【作者】 王汉坤；

【导师】 江泽慧；

【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， 2013， 博士

【摘要】 纳米纤维素纤丝（NCF）及其复合材料由于具有纤维素独特的化学分子结构以及纳米尺寸效应，具备许多特殊的物理力学性能，在先进材料、光电子器件、包装、医药等许多重要领域应用前景广阔。本文以竹材为原料制备NCF及其应用产品，首先比较了竹纤维和薄壁细胞制备NCF的差异。在此基础上，基于产业化前景考虑，分别以商业竹浆、竹材加工剩余物为原料，研究NCF制取技术。最后以NCF溶胶为起始材料，重点开展NCF薄膜、NCF气凝胶以及NCF酚醛树脂纳米复合材料制备与性能研究，探讨竹基NCF的可能应用途径。论文的主要研究结论如下：薄壁组织细胞和竹纤维经过高压均质化处理均可制备出高质量的NCF溶胶，但解离过程不同，竹纤维均质化过程包括纤维的分段、纤维段的解离、细胞壁的破碎、纤丝束的分离四个步骤。薄壁组织细胞则分为细胞的破碎、壁层的解离、纤丝束的分离三个步骤，总体而言，竹纤维的细胞壁结构比较致密，使用现有处理技术获得高质量的NCF需要较多工序，能耗较大。在制备过程中使用饱和盐溶液取代纯水作为分散剂可将溶液的粘度降低几个数量级，提高生产效率。工业竹浆纤维为原料，使用高压均质化技术可以制备出的高质量NCF溶胶，但适当的机械预处理必不可少；高速匀浆处理可以促使纤维细胞壁外层的剥离，超声处理则对于竹纤维分丝帚化有明显作用；将超声波预处理与高速匀浆处理相结合是竹浆纤维高压均质化前处理的有效方法，可解决进料口的堵塞以及均质化前期样品破碎不均匀的问题；润胀剂的使用可以取代机械预处理，从而降低NCF能耗。竹加工剩余物中薄壁组织细胞的比例高达80%，是制备NCF的良好原料，其经过筛分和化学预处理才能用于NCF制备；超声波破碎是一种非常适合从薄壁基本组织中制备NCF的方法，经过化学预处理的薄壁基本组织在超声50min左右可获得质量优异的NCF溶胶。超声波破碎时，溶液的溶度过高会降低超声波的空化效应，以低于0.5wt%的浓度为宜；对于薄壁细胞来说，超声波破碎和高压均质化均可制备出高质量的NCF溶胶，但超声波在薄壁细胞破碎方面的效果优于后者，高压均质化对细胞壁的解离作用更加明显。NCF经真空抽滤可制备出结构致密、力学性能优异的NCF薄膜材料。超声处理40minNCF所制备薄膜材料的物理、力学性能较宜，模量和强度分别为12.6GPa和141MPa。处理时间、薄膜厚度、含水率等因素对薄膜的力学性能影响显著。通过控制干燥时气流走向和干燥时间可以制备出一定取向的NCF薄膜。力学性能测试表明薄膜正交方向的抗拉强度和弹性模量相差约20%，两个方向在断裂伸长率和蠕变性能上存在显著差异。NCF经冷冻干燥可制备出超轻高韧的气凝胶，本文制备的NCF气凝胶材料密度最低可达0.5×10^-3g/cm³，密度约为目前世界最轻固体材料的2.5倍。冷冻方式对NCF气凝胶的微观结构有显著影响。超低温冰箱和液氮制备的NCF气凝胶效果较好；NCF气凝胶材料具有优良的能量吸附性能，密度为10mg/cm³的NCF气凝胶的能量吸附值达220kJ/m3，与密度为其5倍的聚苯乙烯泡沫相近；NCF气凝胶整体上NCF束属于无规排列，但通过快速冷冻方法可以实现局部NCF束的定向排列。采用浓缩冻干法制备的NCF气凝胶作为负载酚醛树脂的载体，可以制备出低树脂负载率（PF含量小于15%） NCF/PF复合材料，复合材料的强度和模量分别为150MPa和5GPa。该工艺可以使酚醛树脂在复合材料中得到均匀的分布。在高湿度条件下，NCF/PF复合材料的吸湿性要低于纯NCF薄膜材料；在相同含水率下，两者的弹性模量、断裂强度和断裂伸长率差异不大。更多还原

【Abstract】 Nano-cellulose fibrils （NCF） and its composites own a lot of special physical andmechanical properties due to the unique chemical molecular structure and nano-size effect.This special material is very potential in the application of some important areas, such asadvanced materials, optoelectronic devices, packaging and pharmacy. In this paper, bamboowas for the first time taken as raw material to prepare NCF and its products, and the differencesfor preparing NCF by bamboo fibers or parenchyma cells were compared. Besides, based onindustrial prospects, the technology for preparing NCF was studied by taking commercialbamboo pulp and bamboo processing residues as raw materials. Finally, the preparation andproperty of NCF film, NCF aerogels and NCF/phenolic resin composites based on NCF solwere focused on and the potential application on bamboo-based NCF was also discussed.Both parenchyma cells and bamboo fibers after homogenization could be used to prepareNCF sol with high quality, but differences exist in the dissociation process. In thehomogenization process of bamboo fibers the four steps include the fiber segment, thedissociation of the fiber segment, the cell wall crushing, the separation of fiber bundles. Whilefor Parenchyma cells, there are only three steps including cell disruption, parietal dissociation,the separation of fiber bundles. Overall, the cell wall structure of bamboo fiber is very dense,which is responsible for high energy consumption and a lot of processes by using existingprocessing techniques. The efficiency of producing NCF could be improved by taking saturatedsalt solutions as a substitution for purified water to reduce the viscosity of the solution.NCF sol with high quality could be prepared by the use of high pressure homogenizationtechniques when taking industrial bamboo pulp as the raw material, while appropriatemechanical pretreatment is also essential. Homogenizing treatment with high speed couldinduce the strip of the outer cell wall, and then ultrasonic treatment plays a significant role inthe devillicate of bamboo fibers. The method which combines ultrasonic pretreatment withhigh-speed homogenizer is an effective way to avoid the inlet blockage and uneven crush before high-pressure homogenization. Swelling agent used as a method to pretreat bamboopulp could replace mechanical pretreatment, thereby reducing energy consumption forpreparing NCF.Parenchyma cells up to80%of bamboo processing residue is a good raw material, whichcould be used for preparing NCF after sieving and chemical pretreatment. Ultrasonic treatmentis a very suitable method to produce NCF by parenchyma cells, and parenchyma cells withchemical pretreatment could be prepared into excellent NCF sol by50-min ultrasonic treatment.Less than0.5wt%of solution concentration should be used because during the ultrasonicprocess high concentration may reduce the ultrasonic cavitation effect. For the parenchymacells, the ultrasonication and high pressure homogenization could both be used to prepare NCFsol, but in terms of parenchyma cell disruption, the ultrasonication is better, while thehigh-pressure homogenizing effect on the cell walls is more apparent.NCF film material with compact structure and excellent mechanical properties can beprepared by vacuum filtration. After40-min ultrasonic treatment, its physical and mechanicalproperties can be stable, and its modulus and strength were respectively12.6GPa and141MPa.The processing time, the film thickness, moisture content and other factors significantly affectthe mechanical properties of the material. By controlling the drying air flow direction and thedrying time NCF film with certain orientation can be prepared. Results show that there is adifference of about20%in the tensile strength and elastic modulus at the perpendiculardirection and in terms of creep and elongation at break for different directions, there aresignificant differences in performance.NCF aerogels with high toughness and very low density can be prepared by freeze drying,and the density of NCF aerogels could be as low as0.5×10^-3g/cm³, which is2.5times as thatof the world’s lightest solid material. The freezing method has a significant influence NCF onaerogel microstructure. Better NCF aerogels could be prepared by an ultra-low temperaturefreezer or liquid nitrogen. NCF aerogel material has excellent energy adsorption. Energyabsorption value of NCF aerogels with a density of10mg/cm³could be up to220kJ/m3, whichis very close to that of the polystyrene foam with5-time density. NCF bundles as a whole in NCF aerogels are arranged at random, but local NCF bundle orientation can be achieved byrapid freezing method.NCF/PF composite materials with low resin load ratio （PF content of less than15%）could be prepared using NCF aerogels made by concentration and freezing drying as a loadcarrier in phenolic resin. The strength and modulus of this composite material wererespectively150MPa and5GPa. This process can make the phenol resin uniformly distributein the composite material. At high humidity, hygroscopicity of NCF/PF composite material islower than that of pure NCF film material; besides, at the same moisture content, littledifference exists in the elastic modulus, breaking strength and elongation at break.更多还原