Structural changes of regenerated cellulose dissolved in FeTNa,NaOH/thiourea,and NMMO systems

Regenerated cellulose was prepared from microcrystalline cellulose (MCC) via dissolution in three well‐known nonderivatizing systems: ferric chloride/sodium tartarate/sodium hydroxide (FeTNa), sodium hydroxide/thiourea (NaOH/thiourea), and N‐methylmorpholine‐N‐oxide (NMMO) systems. The effect of regeneration using the different systems on the supramolecular structure of the regenerated celluloses was studied using X‐ray diffraction and Fourier transform infrared (FTIR). The effect of regeneration on supermolecular structure, morphology, and thermal stability of regenerated celluloses were studied using scanning electron microscopy (SEM) and thermogravimetric analysis (TGA). The effect of regeneration systems used on the chemical reactivity of cellulose toward carboxymethylation, acetylation, and cyanoethylation reactions was briefly studied. The results showed dependence of all the aforementioned properties on the dissolution reagent used in spite of that all studied reagents cause the same change in cellulose crystalline structure (from cellulose I to cellulose II). The degree of polymerization, crystallinity, and thermal stability of the regenerated cellulose (RC) samples were in the following order: NaOH/thiourea RC > FeTNa RC > NMMO RC. SEM micrograph showed unique surface for the NMMO RC sample. The reactivity of the different regenerated cellulose samples toward carboxymethylation, cyanoethylation, and acetylation depended mainly on the reaction system and conditions used rather than on crystallinity of regenerated cellulose. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Investigations in modified alkaline iron-tartrate complex solvent for cellulose

A simple method of preparing a stable alkaline iron-tartrate complex solvent (FeTNa (NaCl)) solvent starting from anhydrous ferric chloride was developed. The solvent having the composition: 300 g/l complex, 2N free alkali and 37.5 g/l sodium tartrate as stabiliser, dissolves cotton samples of a high degree of polymerization under higher ambient temperature conditions like those in India. In contrast to solutions in other solvents, cellulose solutions in FeTNa (NaCl) solvents are practically non-sensitive to air exposure. Intrinsic viscosity values were determined for a large number of cellulosic samples. The influence of the viscosity gradient on several viscosity functions was found to be of the same order as in other FeTNa solvents of similar compositions. Fractional precipitation of cellulose dissolved in this solvent was investigated by adding different quantities of aqueous solutions of mannitol.     

溶解纤维素的溶剂体系研究进展

介绍了溶解纤维素的有机溶剂体系和水溶剂体系,比较了各种溶剂的溶解机理和特点,重点阐述了N-甲基氧化吗啉(NMMO)和以碱金属氢氧化物为基础的溶剂体系,并简单介绍纤维素溶液的利用。     

纤维素溶剂的研究进展

简要介绍了两种传统纤维素溶解方法:粘胶法和铜氨法,对目前研究较多的几种纤维素新溶剂体系,例如:离子液体体系、N-甲基吗啉-N-氧化物、氢氧化钠/溶胀剂等进行了详细的介绍,指出了不同溶剂体系的溶解机理和优缺点,认为未来纤维素溶解技术必将趋于绿色无污染化。     

Crystallinity and heats of crystallization of cellulose: A microcalorimetric investigation

We have used a sensitive adiabatic microcalorimeter to study cellulose dissolution in its metal complex solvents cadoxen and ferric sodium tartrate (FeTNa). Heats of crystallization of cellulose I and II have thereby been estimated and range from ?4.07 kcal/mol to ?5.43 kcal/mol. A solvent-dependent heat of reaction factor has been invoked to explain differences in the heats of crystallization obtained by the two solvents. Conversion of cellulose I to cellulose II is an exothermic process with an enthalpy change of about ?6.0 cal/g cellulose. The crystallinities of various cellulose samples have been determined using these thermodynamic data and have been found to be generally consistent with values given by more traditional means.     

Viskosimetrische bestimmung des polymerisationsgrades von oxycellulose mit hilfe der EWNN-methode

To determine the limiting viscosity number [η] of nitrous oxidized cellulose in diluted solution, the iron tartrate complex method (FeTNa) was used. Existing methods of the [η]-values calculation using polynomials for various types of polymers and various solvent measuring systems and also the polynomial for pure cellulose have been shown to be inapplicable. Therefore, an empirical calculation formula in explicit form with A₁ = ?2.348, A₂ = 3.485 and A₃ = 0.006 (η_sp: specific viscosity, c: concentration g/100 ml) has been suggested enabling calculation of the [η]-value of oxidized cellulose from a measurement of a single concentration of the sample. For the calculation of the average polymerization degree according to the Staudinger-Mark-Houwink equation it was possible to apply the same constant in case of oxidized cellulose as available for unoxidized one.     

Thermal properties of cellulose triacetate as prepared from low-grade dissolving pulp

Because cellulose triacetate is prepared from low-grade dissolving pulp, a considerable amount of the insoluble residue was present in the acetylation medium of the acetic acid/acetic anhydride/sulfuric acid system. To reduce the insoluble residues, a solvent, such as nitromethane, nitroethane, or dichloroacetic acid, added to the acetylation medium was found to be very effective for its reduction. By exploring the optimum conditions for acetylation with these solvents, nitromethane added and dichloroacetic acid added systems with solvent/acetic acid = 3/7 (v/v) were found to have a particularly high transmittance at λ = 670 nm in their acetylation solution with a low insoluble residue. The obtained acetates revealed good thermal properties similar to that from high-grade dissolving pulps. Therefore, a high quality cellulose triacetate can be manufactured from acetylation systems with even low-grade dissolving pulps with an appropriate solvent added. © 1996 John Wiley & Sons, Inc.     

不同溶解方法制备的纤维素/[BMIM]Cl纺丝液的性能比较

以离子液体1-丁基-3-甲基咪唑氯盐([BMIM]Cl)为溶剂,分别采用直接溶解法和间接溶解法(即在含水[BMIM]Cl中溶胀后再减压蒸馏去除多余的水使之溶解)制备了纤维素/[BMIM]Cl纺丝液,系统地比较了这两种纺丝液的流变行为及可纺性。结果表明:相同条件下,直接溶解法制备的纤维素/[BMIM]Cl纺丝液的表观黏度最大,而间接溶解法制得的纺丝液的表观黏度随着溶胀时[BMIM]Cl的初始含水率的增加而下降。与直接溶解法相比,间接溶解法制得的纺丝液溶解均匀、流动性能好、纺丝过程中断头次数少、可纺性能提高,所得到的再生纤维素纤维具有更好的力学性能。     

A new process for dissolution of cellulose in ionic liquids

A new dissolving process (two‐step dissolving process), that is, cellulose was first swelled to the maximum in aqueous 1‐butyl‐3‐methylimidazolium chloride ([BMIM]Cl) solution, and then dissolved by stirring under vacuum to remove excessive water, was developed to prepare the cellulose/[BMIM]Cl spinning dope with high quality. The results showed that the initial water contents in [BMIM]Cl have great influence on the swelling and dissolution of cellulose, and the suitable swelling range of aqueous [BMIM]Cl solution, in which cellulose can be swollen but not dissolved, was 2–5% water content. In this range, the higher water content in aqueous [BMIM]Cl solution, the more swelling time would be taken for cellulose to reach the maximal swelling ratio. Based on these results, cellulose/[BMIM]Cl spinning dopes were prepared by using two‐step dissolving process. In the range of our experiments, cellulose spinning dopes prepared by the two‐step dissolving process had better properties, such as fewer particles, lower apparent viscosity, and higher uniformity, compared with the direct dissolving process. By using this new dissolving process, the spinning performance of cellulose/[BMIM]Cl dopes was improved, and the mechanical properties of regenerated cellulose fibers were better than those prepared by the direct dissolving process. Therefore, it is a good way to prepare cellulose/[BMIM]Cl spinning dopes by using the new dissolving process. POLYM. ENG. SCI., 2012. © 2012 Society of Plastics Engineers     

Cellulosic nanocomposites. I. Thermally deformable cellulose hexanoates from heterogeneous reaction

Partially derivatized cellulose esters were prepared from dissolving‐grade wood pulp fibers by reaction with a mixed p‐toluene sulfonic/hexanoic anhydride system in a nonswelling (cyclohexane‐based) reaction medium. The partially derivatized pulp fibers, which failed to undergo a significant change in shape or appearance during the modification, proved to be resistant to swelling (in water), were thermally deformable, and retained their biodegradability. Because X‐ray diffractometry provided evidence for the presence of unsubstituted, ordered cellulose with cellulose I morphology, the thermally reshaped and consolidated sheets were found to consist of commingled mixtures of cellulose esters and cellulose I. The transparent or semitransparent consolidated sheets (depending on the degree of substitution) were found to represent composites in which cellulose I serves as a discontinuous inclusion that reinforces a continuous, partially ordered cellulose ester matrix. The composites, which revealed cohesive or adhesive failure at rupture, depending on the degree of substitution, had modulus values and tensile strengths as high as 1.3 GPa and 25 MPa, respectively. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 2242–2253, 2000     

Significance of the intrinsic viscosity ratio of unsubstituted and nitrated cellulose in different solvents

It has been studied the intrinsic viscosity ratios of cellulose solutions in different solvents and of the corresponding nitrates dissolved in aceton using cellulose samples from different origins and with different degrees of polymerization. The results demonstrate that with FeTNa and CdEn as solvents, molecular dispersed solutions are only produced with cellulose having a DP≤3000. FeTNa is limited to cotton cellulose only. Contrary to this, the intrinsic viscosity ratio [η]/[η] shows independence from the range of degree of polymerization and the origin of cellulose, confirming thus once more the polymeranalogous course of nitration. Its value referred to a degree of substitution S = 2.90±0.02, to absolute dry and pure cellulose and to standardized viscosity measurements amounts [η]_Ac/[η]_CuEn = 1.95±0.05. Determination of the intrinsic viscosity ratio permits, therefore, to obtain information in respect of the polymeranalogous and homogeneous character of the cellulose nitrate, and, in connection with determinations of yield of nitration, in respect of the purity of the corresponding unsubstituted cellulose. Basing on the constant value of the intrinsic viscosity ratio [η]_Ac/[η]_CuEn, and using the quotients [η]_FeTNa/[η]_CuEn and [η]_CdEn/[η]_CuEn, there has been derived the [η]-DP-relationships for unsubstituted cellulose in the respective solvents.     

棉纤维在LiCl/DMAc极性溶液中的溶解性能研究

采用不同方法将棉纤维活化并溶解在LiCl/DMAc极性溶液中,研究了活化方法、溶解温度、时间及LiCl浓度对棉纤维素溶解性的影响。结果表明:DMAc热活化法为较好的活化方法;提高溶解温度,延长溶解时间及提高LiCl浓度均有利于棉纤维溶解;棉纤维在LiCl质量分数为12%的LiCl/DMAc溶液中,150℃下搅拌4h,溶解度可达3%。碱活化法使棉纤维素聚合度大幅度降低,可提高棉纤维溶解度至8%。通过扫描电镜和X射线衍射方法研究了棉纤维在前处理和溶解过程中的形态和结构变化,初步揭示了纤维素高温处理后在低温下发生溶解的机理。     

粘胶纤维和Lyocell纤维生产中溶解机理的探讨

溶解技术是纤维素纤维制造过程中关键的技术，溶解的效果直接影响过滤、纺丝成形和最终产品的质量。纤维素溶解的详细机理非常复杂，但基本上都可以从分子间氢键的破坏方面得到解释，本文着重就粘胶纤维和Lyoeell纤维生产中纤维素不同的溶解过程和溶解机理作了初步探讨。     

天然纤维素的溶解技术及其进展

本文系统介绍了近年来天然纤维素的溶解技术及其进展。内容包括天然纤维素的制备与分离、天然纤维素的溶解机理及所用的溶剂、天然纤维素溶解技术的发展趋势等。     

Some aspects of increasing the efficiency of the dissolving process in viscose preparation

Conclusions It is possible to considerably reduce the consumptiom of cooling energy in the dissolution stage (by 1.2 GJ/metric ton) and to raise the quality indices of viscose if it is prepared in continuous apparatus.Industrial testing of the method of dissolving cellulose xanthate at high shear velocity gradients has demonstrated the possibility of shortening the process time from 4 to 1.5–2 h.Translated from Khimicheskie Volokna, No. 6, pp. 18–19, November–December, 1989.     

Structural changes of cellulose,wood, and paper under shear deformation and high pressure

Structural changes of wood and its components have been studied after shear deformation under high pressure (SDHP) at up to 6 GPa. Cellulose amorphization and chain depolymerization was observed. Approximately 30% of microcrystalline cellulose was soluble in water after a 360-degree twist of the Bridgman anvils. The water-insoluble part was re-crystallized into cellulose II lattice. Repeated treatment applied to the nondissolved part of the sample, the so-called cascade experiment, permits the dissolving of about 30% of the residual nondissolved material once again. Extraction with water, followed by 10% sodium hydroxide, allows almost complete dissolving of microcrystalline cellulose (98%). Water-soluble saccharides were studied by HPLC and ¹³C NMR. It was found that destruction of the wood lignin network needs more severe treatment conditions than cellulose destruction does. Lignin domains in wood act as “grinding stones” during cellulose destruction. Long-living lignin free radicals have been detected with EPR after SDHP. ¹³C NMR CP/MAS spin diffusion studies showed that SDHP leads to separation of wood components into different biopolymer domains, which turns the system toward thermo-dynamic equilibrium. SDHP does not permit achievement of initial compulsary compatibility of components in native wood. SDHP technique appears as a promising method for wood delignification and carbohydrate saccharification in the solid state without using harmful chemical reagents of solvents, which is important for technological safety and ecology. © 1994 John Wiley & Sons, Inc.     

超声波处理对纤维素碱脲体系溶解性能的影响

采用碱／尿素／水体系、碱／尿素／硫脲／水体系分别制备纤维素溶液,在溶解的不同阶段用超声波进行处理,并利用光学显微镜、偏光显微镜和X射线衍射对溶解效果进行表征。研究结果表明：溶解之前对纤维素原料的超声波处理主要是对纤维形态结构和超分子结构的破坏,略微增大溶解度;溶解过程中对纤维素溶液超声波处理则可以强化润胀,促进分散,显著增大纤维素的溶解度;在碱／尿素／水体系中超声波对溶解的促进作用强于在碱／尿素／硫脲,水体系中。     

TAC光学薄膜棉胶制备工艺技术研究——搅拌工艺对棉胶溶液溶解质量的影响

作为液晶显示光学用TAC薄膜,与TAC感光片基相比,对表观点状缺陷的控制标准由毫米级升至微米级,数量控制标准也更为严格.而解决这一问题的关键是提高棉胶溶液中三醋酸纤维素的溶解质量,而三醋酸纤维素溶解质量的好坏受很多种因素的影响.在诸多因素中,搅拌作为物料混合的一种动力,能促进溶剂分子间与高分子物质的相互接触渗透,加大彼此的相互作用力,在提高棉胶液溶解质量方面起着不可替代的作用.本文通过精心的实验设计,探讨了搅拌动力及搅拌方式在棉胶溶液制备过程中对溶解质量的影响,并确立了可量化的棉胶溶解质量评价方法,显著改善了棉胶溶液的溶解质量.     

In situ X-ray scattering investigations of solutions of cellulose in N-methylmorpholine-N-oxide during shear flow

There are conflicting reports that concentrated solutions of cellulose in N-methylmorpholine-N-oxide (MMNO) exhibit liquid crystal structures as is the case for many cellulose derivatives. We have prepared cellulose/MMNO solutions using two different approaches with compositions in the range 9 to 34% w/w. We have subjected these solutions to in situ X-ray scattering studies during shear flow. Such solutions do not develop any significant level of preferred orientation during shear flow. Such zero macroscopic orientation contrasts with the behaviour of related lyotropic liquid crystal polymers based on cellulose derivatives and with other liquid crystal polymer systems, for which, in all cases, a substantial level of preferred orientation develops during shear flow. We conclude that the range of cellulose/MMNO solutions studied here do not exhibit liquid crystal phases.     

反应挤出原位制备纤维素马来酸酯

以离子液体1-丁基-3-甲基咪唑氯盐([Bmim]C)l作反应介质,采用马来酸酐对纤维素进行原位化学改性。利用双螺杆挤出机的剪切作用来提高纤维素在[Bmim]Cl中的溶解效率,并促进马来酸酐与纤维素的酯化反应。红外光谱(FTIR)结果证明了纤维素马来酸酯的生成,导致纤维素的氢键网络结构破坏,同时也破坏了纤维素的规整度,降低了纤维素的结晶度。热重分析(TGA)结果显示:马来酸酐支链阻碍了纤维素主链的运动,使改性纤维素的热稳定性明显高于未改性纤维素。当马来酸酐与纤维素质量比为0.8、螺杆转速为50 r/min时,改性纤维素在[Bmim]Cl中的溶解度达到20%,是未改性纤维素溶解度的2倍。