During the last years the research on chitosan as a wood preservative has been enhanced. Up to now, most of the research has been applied to the anti-fungal properties of chitosan, and no research was conducted on the solution stability of chitosan solutions in repeated trials by impregnation of wood, or on the mechanical properties of chitosan-treated wood. In this paper, the stability of high- and low-molecular weight chitosan solutions (2,4% (w/v) concentration) was investigated in 15 repeated impregnation cycles using pine (Pinus sylvestris) samples. Changes in the following parameters of the treatment solution were examined: uptake of chitosan, viscosity, pH, molecular weight and concentration. In addition, the following mechanical properties of chitosan-treated pine were determined using a paired experimental design: modulus of elasticity (MOE), static bending, impact bending strength, static hardness, shear strength, tensile strength, compression strength and adhesion of paint to wood. Overall, an average chitosan uptake by the pine samples in the order of 15 to 16 kg/m³ was obtained. In the trials for determination of solution stability, the uptake, viscosity and concentration remained unchanged. However, the pH of the solutions increased, and the average chitosan molecular weight decreased, with the high molecular weight chitosan displaying larger changes than low molecular weight chitosan. No significant changes in the mechanical properties of pine treated with high-and low molecular weight chitosan (2,4% (w/v) concentration) were determined as compared to untreated wood samples.

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