Structure and properties of novel fibers spun from cellulose in NaOH/thiourea aqueous solution

Cellulose was dissolved rapidly in a NaOH/thiourea aqueous solution (9.5:4.5 in wt.-%) to prepare a transparent cellulose solution, which was employed, for the first time, to spin a new class of regenerated cellulose fibers by wet spinning. The structure and mechanical properties of the resulting cellulose fibers were characterized, and compared with those of commercially available viscose rayon, cuprammonium rayon and Lyocell fibers. The results from wide angle X-ray diffraction and CP/MAS 13C NMR indicated that the novel cellulose fibers have a structure typical for a family II cellulose and possessed relatively high degrees of crystallinity. Scanning electron microscopy (SEM) and optical microscopy images revealed that the cross-section of the fibers is circular, similar to natural silk. The new fibers have higher molecular weights and better mechanical properties than those of viscose rayon. This low-cost technology is simple, different from the polluting viscose process. The dissolution and regeneration of the cellulose in the NaOH/thiourea aqueous solutions were a physical process and a sol-gel transition rather than a chemical reaction, leading to the smoothness and luster of the fibers. This work provides a potential application in the field of functional fiber manufacturing.     

Novel Fibers Prepared from Cellulose in NaOH/Urea Aqueous Solution

Summary: Novel regenerated cellulose fibers have been successfully spun from the cellulose dope in NaOH/urea aqueous solution, which could rapidly dissolve cellulose. The fibers possess circular cross‐sections as well as relatively high molecular weight, and a crystallinity index with cellulose II family crystal structure, leading to good mechanical properties. This technology is simple, cheap, and environmentally friendly, promising to substitute for viscose rayon production having hazardous byproducts.

SEM micrograph of the cross‐section of the novel cellulose fibers generated here.     

Influence of finishing oil on structure and properties of multi-filament fibers from cellulose dope in NaOH/urea aqueous solution

Cellulose multi-filament fibers have been spun successfully on a pilot plant scale, from a cellulose dope in 7 wt% NaOH/12 wt% urea aqueous solution pre-cooled to −12 °C. Coagulation was accomplished in a bath with 10 wt% H₂SO₄/12 wt% Na₂SO₄ and then 5 wt% H₂SO₄ aqueous solution. By using different finishing oil, including H₂O, 4% glycerol aqueous solution, 2% polyvinyl alcohol (PVA) aqueous solution, 2% polyethylene glycol octyl phenylether (OP) aqueous solution, mobol and 2%glycerol/1%PVA/1%OP aqueous solution (PGO), we prepared six kinds of the cellulose multi-filaments, with tensile strength of 1.7–2.1 cN/dtex. Their structure and properties were investigated with scanning electron microscope (SEM), ¹³C NMR solid state, wide-angle X-ray diffraction (WAXD) and tensile testing. The cellulose fibers treated with PGO possessed higher mechanical properties and better surface structure than others. Interestingly, although the orientation of the cellulose multi-filaments is relatively low, the tensile strength of the single-fiber was similar to that of Lyocell. It was worth noting that the dyeability of the multi-filament fibers was superior to viscose rayon.     

Analysis of regenerated cellulose fibers with ionic liquids as a solvent as spinning speed is increased

In order to improve the spinning efficiency, the spinning experiments with cellulose/1-butyl-3-methylimidazolium chloride solution were done whilst increasing spinning speed. It was found that the tenacity and initial modulus of regenerated cellulose fibers increased but the elongation at break decreased slightly with increasing spinning speed at constant draw ratio. Further, the synchrotron wide-angle X-ray diffraction and small-angle X-ray scattering were carried out to illustrate the relationship between the structure and the mechanical properties. It was shown that the crystal orientation, crystallinity, amorphous orientation factor as well as orientation of the microvoids along the fiber increased with the spinning speed as the diameter of the microvoids in the fiber decreased. From the analysis of the spinline stress, it is clear that the spinline stress increased when both extruding and draw speed increased at constant draw ratio. This resulted in the improvement of supramolecular structure and mechanical properties of the regenerated cellulose fibers.     

Degradation of viscose fibers during acidic treatment

Novel developments in the fiber sector require additional investigation of their behaviour during the production process. In the core step of the viscose process, cellulose fibres are regenerated in an acidic spinning bath. To investigate the influence of hemicellulose content and temperature on the kinetics of fiber degradation, standard and hemicellose-enriched fibers were treated in the acidic standard spinning bath for time periods up to 292 h. Viscose samples of different hemicellulose content were prepared under standardized conditions and the never dried fibres were subjected to long term degradation in the standard spinning bath at 40, 50 and 60 °C. The changes in the degree of polymerization (DP), molar mass distribution, hemicellulose and the generation of the total organic carbon in the spinning bath were monitored. Further, the changes in crystallinity and the level-off-DP of the fibers were determined to improve the accuracy of the existing degradation model. Changes in morphology of the fibers were monitored by optical microscopy and scanning electron microscopy.     

Dry jet-wet spinning of strong cellulose filaments from ionic liquid solution

Considerable growth is expected in the production of man-made cellulose textile fibers, which are commercially produced either via derivatization to form cellulose xanthate (viscose) or via direct dissolution in N-methylmorpholine N-oxide (Lyocell). In the study at hand, cellulosic fibers are spun from a solution in the ionic liquid [DBNH] [OAc] into water, resulting in properties equal or better than Lyocell (tensile strength 37 cN tex^?1 or 550 MPa). Spinning stability is explored, and the effects of extrusion velocity, draw ratio, spinneret aspect ratio and bath temperature on mechanical properties and orientation are discussed. With the given set-up, tenacities and moduli are improved with higher draw ratios, while elongation at break, the ratio of wet to dry strength, modulus of resilience and birefringence depend little on draw ratio or extrusion velocity, elastic limit not at all. We find the process robust and simple, with stretching to a draw ratio of 5 effecting most improvement, explained by the orientation of amorphous domains along the fiber axis.     

Spinnability of Polyacrylonitrile Gel Dope in the Mixed Solvent of Dimethyl Sulfoxide/Dimethylacetamide and Characterization of the Nascent Fibers

In this work, acrylonitrile copolymers were prepared via precipitation polymerization. The copolymer solutions prepared at various ratio of dimethyl sulfoxide and dimethylacetamide were tested to prepare the nascent fibers by one-step wet-spun method. The effect of temperature, solvent ratio, molecular weight and the solid content on the rheological properties of polyacrylonitrile gel solution in different mixed solvent were studied. It was shown that the viscosity decreased with the increase of the temperature and fluctuated with the different solvent ratio reaching the minimal value at the ratio of dimethyl sulfoxide to dimethylacetamide equal to 1.25. The crystallinity of copolymers and the structure of the nascent fiber surface also depended from the solvent ratio in polymerization. The optimum conditions for spinnability of copolymers were determined. The high-quality polyacrylonitrile precursor was achieved with the controllable range of 0.5–0.8 dtex and the toughness of polyacrylonitrile precursor was greater than 6.0 cN/dtex after the wet spinning process, while the tensile strength of carbon fiber is up to 6.25 GPa after their pre-oxidation and carbonization process.     

Investigations on the structure of regenerated cellulose fibers; Herrn Professor Janeschitz-Kriegl zum 70. Geburtstag mit den besten Wünschen gewidmet

A review is given on comparative investigations onto the structure of regenerated cellulose fibers of the regular viscose type (modal) and of solvent spun fibers of the lyocell type, namely the NMMO fiber spun from a solution of cellulose in N–methylmorpholine N–oxide and water. It was found that in the lyocell fiber the mechanical properties in the wet state detoriate less. This is explained by an increased length of the crystallites, less clustering of the crystalline regions, and a shorter and better oriented amorphous portion. These structural features could be caused by a different spinning mechanism due to a preordered spinning solution in which the stiff complexed cellulose molecules are oriented lengthwise in the spinning direction. This will greatly facilitate their orientation during fiber formation in the elongtional deformation velocity field of the draw down zone.     

Structure and thermal properties of bamboo viscose,Tencel and conventional viscose fiber

Comparative investigations of new regenerated cellulosic fibers, bamboo viscose fiber and Tencel, together with conventional viscose fibers have been carried out to explain the similarity and difference in their molecular and fine structure. The analyses jointly using SEM, XRD and IR reveal that all the three fibers belong to cellulose II. Tencel consists of longer molecules and has a greater degree of crystallinity, while bamboo viscose fiber has a lower degree of crystallinty. TG-DTG-DSC study shows three fibers resemble in thermal behavior with a two-step decomposition mode. The first step is associated to water desorption, suggesting that bamboo viscose fiber holds better water retention and release ability, the second a depolymerization and decomposition of regenerated cellulose, indicating that Tencel is more thermally stable in this process than bamboo and conventional viscose fiber.     

Dissolution of rayon fibers for size exclusion chromatography: a challenge

Application of size exclusion chromatography (SEC) for the analysis of cellulose samples is often limited due to poor solubility in the solvent system N,N-dimethylacetamide/lithium chloride (DMAc/LiCl). Hence different activation or derivatization methods have been developed and published. Most of these methods are laborious, influence the molar mass distribution or do not support dissolution of manmade fibers, such as viscose rayon. In this study, we have evaluated different activation methods for their applicability in viscose rayon dissolution and we present a novel method for activation. We found that an additional solvent exchange step with dimethyl sulfoxide (DMSO) increases and accelerates solubility of viscose fibers in DMAc/LiCl for subsequent SEC analysis. The improved dissolution by DMSO activation is mainly due to increased swelling and improved action towards the outer skin of the fiber. The novel approach has also been applied to the even more difficult dissolution of oxidized viscose fibers.     

高力学强度细菌纤维素气凝胶纤维的连续化制备

气凝胶纤维因其高外表面积和高柔韧性在能量管理系统中具有潜在应用而引起了广泛关注.但是,目前制备的气凝胶纤维力学强度较低,限制了其实际应用.为提高气凝胶纤维力学性能,在始终保持细菌纤维素(BC)纳米纤维处于湿态下,利用NaOH/尿素/硫脲复合溶剂直接低温溶解原生BC,获得透明的BC纺丝原液;通过湿法纺丝制备了BC水凝胶纤维,经过水洗和冷冻干燥后处理,制得BC气凝胶纤维.采用偏光显微镜(POM)、13C核磁共振(13C-NMR)和高级旋转流变仪研究BC在复合溶剂中的溶解过程与状态;利用全反射傅里叶变换红外吸收光谱(ATR-FTIR)、X射线衍射(XRD)和热失重(TG)研究BC溶解前后结构与性能变化;利用场发射扫描电镜(FESEM)、全自动比表面积和孔径分布分析仪、单丝强力仪对获得的BC气凝胶纤维结构与性能进行表征.结果表明,复合溶剂在?15℃条件下可以直接溶解原生湿态BC,最高溶解浓度为3 wt%;采用湿法纺丝制得高度多孔的连续BC气凝胶纤维,比表面积高达192 m^2/g且具有优异的力学性能,断裂强度和杨氏模量高达(9.36±1.68)MPa和(176±17.55)MPa,如0.4 mg BC气凝胶纤维可以支撑高于其本身质量5×10^4倍的重物.     

Fiber formation via solution spinning of the cellulose/ammonia/ammonium thiocyanate system

Fiber formation via the cellulose/ammonia/ammonium thiocyanate system by wet spinning has been investigated. This report presents a characterization of the structure and tensile properties of fibers spun under various coagulation conditions. Microscopic observations showed that the molecular size of coagulant was the dominant factor governing the crosssectional shape of the fibers. Density, birefringence, and crystallinity data indicated that a higher cellulose concentration and lower coagulation temperature favored development of a fiber with a denser and more oriented structure. Under optimum conditions, a welldefined fibrillar structure was obtained. Fiber tensile property measurements suggested the existence of a linear relationship between the fiber breaking tenacity and the product of the square of the Hermans' orientation factor and the infrared crystallinity index.     

Biobased films prepared from NaOH/thiourea aqueous solution of chitosan and linter cellulose

In the present study, films based on linter cellulose and chitosan were prepared using an aqueous solution of sodium hydroxide (NaOH)/thiourea as the solvent system. The dissolution process of cellulose and chitosan in NaOH/thiourea aqueous solution was followed by the partial chain depolymerization of both biopolymers, which facilitates their solubilization. Biobased films with different chitosan/cellulose ratios were then elaborated by a casting method and subsequent solvent evaporation. They were characterized by X-ray analysis, scanning electron microscopy (SEM), atomic force microscopy (AFM), thermal analysis, and tests related to tensile strength and biodegradation properties. The SEM images of the biofilms with 50/50 and 60/40 ratio of chitosan/cellulose showed surfaces more wrinkled than the others. The AFM images indicated that higher the content of chitosan in the biobased composite film, higher is the average roughness value. It was inferred through thermal analysis that the thermal stability was affected by the presence of chitosan in the films; the initial temperature of decomposition was shifted to lower levels in the presence of chitosan. Results from the tests for tensile strength indicated that the blending of cellulose and chitosan improved the mechanical properties of the films and that an increase in chitosan content led to production of films with higher tensile strength and percentage of elongation. The degradation study in a simulated soil showed that the higher the crystallinity, the lower is the biodegradation rate.     

Progress in cellulose shaping: 20 years industrial case studies at Fraunhofer IAP

Cellulose, the most abundant renewable organic material on earth, exhibits outstanding properties and useful applications, but also presents a tremendous challenge with regard to economical and environmentally friendly chemical processing. The viscose process, more than 100 year old is still the most widely utilized technology to manufacture regenerated cellulose fibers and films. Viscose fibers are produced today worldwide on a 5 million ton scale with various fiber types ranging from high performance tire yarn to textile filaments and staple fibers with excellent properties close to those of cotton. At Fraunhofer IAP, the technical equipment for viscose preparation, wet spinning of fibers, hollow fibers, and tube-like films is available on a min-plant scale. Research focused on raw materials testing, process optimization with regard to economic and ecological aspects, structural analysis of cellulose during processing, and structure–property relations of fibers and films. Similar to the viscose process, cellulosic fibers can be produced via cellulose carbamate as an environmentally friendly route. In a close cooperation of Fraunhofer IAP with industrial partners, a specific process based on cellulose carbamate was developed on a pilot plant scale, giving fiber properties close to those of conventional viscose fibers. In recent decades the N-methylmorpholine-N-oxide (NMMO)-technology turned out to be a nonderivatizing commercial alternative to the still dominant viscose route. From the very beginning, Fraunhofer IAP has been engaged in investigating the structure formation of cellulose fibers precipitated from NMMO-water solution, revealing structural reasons for the fibrillation tendency of these fibers and means to overcome them. Starting from fiber formation via dry-jet wet spinning, for the first time the blown film formation and the meltblown nonwovens technology were developed for cellulosics on a pilot plant scale at Fraunhofer IAP. Based on the elastic behavior of the dope at elevated temperatures, cellulose can be processed like a melt in the air-gap, offering new possibilities of shaping cellulose like meltable mass polymers. Combining cellulose carbamate with NMMO-monohydrate as a solvent, higher polymer concentrations in the dope and outstanding mechanical properties of the resulting fibers were achieved.     

纳米SiO2改性超高分子量聚乙烯纤维的制备及其结构性能研究

采用萃取阶段加入纳米粒子的方式,制得纳米SiO2改性的超高分子量聚乙烯(UHMWPE)纤维.借助于扫描电镜、声速法、WAXD、DSC、TMA和强力测试等手段,研究了纳米SiO2对UHMWPE纤维结构和性能的影响.结果表明,纳米SiO2粒子在UHMWPE纤维中可达到均匀分散,分散尺寸约为50～100nm;改性后纤维取向度、结晶度基本不变,纤维横向晶粒尺寸大大降低,纤维力学强度稍有增加,力学模量大大增加(由1359.2cNdtex增加到1505.9cNdtex),同时,纤维热性能和热力学性能也得到大大改善.     

Gel spinning of poly(vinyl alcohol) from dimethyl sulfoxide/water mixture

Gel spinning of poly(vinyl alcohol) (PVA) was attempted from the PVA dope prepared from the mixture of dimethyl sulfoxide (DMSO) and water. The DMSO/H₂O = 80/20 (w/w) mixture and methanol were found to be the best solvent for the spinning dope and the coagulant, respectively, to give PVA fiber with the highest drawability. PVA fiber with the highest strength and Young's modulus were obtained from the undrawn gel fibers when subjected to hot two-stage drawing under conditions such as to produce maximum drawability. Furthermore, higher draw ratios of PVA fiber were attained at 6 wt % dope by lowering the coagulating temperature of methanol. In the present work, the highest tensile strength (2.8 GPa) and the highest Young's modulus (64 GPa) were realized, when the spinning dope was prepared from PVA with DP of 5,000 and the DMSO/H₂O (80/20) mixed solvent to have the PVA concentration of 6 wt %, the coagulating temperature of methanol was ?20°C, and the two-stage drawing was carried out at 160 (first) and 200°C (second). The PVA fiber prepared under this gel spinning condition could be elongated to 45 times draw ratio. The very high drawability of PVA fibers obtained from the DMSO/H₂O (80/20) mixture dope was ascribed to the ability of the DMSO/H₂O mixture to promote gelation. © 1994 John Wiley & Sons, Inc.     

Physico-chemical,Tensile, and Thermal Characterization of Napier Grass (Native African) Fiber Strands

This article presents the extraction and effect of alkali treatment on the physical, chemical, tensile, and thermal characteristics of fiber strands obtained from Napier grass, a renewable biomass. In order to improve these properties, the Napier grass fiber strands were treated with sodium hydroxide. The alkali treatment was carried out using NaOH solution at three different concentrations (5, 10, and 15%) for 2 h. Characterization of untreated and alkali-treated Napier grass fiber strands was carried out by studying the chemical composition, surface morphology, functional group variation, crystallinity, and tensile and thermal behavior. It was found that untreated fiber strands have lower cellulose content, crystallinity, tensile properties, and thermal stability than alkali-treated fiber strands. Napier grass fiber strands treated with 10% NaOH showed optimum tensile strength, modulus, and percentage elongation with an improvement of 51.9, 47.3, and 12.1% respectively. Based on the properties determined for alkali-treated Napier grass fiber strands, we expect that these fibers will be suitable for use as a reinforcement in natural fiber composites.     

A Rapid Process for Producing Cellulose Multi‐Filament Fibers from a NaOH/Thiourea Solvent System

Summary: Cellulose was dissolved rapidly in 9.5 wt.‐% NaOH and 4.5 wt.‐% thiourea aqueous solution pre‐cooled to −5 °C to prepare a transparent solution. Novel cellulose multi‐filament fibers were spun successfully, for the first time, from the cellulose dope on an extended laboratory scale. The results from ¹³C NMR, scanning electron microscopy and wide angle X‐ray diffraction (WAXD) patterns indicated that the fibers exhibited cellulose II character and possessed a circular cross‐section and smooth surface. The tensile strength of the novel fibers reached 1.9–2.2 cN · dtex⁻¹. 2D WAXD and SAXS patterns revealed that, with a drawing progress, the orientation factor increased and mechanical properties were improved.

SEM micrographs of the novel multi‐filament fibers spun from cellulose solution in a NaOH/thiourea aqueous system pre‐cooled to −5 °C on an extended laboratory scale.     

Self-reinforced cellulose nanocomposites

A self-reinforced cellulosic material was produced exclusively from regenerated cellulose microcrystals. The level of reinforcement was controlled by tailoring the crystallinity of cellulose by controlling the dissolution of microcrystalline cellulose (MCC) before its regeneration process. After the cellulose regeneration a self-reinforced material was obtained in which cellulose crystals reinforced amorphous cellulose. This structure was produced by dissolution of MCC in a non-derivatising cosolvent N,N-dimethylacetamide/LiCl followed by subsequent cellulose regeneration in distilled H₂O. The reduction of the overall crystallinity of self-reinforced regenerated cellulose was dependent on the dissolution time of the cellulose precursor. The crystallinity of regenerated cellulose was determined by wide angle X-ray diffraction. A reduction in crystal size from microcrystalline cellulose to regenerated cellulose was observed with increasing dissolution time in DMAc/LiCl cosolvent. The reduction in degree of crystallinity of regenerated cellulose led to a decrease in the tensile mechanical performance and thermal stability of the regenerated cellulose. The controlled dissolution of microcrystalline cellulose resulted in the modification of structural, physical, thermal properties and moisture uptake behaviour of regenerated cellulose.     

PVA微晶交联和SA/PAA双网络协效增强增韧SA纤维

为了提高海藻酸钠(SA)纤维的断裂强度和断裂伸长率, 以丙烯酸(AA)为化学交联组分, SA为离子交联组分, 聚乙烯醇(PVA)为微晶交联组分, 采用湿法纺丝和冻融循环方法制备含有PVA微晶交联点和海藻酸钠/聚丙烯酸(SA/PAA)双网络结构的海藻酸钠/聚丙烯酸/聚乙烯醇(SA/PAA/PVA)复合纤维. 通过流变性能、 力学性能、 红外光谱、 X射线衍射仪(XRD)和扫描电子显微镜(SEM)测试研究了交联剂N,N-亚甲基双丙烯酰胺(MBA)含量和PVA微晶交联对SA/PAA/PVA纺丝原液和复合纤维的结构与性能的影响. 结果表明, 当MBA质量分数为0.5%时, 纺丝原液的损耗模量(G″)最小, 可纺性最好, 复合纤维的断裂强度达到2.83 cN/dtex, 断裂伸长率达到9.38%, 比再生SA纤维分别提高了15.98%和38.96%; PVA冷冻之后形成微晶交联点并且PAA和PVA已经复合到体系中; PAA和PVA的加入提高了复合纤维的结晶度; 复合纤维的表面形貌趋于光滑和规整, 纤维断面更加致密.