Influence of resin molecular weight on bonding interface, water resistance, and mechanical properties of bamboo scrimber composite

•Brominated PF resin (BrPF) and Moso bamboo were used to create bamboo scrimber composites (BSC)•BrPF resins with varied molecular weights had various degrees of bamboo penetration.•Resin and bamboo cell walls experienced multi-scale bonding phenomena.•Influence of resin molecular weight on its water resistance, and mechanical properties of BSC was evaluated. The bamboo/resin bonding interface significantly influences the preparation and final properties of bamboo scrimber composites (BSCs). Here, BSCs were prepared with different molecular weights of brominated phenol–formaldehyde resin (BrPF, Mw = 542–2001) and Moso bamboo as raw materials and their physicomechanical properties were evaluated. The macroscopic distribution and microscopic penetration of the resin at the bonding interface depended on the resin’s molecular weight distribution. High-molecular-weight resin was distributed in the damaged bamboo cell cavity near the bondline, while low-molecular-weight resin penetrated the cell wall. Excessive penetration by low-molecular-weight resin induced a severe lack of resin at the bondline. The resin and the bamboo cellulose experienced a cross-linking reaction at the molecular level, generating secondary forces such as polar forces and hydrogen bonds. The molecular weight distribution of the resin had a significant effect on the physical and mechanical properties of BSC. With increasing resin molecular weight, the water resistance of the BSC gradually increased, the bending performance and compressive strength gradually decreased, and the shear strength initially increased and then decreased. The bonding mechanism of BSC was studied at multiple scales, and the influence of resin molecular weight on its physicomechanical properties was investigated.