Study on the Effect of Wood Moisture Content on Wood Surface Adhesion

As a viscoelastic and anisotropic material, wood exhibits significant variations in surface adhesion force under different moisture conditions, directly affecting friction during cutting processes. This study systematically investigates the effects of moisture content, tree species (Pine and Ash), and wood sections on the interfacial adhesion force between wood and cutting tools to establish a theoretical basis for understanding friction mechanisms in wood machining. Using a high-precision uniaxial mechanical testing system, the effects of wood moisture content, tree species, and sections on surface adhesion force were examined under different moisture content conditions. In this experiment, pine and ash were selected as examples; the study shows that the adhesion force increases with rising wood moisture content. When the moisture content transitions from an absolutely dry state to an air-dry state, the surface adhesion force increases slowly, primarily due to van der Waals forces, resulting in smaller and gradual changes. As the moisture content rises from the air-dry state to the green wood state, the surface adhesion force increases more significantly. This is mainly attributed to the increasing content of absorbed water due to moisture absorption, which forms liquid bridges through capillary action in the contact area, enhancing adhesion force. However, as the moisture content continues to rise, the thickening water molecular layer on the wood surface stabilizes the capillary force, leading to a more stable adhesion force. Additionally, the microscopic structure of different tree species and wood sections may also influence the surface adhesion force.