Effect of natural tung oil on wood shrinkage during the thermal modification process

Abstract

The non-negligible shrinkage and volume loss caused by heat treatment would reduce the availability and product value of wood. In this study, natural tung oil was innovatively used to alleviate heat-reduced shrinkage in thermal modification. The mass changes, dimensional shrinkage and volume loss, chemical structures, morphological characteristics, as well as pore structures of wood were studied. The results demonstrated that the volume loss was significantly reduced after tung oil heat treatment, especially at high temperatures (reduced by 85.27% at 210 °C for 6 h). Tung oil could separate oxygen and mitigate the thermal decomposition of wood components. Additionally, tung oil had impregnated the wood and occupied transportation passages of volatile degradation products, such as vessels and pits. Although severe shrinkage appeared in air heat-treated samples, the porosity increased and part of the micropores transformed into mesopores and macropores. While tung oil heat-treated samples had a lower proportion of macropores and porosity than that of the control and the air heat-treated ones. Overall, tung oil heat treatment was facile, eco-friendly and highly efficient in maximizing actual lumber recovery and improving the product value of wood without any harmful chemicals, as well as saving wood resources.