Physical and mechanical properties of wood treated with chitosan-caffeine formulations

There is growing interest in developing natural wood preservatives, particularly in response to the escalating challenges posed by environmental degradation. Caffeine is a bio-based preservative that improves decay resistance of treated wood, however it is also sensitive to leaching from wood when exposed to water. Combining chitosan-caffeine formulations limits the leaching of caffeine from impregnated wood, thereby increasing its resistance even under outdoor conditions. This research aimed to evaluate the properties of wood impregnated with chitosan-caffeine formulations, focusing on wettability (contact angle measurement), mechanical properties (bending strength), and sorption behavior. The contact angle measurement revealed that wood treated with chitosan and chitosan-caffeine formulations exhibited an improvement in water resistance compared to untreated wood and wood treated with caffeine alone. However, this resistance showed only for short-term application. Both caffeine and chitosan treatments reduced the equilibrium moisture content during adsorption and desorption phases in the relative air humidity range from 0 to 0.95. The application of chitosan-caffeine formulations for wood impregnation resulted in a reduction in equilibrium moisture content, as well as hygroscopicity of the treated wood. Treatment with all formulation variants had no effect on the mechanical parameters, including modulus of elasticity and modulus of rupture. In addition, FTIR results indicated that both caffeine and chitosan interact with wood components. These findings suggest that chitosan-caffeine formulations are promising as natural wood preservatives, offering an improved hygroscopicity while maintaining the mechanical properties of the treated wood.