Influence of longitudinal parts of bamboo on the properties of bamboo scrimber

Abstract

As an important structural unit of bamboo, the number of vascular bundles gradually decreases and the proportion gradually increases from bottom to top. This gradient distribution of vascular bundles leads to the variability of the mechanical properties of bamboo in the longitudinal direction, which seriously threatens the reliability of bamboo matrix composites. Bamboo scrimber, a novel bamboo-based composite, is particularly sensitive to this variability, necessitating the use of conservative safety factors and thereby limiting its broader application. In this study, bamboo culms were segmented into three equal sections—bottom, middle, and top—to fabricate bamboo scrimber with consistent density and resin content. This approach aimed to investigate how the longitudinal parts influence the properties of bamboo scrimber. The investigations revealed that structural differences in longitudinal parts of bamboo significantly impacts the properties of bamboo scrimber. In terms of mechanical performance, no notable differences in shear properties were observed across the different sections. However, bamboo scrimber derived from the bottom section (BS-bottom) showed lowest bending and compressive strength compared to that from the middle (BS-middle) and top sections (BS-top). This variation in mechanical properties was correlated with the distribution of vascular bundles in each section. Regarding hygroscopicity, bamboo scrimber demonstrated consistent performance despite variations in lignin, hemicellulose, and cellulose content among the sections. This consistency is attributed to the uniformity in group types and crystal structure across the bamboo scrimber, which minimized differences in moisture absorption. Water resistance tests revealed that the BS-top had the highest water absorption and dimensional expansion, likely due to the higher residual rate of bamboo yellow in the oriented bamboo fiber mat, which reduced the bonding strength within the bamboo scrimber. These findings provide essential data for minimizing variability in bamboo scrimber properties and informs the hierarchical utilization of bamboo, thereby enhancing its application potential.