Manufactuirng Technology And Mechanism Of High Performance Bamboo-based Fiber Composites

China has the most abundant bamboo resources and an excellent utilization of the bambooindustry, which is one of the four highlight forest industries in China. Bamboo scrimber is amainstream product of the bambood industry that was realized after more than ten years ofdevelopment. This material, which is a novel engineered composite made from parallelbamboo bundles, can be used for flooring, furniture, building, and other civil engineeringapplications. Compared with traditional bamboo scrimber, bamboo-based fiber composites(BFC), which are second-generation products from bamboo scrimber, has higher raw materialutilization rate, gretaer productive efficiency, and more added value. As the advanced andfrontier technology, the BFC have been attracted extensive attention in bamboo industry.In this paper, oriented bamboo fiber mat (OBFM) was fabricated from Bambusa emeiensisand Phyllostachys pubescens by using differential asynchronization dotted/linear shapedcracking minimally invasive technique as well as situ controllable fiber separation technology.Then, bamboo-based fiber composites (BFC) were fabricated from OBFM and low-molecularweight phenolic formaldehyde resin. The effects of technoglocial factors (e.g. fibrosis degree,resin content, and density) on the water resistance and mechanical properties of BFC wereexplored by performing full factorial experiment (three factors and four levels). In addition,several analytical equipment, including an asultra-depth3D microscopy system (UDM), anelectron scanner microscope (SEM), a micro computed tomography (Micro-CT) scanner, acontact angle measuring device, and a universal mechanical tester, were employed toinvestigate the mechanism of water resistance and the mechanical properties of BFC.Severalconclusions were drawn from these experiments:(1) Compared with bamboo bundles, OBFM prepared through the proposed method hadapproximately five times higher productivity and more than90%primary bamboo utilization rate; moreover, its maximum diameter of a single fiber bundle (less than2mm) is only about40%that diameter of bamboo bundles.(2) Separation mechanism of OBFM: the cortex and myelocytes on the outer and innerlayers of bamboo are short cells that would be damaged or fallen away by the friction andcutting force of differential asynchronization dotted/linear shaped cracking minimally invasivetechnique and would then be separated from the bamboo. Bamboo fibers are long and solidcells, and they have strong pressure resistance; by contrast, vessels and parenchyma cells areshort and thin cells, and they have big cell room and poor pressure resistance. Such differencesallow the separation of the fiber from the vessels and parenchyma cells through the extrusionand cutting force of situ controllable fiber separation technology while maintaining the highperformance of bamboo fiber.(3) The physical and mechanical properties of BFC are controllable. Differentperformance levels of BFC can be fabricated by adjusting fibrosis degree, resin content, anddensity according to meet the requirement of the water resistance and mechanical properties ofnational standard of bamboo scrimber.High-water resistance BFC prepared under4degrees of defibering,16%resin content,and1.30g/cm3density yielded less than2.08%thickness swelling, less than0.78%widthswelling, and less than2.35%water absorption in28h circular boiling–drying–boilingtreatment. High-strength BFC prepared under3degrees of defibering,10%resin content and1.30g/cm3density yielded a static bending intensity of398MPa and a modulus of elasticity of32.3GPa in static bending.(4) A mathematical model of water absorption of BFC was established. Free water of BFCis correlated with porsity, and the absorbed water of BFC are correlated with the phenolic resinfilm and amount of hydroxy on the cell surface.(5) The water resistance improvement mechanism of BFC involves the formation ofhydrophobic film and glue nails: (a) Formation of hydrophobic film: phenol resin penetrated into the surface of bamboofiber bundles through cracks caused by defibering during the immersed process, thus formingan excellent three-dimensional network of thin protecting water-resistant film on the surface ofbamboo fiber bundles.(b) Formation of glue nails: phenolic resin penetrated into lumens of thin-walled cellssuch as vessels and parenchyma cells through cracks caused by defibering during the immersedprocess, thus forming glue nails in the cell cavity. These glue nails would fix the intensivelydistributed parenchymal cells tightly.(6) The reinforcing mechanism of the mechanical properties of BFC includes compactiondense reinforcement and enhancement of intensity of interface:(a) Compaction dense reinforcement: compaction of parenchyma cells and vesselsincreases the bamboo fiber ratio. Increasing the volume fraction of fiber leads to enhancedmechanical properties because bamboo fiber has better mechanical properties than parenchymacells and vessels.(b) Enhancement of intensity of interface: phenolic resin adhesive forms glue nails thatlink fiber and fiber, fiber and parenchyma cells, as well as parenchyma cells and parenchymacells; such links enhance the interfacial properties of the intercellular layer, improve the stresstransfer among fibers, and develop the load-carrying property of fiber more effectively.