【作者】 郭义；

【导师】 周金平；

【作者基本信息】 武汉大学 ， 高分子化学与物理， 2011， 博士

【摘要】 随着石油资源的枯竭和环境污染的日益恶化,研究和开发以天然高分子为原料的功能材料已成为高分子科学的前沿领域之一。纤维素是自然界最丰富的可再生资源,是未来主要的化工原料之一。目前,我国仍然采用传统、落后的黏胶法生产人造丝、玻璃纸和无纺布,生产过程中由于大量使用CS2而造成环境污染并损害人体健康。因此,开发无污染的纤维素新溶剂以及新的加工方法已成为纤维素工业发展的关键。CarbaCell工艺是指以纤维素氨基甲酸酯(CC)为原料生产纤维素纤维和膜的新工艺。与黏胶法相比,CarbaCell工艺对纤维素浆料要求低,产品易于处理、运输及储存且没有毒性。同时,该方法可以最大限度的利用原有黏胶纤维生产设备,节约了对生产设备的投资。然而,作为CarbaCell工艺生产人造丝和玻璃纸的中间体,CC的合成条件苛刻,生产过程能耗大、成本高,由此制约了CarbaCell工艺的工业化。微波合成是一类高效节能的化工新技术,具有速度快、受热体系温度均匀、无滞后效应以及热效率高的特点。本工作通过微波加热快速合成CC,并对产物的结构、性质和流变行为进行深入研究,进而通过湿法纺丝和流延成膜制备纤维素功能材料。本论文的主要创新有以下几点：1)首次利用微波加热法在无催化剂、无溶剂条件下快速合成CC,系统地考察了反应条件对CC合成的影响,并对产物的结构和性能进行了表征；2)以7 wt%NaOH水溶液作为溶剂,首次研究了CC/NaOH溶液的动态黏弹行为,阐明了温度、浓度、氮含量和分子量对溶液流变性能以及溶液-凝胶转变的影响；3)通过实验室小型纺丝和制膜设备制备出新型纤维素氨基甲酸酯纤维和膜,并研究了它们的结构和性能。本论文的主要研究内容和结论包括以下几个部分。首先,通过微波加热快速合成纤维素氨基甲酸酯(CC),系统考察了微波功率、反应时间、纤维素来源及其分子量、纤维素/尿素混合物的配料比等因素对CC合成的影响,并通过元素分析、FT-IR、NMR、XRD和TGA等对CC的结构和理化性质进行了表征。研究表明,不同聚合度和结晶度的各种纤维素原料均可通过此方法合成得到CC。低功率(170W)下,反应需要较长时间(15～20min)；而高功率(425W)下,反应伴随着纤维素的碳化和交联。因此,采用微波功率为255W,单次反应时间为2～5min进行反应为最佳。随着纤维素/尿素混合物中尿素含量从9.8wt%增加到50.4wt%,所得CC的氮含量从1.255%增加到2.924%；随着反应混合物质量的增加以及间隔微波反应次数的增加,CC氮含量增加。随着氨基甲酸酯基团的引入,纤维素的氢键和晶体结构被部分破环,结晶度降低,但仍保持纤维素Ⅰ型晶体结构。微波合成CC不使用有毒溶剂、无原料损失、无催化剂、无环境污染,且能耗低,是一种高效、绿色的合成新方法。CC能很好地溶解在-5～5℃的610 wt%NaOH水溶液中,由此得到透明、稳定的溶液。采用ARES-RFSⅢ型流变仪研究了CC在7 wt% NaOH水溶液中的动态黏弹行为。研究表明,CC溶液的凝胶化过程与温度、CC浓度、氮含量及分子量有关。加热可导致CC溶液转变为凝胶,且其溶液-凝胶化转变为热不可逆过程。随着CC(Mη=7.78×104)浓度从3.0 wt%增加到4.3 wt%,溶液的表观凝胶化温度从36.5℃降低到31.3℃。随着CC氮含量从1.718%增加到5.878%,溶液的表观凝胶化温度由35.7℃降低到27.5℃。随着CC分子量从6.35×104增加到9.56×104,溶液的表观凝胶化温度从38.2℃下降到34.4℃。CC溶液在30℃时的凝胶化时间较短,但在15℃时溶液较为稳定、可长时间储存。体系的溶液-凝胶化转变同样可通过Winter-Chambon理论来精确确定。将7 wt% NaOH水溶液预冷至-7℃迅速溶解CC得到纺丝原液。以10wt% H2SO4溶液为凝固浴,由实验室小型纺丝设备成功制备出再生纤维素氨基甲酸酯纤维(RCC),并通过元素分析、光学显微镜、SEM、XRD、13C NMR以及拉力测试等对纤维的形貌、结构和性能进行表征。经过溶解、纺丝和再生过程,CC的氨基甲酸酯基团大部分被水解,其晶体结构由纤维素Ⅰ转变为纤维素Ⅱ。RCC纤维具有圆形的截面和光滑致密的表面结构。随着纺丝拉伸速率的提高,纤维的纤度降低、拉伸强度升高、断裂伸长率呈下降趋势。单丝的拉伸强度为0.8～1.3cN/dtex,断裂伸长率为20～30%。RCC纤维的取向度较低(在0.14～0.19之间),可望通过改进纺丝设备来提高纤维的取向度,由此大幅提高其强度。RCC纤维具有良好的染色性能,在纺织领域具有潜在应用。以10wt%H2SO4溶液为凝固浴,由CC/NaOH溶液制备出一系列再生纤维素氨基甲酸酯膜(CCF),并通过元素分析、FT-IR、SEM、XRD、TGA、DMA以及拉力测试等对膜的结构和性能进行表征。CC在溶解和再生过程中,氨基甲酸酯基团被部分水解,晶体结构由纤维素Ⅰ型转变为纤维素Ⅱ型,且结晶度降低。CCF膜具有均匀致密的结构,并具有良好的热稳定性和热力学性质。CCF膜具有优良的力学性能,其拉伸强度为60～70 MPa,伸长率在10～15%之间,并显示良好的透光性能。因此,再生纤维素氨基甲酸酯膜在食品包装和生物材料等领域有着广泛的应用前景。本论文为纤维素氨基甲酸酯的合成提供了新的方法和途径。同时,论文阐明了纤维素氨基甲酸酯独特的溶液-凝胶化转变行为,并由此制备出新型纤维素材料。这些研究成果将为CarbaCell工艺的工业化提供重要的信息和科学依据,具有重要的学术价值和应用前景。更多还原

【Abstract】 Nowadays, with the decreasing of oil resources and worsening environmental pollution, research and development of the natural polymers have been one of the superior areas of polymer science. As the most abundant renewable resources on the earth, cellulose will be one of the main chemical raw materials. In our country, the viscose process is still occupied the leading position in the regenerated cellulose fiber and cellophane industries, although this process generates several environmentally hazardous byproducts, which include CS2, H2S and heavy metals. Therefore, the development of non-polluting solvent and novel process is the key to the development of cellulose industry. CarbaCell process is a novel technology to produce cellulose fibers and films. In comparison with the viscose process, CarbaCell process has the advantage of a better ecological compatibility such as the use of the innocuous urea, relatively stable of cellulose carbamates (CCs), and most of the conventional equipment of a viscose plant can be used without any problems. The starting point of this process is the transformation of cellulose with urea into CCs. There were many rigorous conditions in the conventional synthetic methods of CCs, which had major limitations for potential technical applications. Therefore, industrial CC production sites have not yet been established. The use of microwave heating as a source of heat in synthetic chemistry offers a promising alternative. It displays a number of advantages over conventional heating, such as non-contact heating, better control over the heating process, rapid heating, high rate of reactions and high product yields. In this thesis, we provided a novel method for the microwave-assisted synthesis of CCs, and the structure and properties of the CCs were studied. Moreover, cellulose functional materials were prepared by wet spinning and film casting from CCs.The novel creations of this work are as follows. (1) We presented an efficient solvent-free and catalyst-free microwave synthesis of cellulose carbamate for the first time. The reaction conditions on the nitrogen content of CCs were investigated, and the structure and properties of CC were studied. (2) Dynamic viscoelastic properties of cellulose carbamate dissolved in NaOH aqueous solution were systematically studied for the first time. The shear storage modulus and loss modulus as a function of the angular frequency, concentration, nitrogen content, molecular weight, temperature, and time were analyzed and discussed in detail. (3) Novel regenerated CC fibers and films have been prepared from CC/NaOH aqueous solutions and the structure and properties of the materials were investigated. The main contents and conclusions in this thesis are divided into the following parts. Firstly, an efficient microwave synthesis of CCs was reported for the first time. The types of raw cellulose materials, the effects of the reaction conditions including the urea content in the mixture, mass of the mixture and pulsed times of microwave irradiation on the nitrogen content of CC samples were investigated in detail. Structure and properties of the CCs were characterized by elemental analysis, FT-IR, XRD, NMR and TGA. It has been found that various sources of cellulose such as cotton linter, wood pulp, bagasse pulp and reed pulp with different degree of polymerization (DP) and crystallinity (χc) were appropriately for the method. The reaction needed a long continuous time (15～20 min) at a low power level (170 W), and was accompanied with carbonization and cross-linking at a relatively high power level (425 W). Therefore,255 W was chosen as the reaction power in the work. The nitrogen content of CCs increased from 1.255 to 2.924%, when with the urea content increased from 9.8 to 50.4 wt%. With an increase of the mixture mass and the pulsed microwave energy times, the nitrogen content of the CCs increased. With the introduction of carbamate groups, the density of hydrogen bonds reduced and the crystalline structure of the native cellulose was partially destroyed. Theχc value of CC decreased, but CCs remained the cellulose I crystalline form. Because of the absence of harmful solvents, no loss of raw materials, and being pollution-free and catalyst-free, the method is a novel, efficient and green procedure.CCs display good solubility in 6～10 wt% NaOH solutions at the temperature from -5 to 5℃, and a transparent and stable solution could be obtained. The rheological properties and sol-gel transition behaviors of CC/NaOH solutions were investigated by using dynamic viscoelastic measurement. The results revealed that the CC solutions could be changed into gels by heating, and the sol-gel transition was a thermoirreversible process. The gelation behavior of the CC/NaOH solutions was very sensitive to the test temperature and concentration, nitrogen content and molecular weight of CCs. The apparent gelation temperature of the CC solutions decreased from 36.5 to 31.3℃with the CC concentration increased from 3.0 to 4.3 wt% and decreased from 35.7 to 27.5℃with the nitrogen content increased from 1.718 to 5.878%, and that of 3.8 wt% CC solutions decreased from 38.2 to 34.4℃with the increasing molecular weight from 6.35×104 to 9.56×104. The apparent gelation time of the CC solution was relatively short at 30℃, but the solution was stable for a long time at about 15℃. The Winter-Chambon criterion can also be applied in the CC solution system to clarify their dynamic viscoelastic behavior. Regenerated cellulose carbamate fibers (RCC) have been spun successfully on a small and simple homemade wet-spinning apparatus from a CC dope in 7 wt% NaOH aqueous solution. Morphology, structure and properties of RCC were characterized by elemental analysis, optical microscopy, SEM, XRD,13C NMR, and mechanical testing. The carbamate groups were hydrolyzed mostly during the dissolution, spinning and coagulation process, and the CC crystals of the fibers were completely transformed from celluloseⅠtoⅡduring the coagulation process. RCC had circular cross section and smooth dense structure. With the increasing of the spinning draw ratio, the titer of RCC fibers decreased, the tensile strength increased and the elongation at break decreased. The tensile strength and elongation at break of the monofilament was in the range of 0.8～1.3 cN/dtex and 20～30%, respectively. The results of 2D WAXD indicated that the orientation of RCC fiber was very low, which was between 0.14 and 0.19. It is expected to improve spinning equipment to increasing the orientation, and then increasing the fiber strength greatly. RCC fiber had good dyeing properties, which has potential applications in the textile fields.A series of regenerated CC films (CCF) were prepared from CC/NaOH dope by using 10 wt% H2SO4 solution as the coagulation bath. The structure and properties of CCF were characterized by elemental analysis, FT-IR, SEM, XRD, TGA, DMA and mechanical test. The carbamate groups were hydrolyzed mostly during the dissolution and coagulation process. The crystals of CCF were completely transformed from celluloseⅠtoⅡduring the coagulation process, and theχc values of CCF decreased. CCF possessed homogenous structure and good thermal stability, as well as thermodynamic properties. The tensile strength and elongation at break of the CCF films were in the range of 60～70 MPa and 10～15%, respectively. Moreover, CCF films had excellent optical transmittance. Therefore, CC films have potential application in food packaging and biological materials.The thesis provided a new pathway for the synthesis of cellulose carbamate. Meanwhile, this work clarified a unique sol-gel transition of the cellulose carbamate solution, and the novel cellulose materials were prepared. The thesis provided some meaningful information and scientific evidence for the industrial application on the CarbaCell process. Therefore, there are great scientific significance and prospects of applications.更多还原