The effects of moisture content on the bonding interfacial properties of glued bamboo

Glued bamboo is often used in outdoor environments where humidity changes constantly. It is necessary to investigate the effects of changing moisture content, induced by environmental humidity, on the bonding performance of glued bamboo. In this study, glued bamboo was processed using Moso bamboo and phenol-formaldehyde (PF) resin with three typical assembling structures: outerlayer-outerlayer (A-A), outerlayer-innerlayer (A-B), and innerlayer-innerlayer (B-B). The microstructures of the bonding interphase were observed using fluorescence microscopy and scanning electron microscopy (SEM). The moisture content (MC) and thickness swelling (TS) of glued bamboo were measured after conditioning under different environmental humidity levels. The lap-shear test (LShT) and digital image correlation (DIC) were used to study the bonding performance of glued bamboo. Results indicated that PF resin penetrated more easily into the bamboo innerlayer due to the presence of more parenchyma cells on the inner side. When conditioned under different humidity environments, both MC and TS increased with rising humidity. Bonding strength decreased significantly with increased MC, especially for specimens with A-A and A-B structures. However, energy absorption was better when specimens were conditioned at 95% relative humidity (RH). Strain distribution was more uniform in specimens conditioned in high humidity environments. After soaking in water, shear strain was minimal due to the low strength of glued bamboo. The influence of MC on the bonding interfacial properties of glued bamboo, as indicated in this paper, will contribute to understanding the failure mechanism of bamboo-based composites for outdoor use.