Electrospinning of cellulose‐based nanofibers

Cellulose derivatives of carboxymethyl cellulose sodium salt (CMC), hydroxypropyl methylcellulose (HPMC), methylcellulose (MC), and enzymatically treated cellulose have been electrospun, and the microstructure of the resulting nanofibers has been analyzed by scanning electron microscopy (SEM). Before electrospinning, the solutions were characterized by viscometry and surface tension measurements, and the results were correlated with spinnability. Four different CMC derivatives, varying in molecular weight (M_w), degree of substitution (DS), and substitution pattern, have been electrospun in mixtures with poly(ethylene oxide) (PEO), and nanofibers of various characteristics have formed. The CMC‐based nanostructures, i.e., the nonwoven sheet and individual nanofibers, proved to be independent of M_w and DS but largely dependent on the substitution pattern. The nonwoven sheets varied in homogeneity, and beads appeared on the individual fibers. Depending on the chemical nature of the CMC, the extraction of PEO resulted in pure CMC nanostructures of varying appearance, indicating that the distribution of PEO and CMC in the nanofibers also varied. Two different HPMC derivatives, varying in DS, were electrospun into nanofibers. Homogeneous nonwoven sheets based on nanofibers of similar appearance are formed, independent of the substitution content of the HPMC sample. Preliminary fibers were obtained from enzymatically treated cellulose in a solvent system based on lithium chloride dissolved in dimethyl acetamide (LiCl: DMAc). © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 1473–1482, 2007     

不同预处理条件下纤维素的结构变化及其在DMAc/LiCl中的溶解

介绍了乙二胺、氢氧化钠和高温等三种不同的纤维素预处理方法。研究预处理后纤维素的结构变化,讨论预处理过程中的转化机理,并通过X射线衍射对纤维素结晶度的变化进行表征,证明乙二胺预处理后纤维素的结晶度下降最大。纤维素经过预处理后可以溶解在DMAc/L iC l中,讨论其溶解机理,通过对比三种预处理纤维素的溶解性能,表明经过乙二胺预处理之后的纤维素在DMAc/L iC l中溶解性能最好,氢氧化钠预处理的纤维素次之,高温预处理的纤维素溶解性能相对较差。     

细菌纤维素在LiCl/DMAc溶剂体系中的溶解性能研究

纤维素经过活化后可以溶解在LiCl/DMAc溶剂体系中,研究了乙二胺活化对细菌纤维素溶解性能的影响,得到最佳活化条件;研究了LiCl的浓度、溶解温度和搅拌时间对溶解性能的影响,得到最佳溶解条件;研究了细菌纤维素在LiCl/DMAc极性溶剂体系中的溶解机理。     

Comparative study of homogeneous solvents for the esterification crosslinking of cellulose with 1,2,3,4‐butanetetracarboxylic dianhydride and water absorbency of the reaction products

Superabsorbent hydrogels were prepared via esterification crosslinking of cellulose with 1,2,3,4‐butanetetracarboxylic dianhydride (BTCA) in three solvent systems: lithium chloride (LiCl)/N‐methyl‐2‐pyrrolidinone (NMP), LiCl/N,N‐dimethylacetamide (DMAc), and tetrabutylammonium fluoride/dimethyl sulfoxide (TBAF/DMSO). The absorbency of the hydrogels was strongly dependent on the BTCA feed to cellulose ratio as well as the nature of the solvent system used. The rate of cellulose esterification was enhanced in TBAF/DMSO relative to the other systems, and the highest water absorbency of the hydrogels (987 g g^?1 polymer) was also achieved using this system. The hydrogels obtained in the TBAF/DMSO system had a similar degree of both crosslinking and grafting, indicating that both reactions were promoted to the same extent in this solvent, whereas crosslinking was preferentially enhanced over grafting in the LiCl/NMP and LiCl/DMAc systems. The difference in the composition of the hydrogels was attributed to the difference in the electronegativity of the fluoride and chloride anions in these solvents. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Shear‐induced morphology changes in N,N′‐dimethylacetamide/lithium chloride pretreated cellulose

A new mechanochemical treatment was performed on cellulose with the objective of modifying its morphology, reducing its crystallinity, and enabling better dissolution. Cellulose treated with N,N′‐dimethylacetamide (DMAc)/lithium chloride (LiCl) was subjected to shear with natural rubber as the carrier and shear‐transfer medium. When cellulose was subjected to such a mechanochemical treatment, significant changes in its surface morphology and a decrease in crystalline index were observed. The dissolution of the mechanochemically treated cellulose samples in DMAc/LiCl was found to be better compared with the dissolution of samples subjected to either mechanical shear or the chemical action of DMAc/LiCl independently. Chemical interactions between DMAc/LiCl and cellulose were enhanced synergistically under shear‐induced deformation. When shear alone was used in the absence of a DMAc/LiCl treatment, changes in the morphology, crystalline index, and dissolution were found to be negligible. The shear‐induced cellulose samples were characterized with Fourier transform infrared spectroscopy, X‐ray diffraction, scanning electron microscopy, energy‐dispersive X‐ray spectroscopy, and thermogravimetric analysis. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44809.     

Structopendant unsaturated cellulose esters via acylation in homogeneous lithium chloride/N,N-dimethylacetamide solutions

Novel acylation reactions of cellulose were accomplished with a series of unsaturated carboxylic acids or their respective anhydrides including crotonic acid (CRA), methacrylic acid (MAA), vinyl acetic acid (VAA), fumaric acid monoethyl ester (FAME), and cinnamic acid (CINA) in lithium chloride (LiCl)/dimethylacetamide (DMAc) homogeneous solutions. The acylation reactions were conducted at room temperature using dicyclohexylcarbodiimide (DCC) as a condensation agent and 4-dialkyl-aminopyridine (4-[N,N-dimethylamino-] or 4-pyrrolidino-pyridine, DMAP or PP) as a catalyst. A reaction mechanism is proposed based on experimental evidence. The acylated cellulose derivatives obtained from CRA, MAA, or their anhydrides exhibit poor solubility in organic solvents. Side reactions, e.g., the Michael addition, likely occur at the high temperatures required for reaction of these acyl groups. However, acylation of cellulose with VAA, FAME, and CINA is facile with derivatives readily soluble in DMSO. The structures of these derivatized celluloses were characterized with FTIR and ¹H-NMR spectroscopy and degrees of substitution were calculated. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 293–305, 1997     

聚丙烯腈/棉纤维素薄膜的制备与性能研究

以N,N二甲基乙酰胺/无水氯化锂（DMAc/LiCl）为溶剂配置聚丙烯腈（PAN）和棉纤维素溶液,采用旋涂法制备不同比例的PAN/棉纤维素薄膜。通过旋转黏度计对PAN/棉纤维素共混溶液的表观黏度进行研究,采用X射线衍射仪、傅里叶红外光谱仪、电子万能试验机以及吸水性能测试对PAN/棉纤维素薄膜的结构和性能进行了研究。结果表明,共混溶液的表观黏度随着纤维素含量的增加逐渐增大;DMAc/LiCl溶剂对PAN和棉纤维素的溶解为直接溶解,没有发生衍生化反应;PAN和棉纤维素均保持各自结晶结构不变;当棉纤维素含量为2.0 %（质量分数,下同）时,复合薄膜的拉伸强度和断裂伸长率达到最大值;棉纤维素含量越高,复合薄膜的吸水性越好。     

Investigation of the cellulose/LiCl/dimethylacetamide and cellulose/LiCl/N-methyl-2-pyrrolidinone solutions by 13C NMR spectroscopy

The cellulose/lithium chloride/dimethylacetamide (DMAc) and cellulose/lithium chloride/N-methyl-2-pyrroilidinone (NMP) solutions were investigated by ¹³C NMR spectroscopy. Well-resolved spectra were obtained for both solutions and indicated that cellulose was present in these systems in the form of underivatized cellulose. The change in ¹³C chemical shifts of DMAc and NMP in the presence of LiCl and LiBr was compared with that of several salt/aprotic solvents, and the results point to the existence of a cellulose–LiCl–DMAc (or NMP) complex in which the lithium cation is strongly bound to the amide carbonyl oxygen and the chloride anion involved in the dissociation of the cellulose hydrogen bonds. Spin–lattice relaxation times (T₁ of the ¹³C carbons of the solvent molecules, DMAc and NMP, show a large decrease in T¹ for all solvent carbons upon addition of LiCl. Further decrease in T₁ is observed when cellulose is introduced to the LiCl/NMP but not to the LiCl/DMAc systems. These observations are attributed to slower molecular motions of DMAc and NMP in the presence of LiCl, and, in the case of NMP, in the presence of cellulose.     

阳离子絮凝剂在纤维素/离子液体中的均相合成

纤维素在离子液体中有良好的溶解性能形成均相体系,文中制备了1-烯丙基-3-甲基氯代咪唑[Amim]Cl离子液体,与丙烯酰胺进行接枝共聚合及阳离子化,合成不同聚合度的纤维素阳离子絮凝剂,并与LiCl/DMAc体系进行比较,探讨其絮凝性能.结果显示:纤维素在[Amim]Cl中溶解性能良好、接枝共聚反应活性较好;纤维素聚合度...     

Application of optical microscopy as a screening technique for cellulose and lignin solvent systems

Rapid and facile screening techniques to determine the effectiveness of solvents for cellulose or biomass dissolution can advance biomass processing research. Here, we report the use of a simple optical microscopy method to screen potential cellulose and lignin solvents. The described methodology was used to screen the dissolution of cellulose and lignin in two imidazolium‐based ionic liquids (ILs), two phosphonium‐based ILs, as well as a N,N‐dimethylacetamide/lithium chloride (DMAc/LiCl) solution in less time than other techniques. The imidazolium‐based ILs and the DMAc/LiCl were found to dissolve both cellulose and lignin. Also, it was observed that one of the phosphonium‐based ILs dissolved lignin and not cellulose, demonstrating a potential for biomass fractionation applications. © 2011 Canadian Society for Chemical Engineering     

Preparation and flocculation behavior of cellulose‐g‐PMOTAC copolymer

As a contribution to the wider use of biodegradable materials, this article reports the synthesis and testing of cationic polyelectrolyte cellulose derivatives for use as flocculation chemicals. Cellulose macroinitiator is synthesized in DMAc/LiCl solvent system by direct acylation of cellulose with 2‐bromoisobutyryl bromide. Cellulose‐graft‐poly(N,N‐dimethyl aminoethyl methacrylate) (cellulose‐g‐PDMAEMA) copolymers are prepared by copper‐mediated radical polymerization in homogeneous medium. Formation of the macroinitiator and graft copolymers is confirmed by ATR‐FTIR and ¹H NMR. Quaternization of the graft chains to poly(methacryloxyethyl trimethylammonium chloride) (PMOTAC) produces cellulose‐g‐PMOTAC, which performs similarly to a commercial product in flocculation of pulp and kaolin. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40448.     

Effect of solvent exchange on the pore structure and dissolution behavior of cellulose

Effect of solvent exchange, i.e., the sequential immersion in water, acetone, and DMAc on the pore structure of cellulose and its dissolution behavior in lithium chloride/N,N‐dimethylacetamide (LiCl/DMAc) was investigated by using size exclusion liquid chromatography (SEC), dynamic light scattering (DLS), and small‐angle X‐ray scattering (SAXS). In the SEC experiment, poly(styrene)s, diethyl phthalate, and acetone were used as probe solutes and 2‐butanone was used as an eluent. Capacity factor of these solutes in the solvent‐exchanged cellulose were larger than those in the untreated one. This was remarkable when diethyl phthalate and acetone were used as solutes. Since the molecular radii of these solutes were estimated to be less than 1 nm, it was shown that the solvent exchange increases the amount of pores within cellulose with the radii of less than 1 nm. In the SAXS experiment, structural difference between the solvent exchanged and the untreated celluloses was observed when the celluloses were immersed in acetone. Values of specific inner surface and average chord length calculated from SAXS profile showed that the amount of small pores was increased in the solvent exchanged cellulose. Considering the results from SEC, DLS, and SAXS measurements, facilitated dissolution of the solvent exchanged cellulose in LiCl/DMAc was attributed to the increase in the pores with the radii of less than 1 nm. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 3976–3984, 2007     

纤维素浆粕和Lyocell纤维在LiCl/DMAc中溶解差异的研究

为了研究Lyocell工艺中纤维素相对分子质量分布的变化,分析了纤维素浆粕和相应的由浆粕生产出的Lyocell纤维在LiCl/DMAc中的溶解情况,发现两者存在很大差异,分别从纤维素的晶型、取向和形态结构等方面分析原因。结果表明:由于Lyocell纤维(纤维素II)比纤维素浆粕(纤维素I)在热力学上更稳定,分子间的氢键更多,且Lyocell纤维的取向较纤维素浆粕高,纤维结构较致密,使得溶剂的渗透和氢键的破坏更加困难,因此Lyocell纤维在LiCl/DMAc中的溶解比纤维素浆粕差。     

超细纤维与丙烯酰胺接枝共聚物的制备及表征

纤维素是大自然中经光合作用可以不断再生的丰富的天然资源．也是人类应用最早、最广泛的天然高分子材料之一。从可持续发展战略着眼．充分利用木质纤维这一价廉物丰、无毒．且具有生物可降解性和环境协调性的可再生资源具有深远意义．     

纤维素LiCl/DMAc体系的溶液特征

本文研究了纤维素LiCl／DMAc体系的溶液特征。实验结果证明该体系具有良好的时间稳定性和热稳定性，能在常温下近30天内没有明显的粘度降低；在100℃高温下，4h不降解。同时测定了溶液的特性粘数和Huggins常数，Huggins常数在0．4～0．6之间，对比纤维素的铜乙二胺（Cuen）溶液，发现特性粘数[η]LICI/DMAc＞[η]Cuen，无扰尺寸ALiCi／DMAc＞ACuen，可见在LiCl／DMAc体系中，溶剂与纤维素分子表现出更强的相互作用力，分子链充分伸展。该体系的特性粘数、粘度常数不仅与温度、溶剂有关，而且是LiCl浓度的函数，具有与聚电解质溶液相类似的性质。这可能是因为纤维素分子链上的H质子和溶液中的Cl-离子相互作用，而使纤维素分子带上部分电荷，相互排斥而引起的。因此利用M－H方程测分子量，粘度常数的确立必须考虑诸多因素的影响，否则会导致分子量的高估。     

Optimization of nanofiber-caproate/laurate esters synthesis,their characterization,and usage as emulsifier in o/w emulsion

The aim of this study is to optimize the esterification of nanofibers with caproyl/lauroyl chlorides at different substitution degrees' (DS) and to investigate the usage of nanofiber derivatives in model emulsions. First, cellulosic material was obtained and milled into nanofibers using a micro-fluidizer. Then, these nanofibers were esterified with caproyl/lauroyl chlorides in a solvent of DMAc/LiCl with DMAP as an acid scavenger. The esterification of nanofibers with caproyl/lauroyl chlorides was optimized for fatty acid chloride mole and reaction time. Esterification reactions were carried out at 80°C with various molar ratios of acyl chlorides (3–15 moles) versus anhydroglucose unit of nanofibers and for various time durations (30–360 min). The hydrophobic derivatives with DS in the range of 0.34–2.77 were successfully obtained. Using the data obtained as a result of the optimization, nanofiber-fatty acid esters with different DS (0.50–2.75) were produced and characterized. Analyzes showed that the esterification process was successful and as the degree of esterification increased, the crystallinity index and thermal stability of the derivatives decreased. Then, the nanofiber-caproate/laurate esters with different DS were used as emulsifier (0.5 wt%) in an oil-in-water model emulsion containing 25 wt% oil and the emulsions were analyzed. The nanofiber caproate/laurate esters with a DS of 0.50–1.25 were suitable for o/w emulsions, while samples with a DS of 2.00 and above were not found suitable. Emulsions prepared by using nanofiber derivatives with 1.25 DS had higher G′ and G″ and viscosity values and lower droplet sizes than those of other group.     

Preparation of Internally Plasticized Ester of Cellulose Irradiated by Microwave and Its Properties

This paper demonstrates esterification of cellulose with long-chain carboxylic acid in a homogeneous phase irradiated by microwave. The esterification reaction system was cellulose, fatty acid, and LiCl/dimethylacetamide (LiCl/DMAc) using p-toluenesulfonyl chloride (Ts-Cl) as activating reagents. It was found that the use of a microwave resulted in a dramatic drop in reaction time (90s), two orders of magnitude faster than conventional reaction under heating. The degrees of substitution (DS) and molar yields of fatty acid, Ts-Cl amounts and reaction time, as well as the property of final products, were studied. Partially derivative celluloses, which underwent a significant change in morphological structure during the modification, presented obvious glass transition compared to starting cellulose. In agreement with this, the crystallization property of the internally plasticized esters was different from cellulose. Together, these results indicated the reaction of acylation.     

Cellulose in lithium chloride/N,N-dimethylacetamide, optimisation of a dissolution method using paper substrates and stability of the solutions

Activation and dissolution in lithium chloride/N,N-dimethylacetamide (LiCl/DMAc) of cellulose from paper substrates are studied. The importance of the multiple parameters involved such as salt concentration, sample source and preparation is shown in a literature review. The experiments are carried out in order to perfect the method of activation and dissolution of paper containing different kinds of additives, typically found in historic papers. The suitability and efficiency obtained in the different trials are evaluated. The final procedure involves the activation by solvent exchange, with a water/methanol/DMAc sequence, followed by dissolution in 8% LiCl/DMAc at 4 °C. A study of the stability of the cellulose solutions in the experimental conditions showed that no degradation nor aggregation occurred during the solvation process and even after several months and confirmed the non-aggressiveness of LiCl/DMAc.     

细菌纤维素再生前后结构与性质上的差异

对比研究了细菌纤维素和再生细菌纤维素的结构与性质上的差异,揭示了细菌纤维素在氯化锂（LiCl）／二甲基乙酰胺（DMAc）溶剂体系下溶解,经水浴凝固再生前后的形貌、大分子结构、晶型及尺寸、物理机械性能、含水保湿性上的变化,为再生细菌纤维素的应用提供理论依据。     

Aerocellulose based on all‐cellulose composites

Novel aerogels (or aerocellulose) based on all‐cellulose composites were prepared by partially dissolving microcrystalline cellulose (MCC) in an 8 wt % LiCl/DMAc solution. During this process, large MCC crystals and fiber fragments were progressively split into thinner crystals and cellulose fibrils. The extent of the transformation was controlled by using cellulose concentrations ranging from 5 to 20 wt % in the LiCl/DMAc solution. Cellulose gels were precipitated and then processed by freeze‐drying to maintain the openness of the structure. The density of aerocellulose increased with the initial cellulose concentration and ranged from 116 up to 350 kg m^?3. Aerocellulose with relatively high mechanical properties were successfully produced. The flexural strength of the materials reached 8.1 MPa and their stiffness was as high as 280 MPa. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010