The Effect of Thermo-Vaccum Treatment on the Physical and Mechanical Properties of 20 Lesser-Known Timber Species from Sri Lanka

Abstract

Wood is a valuable material that is often utilised in indoor and outdoor settings. This study aimed to evaluate the effect of heat treatment on the strength, dimensional stability, and colour of 20 selected timber species, to compare the performance of thermally-modified wood with untreated seasoned wood, and to recommend suitable thermal modification. Modulus of Rupture (MOR), Modulus of Elasticity (MOE), Compression parallel to grain (CPN), and wood density were measured in 20 lesser-known timber species grown in Sri Lanka. In addition, moisture content, volumetric shrinkage, water absorption, weight loss, and colour were evaluated. Timber samples were taken at the breast height of mature trees and prepared according to the BS 373:1957 standard [2]. The mechanical properties were measured through the UTM (UTM 100 PC). Thermal modification was done at 180°C and 250 mbar. A paired t-test was carried out to interpret the significant differences between samples, and regression analysis was done to identify the relationship between density and the strength properties of the control and the thermally-modified samples. Due to thermal treatment, MOR and MOE decreased in the treated samples, showing a reduction in bending strength and stiffness, while CPN increased, but these changes were not statistically significant. A strong positive correlation between MOR and MOE was observed in the control samples. It significantly weakened after heat treatment (R² = 0.24 to 0.77), the relationship between MOR and density increased after heat treatment. (R² = 0.14 to 0.37), and the relationship between MOE and density decreased after heat treatment (R² = 0.09 to 0.02). The relationship between CPN and density increased slightly after heat treatment (R² = 0.04 to 0.12), the moisture absorption of the treated samples decreased, but not significantly (p < 0.05), and the timber colour became darker. Heat treatment gently enhanced the physical and mechanical properties of the selected wood species.