Study On The Preparation Of Lyocell Fibers With High Performance By Using Carbon Nanotubes As The Additives

Lyocell is a new kind of regenerated cellulose fiber. It is not only used in the textile field, but also expected be used as the industrial fibers such as tire cord, precursor of carbon fiber and conducting fiber etc after being modified. As a quasi-one dimensional materials, the carbon nanotubes (CNTs) have received much attention due to their remarkable properties, such as large aspect ratio and specific surface area, excellent electrical and mechanical properties. Therefore, it is an effective way to prepare the high performance fibers by using CNTs as the additives.Up to now, only Lu et al have prepared Lyocell fiber modified with the multi-walled carbon nanotubes(MWNTs), but it has not yet reached the standard of high performance industrial fiber., and now there are no reports on single-walled carbon nanotubes (SWNTs) modified Lyocell fiber in the world. Because there are different structure and properties between SWNTs and MWNTs, the enhancement effect on polymers are also different. In this thesis, SWNTs and MWNTs were used as the additives of Lyocell process, respectively. The purification and functionalization of CNTs, as well as their dispersion stability in the NMMO aqueous solution were studied. Then, two kinds of CNTs/Lyocell composite fibers were prepared by an appropriate spinning equipment, the effects of the kinds of CNTs on the structure and properties of CNTs/Lyocell composite fibers were compared, and SWNTs were chosen to modify Lyocell fiber. Based on these works, the effect of SWNTs on the rheological behaviors and spinnability of the SWNTs/cellulose/ NMMO·H2O spinning dope were also investigated. In addition, the SWNTs/Lyocell composite fiber was also prepared through a combination of other ways, such as increasing the DP of cellulose pulp, optimizing of the spinning device, heat treatment of the never dried as-spun CNTs/Lyocell composite fiber and adding NH4C1, in order to further improve the properties of Lyocell fiber.In this thesis, the purification, functionalization of CNTs and their dispersion stability in the NMMO aqueous solution were studied firstly. The results from TEM, FE-SEM, Raman and FTIR showed that the purities of both kinds of CNTs were increased and the carboxylic and hydroxyl groups existed on the surface of CNTs after being treated with the nitric acid. The results by sedimentation test, absorbance analysis and microscope further showed that the dispersion of CNTs in NMMO aqueous solution was improved by purification and functionalization, and SWNTs have better dispersion in NMMO aqueous solution, compared with MWNTs. The CNTs treated with the nitric acid and modified with appropriate amount of sodium dodecylbenzene sulfonate (SDBS) could be dispersed uniformly in the NMMO aqueous solution.In this thesis, SWNTs and MWNTs were used as additives, and the CNTs/ Lyocell composite fibers with different CNTs contents were spun by self-made single filament spinning device without metering pump, then the effects of the kinds of CNTs on the structure and properties of the CNTs/Lyocell composite fibers were compared. The results of the WAXD and SEM showed that the kind of CNTs had no influence on the crystal structure of Lyocell fiber, both kinds of CNTs/ Lyocell composite fibers still have the cellulose II crystal structure, and an appropriate amount of CNTs could be dispersed uniformly in the Lyocell matrix. With the increase of the CNTs content, the surfaces of CNTs/Lyocell composite fibers become more and more rough. The results of TGA and low current-high resistance meter showed that the thermal stability and volume conductivity of the CNTs/Lyocell fibers were increased with the addition of CNTs, and SWNTs/Lyocell composite fibers have higher thermal stability and volume conductivity than MWNTs/Lyocell fibers. In addition, an appropriate amount of CNTs could improve the mechanical properties of the composite fiber. Compared with the pure Lyocell fiber, the tensile strength and modulus of the composite fiber containing 1% SWNTs (MWNTs) were increased by 24.2%(18.8%) and 55.8% (47.9%), respectively, which means that the enhancement effect of SWNTs is more obvious than MWNTs. Therefore, SWNTs were chosen as the additive for subsequent research.Based on the above work, the rheological and spinning properties of SWNTs/ cellulose/NMMO·H20 spinning dope were studied by HAKEE rheometer and the above spinning device. The results showed that the cellulose/NMMO·H20 spinning dope filled with SWNTs belongs to the typical shear thinning fluid. The apparent relative molecular weight of cellulose, viscosity and elasticity of the dope were increased firstly with the addition of SWNTs and reached the highest value with 3% SWNTs, and then decreased with the further addition of SWNTs. At the same SWNTs content, the viscosity and elasticity of the dope were increased with the increasing of the DP of cellulose pulp. It was found that the uniformity and spinnability of cellulose/NMMO·H2O spinning dope decreased with the increasing of SWNTs content, and the spinning process was run smoothly if the content of SWNTs was not higher than 1%. Therefore, SWNTs content used in the following research was no more than 1%.In order to prepare Lyocell fiber with high performance, the SWNTs/Lyocell composite fibers with different SWNTs content were prepared by increasing the DP of cellulose pulp, using a multi-filaments spinning device with metering pump and a finer spinneret with smaller diameter spinning SWNTs/Lyocell fiber The structure and properties of SWNTs/Lyocell composite fibers were characterized with WAXD, two dimentional X-ray diffraction, tensile meter and SAXS. The results showed that when the SWNTs content was no more than 1% and the draw ratio was same, with the increasing of SWNTs content, the crystallinity and crystal orientation factor of SWNTs/Lyocell composite fiber were increased, the average micropore size was decreased, and then mechanical properties of fibers were improved. Moreover, at the same S WNTs content, with the increasing of draw ratio, the crystallinity and crystal orientation factor of SWNTs/Lyocell composite fiber were also increased, and average micropore size was decreased, and the mechanical properties of fibers was also improved. In addition, the optimum heat treatment conditions were determined for the never dried as-spun SWNTs/Lyocell composite fiber through the orthogonal test method. After the heat treatment, the mechanical properties of SWNTs/Lyocell composite fiber were improved significantly. Compared with Lyocell fiber without heat treatment, the tensile strength and initial modulus of 1%SWNTs/Lyocell composite fiber were increased by 14.0% and 58.4%, respectively.