Tunable Physical-Mechanical Properties of Eco-Friendly and Sustainable Processing Bamboo Self-Bonding Composites by Adjusting Parenchyma Cell Content

Parenchyma cells (PCs) and bamboo fibers (BFs) are the main component units of natural bamboo. However, PCs have long been discarded as waste during the industrial processing and utilization of bamboo, i.e., papermaking, textile, and composites, because of their inferior mechanical properties and higher hygroscopicity compared to the BFs. Here, we proposed to mechanically separate PCs from BFs and subsequently recombine them to generate formaldehyde-free bamboo self-bonding composites (BSCs), which physical–mechanical properties were tuned for the first time by adjusting the PC content. The PC effects were examined on the formation and material properties of the BSCs in terms of microstructure and physical–mechanical properties. Microscopic observation revealed that PCs with a high cavity-to-cell wall ratio were more likely to deform and bridge adjacent particles during hot pressing, thus forming a dense interlocking structure with heat-sealed points between the BFs. The inclusion of the PCs into the BSCs led to much lower water absorption and thickness swelling than without the PCs. The BSCs containing 40% BFs and 60% PCs had a thickness swelling of 13.3%, fulfilling the performance requirements of commercial high-density fiberboards used in humid environments. The 40% BFs/60% PCs made BSCs also exhibited the highest flexural strength, flexural modulus, and internal bonding strength, increasing by 99.8, 60.8, and 189.9%, respectively, compared with sole BF-made BSCs. The eco-friendly and formaldehyde-free BSCs with tunable properties are promising for use in furniture, packaging, and interior decorations.