Mineralization of heat-treated fir wood with magnesium oxychloride: study of physical and structural properties

This study aimed to investigate the effects of mineral impregnation on fir wood using magnesium-based compounds. Two methods, combination and separate treatment, were used to impregnate heat-treated and non-treated samples. The Bethel method, involving vacuum and pressure, was employed for the impregnation process. The impregnated samples underwent assessments for weight gain, volumetric bulking, water soaking tests, water droplet contact angle, mechanical properties, and fire resistance. Additionally, SEM and EDAX analyses were conducted to evaluate the changes in the wood structure pre- and post-impregnation. The findings revealed the filling of pores and cavities in certain areas with Sorel cement, particle accumulation in cell walls and cell lumina, and an increase in the presence of Mg, Cl, and O elements in the impregnated samples. Furthermore, the physical property analyses indicated improved wood properties post-impregnation, with the combination impregnation method demonstrating the most notable performance in terms of weight gain percentage. Electron microscopy confirmed the formation of the magnesium oxychloride cement structure within the cell voids of both types of wood. The mineralization of the wood structure with magnesium compounds resulted in increased dimensional stability, reduced water absorption, and enhanced bulking and density of the wood. Moreover, the contact angle of water droplets on the wood’s surface decreased following impregnation with magnesium compounds, while the surface roughness of the wood increased. Mineral impregnation significantly enhances the bending strength, modulus of elasticity, impact resistance, and fire resistance of wood, regardless of heat treatment. The combined impregnation method consistently outperforms the other method.