Structure and physical properties of high-density bamboo scrimber made from refined bamboo bundles

Bamboo is comprised of parenchyma and vascular bundles, which contain vessels, sieve tubes, and fiber cells exhibiting numerous cavities or loose structures. Bamboo bundles undergo a series of mechanical rolling and disintegration processes to transform them into longitudinally continuous and transversely separated bamboo bundles and there is still a significant amount of vascular bundles and parenchyma that remain undissociated. Partial vessels, sieve tubes, and a majority of the parenchyma cell cavities are still discernible in the bamboo scrimber through the process of hot pressing, which significantly diminishes properties of bamboo scrimber, such as the strength, rigidity, and the water resistance. Therefore, this paper presented a new type of bamboo scrimber made from refined bamboo bundles, which is called high-density bamboo scrimber. That is, based on conventional bamboo bundles, a small amount of NaOH was employed to selectively eliminate a portion of the hemicellulose and soften bamboo bundles. Subsequently, a mechanical hammering technique was employed to disintegrate the bamboo bundles into single vascular bundles and surrounding parenchyma. This process increased the resin infiltration pathways and a multi-scale bonding interface structure was formed, and the densification and physical properties of the bamboo scrimber were improved. In high-density bamboo scrimber, the fiber cells maintained their original structural morphology, while the vessel cells and parenchyma cells were completely compacted, resulting in indistinguishable cell contours, and there was no discernible demarcation between the vascular bundles and parenchyma. Compared to ordinary bamboo scrimber, the bending strength, bending modulus, and maximum displacement of high-density bamboo scrimber exhibited a significant increase of 40.1%, 37.3%, and 18.2% respectively. The water resistance, surface roughness after sanding, and mildew resistance of this particular bamboo scrimber were better than those of ordinary bamboo scrimber. High-density bamboo scrimber exhibited a broader spectrum of applications within architectural structures.