liu, Tongtong Li, Jianing Li
Abstract
Rubberwood, a fast-growing material for furniture and construction, is prone to cracking, deformation, and discoloration during traditional kiln drying, reducing its utility and appearance. Vacuum drying helps release internal stress, maintain color, and improve stability. This study compared six vacuum drying conditions for pith rubberwood, examining drying performance and color changes under varying temperatures and pressures. Drying rates ranged from 0.21%/h (40°C, 0.04 MPa) to 0.92%/h (80°C, 0.02 MPa), a 4.4-fold difference. Temperature had a greater impact; at 0.02 MPa and 0.04 MPa, raising the temperature from 40°C to 80°C increased drying rates by 4.18 and 3.76 times, respectively. The vacuum level and temperature interactively affect longitudinal uniformity, moisture content (M) deviation in thickness ranges from 1.37% (0.04 MPa, 40°C) to 2.98% (0.04 MPa, 80°C), a 2.2-fold increase, with higher vacuum levels reducing M gradients. M deviation ranged from 1.37% (40°C, 0.04 MPa) to 2.98% (80°C, 0.04 MPa), a 2.2 – fold difference. Color change was more affected by vacuum. The best color preservation was at 0.02 MPa and 80°C, and the worst at 0.04 MPa and 40°C. Temperature more strongly influenced residual stress, while wood shrinkage was significantly affected by both vacuum and temperature.