【作者】 鲁江；

【导师】 邵惠丽；

【作者基本信息】 东华大学 ， 材料学， 2010， 博士

【摘要】 Lyocell纤维是一种新型的纤维素纤维,其原料资源丰富,生产工艺简单先进,对环境污染小,符合低碳和可持续发展要求。因此,Lyocell纤维有望替代生产工艺严重污染环境的粘胶纤维。Lyocell纤维具有手感好、干强及湿强度均较高及吸湿透气性佳等诸多优良的性能,可广泛应用于服装领域；其经过改性研究,还有望开发成炭纤维原丝、轮胎帘子线用纤维、导电纤维、抗菌纤维等。因此,Lyocell纤维在工业、航天、军事、医疗等领域有着广泛的潜在的应用前景。迄今为止,国内外对Lyocell纤维进行改性的研究报道不多,其中,将碳纳米管添加至Lyocell中进行改性的研究更未见有报道。为此,本论文将采用多壁碳纳米管(MWNTs)添加剂对Lyocell纤维进行改性研究,探讨了MWNTs的化学纯化及表面功能化改性、改性MWNTs在N-甲基吗啉-N-氧化物(NMMO)水溶液中的分散稳定性及其对Lyocell纺丝原液流变性能、纺丝性能及纤维结构与性能的影响。在此基础上,以MWNTs/Lyocell纤维为原丝制备了MWNTs/Lyocell基炭纤维,并对其结构与性能进行了研究。除此之外,本论文还初步探讨了纳米级炭黑、单壁碳纳米管(SWNTs)添加剂对Lyocell纤维结构与性能的影响。本论文首先研究了MWNTs的化学纯化、表面功能化改性及其在NMMO水溶液中的分散稳定性。TEM、TGA、FTIR和Raman光谱等分析结果表明：通过硝酸纯化处理,提高了MWNTs的纯度,并在MWNTs表面引入了羧基和羟基等官能团,提高了MWNTs的表面活性。沉降试验及显微镜观察结果进一步表明：在上述纯化基础上利用适量的十二烷基苯磺酸钠对MWNTs再进行表面功能化改性可使MWNTs在NMMO水溶液及纤维素/NMMO·H2O溶液中的分散稳定性得到显著提高。本论文采用哈克流变仪、自制的无计量泵的气压式单孔纺丝装置及带有计量泵的多孔纺丝装置等研究了MWNTs添加量对Lyocell纺丝原液流变性能及纺丝性能的影响。研究结果表明：添加了MWNTs的纤维素/NMMO水溶液为切力变稀流体,且随着溶液中MWNTs添加量的增加,溶液体系中纤维素的表观相对分子质量、溶液粘度、粘流活化能、结构粘度指数及弹性先逐渐增大,当MWNTs含量增至1%时,它们均达到最大值,但随着MWNTs含量的进一步增加,这些参数反而又出现下降的趋势。另外,研究还发现,MWNTs含量对纤维素/NMMO·H2O纺丝原液均匀性和纺丝性能也有一定的影响。在本论文实验范围内,MWNTs含量控制在1%及以下时,溶液均匀性和纺丝性能较好。本论文在上述研究基础上,进一步采用强力仪、SEM、FESEM、WAXD、二维X光衍射、TGA及低电流高阻测量仪等对含MWNTs的Lyocell纤维的结构与性能进行了分析。结果发现：MWNTs的添加对Lyocell纤维的晶型结构及结晶度没有明显的影响,但使纤维的热稳定性有了一定程度的提高；适量的MWNTs可以均匀分散在Lyocell纤维基体中并可使其力学性能有效改善。其中,1%MWNTs含量的Lyocell纤维的初始模量和强度分别比未添加MWNTs的Lyocell纤维提高了41.9%和22.2%。另外,通过适当提高喷头拉伸比也可改善MWNTs/Lyocell纤维的力学性能；纤维中,MWNTs是基本沿纤维轴取向的,且沿纤维轴取向的程度随喷头拉伸比的增大而逐渐增大。此外,在保证可纺性的条件下,尽可能提高纤维中MWNTs的含量并设法减小纤维成型时所受的拉伸作用对提高该纤维的导电性能也是有利的。在本论文研究范围内,较低拉伸作用下制得的5%MWNTs/Lyocell纤维的体积电导率比纯Lyocell纤维的体积电导率提高了约5个数量级。本论文还进一步以含MWNTs的Lyocell纤维为原丝探索制备了MWNTs/ Lyocell基炭纤维,并与纯Lyocell基炭纤维进行了比较研究。结果发现：含适量MWNTs的Lyocell纤维同纯Lyocell纤维一样表面光滑,截面为圆形。但相比之下,含适量MWNTs的Lyocell纤维强度更高、结构更致密,更适合作为炭纤维原丝。对Lyocell原丝及MWNTs/Lyocell原丝在不同温度分段预氧化和碳化处理后,发现两种纤维的结晶度均随着处理温度的提高而逐渐减少。当经过250℃热处理后,两种纤维的晶区结构均遭到了比较严重的破坏,原有的纤维素Ⅱ晶型的单斜晶系已不复存在。进一步经碳化处理后,纤维的结晶结构已从原丝纤维素Ⅱ的单斜晶系转变为炭纤维的二维乱层石墨结构,且结晶度较低。但MWNTs/Lyocell原丝中的MWNTs在制备炭纤维的过程中一直保持着自身的结晶结构。研究还发现原丝的制备工艺及其粗细、原丝中MWNTs添加量等因素均对最终炭纤维的结构产生重要的影响。在本论文研究条件下,相对于纺丝工艺A而言,由纺丝工艺B制备的原丝直径更细更均匀,由其制得的炭纤维的表面普遍比较光洁,纤维中没有明显的孔洞缺陷。其中,由1%MWNTs/Lyocell原丝制备的炭纤维形态结构较光滑、孔洞缺陷数量少且尺寸较小,其强度和模量分别比纯Lyocell基炭纤维提高70%和116%。与此同时,本论文还初步探讨了纳米级炭黑、SWNTs添加剂对Lyocell结构与性能的影响,研究发现：虽然炭黑的添加不利于纤维力学性能的提高,但促进了纤维导电性能的改善,在一定的研究范围内,MWNTs/炭黑/Lyocell纤维的导电性相对于MWNTs/Lyocell纤维有了一定程度的提高；由于SWNTs比MWNTs具有更完善的结构和更优良的电学性能,当纤维中碳纳米管含量相同时,添加SWNTs的Lyocell纤维力学性能、体积电导率及热稳定性均普遍优于添加MWNTs的Lyocell纤维,而Lyocell纤维形态结构随SWNTs添加量的变化规律则与添加MWNTs时的情况相似。更多还原

【Abstract】 Lyocell fiber is a new kind of regenerated cellulose fiber and is expected to replace the rayon fiber in the future due to its simple, advanced and environmentally friendly process. Lyocell fiber has lots of excellent properties such as high dry strength and wet strength, good hand-feeling and water-absorbing properties, and so on. Therefore, it is widely used in the textile field. It can expectedly be used as precursor of carbon fiber, tire cord, electrical conductive fiber and anti-bacterium fiber etc. after being modified and will have wide potential application prospects in such fields as industry, spaceflight and medical treatment etc..To the date, there are a few reports on modified Lyocell fiber and no work has been reported on Lyocell fiber modified with carbon nanotubes (CNTs). In this thesis, multiwalled carbon nanotubes (MWNTs) were used as an additive of Lyocell process. The purification and functionalization of MWNTs, as well as their dispersion stability in the NMMO aqueous solution were studied. Moreover, the effect of MWNTs on the rheological behaviors and spinnability of the spinning dope, the structure and properties of MWNTs/Lyocell composite fiber were also investigated. Based on these works, the MWNTs/Lyocell-based carbon fibers were prepared by using MWNTs/Lyocell composite fibers as the precursor. In addition, the effects of the other additives such as nano-scale carbon black and single-walled carbon nanotubes (SWNTs) on the structure and properties of Lyocell fiber were further studied.In this thesis, the purification and functionalization of MWNTs, and their dispersion stability in the NMMO aqueous solution were studied firstly. The results from TEM, TGA, FTIR and Raman showed that the purity of MWNTs was increased and the carboxylic and hydroxyl groups existed on the surface of MWNTs after being treated with the nitric acid. The results by sedimentation test and using microscope further showed the MWNTs modified with appropriate amount of sodium dodecylbenzene sulfonate (SDBS) could be dispersed uniformly in the NMMO aqueous solution and cellulose/NMMO·H2O solution.The effect of MWNTs on the rheological behavior and spinnability of the cellulose/NMMO·H2O solution were also studied by HAAKE rheometer and two types of spinning devices. The results showed that the cellulose/NMMO·H2O solution filled with MWNTs belongs to the typical shear thinning fluid. The apparent relative molecular weight of cellulose, viscosity, flow activation energy, structural viscosity index and elasticity of the solution were increased firstly with the addition of MWNTs and reached the highest value with 1% MWNTs, and then decreased with the further addition of MWNTs. In the range of our experiments, it was found that the uniformity and spinnability of cellulose/NMMO·H2O spinning dope were also affected by the MWNTs content, and the spinning process was run smoothly if the content of MWNTs was not higher than 1%.Based on the above works, the structures and properties of MWNTs/Lyocell composite fibers were further investigated by using tensile meter, SEM, FESEM, WAXD, TGA, two dimentional X-ray diffraction and low current-high resistance meter etc.. It was found that by the addition of MWNTs the crystal structure and crystallinity of Lyocell fiber were hardly affected, while its thermal stability was increased in some extent. An appropriate amount of MWNTs could be dispersed uniformly in the Lyocell matrix and that could improve the mechanical properties of the resultant composite fiber. Compared with the pure Lyocell fiber, the modulus and tenacity of the composite fiber containing 1% MWNTs were increased by 41.9% and 22.2%, respectively. Moreover, the mechanical properties of MWNTs/Lyocell composite fibers could be also improved by increasing the jet stretch ratio appropriately. In addition, MWNTs in the fiber almost aligned along the axis of the fiber and the orientation of MWNTs increased with the increasing jet stretch ratio. In our case it was found that more MWNTs content and lower jet stretch ratio could improve the electrical conductivity of the composite fiber. The volume conductivity of the 5% MWNTs/Lyocell composite fiber prepared under a weaker spinneret draft was 5 orders higher than that of pure Lyocell fiber.The MWNTs/Lyocell based carbon fiber was prepared by using the MWNTs/Lyocell composite fiber as precursor and compared with the pure Lyocell based carbon fiber. The results showed that both MWNTs/Lyocell composite fiber and pure Lyocell fiber had smooth surface and round cross-section. Compared with pure Lyocell fiber, the composite fiber with appropriate amount MWNTs was much more suitable for using as carbon fiber precursor due to its higher tenacity and more compact structure. The Lyocell fiber and MWNTs/Lyocell composite fiber were treated under different pre-oxidation and carbonization temperatures. It was found that the crystallinities of the two kinds of fibers were gradually decreased with the increasing of the treatment temperature. After being treated at 250℃, the crystal structures of MWNTs/Lyocell composite fiber and Lyocell fiber were seriously damaged and the monoclinic crystal system of their original celluloseⅡdisappeared. The monoclinic crystal system of cellulose II of precursor was converted to a two-dimensional turbostratic graphite structure of carbon fiber after carbonization but the crystal sturcture of MWNTs was always kept in the fiber during the treatment process. The resultant carbon fiber had low crystallinity. It was further fount that the structure of carbon fiber was affected by the spinning process of precursor, its fineness and the content of MWNTs in the precursor and so on. The diameter of precursor made from spinning process B was finer and more uniform than that from the spinning process A. Therefore, the surface of resultant carbon fiber was more smooth and no obvious hole flaw existed in the carbon fiber. Compared with Lyocell-based carbon fiber, the tenacity and modulus of 1% MWNTs/Lyocell-based carbon fiber were increased by 70% and 116%, respectively.At the same time, the effects of the other additives such as nano-scale carbon black and SWNTs on the structure and properties of Lyocell fiber were also investigated. It was found that by the addition of carbon black the mechanical properties of the composite fiber were decreased, but its conductivity was improved. Compared with the MWNTs/Lyocell composite fiber, the conductivity of MWNTs /carbon black/Lyocell composite fiber was improved in some extent. Furthermore, because SWNTs had more perfect structure and better electricity property than MWNTs, the mechanical properties, volume conductivity and thermal stability of SWNTs/Lyocell composite fiber were better than those of MWNTs/Lyocell composite fiber in the case of the same carbon nanotubes’content. In addition, the variation of the morphological structure of composite fibers with the addition of SWNTs was similar to that of the MWNTs/Lyocell composite fibers.更多还原