A novel bamboo engineering material with uniform density, high strength, and high utilization rate

Abstract

Bamboo has attracted much attention and gained economic and environmental values for its excellent properties such as fast growth, short rotation, sustainability, and high strength. One of the bamboo engineering products most widely used in construction, furniture, etc. is the laminated bamboo board which is made of bamboo strips. However, the arc-shape makes bamboo strips must be planed on four sides to be rectangular before assembling and gluing. After the quadrilateral planning process, a large part (60–70%) is removed. On the other hand, due to the non-uniform distribution of vascular bundles, bamboo is characterized by heterogeneity confined to decreased density and mechanical strength from the outer to the inner part, which causes the difficulty of stable quality control of engineered bamboo products. To increase the rate of bamboo utilization and achieve the goal of homogenization, this study proposed an integrated thermo-hydro-mechanical treatment combining flattening and homogenization on arc-shaped bamboo strips. Fresh bamboo strips with 70% moisture content were compressed at 170 °C with customized vapor releasers for 20 min. After the integrated treatment, arc-shaped bamboo strips were flattened and densified with a compression set of around 44%. The average density reached up to 1.10 g/cm3 from 0.67 g/cm3. And treated bamboo exhibited a relatively uniform density throughout its thickness. The increases of fiber bundle fraction and the density of parenchyma tissues were basic reasons for the density homogenization. The longitudinal tensile tests showed that the treated bamboo had remarkable mechanical performances. After treatment, tensile strength and modulus of elasticity (MOE) of bamboo increased by 52.6% and 35.4%, respectively.