Combining boron acid and heat treatment for enhanced durability of Cunninghamia konishii plantation wood

Abstract

This study evaluated the combined effects of boric acid treatment and heat modification on the durability and mechanical properties of Cunninghamia konishii plantation wood. The results indicated that boric acid treatment significantly improved the termite resistance of C. konishii wood. With a boric acid absorption level of 6.8 kg/m³, the treated wood exhibited a mass loss of only 1.3–2.9 % (meeting the <3 % termite resistance standard), compared to 12.5–21.8 % mass loss in untreated samples. Meanwhile, boron treatment was applied and increased termite mortality to over 99 %. Both boric acid and boron treatments have proven the efficacy in increasing wood durability, in terms of resisting brown-rot fungi and significantly reducing mass loss under specific conditions. This study results demonstrated that heat treatment alone improved wood dimensional stability by reducing wood swelling, with a consequent decrease in the wood air-dried density, from 398 kg/m³ to 373–396 kg/m³. It was also observed that the heat treatment increased the modulus of elasticity (MOE) but decreased the modulus of rupture (MOR). Furthermore, when combined with boric acid treatment, the heat treatment further increased the compressive strength and hardness of wood, but decreased the MOR and shear strength. An optimal treatment, involving a boric acid concentration of 6.8 kg/m³ at 170 °C for 2 hours, was conducted to assess its effectiveness in enhancing both durability and mechanical properties of wood, aiming to seek a balance between these crucial factors for wood applications.