Effect of Modification with Phenol Formaldehyde Resin on the Mechanical Properties of Wood from Chinese Fir

Samples of Chinese fir were treated with either low-molecular-weight or commercial phenol-formaldehyde (PF) resins. The macroand micromechanical properties of the treated and untreated samples were determined. The average longitudinal tensile modulus of elasticity (MOE) was 30.88% larger for the samples treated with the low-molecular-weight PF resin than it was for the untreated samples. The average MOE of the samples treated with the commercial PF resin was 29.84% less than that of the untreated samples. The micromechanical properties of the samples were investigated through nanoindentation studies. For the samples modified with low-molecular-weight PF resin, the values of average MOE and hardness were 32.94 and 32.93%, respectively, greater than those of the untreated samples. In contrast, the average MOE and hardness values were 11.99 and 18.14%, respectively, greater for the samples modified with commercial PF resin compared to the untreated samples. It could be inferred that the low-molecular-weight PF resin was able to diffuse into the nanopores in the S2 layer of the tracheid cell wall of the Chinese fir, thereby improving its macromechanical properties. Modification with low-molecular-weight PF resin was an effective way to enhance the longitudinal macromechanical properties of wood from the Chinese fir.