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 themain componentunits of natural bamboo. However, PCs have long been discarded aswaste during the industrial processing and utilization of bamboo,i.e., papermaking, textile, and composites, because of their inferiormechanical properties and higher hygroscopicity compared to the BFs.Here, we proposed to mechanically separate PCs from BFs and subsequentlyrecombine them to generate formaldehyde-free bamboo self-bonding composites(BSCs), which physical-mechanical properties were tuned forthe first time by adjusting the PC content. The PC effects were examinedon the formation and material properties of the BSCs in terms of microstructureand physical-mechanical properties. Microscopic observationrevealed that PCs with a high cavity-to-cell wall ratio were morelikely to deform and bridge adjacent particles during hot pressing,thus forming a dense interlocking structure with heat-sealed pointsbetween the BFs. The inclusion of the PCs into the BSCs led to muchlower water absorption and thickness swelling than without the PCs.The BSCs containing 40% BFs and 60% PCs had a thickness swelling of13.3%, fulfilling the performance requirements of commercial high-densityfiberboards used in humid environments. The 40% BFs/60% PCs made BSCsalso exhibited the highest flexural strength, flexural modulus, andinternal bonding strength, increasing by 99.8, 60.8, and 189.9%, respectively,compared with sole BF-made BSCs. The eco-friendly and formaldehyde-freeBSCs with tunable properties are promising for use in furniture, packaging,and interior decorations. Tunablewater resistance and mechanical properties of formaldehyde-freebamboo self-bonding composites can be achieved by adjusting parenchymacell content.