Surface properties and paintability of Nusantara superior teak wood modified by bio based chemical impregnation and thermal curing

Nusantara superior teak (NST) ( Tectona grandis Linn. F), engineered through genetic technology, exhibits rapid growth, possesses straight, cylindrical trunks, and features heartwood predominantly in the radial direction. Regrettably, short-rotation teak does not possess the requisite durability for exterior applications, lacking the weather resistance essential for optimal aesthetics, paint adherence, and longevity. This study aimed to evaluate the effectiveness of NST woods subjected to chemical modification using carboxylic acids (lactic acid/LA and citric acid/CA) and alcoholic compounds (glycerol/Gl), followed by heat curing, in enhancing wood surface properties and resistance to color changes due to weather exposure outdoors. Seven treatments, utilizing LA/CA/Gl individually and in combinations (either two or three), were infused into the wood structure, followed by thermal curing at 150 °C and 180 °C. The findings demonstrated that heat–chemical modification effectively maintained the key surface characteristics of NST wood, with no significant differences observed compared to the unmodified (control). Although the adhesion performance water-based acrylic paint on the treated NST wood was slightly lower than that on the control, the modified wood still exhibited promising surface stability after treatment. Notably, the integrated treatment using 10% lactic acid (LA) and 10% citric acid (CA), followed by heat curing at 180 °C, produced the satisfactory weathering performance, as evidenced by the lowest degree of color alteration (lowest Δ E * value), which still belongs to the criteria of medium/moderate color changes. These results suggest that the LA–CA heat-curing treatment is an effective strategy for enhancing the color stability and weathering resistance of NST wood while generally preserving its surface quality.