No abstract

As a new type of green environmental protection material for outdoor use, the water resistance of bamboo scrimber composite (BSC) is crucial—the primary reason for a decrease in water resistance being bonding interface failure. From a bonding interface structure perspective, the influence mechanism of the resin content and density on the water resistance of BSCs remains unknown. Therefore, in this study, BSCs were prepared using Moso bamboo and phenol-formaldehyde resin, and the changes in the macroscopic and microscopic bonding interfaces before and after 28-h water-resistance tests were observed and analyzed. The results showed that the water resistance of the BSC increased with increasing resin content, with higher thickness swelling rates (TSRs) observed at higher densities. Obvious cracks were found at the macroscopic interface after 28-h tests, with higher resin contents leading to fewer and smaller cracks. With increasing density, the longitudinal fissures due to defibering process decreased, having an effect on width swelling rates (WSRs). Furthermore, porosity measurements revealed changes in the microscopic bonding interface; the difference in porosity before and after testing (D-value) showed the same trend as water resistance. Generally, we conclude that the macroscopic and microscopic bonding interface structures are closely related to BSC water resistance.

The water resistance of bamboo scrimber used in outdoor environments greatly affects its applications and lifecycle. Physical and chemical studies have been conducted to investigate the influence of the hot-pressing temperature during thermo-mechanical densification on the water resistance of outdoor bamboo scrimber. Investigated parameters included the failure mode of surfaces, the vertical density profile, and the change of chemical components, which provides theoretical support for optimizing bamboo scrimber for outdoor applications. Here, the vertical density profiles of bamboo scrimber were measured using an X-ray density profiler, and the response of cells and bonding interfaces of bamboo scrimber to water absorption were recorded by using extended depth-of-field 3D microscopy and field emission scanning electron microscopy (FE-SEM). The composition was evaluated by X-ray diffraction (XRD), Fourier-transform infrared (FT-IR) spectroscopy, and X-ray photoelectron spectroscopy (XPS) to investigate the effect of temperature on water resistance during thermo-mechanical densification. The water resistance of bamboo scrimber significantly improved as the temperature increased from 140 °C to 170 °C. The spring-back from the compressive deformation of cells and cracks was the main failure mode, and showed a negative correlation upon increasing the temperature. The moderate increase in cellulose crystallinity, the increase in the polymerization degree of the PF resin, and the thermal degradation of hemicelluloses explained the failure behavior of the bamboo scrimber at the molecular level.