【作者】 余养伦；

【导师】 于文吉；

【作者基本信息】 中国林业科学研究院 ， 木基复合材料科学与工程， 2014， 博士

【摘要】 我国是世界上最大的竹材资源拥有国和生产国，竹产业是我国林业的四大朝阳产业之一，重组竹由竹束或纤维化竹单板为构成单元，按顺纹组坯、经胶合压制而成的板方材，历经了10余年的发展，成为了竹产业的主流产品之一。竹基纤维复合材料作为重组竹的第二代产品，与传统的重组竹相比，具有原料的一次利用率高、生产效率高和产品附加值高等特点，是竹产业研究的热点和前沿技术之一。本文以慈竹和毛竹为研究对象，采用竹材青黄差速异步点/线裂微创技术和纤维原位可控分离技术，制备了纤维化竹单板，采用3因素4水平全因子试验，探讨了疏解度、浸胶量和密度等工艺因子对竹基纤维复合材料的耐水性能和力学性能的影响；在此基础上，采用超景深三维显微镜、扫描电子显微镜、CT扫描仪、接触角、万能力学试验机等先进仪器设备，对竹基纤维复合材料耐水性的改善机制和力学性能的增强机理进行了研究，得出如下结论：（1）采用竹材青黄差速异步点/线裂微创技术和纤维原位可控分离技术，制备出的纤维化竹单板，与竹束相比，其生产率提高约5倍左右；竹材一次利用率可达到90%以上；纤维束直径减小了约60%；单股最粗的纤维束直径在2mm以下。（2）纤维化竹单板的分离机理：竹青和竹黄表面难以胶合的皮层和髓细胞均为短细胞，在竹材青黄差速异步点/线裂微创技术产生的摩擦力和切割力的作用下，这些短细胞发生了脱落和破坏，实现了分离的目的；竹纤维细胞长、实心，抗压强度大；导管和基本组织细胞短、壁薄、腔大，抗压强度小，在纤维原位可控分离技术产生的挤压力和切割力的作用下，实现了纤维、导管和基本组织之间的分离，并最大限度地保留了竹纤维的强度，使其不受损伤。（3）竹基纤维复合材料的物理力学性能是可控的，可以根据目标产品对耐水性能和力学性能的需求，通过对疏解度、浸胶量和密度等工艺的调整，生产出满足《重组竹》国家标准（报批稿）要求的各层级的竹基纤维复合材料，采用疏解度为4度，浸胶量为16%，制备的密度为1.30g/cm3的高耐水性竹基纤维复合材料，经过28h（煮-干-煮）循环处理，其吸水厚度膨胀率小于2.08%，吸水宽度膨胀率小于0.78%，吸水率小于2.35%；采用疏解度为3度，浸胶量为10%，制备的密度为1.30g/cm3的高强度性竹基纤维复合材料，其静曲强度达到398MPa，弯曲弹性模量达到32.3GPa。（4）建立了竹基纤维复合材料吸水性的数学模型，竹基纤维复合材料自由水与材料的空隙度有关，吸着水与细胞壁表面形成的酚醛树脂胶膜层和羟基的数量有关。（5）竹基纤维复合材料耐水性的改善机制包括憎水胶膜层和胶钉的形成两方面：（a）憎水胶膜层的形成：酚醛树脂胶黏剂通过疏解形成的裂纹，渗透到竹纤维束的表面，在竹纤维束的表面形成一层连续的酚醛树脂胶膜层；（b）胶钉的形成：酚醛树脂胶黏剂通过疏解形成的裂纹，渗透到导管和基本组织等薄壁细胞的细胞腔内，在细胞腔内形成胶钉，将密实的薄壁细胞固定，使之不反弹。（6）竹基纤维复合材料力学性能的增强机理包括压缩密实增强和界面增强两方面：（a）压缩密实增强：基本组织和导管等薄壁细胞受到压缩密实，致使单位体积内竹纤维百分比增加；竹纤维力学性能远大于基本组织和导管，竹纤维比例的增加提高了竹基纤维复合材料的力学性能；（b）界面增强：酚醛树脂胶黏剂在纤维与纤维、纤维与基本组织以及基本组织与基本组织之间形成了胶钉链接，增强了胞间层的界面性能，改善了纤维之间的应力传递，更有效地发挥了纤维承载性能。更多还原

【Abstract】 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.更多还原