Synthesis Of Cellulose Carbamates And The Construction Of Novel Cellulose Materials

Nowadays, with the decreasing of fossil resources, increasing energy demands and worsening global warming, research and development of the renewable products from biomass resources have been one of the superior areas of polymer science. As a widely abundant renewable organic material, cellulose exhibits outstanding properties and various applications. However, viscose process has long been favored in the regenerated cellulose (RC) industry, although this process generates several environmentally hazardous byproducts including CS2, H2S, and heavy metals. Therefore, the development of environmentally friendly solvent and process is the key to the development of cellulose industry. CarbaCell process is a promising substitute for the traditional viscose process, and employs cellulose carbamate (CC) as active intermediate for fiber spinning. In comparison with the viscose process, the CarbaCell process has the advantage of a better ecological compatibility, and much of the conventional equipment of a viscose plant can be used without any problems. However, the CarbaCell process has not yet been established on the industry scale due to limitations presented by the catalyst, organic solvents and temperature in the synthesis stage. Moreover, the complete dissolution of CC requires complex pretreatment and an extended dissolution period. Here, we have demonstrated the utility of synthesis of CC with low content of urea. Novel cellulose fibers, membranes and cellulose based ZnO nanocomposite films were successfully prepared from CC in NaOH/ZnO aqueous solution.The novel creations of this work are as follows.1) CC was successfully syntheised from cellulose/urea mixtures with low content of urea through convential heating. The reaction conditions on the nitrogen content of CC were investigated, and the result showed that washed and unwased reaction products could well dissolved in NaOH/ZnO solutions.2) Novel cellulose fibers were successfully prepared from CC-NaOH/ZnO aqueous solutions via a pilot machine. Structure and physical properties of the fibers as a functional of post-processing spinning steps and drawing ratio were systematically studied.3) In order to demonstrate the utility of the microwave-assisted synthesis and the NaOH/ZnO solvent system, a cellulose-fiber fabrication process was developed on an industrial scale and the obtained cellulose multifilament exhibited excellent physiochemical properties.4) Regenerated cellulose membranes were prepared from CC-NaOH/ZnO solutions by coagulating with H2SO4 solution. The pore size, physical properties and water flux of the membranes as a function of the coagulation conditions were analyzed and discussed.5) The identities of CC-NaOH/ZnO solution were used to prepare cellulose based ZnO nanocomposite films through one-step coagulation, and the prepared nanocomposite possessed UV-blocking properties and antibacterial activitiesThe main contents and conclusions in this thesis are divided into the following parts. Firstly, CC was successfully prepared from cellulose/urea (CU) mixtures with low content of urea through conventional heating method. Urea content, reaction temperature and reaction time on the nitrogen content of the reacted CU (RCU) mixtures and CC were systematically investigated. The structure and solubility of RCU mixtures and CC were characterized with elemental analysis, FT-IR, XRD,13C NMR and solubility testing. The result indicated that the urea content of the mixture should be optimized between 3.4 and 4.6 wt% for enhancing the solubility of CCs. The reaction temperature and time were set a maximum of 170? and 2.0 h to avoid the carbonization and cross-linking of cellulose. CCs retained the cellulose I crystalline form, and the CI values and degree of polymerization hardly changed with the incorporation of carbamates. Especially, RCU mixtures without washing could be also well dissolved in NaOH/ZnO aqueous solutions and its solubility could reach 97%. Because of the low consumption of urea and no wastewater discharge, the economic and green process reported here would be particular beneficial for industrialization.Regenerated cellulose (RC) filaments were successfully spun from CC in a NaOH/ZnO solution through a freeze-thaw process on a pilot scale. Through SEM, FT-IR,13C NMR, XRD and 2D WAXD characterization methods, the effect of post-processing spinning steps and drawing ratio on the structure and properties of the RC filaments were investigated. The coagulation of CC transition was determined as a predominantly physical sol-gel process. The fibers exhibited cellulose II characteristics and displayed a circular cross section and homogeneous structure. Following washing, plasticizing and drying processes, the small voids on the surface of the fibers gradually disappeared, and showed a much denser structure. An increased drawing ratio provided improved tenacity and degree of orientation in the fibers, reaching 2.36 cN/dtex and 85%, respectively. Furthermore, RC filaments demonstrated excellent dye properties, and K/S values were determined in the range of 50-53 for the reactive blue dye.Based on the previous work, an industrialized wet-spinning test line with CC as an intermediate was built. The method included the microwave-assisted synthesis of CC, dissolution of CC in NaOH/ZnO solution, and wet fiber-spinning, which were characterized with FTIR, XRD,13C NMR, dynamic viscoelastic measurement, SEM and 2D WAXD. The result showed that CC samples with a nitrogen content of 1.042?1.785% could be successfully prepared from industrial urea via pilot microwave equipment. It was believed that the added ZnO was beneficial for the dismantlement of the intermolecular hydrogen bonds, enhancing the solubility and stability of CC-NaOH solution. As a result, the concentration of CC could be reached to 8-9 wt% as the degree of polymerization of CC was about 400. Moreover, the gelation temperature of CC solution could be raised significantly with adding of ZnO. Cellulose filaments were successfully spun from the spinning dope on an improved R535 viscose filament yarn spinning machine through an H2SO4/Na2SO4 coagulant bath. The filaments possessed a circular dense microstructure with a homogeneous structure. The tensile strength and elongation at break of the multifilament in dry state were 2.58 cN/dtex and 12.1%, respectively. Moreover, the chromaticity of the novel fibers was found superior to that of viscose rayon. The novel method was intentionally similar to the existing viscose system, therefore allowing for cost-effective implementation in industry. In particular, the total cost for producing a ton of novel cellulose filaments was estimated to save 15?20% when compared to the conventional viscose method.Regenerated cellulose (RC) membranes were prepared from CC-NaOH/ZnO solutions by coagulating with H2SO4 solution. Furthermore, the concentration of coagulant, coagulation temperature and coagulation time on the structure and properties of the membranes were investigated in detail. The results from XRD and elemental analysis revealed that the membranes displayed the cellulose ? crystalline and the nitrogen content of the membranes was in the range of 0.54-0.77%. The concentration of coagulant, and coagulation temperature had obvious influence on the formation of membranes pores, mechanical property and water permeability. However, the structure and properties of RC membranes hardly changed with the coagulation time. The apparent pore diameters 2re of the RC membranes in the free surface and inner section were in the range of 197?624 and 115?589 nm, respectively. The water permeability determined by flow rate method varied from 10.93 to 23.66 mL·h-1·m-2·mmHg-1, and was related well with 2re in the membrane. The RC membranes coagulated with 3 wt% H2SO4 at 10? for 10?15 min exhibited good tensile strength and elongation at break (?b= 120 MPa and ?b=15%).The identities of CC-NaOH/ZnO solution were used to prepare cellulose based ZnO nanocomposite (RCZ) films through one-step coagulation in Na2SO4 solutions. Structure, morphology and properties of the RCZ films were characterized using XRD, FTIR, XPS, SEM, TEM and antibacterial activity tests. With an increase of ZnO concentration from 0.4 to 1.6 wt% in the solvent, the ZnO content of the nanocomposites increased from 2.7 to 15.1 wt%. ZnO nanoparticles with the size of 15?19 nm agglomerated into large particles with the size of 1.0?2.4?m, which were firmly embedded in the cellulose matrix. The strong interactions occurred between ZnO particles and cellulose matrix in the RCZ films. The tensile strength and Young's modulus of RCZ films were enhanced with the incorporation of ZnO nanoparticles. RCZ films displayed good UV-blocking properties and high stability in neutral media. Particularly, RCZ films exhibited excellent antibacterial activities against E. coli and S. aureus. A dramatic reduction in viable bacteria was observed within 3 h of exposure and all of the bacteria were eliminated within 6 h.This thesis created a novel process for synthesis of CC, dissolution of CC, and wet-spinning of cellulose mulifilament, resolving a serious of scientific and technological problems from basic theory to industrial trial. In particular, on April 23, 2015, the project assessments with the theme of "Technology and apparatus for wet-fiber spinning of cellulose multifilament through a Carbamate mhthod" was held by China Textile Industry Association in Xiaogan, Hubei province. After investigation, inquiries and discussion, the expert group leading by Prof. Shicheng Jiang drew the conclusion that the overall technology had reached the international advanced level, in which technology of cellulose activation and dissolving had achieved international leading leve. Moreover, RC membranes with different pore structure and RCZ films exhibiting excellent antibacterial activities were successfully constructed via a simple approach. Therefore, we provided important scientific proofs to producing RC fibers through a novel cellulose carbamate process in industry, which would accelerate the upgrade and renovations of viscose industry. The topic of this thesis well accorded with the target of our country for a sustainable development, showing great scientific significance and prospects of applications.