The Optimization of Thermo-Mechanical Densification to Improve the Water Resistance of Outdoor Bamboo Scrimber

Abstract

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.