Impact of thermal treatment on the properties of assacú (Hura crepitans L.) and murici (Byrsonima crispa A.Juss.) Amazon woods

Background: White and low-density Amazon woods, such as assacú (Hura crepitans L.) and murici (Byrsonima crispa A.Juss.), have restricted use, given their low physical-mechanical strength and low natural durability. Physicochemical changes caused by heat treatment can improve different quality traits of these woods, such as changing the visual appearance from white to brown tones, improving dimensional stability, moisture control, and resistance to attack from biological organisms. Methods: Assacú and murici wood samples were heat treated (180 and 220°C) for 60 minutes in a muffle kiln. The physical (moisture, mass loss, density, shrinkage, swelling), mechanical (dynamic modulus of elasticity), and chemical (extractives, solubility in hot water, lignin, and holocellulose) properties were evaluated following treatment and compared with those measured before treatment. Results: The heat treatments T2 (180°C) and T3 (220°C) reduced the moisture content; however, the T3 treatment caused a more intense mass loss. For murici wood, this mass loss was 14%. The anisotropy coefficient was reduced for assacú wood by 1.30 and 1.03% for the T2 and T3 treatments, respectively, improving the dimensional stability of this wood. The density and modulus of elasticity were affected by the treatment, thus reducing the strength of the wood. The extractive content of the woods increased by 4.99 and 7.49% for sampled of assacú and murici, respectively, that were treated at 220°C. For the primary metabolites, holocellulose and lignin, degradation of these compounds occurred due to the decrease in their concentrations. The linear analysis of the studied variables indicated a high correlation between the physical properties and the chemical components of the woods (e.g., anisotropy coefficient x lignin and holocellulose x apparent density, r > 0.95). Conclusions: The heat treatment of Amazon woods directly influenced their physical-mechanical and chemical properties. In general, the higher temperature treatment caused the greatest changes in the studied species, and the exposure to heat caused noticeable changes in their colour. Heat treatment is a useful process for the forestry sector since heat-treated wood can be used to manufacture high-value-added products, such as fine furniture, residential floors, musical instruments, and non-structural components.