Superheated Steam Vacuum Drying of Rubberwood

Abstract

The effect of superheated steam vacuum drying (SSVD) on the drying time and mechanical properties of rubberwood was studied. Rubberwood boards with dimensions of 1000 mm × 76.2 mm × 25.4 mm were dried at 86.7–89.3 kPa vacuum pressure (14.6–12.0 kPa absolute) and temperatures of 60, 70, and 80°C. Superheated steam at 110°C was injected intermittently to relieve stress buildup in wood and eliminate cracking. The prong test was used to evaluate the initial acceptability of the dried wood and the mechanical properties of wood were measured. From this study, the total drying time was reduced from 168 h to less than 20 h (MC reduction from 0.80 to 0.06 db). In addition, compared to the reference values shown in the parentheses, the shear parallel-to-grain, the compression parallel-to-grain, the compression perpendicular-to-grain, the modulus of rupture (MOR), the modulus of elasticity (MOE), and the hardness for the optimum drying temperature of 70°C were 28.87 (11.0) MPa, 59.09 (32.0) MPa, 21.09 (5.0) MPa, 101.97 (66.0) MPa, 9838.5 (9240.0) MPa, and 6475 (4350) N, respectively. Thus, the vacuum-dried wood showed a 32% increase in hardness, a 12% increase in compression parallel-to-grain, and an 88% increase in shear parallel-to-grain.