Investigation of the microstructure, chemical structure, and bonding interfacial properties of thermal-treated bamboo

Thermal-treated (TMT) bamboo and TMT bamboo-based panel have a great potential application in the outdoor constructions. In this paper, the effects of the changes in terms of microstructure, chemical structure, and surface wettability of bamboo after TM on the adhesive penetration and shear strain distribution of glued TMT bamboo were investigated with scanning electron microscopy (SEM), Fourier transform infrared (FTIR), fluorescent microscopy, and digital image correlation (DIC). Results indicated that the partial pits on cell walls became smaller due to the shrinkage of bamboo cells and partial pits were covered by the coagulation of lignin after thermal treatment (TM). Both the changes in surface morphology, microstructure and the degradation of hemicelluloses decreased the permeability of phenol-formaldehyde adhesive on bamboo surface. The average penetration and effective penetration depth of phenol-formaldehyde adhesive on the TMT bamboo which was treated at 190 °C for 3 h decreased by about 24% and 37%, respectively, as compared to the control. The failure mode of glued TMT bamboo was mainly manifested as interlayer slipping and the strain accumulated in the bonding interphase of glued TMT bamboo during lap-shear test, which indicated that TM negatively affected the bonding performance of bamboo and phenol formaldehyde (PF) adhesive. As expected, the bonding strength of glued TMT bamboo at 190 °C for 3 h decreased by 63% in comparison with the control.