【作者】 刘琳；

【导师】 姚菊明；

【作者基本信息】 浙江理工大学 ， 纺织工程， 2011， 博士

【摘要】 天然桑蚕丝是一种综合性能优异的生物质蛋白纤维,其织物光泽华丽、透气性好、质地柔软、手感好、穿着舒适,几千年来一直作为一种高档的纺织原料而闻名于世。作为天然高分子纤维的桑蚕丝,其独特的物理化学性能和优异的纤维特性一直是众多学者人工模拟纺制所追求的目标。然而在人们对蚕丝的溶解、再生蛋白原液的种类和浓度、凝固浴以及后处理等纺丝条件进行了一系列广泛而深入的研究后,所得再生丝纤维的力学强度仍然无法与天然蚕丝相媲美。另一方面,纤维素是自然界中分布最广、含量最多的天然生物质原料,它来源丰富、质轻价廉、生物相容性好、可生物降解；而纤维素纳米晶须(Cellulose nanowhisker, CNW)是一种源于纤维素的纳米单晶体,其杨氏模量和抗张强度比纤维素有指数级增长,分别高达150 GPa和10 GPa左右,且其长径比大,表面含有大量羟基。因此,CNW作为聚合物基质的增强体具有无可比拟的优势。本论文针对目前人工纺制再生丝蛋白纤维力学强度差的问题,以蚕桑业的废弃资源——桑枝皮和废蚕茧为主要原料,首先从桑枝皮中提取桑枝皮纤维素并制备纤维素纳米晶须,再将其与废弃茧丝的丝素蛋白(Silk fibroin, SF)溶液相混合,制备高浓度的再生丝素蛋白/纤维素纳米晶须(SF/CNW)混合溶液作为纺丝液,利用自制的纺丝设备,以甲醇为凝固浴,湿法纺丝制备纤维素纳米晶须增强再生蚕丝蛋白纤维。研究了纤维素纳米晶须增强再生蚕丝蛋白纤维形成过程中聚集态结构的变化,考察了纳米晶须的引入对再生蚕丝蛋白复合纤维结构、性能的影响,以及晶须与丝素蛋白基质间的相互作用,初步探讨了纳米晶须对再生蚕丝纤维的增强机制,对高分子材料的发展具有积极的促进作用,同时也为制备高性能的新型纺织材料提供科学依据；另外,在纤维素纳米晶须制备过程中,为实现桑枝皮纤维的清洁化生产及废弃桑枝皮的高值化利用,采用酸抽—碱煮两步法从桑枝皮中先提取副产物——果胶,再采用二次碱煮提取桑枝皮纤维,并对碱煮脱胶废液进行回收处理,提高桑蚕业资源利用附加值并降低脱胶过程中对环境造成的二次污染。采用酸抽—碱煮两步法从桑枝皮中先后提取出桑枝皮果胶和纤维素,所得果胶具有不同的酯化度；桑枝皮纤维经硫酸水解制得的纤维素晶须呈纳米级棒状,长度约为300～400 nm,直径约为20 nm,其结晶度高达86.4%,表现出不同于普通纤维素的热分解行为,具有低温和高温两个热分解阶段,最高热分解温度达567℃,纤维素纳米晶须大的长径比、高的结晶度和热稳定性显示了其作为聚合物基质增强体的巨大潜力。通过对再生丝素蛋白溶液浓度可纺性研究发现,当浓度为27%左右时,再生丝素蛋白溶液具有良好的可纺性,初生纤维表面和截面形貌最佳,综合力学性能最好；确定了27%为SF/CNW混合液的纺丝浓度,不同比例SF/CNW混合液流变特性研究表明,混合溶液呈切力变稀型流体特性,且在较低剪切速率时,较小的速率改变,即会引起表观黏度的明显下降,因此剪切速率应控制在表观黏度变化比较稳定的初始阶段,随着纺丝液中CNW含量由1%增加至7%,SF/CNW混合液的表观黏度呈现先增后降的趋势,其流动特性指数n变小,结构黏度指数△η变大,因此应控制CNW含量低于7%；混合液表观黏度对温度和时间稳定性研究表明,SF/CNW混合液表观黏度在5-25℃范围内保持稳定,当温度超过25℃时,混合溶液黏度开始下降,且存放5d仍可以保持其流变学特性稳定。在优化的纺丝工艺条件下,成功制备了力学强度优异的纤维素纳米晶须增强再生蚕丝蛋白纤维,且力学强度随着CNW含量的增加而升高,当CNW含量为5%时,再生丝纤维的力学性能达到最佳,其杨氏模量、拉伸强度分别达到28.84GPa、728.51 MPa,是天然桑蚕丝的1.8倍和1.5倍,而断裂伸长率为20.3%,与天然桑蚕丝相近。通过对纤维素纳米晶须增强再生蚕丝蛋白纤维形成过程中结构与性能的关系研究发现,经60℃热空气拉伸处理的再生纤维具有较好的结晶性和分子取向；纤维素纳米晶须在丝素蛋白基质中均匀分散,纳米晶须与基体之间存在强的界面结合；动态热机械分析也表明,由于纤维素纳米晶须的加入,限制了其附近丝素蛋白无定形区分子链的自由运动,在CNW分散相和SF连续相之间形成了界面相互作用,显著提高了再生丝纤维的储能模量,从而使其玻璃化转变温度升高。在丝素蛋白基质中引入引入长径比大、结晶性好、强度高的纤维素纳米晶须,显著提高了再生蚕丝蛋白复合纤维的力学强度和热稳定性,说明利用纳米晶须改善人工纺制再生蚕丝蛋白纤维的力学性能,是十分有效的。再生蚕丝纤维的优良性能一直是人们追求的目标,通过探明纤维素晶须增强蚕丝纤维的凝聚态形成过程、结构与功能的关系,以及晶须——蛋白质之间相互作用等,提出了晶须分散相与丝素蛋白连续相之间形成微界面区,在后拉伸过程中,丝蛋白纤维分子链规整性进一步调整,纤维状晶须沿纤维轴向排列的增强机制,这对功能高分子纤维的发展具有积极的促进作用；同时,本论文是蚕桑业废弃物的再加工、循环利用,使其物尽其用,延长了蚕桑产业链,对实现农民增收、保护环境具有良好的经济和社会效益,且符合国家发展循环经济的政策。更多还原

【Abstract】 Bombyx mori silk is one of the most valuable materials for clothing industry due to its outstanding glossiness property, wearing comfort, and physiological properties (compatibility, biodegradability, thermo-insulating, etc). In order to produce specialty materials, silk processing techniques have been investigated for artificial silk, including spin dopes, concentration, coagulation bath, post-drawn, etc. But the mechanical properties of artificial silk fibre do not compete with native silk yet.Cellulose is one of the most ubiquitous and abundant bioresourse polymers on the planet, giving the renewability and biocompatibility. Cellulose nanowhisker (CNW), a nanocrystal prepared by acid hydrolysis of native cellulose, usually has good mechanical properties, high aspect ratio, and strong interfacial adhesion between the CNW and the matrix. Thus, it can be used as the reinforcing agent in environmental-friendly composite materials due to its special physical properties.In an effect to improve the mechanical properties of artificial silk fiber and utilize waste materials, CNW suspension was prepared by acid hydrolysis of cellulose from mulberry branch-barks (Morus alba L.), and subsequently mixed with regenerated silk fibroin (SF) solution to obtain concentrated SF/CNW aqueous solutions as spinning dopes. Then reinforced artificial silk fibers by cellulose nanowhisker (SF/CNW) were produced by wet spinning through methanol coagulant to investigate the relationship between SF matrix and CNW reinforcing agent. To realize the environmental-friendly production of mulberry cellulose and maximum utilization of sericultural resources, mulberry pectin and cellulose were extracted via two-step method, i.e. acid extraction-alkali treatment, respectively, and the degumming waste liquid was further treated to recycle pectin, hemicellulose, lignin.The extracted pectins from mulberry barks had different degrees of esterification. And the cellulose nanowhiskers presented rod-like with a length of 300-400 nm, and a diameter of 20 nm, and had a crystallinity of 86.4%. The thermal analysis showed a two-stage thermal decomposition behavior of cellulose nanowhisker with a maximum weight loss attained at 567℃. The obtained cellulose nanowhiskers may have the potential application as a reinforcing agent in the field of composite materials.From the research about the spinnability of regenerated SF solution, it was found that the concentration of spinning dope play an important role on the morphologies and mechanical properties of artificial neat SF fibers, when the dope concentration is about 27%, the artificial fibers presented a good surface and cross-section morphology, excellent mechanical properties. There was a rapid initial shear thinning at low shear rate for SF/CNW solution with different CNW content, so it was necessary to control the shear rate according to initial stage of stabile apparent viscosity. Moreover, the characteristic indexes decreased, while the degree of entanglement of SF molecular enhanced with the increase of CNW content from 1% to 7%. And the studies on stability of solution to temperature and storage time indicated that apparent viscosity remained almost unchanged below 25℃, and the SF/CNW dope is rheologically stable for at least 5 days.The SF/CNW fibers with super mechanical strength were successfully fabricated under an optimized technologic processing. The Young’s modulus and tensile strength of SF/CNW fibers with CNW content of 5% reached 28.84 GPa and 728.51 MPa, respectively, which was 1.8 and 1.5 times compared with that of raw silk, respectively, moreover, breaking elongation was 20.3%, near that of raw silk. The spun fiber had well crystallinity and was well-oriented along the long axis after postspinning treatment at 60℃. In other hand, CNW were uniformly dispersed in the SF matrix. Dynamic mechnical analysis revealed that the elastic modulus of SF/CNW fibers increased significantly as a consequence of the reinforcing effect of CNW via the procolation network held by hydrogen bonds, finally leading to increase of glass transition temperature.In conclusion, it was an effective approach to improve the mechanical properties of artificial silk fiber via introduction of CNW with high aspect ratio, well crystallinity, and good mechanical strength. It would be significant for exploiting novel functional materials through investigating formation of aggregation structure, relationship between structure and properties, and interaction of matrix and dispersed phase. Furthermore, this research which was a recycling of sericulture waste resource might possess the potential economic and social benefits.更多还原