| Ionic liquids are called room temperature ionic liquids or room temperature molten salts. They are composed by organic cations and inorganic anions and show a liquid state at room temperature or near room temperature. Ionic liquids have many good properties such as wide liquid path, stable in water and air, good dissolving property, no-volatile and easy to recycle and others, which are regarded as green solvents and used more and more in polymer processing. Imidazole ionic liquids have good dissolving ability of cellulose and attract more and more attention.Up to now, researches of ionic liquids as cellulose solvents are just beginning. There are no detail studies about the regenerated cellulose fibers which were made by using ionic liquids as solvent at home and aboard. For this reason, the different limidazole ionic liquids and cellulose pulps were used to prepare ionic liquids/cellulose solutions and their rheological behaviors were studied. The influence of ionic liquids, cellulose pulps, the spinning parameters and different dissolving processes on the structure and properties of the regenerated cellulose fiber were also studied. A novel cellulose fiber using small-size industrial spinning equipments was finally made. To extend the application range of the novel cellulose fiber, the CNTs/cellulose composite fiber was successful prepared.Two of popular ionic liquids, 1-butyl-3-methylimidazolium chloride ([BMIM]Cl) and the 1-ethyl-3- methylimidazolium acetate ([EMIM]Ac) were chosen as cellulose solvents in this paper. The dissolving process of cellulose pulps in these two ionic liquids was observed using a polarizing microscopy with CCD and a heating stage. The rheological properties of the cellulose solutions were studied by HAAKE rheometer. The degradation of cellulose in ionic liquids was studied by Waters GPC (gel permeation chromatography). The structure and properties of regenerated cellulose fiber made by different ionic liquids were compared. The results showed that [BMIM]Cl and [EMIM]Ac were two direct solvents for cellulose at certain condition. Compared with [BMIM]Cl, the dissolving temperature of [EMIM]Ac was lower. At the same dissolving temperature, the dissolving rate of cellulose in [EMIM]Ac was faster than that in [BMIM]Cl. The dissolving temperatures of cellulose in [BMIM]Cl and [EMIM]Ac were set at 90℃and 60℃respectively for their similar dissolving rate of cellulose at these temperatures. Based on their rheological behaviors, the spinning temperatures of cellulose/[BMIM]Cl and [EMIM]Ac were fixed at 90℃and 60℃respectively because of their similar flow curves at these temperatures. Cellulose degradation happened in the process of cellulose fiber by using [BMIM]Cl and [EMIM]Ac as solvent. Compared with [BMIM]Cl, the degradation of cellulose in [EMIM]Ac was smaller. At the same drawing speed, the regenerated cellulose fiber from [BMIM]Cl had higher crystallinity, crystalline orientation, amorphous orientation and better mechanical properties than that from [EMIM]Ac, which was due to the higher extensional viscosity of cellulose/[BMIM]Cl solution than that of cellulose/[EMIM]Ac solution at the air gap during spinning process.Based on the former analysis, 1-butyl-3-methylimidazolium chloride ([BMIM]Cl) was chosen as cellulose solvent for the following study. To study the influence of cellulose pulps on the properties of cellulose fiber using ionic liquid as solvent, five cellulose pulps with different properties were selected in this paper. The dissolving characteristics of cellulose pulp in ionic liquid and the rheological behavior of cellulose/ionic liquid were studied. The results showed that the higher relative molecular weight and a-cellulose content of cellulose pulp, the more dependence of dissolving rate on temperature and the higher of the elastic modulus and the activation energy of the cellulose solution. Also, the critical shear rate was decreased and the tendency of shear thinning became more apparent with cellulose/ionic liquid solution prepared by higher relative molecular weight and a-cellulose content of cellulose pulp. Therefore, the parameters for dissolution and spinning, such as temperature and so on, should be controlled strictly when the cellulose pulp having a higher relative molecular weight and a-cellulose content was used to prepare cellulose fiber using ionic liquids as solvent. Compared with a-cellulose content, the relative molecular weight of cellulose pulp had more influence on the spinning performance of cellulose solution. The higher the relative molecular weight was, the worse spinning performance would be. When the a-cellulose content in cellulose pulps was similar, the spinnability of cellulose solution would be better with the decreasing of the relative molecular weight of cellulose pulp in our study. The mechanical properties of cellulose fiber would be improved with the higher relative molecular weight and a-cellulose content cellulose pulp. Compared with a-cellulose content, the relative molecular weight played a more important role in the mechanical properties of cellulose fiber. Considered the influence of cellulose pulp on the dissolving in ionic liquid, the rheological behavior, the spinning performance and the mechanical properties of cellulose fibers, cellulose pulp with modulate relative molecular weight and high a-cellulose content would be selected as sample pulp to prepare cellulose fiber using ionic liquid as solvent.In this thesis, the influence of process parameters such as gap length, jet draw ratio, coagulation temperature and coagulation bath concentration on the properties of cellulose fiber were also studied and the effect of each parameters was investigated using orthogonal experiment. Cellulose fiber was prepared with the optimal process parameter on the small-size industrial spinning equipment. The fibrillation and dyeing properties of cellulose fiber with ionic liquid as solvent were compared with Lyocell. The results showed that with the increasing of air gap length, the temperature and the concentration of coagulation bath, the tensile strength and the initial modulus of cellulose fiber using ionic liquid as solvent firstly increased and then decreased. The tensile strength and initial modulus of cellulose fiber increased with increasing the jet draw ratio. The orthogonal experiment results showed that the tensile strength and the initial modulus of cellulose fiber were apparently influenced by coagulation temperature and jet draw ratio. The breaking elongation of cellulose fiber was apparently influenced by the length of air gap. It was found that there were obvious fibrillations on cellulose fiber using ionic liquid as solvent in the wet-abrasion and ultrasonic vibration test. The anti-fibrillation property of cellulose fiber using ionic liquid as solvent was similar with Lyocell. The dying behavior showed that cellulose fiber using ionic liquids as solvent had good dying property with the reactive dye. Comared with Lyocell, the results showed that the dye exhaustion and dye fixing of cellulose fiber using ionic liquid as solvent were similar with Lyocell but the K/S value of the Lyocell was smaller.It was found there were many undissolving particles and gels in the cellulose/ionic liquid spinning solution with the direct dissolving process, which decreased the spinning performance and efficiency. To improve the spinning performance and prepare completely dissolved, more even cellulose spinning solution, a new dissolving process (firstly completely swelling and then dissolving) in ionic liquid was developed in this paper. The rheological properties of cellulose solutions from different dissolving process were investigated by HAAKE rheometer. The results showed that when the water contents in ionic liquid was less than 1%, cellulose fibril dissolved directly in [BMIM]Cl by disintegrating into rod-like fragments. In [BMIM]Cl contained 2-5% water, cellulose fibril exhibited a apparently and homogeneous swelling, whereas the fibril couldn’t be dissolved in this kind of [BMIM]Cl aqueous solution. With more water content in ionic liquid (6%-20%), no obvious swelling and dissolving phenomena were observed on the fibril. In [BMIM]Cl containing 2-5% water, the maximum swelling ratio of cellulose fibril decreased with increasing the water content at the same temperature. Time for cellulose fibril to reach the maximum swelling ratio decreased with the increasing of temperature at the same water content. Cellulose/[BMIM]Cl spinning solution with even, good flow property, good spinnability and good mechanical properties of cellulose fiber could be prepared by first completely swelling and then dissolving process than that made by direct dissolving process.To extend the application of cellulose fiber using ionic liquid as solvent, CNTs/cellulose composite fiber was prepared with treated carbon nanotubes. Firstly, the different treatment methods for carbon nanotubes were investigated and then the influence of the concentration of CNTs on the structure and properties of CNTs/cellulose composited fiber was studied. CNTs/cellulose composite fiber was successful made by small-size industrial spinning equipments. The result showed that the CNTs would have good dispersion in ionic liquid with the methods of CNTs purified with nitric acid, functional modified with SDBS (sodium dodecyl benzene sulfonate) and grinded with ionic liquid. The spinning performance of CNTs/cellulose/ionic liquid solution was not good with high CNTs concentration. CNTs/cellulose composite fiber with good mechanical properties could be prepared with 1% CNTs content. The adding of CNTs in cellulose fiber decreased its volume resistivity and improved its electrical conductivity. The volume resistivity of CNTs/cellulose fiber stepped across antistatic range to semiconductor range with adding of CNTs to certain extence. The tensile strength, the initial modulus and the decomposition temperature of lwt% MWCNTs/cellulose composite fiber have been increased by respectively 39.3%,21.2% and 12.1℃compared to the pure regenerated cellulose fibers made on the small-size industrial spinning equipments. At the same spinning condition the tensile strength, the initial modulus and the decomposition temperature of 1wt% SWCNTs/cellulose composite fibers were improved by 61.3%, 37.2,18.5℃respectively.In conclusion, regenerated cellulose fiber with good properties could be made using imidazole-based ionic liquids 1-butyl-3-methylimidazolium chloride ([BMIM]Cl) as cellulose solvent, selected cellulose pulp with modulate relative molecular weight and highα-cellulose content, using optimal spinning parameter and first swelling and then dissolving process. In addition, CNTs/cellulose composite fiber with good mechanical, electrical and thermal stable properties could be made using ionic liquid as cellulose solvent, which has a bright future in industry application. |
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