纤维素性质对纤维素溶液可纺性以及纤维性能的影响?

采用热台偏光显微镜跟踪观察了不同纤维素浆粕在N-甲基吗啉-N-氧化物一水合物(NMMO·H_2O)中的溶解过程,并利用哈克旋转流变仪分析了其溶液的流变性能。研究结果发现:纤维素的聚合度越高,温度对纤维素的溶解过程影响越大;相同纤维素浓度下,随着纤维素的聚合度的增加,溶液的结构粘度指数(△_η)、粘流活化能(E_η)以及弹性增大,即溶液可纺性下降,粘度对温度更加敏感。在此基础上,进一步探讨了纤维素性质对纤维性能的影响,结果表明Lyocell纤维的力学性能随纤维素聚合度以及纺丝液浓度的提高而提高,可纺浓度随聚合度的提高而下降。     

纤维素在N-甲基吗啉-N-氧化物/水溶液中的溶胀与溶解性能

研究了纤维素在N-甲基吗啉-N-氧化物(NMMO)/水体系中的溶胀、溶解过程对纤维素溶液性能的影响,为纤维素在NMMO/水体系中纺丝成形提供理论依据.利用X-射线衍射(XRD)探索了纤维素溶胀后的结晶结构变化,利用旋转流变仪探讨了纤维素浓度、聚合度等对纤维素溶液流变性能的影响.结果表明:经溶胀后的纤维素,非晶区被部分破坏,使其结晶度下降,从而更易被均匀、快速地溶解;纤维素的聚合度越大,含量越高,其大分子链的解缠及伸展越困难,分子间作用越大,纤维素溶液的流动性越差,越不利于纤维素的纺丝成形.     

纤维素/NMMO·H_2O溶液体系流变性能的研究

利用 Brookfield DV-Ⅱ型粘度计对纤维素/NMMO·H2O 溶液体系的流变性能进行了研究,讨论了温度、纤维素浓度、浆粕聚合度及添加剂等对溶液粘度的影响。结果表明,纤维素/NMMO·H2O 溶液的流动活化能较低,因此其表观粘度随温度的变化不大;纤维素浓度和浆粕聚合度的增加都可使溶液粘度增大,但纤维素浓度对溶液粘度的影响更显著;抗氧化剂没食子酸丙酯(GPE)的加入减缓了加热时溶液粘度的下降,降低了纤维素的氧化降解;二甲亚砜(DMSO)的加入可有效地控制溶液粘度,改善溶液的加工性能。     

竹纤维素/NMMO·H_2O溶液流变性能的研究

采用HAAKE RS150L型旋转流变仪对竹纤维素/NMMO.H2O溶液的流变性能进行了研究。结果表明,竹纤维素/NMMO.H2O溶液为切力变稀流体;随着竹浆粕平均聚合度的增大,溶液的非牛顿指数n减小,而溶液表观黏度η、稠度系数K、黏流活化能Eη和结构黏度指数Δη增加;随着温度的升高,溶液的表观黏度下降,非牛顿指数增大;碱处理竹纤维素/NMMO.H2O溶液的流变性能受竹纤维素原料的聚合度、α-纤维素含量(或半纤维素含量)及杂质含量等因素的综合影响。     

纤维素浆粕性质对其在NMMO溶液中的溶胀性能的影响

将4种聚合度及α-纤维素含量不同的纤维素浆粕在85℃下分别溶解于质量分数为74%,78%,80%的N-甲基吗啉-N-氧化物(NMMO)溶液中,研究了纤维素浆粕性质对其在NMMO溶液中的溶胀性能的影响。结果表明:纤维素浆粕的结晶度越高、聚合度越大、α-纤维素含量越高,溶胀效果越差;在相同实验条件下,浆粕的疏松性对其溶胀效果影响很大,浆粕越疏松,其溶胀效果越好;溶胀过程不会改变纤维素的晶型,但会使纤维素结晶度有所下降;聚合度适中、结晶度较低,疏松的纤维素浆粕适宜作为Lyocell纤维的原料。     

纤维素在多聚磷酸中的液晶性

讨论了纤维素在多聚磷酸溶液中的溶解情况和液晶性。采用适当的配比,纤维素能够溶解于多聚磷酸并形成各向异性溶液,在偏振光显微镜下可观察到彩色图片。溶液温度、纤维素聚合度、纤维素浓度对液晶性均有影响。溶液受热后,彩色图像会消失。     

纤维素氨基甲酸酯溶液的制备及稳定性研究

研究了制备纤维素纤维的新型原料——纤维素氨基甲酸酯(CC)溶液的制备工艺及其稳定性。结果表明:在-5~10℃条件下,用聚合度为350~612的纤维素浆粕(棉浆粕、木浆粕)合成的氮含量(酯化度)为2.34%~3.56%的CC能很好地溶解在质量百分比浓度为8%~11%的NaOH溶液中,形成淡黄色透明溶液,该溶液稳定性良好,可用于纺丝。另外,尿素、AlCl3及ZnCl2在一定范围内对CC有助溶作用。     

纤维素-强碱溶液体系的研究

以富含纤维素95％的亚硫酸盐木浆板为原料、氢氧化钠溶液为溶剂，通过纤维素-强碱溶液体系粘度的变化．对纤维素在强碱液中的溶解情况进行了分析，指出：聚合度低于500的纤维素可溶解在低温碱液中．氧化锌的加入中有助提高碱液的溶解能力。     

尿素嵌入法制备纤维素氨基甲酸酯的研究

探讨了尿素嵌入法制备纤维素氨基甲酸酯(CC)的生产工艺。指出:选用聚合度为450~625、α-纤维素含量大于90/的纤维素浆粕,用14/~16/的氢氧化钠溶液,于40~50℃条件下活化处理30~40min后,与尿素以1∶2~3的比例混合,在137℃的二甲苯体系中反应2~3h,便可得到含氮量为2.4/~3.5/的纤维素氨基甲酸酯产物。该产物在氢氧化钠溶液中可形成良好的稳定溶液,过滤性好,可直接用于纺丝。     

甘蔗渣微晶纤维素特性及其对可得然胶溶液流变特性的影响

为丰富甘蔗渣的综合利用,提高综合产业价值,采用酸解法制备甘蔗渣微晶纤维素,分析甘蔗渣微晶纤维素理化性质及结构,构建甘蔗渣微晶纤维素/可得然胶混合液体系,研究甘蔗渣微晶纤维素对可得然胶溶液流变特性的影响。结果表明,甘蔗渣微晶纤维素聚合度为143,持水力7.55,直径约为10μm,熔融温度为169.5℃,FTIR、XRD分析表明其保留了纤维素基本化学结构。甘蔗渣微晶纤维素能增强可得然胶溶液,在扫描范围内,G′>G″,其流变表现为典型的弱凝胶特性,表明甘蔗渣微晶纤维素在可得然胶溶液中分散性良好,有助于增强溶液体系网络结构,溶液稳定性良好。     

Solubility of bacterial cellulose and its structural properties

Based on experiments conducted, it has been found that bacterial cellulose, like spruce cellulose, is soluble in an aqueous NaOH solution with the concentration of 8.5% at a temperature of −5°C if the polymerization degree of the cellulose does not exceed 400. When 1% of urea is added to the NaOH solution, the solubility of cellulose increases; and, in this solvent, bacterial cellulose may be dissolved so long as its polymerization degree is below 560. The results of these experiments are of great practical importance since they point to the possibility of the preparation of cellulose spinning solutions suitable for fiber formation. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 67:1871–1876, 1998     

Graft copolymerization of vinyl monomers on modified cottons,XXI. Cu++/hydrazine hydrate redox system induced grafting of methyl methacrylate on periodate oxidized cellulose

Periodate oxidized cellulose was grafted with methyl methacrylate using hydrazine hydrate in presence and absence of Cu⁺⁺. The grafting reaction was favoured in presence of Cu⁺⁺ and it was advantageous to treat first the cellulose material with copper sulphate solution rather than to incorporate it in the polymerization system. The graft yields depended upon the concentrations of copper sulphate and hydrazine hydrate, pH, temperature, and time of polymerization as well as degree of oxidation of cellulose. There were optimal concentrations of copper sulphate (6–8 mmol/l) and hydrazine hydrate (2 mmol/l). A polymerization medium of pH 6 and a temperature of 60°C constituted to optimal pH and temperature for grafting. Oxidized cellulose proved to be more amenable to grafting as compared with unoxidized cellulose and the magnitude of grafting relied on the degree of oxidation. A tentative mechanism was also suggested for grafting of cellulose substrates with a vinyl monomer using a Cu⁺⁺-hydrazine hydrate redox system.     

Effect of coagulation conditions on fine structure of regenerated cellulosic films made from cellulose/N-methylmorpholine-N-oxide/H2O systems

The important properties of cellulosic fibers in the conditioned state are mainly influenced by fine structure. In particular, the development of new methods of spinning regenerated cellulosic fibers made from a cellulose/N-methylmorpholine-N-oxide (NMMO)/H₂O system require a better understanding of their fine structures in order to explain their special physical properties. The regenerated cellulosic films were made from cellulose/NMMO/H₂O according to the degree of polymerization and solution concentration (wt %) of cellulose and the concentration (wt %) of NMMO in the coagulation bath. The quantification of crystal content was carried out by the resolution of the wide angle X-ray diffraction intensity distribution on the assumption that all diffracted intensities take the form of a symmetrical Gaussian distribution centering at its Bragg angle. The X-ray diffraction patterns resolved into individual integral intensities showed that the polymorphic structure mixed with part cellulose III and II was obtained for only coagulated cellulose films. The degree of crystallinity and apparent crystalline size of regenerated cellulosic films depended on the degree of polymerization, the solution concentration of cellulose, and the concentration of NMMO. The diameter of the microfibril decreased with an increase in the concentration of NMMO. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 2681–2690, 1999     

棉纤维蒸汽闪爆改性及其化学反应性能

研究采用高压热蒸汽闪爆技术,对棉纤维进行物理改性,并对闪爆前后棉纤维形态、溶解度、聚合度分析表征。通过改性前后棉纤维合成羧甲基纤维素研究发现,闪爆改性后其反应性能有大的提高。     

A method of determining high-molecular fractions in cellulose

Conclusions -- A method has been developed for determining the HMF in sulfate cellulose with a photocolorimetric determination of the weight proportion of individual fractions.-- The proposed method can be used for comparative characterization of the amount and degree of polymerization of the HMF in cellulose in plant laboratories.Translated from Khimicheskie Volokna, No. 2, pp. 56–57, March–April, 1993.     

Rapid acetylation of native cellulose by TFAA and characterization of the products

Acetylation of cellulose (Whatman cellulose powder CF-11 and Egyptian cotton fiber) by the use of the TFAA “impelling” method was examined, and the decrease in the degree of polymerization (DP) during the reaction was determined. Cellulose triacetate can be readily prepared by the TFAA method. When Whatman cellulose powder was used, the degradation of cellulose during acetylation was not observed in reaction times up to 5 hr, and a slight decrease in the degree of polymerization was detected in samples after reaction for more than 12 hr. The number of chain scissions per cellulose molecule for Egyptian cotton fiber was similar in magnitude to that for Whatman cellulose at the reaction time of 8 hr, but the value for Egyptian cotton fiber was considerably larger compared with that for Whatman cellulose after 12 hr.     

竹纤维素在NMMO中溶解再生前后的结构研究

以竹浆粕为原料、N-甲基吗啉-N-氧化物(NMMO)为溶剂,利用傅里叶红外光谱、X射线衍射、热重分析等着重研究了竹纤维素在NMMO中溶解前后结构的变化。研究发现:NMMO溶解纤维素过程属于物理过程,未发生衍生化反应,竹纤维素溶解后聚合度较溶解前有所降低,晶型由纤维素Ⅰ变成了纤维素Ⅱ;热重分析表明纤维素再生前后都具有较好的热稳定性。     

Heterogeneity in the system cellulose-N-methylmorpholine-N-oxide

Conclusions Data obtained by the turbidity spectrum method indicate a comparatively high heterogeneity of cellulose solutions in N-methylmorpholine-N-oxide monohydrate. The particle size of the disperse phase depends on the temperature-time regime of solution preparation.The concentration of the solution and the degree of polymerization of the cellulose exert an effect on the melting point of the cellulose-MMOMH system.Translated from Khimicheskie Volokna, No. 1, pp. 38–40, January–February, 1987.     

Preparation and Characterization of C10–C14 Alkyl Cellulose Ester Sulfate Surfactant

The aim of this work is to synthesize surfactants based on cellulose with different molecular weights. Raw cotton cellulose was tailored into cellulose segments with different molecular weights by a hydrothermal process, then the average degree of polymerization (DP) was determined by viscosimetry and the molecular weight distribution was estimated by gel permeation chromatography. The C₁₀–C₁₄ alkyl cellulose ester sulfate surfactants were prepared by hydrophilic sulfonation and hydrophobic esterification. The surface tension of the surfactants solution was obtained by the Wilhelmy plate method. Results showed that the cellulose segments presented a broader distribution compared with the raw material. The critical micelle concentration (CMC) value decreased from 1.08 to 0.86 wt% as the hydrophobic chain length was increased from 10 to 14. The CMC values of cellulose surfactants with C₁₄-acyl chloride hydrophobization decreased from 1.32 to 0.86 wt% as the DP was decreased from 2,700 to 296.