“Dialdehyde Cellulose” Nanofibers by Electrospinning as Polyvinyl Alcohol Blends: Manufacture and Product Characterization

A nanofiber was obtained by electrospinning of “dialdehyde cellulose” (periodate-oxidized cellulose, DAC) and polyvinyl alcohol (PVA), using only water as the solvent. Celluloses of four different origins were fully oxidized with sodium periodate to water-soluble DAC. Aqueous solution of DAC showed inadequate spinnability regardless of the polymer concentration and the electrospinning conditions used. Addition of PVA improved the solution's viscoelasticity and, consequently, the solution's spinnability. We examined the effects of DAC/PVA composition and electrospinning parameters on fiber morphology. Highly homogeneous nanofibers were prepared from 1:1 up to 2:1 (weight) DAC/PVA blends while samples of lower viscosity or higher relative DAC contents resulted in continuous, beaded fiber networks. Characterization of the electrospun fabrics revealed a highly crosslinked DAC structure reinforced with PVA, strongly interacting through hemiacetal bonds and hydrogen bonding. Fluorescence labeling confirmed the presence of reactive aldehyde functionalities in the electrospun web. The versatile properties of DAC as reactive material can now be imparted on electrospun fiber and nanofiber material – which was not possible so far –further widening the application scope of this interesting cellulose derivative.     

溶剂对醋酸纤维素静电纺丝可纺性的影响

将醋酸纤维素(CA)分别溶于二氯甲烷、甲酸、乙酸和三氟乙酸(TFA)四种溶剂中,用静电纺丝法制备CA纤维。测定了纺丝液的黏度、电导率,并对各种CA溶液电纺纤维的形貌进行表征,分析各种影响可纺性及纤维形貌的因素。结果表明:溶剂的沸点及所配溶液的电导率、黏度是影响电纺丝可纺性的重要因素。以TFA作为溶剂时,8%CA纺丝液具有良好的可纺性。     

Electrostatic polymer processing of isotactic poly(4-methyl-1-pentene) fibrous membrane

Isotactic poly(4-methyl-1-pentene) (P4M1P) is a widely used polymer in industrial applications and specifically, in medical products. Producing micro- or nanofibers would expand the usefulness of P4M1P to a broad range of medical applications. The choice and quality of solvent for the solution used for electrospinning can have a dramatic effect on the spinnability of fibers and on their morphological appearance. In this study, four solvent systems: cyclohexane, cyclohexane/acetone mixture, cyclohexane/dimethyl formamide (DMF) mixture and cyclohexane/acetone/DMF mixture have been investigated. As demonstrated by FE-SEM, electrospun fibers with different morphologies including round, twisted with a roughened texture, curled and twisted-ribbon shapes were formed. The fiber shape and morphology depended strongly on the type and amount of non-solvent used.     

Structural properties and superhydrophobicity of electrospun polypropylene fibers from solution and melt

Isotactic polypropylene (iPP) has successfully been electrospun from both solution and melt using an elevated temperature setup. First, PP nanofibers with two different average diameters (0.8 μm and 9.6 μm) were obtained via electrospinning of iPP in decalin, and the effect of deformation and solidification on the morphological and structural features of the resulting fibers was studied. Secondly, melt electrospun PP fibers with two different average diameters were also fabricated to compare the structures with those of solution electrospun PP fibers. DSC and XRD results show that β form crystals which can increase the impact strength and toughness of electrospun fibers are present in sub-micron scale PP fibers from solution, while fibers from melt mostly show α form crystals. The annealed fibers have changed their morphological forms into α and γ crystal forms. Finally, it is observed that electrospun PP fiber webs both from solution and melt exhibit superhydrophobicity with a water contact angle about 151° which is substantially higher than those of a commercial PP non-woven web and a compression molded PP film, 104° and 112°, respectively. Such superior hydrophobicity was observed for all PP electrospun fibers and it was not altered by the processing scheme (solution or melt) or fiber diameter (sub-micron or micron). Enhanced hydrophobicity of electrospun PP fiber webs contribute to excellent barrier performance without losing permeability when they are applied to protective clothing.     

Study of electrospinning of sodium alginate,blended solutions of sodium alginate/poly(vinyl alcohol) and sodium alginate/poly(ethylene oxide)

Alginate is an interesting natural biopolymer for many of its merits and good biological properties. This paper investigates the electrospinning of sodium alginate (NaAlg), NaAlg/PVA‐ and NaAlg/PEO‐ blended systems. It was found in this research that although NaAlg can easily be dissolved in water, the aqueous NaAlg solution could not be electrospun into ultrafine nanofibers. To overcome the poor electrospinnability of NaAlg solution, synthetic polymers such as PEO and PVA solutions were blended with NaAlg solution to improve its spinnability. The SEM images of electrospun nanofibers showed that the alginate (2%, w/v)–PVA (8%, w/v) blended system in the volume ratio of 70 : 30 and the alginate (2%, w/v)–PEO (8% w/v) blended system in the volume ratio of 50 : 50 could be electrospun into finest and uniform nanofibers with average diameters of 118.3 nm (diameter distribution, 75.8–204 nm) and 99.1 nm (diameter distribution, 71–122 nm), respectively. Rheological studies showed a strong dependence of spinnability and fiber morphology on solution viscosity and thus on the alginate‐to‐synthetic polymer (PVA or PEO) blend ratios. FTIR studies indicate that there are the hydrogen bonding interactions due to the ether oxygen of PEO (or the hydroxyl groups of PVA) and the hydroxyl groups of NaAlg. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

A dynamic liquid support system for continuous electrospun yarn fabrication

Electrospinning is known to be a highly versatile process which is able to produce fibers made out of different compositions with diameter of a few microns down to several nanometers. Current electrospinning technology generally involves the deposition of fibers onto a solid substrate although in some cases, a liquid coagulation bath is used to collect the fibers. However, a liquid collector may offer several advantages over a solid substrate. A novel electrospun fiber manipulation process through the use of a water vortex is described in this communication where continuous yarn was made from electrospun fibers. Preliminary studies on some parameters such as solution feed rate and solution concentration and their impact on fabrication of the yarn and the fiber morphology were carried out.     

Influence of molecular weight and rheological behavior on electrospinning cellulose nanofibers from ionic liquids

Dissolving pulp was depolymerized with 2.5M HCl into cellulose fractions with decreasing molecular weight relative to acid treatment time. The cellulose fractions were dissolved at various concentrations in the ionic liquid 1‐ethyl‐3‐methylimidazolium acetate (EmimAc) with co‐solvent DMSO at ratio 1 : 1 (w/w) and electrospun. Size exclusion chromatography was used to evaluate the molecular weight distributions and the rheological properties were characterized with a cone‐and‐plate rheometer. Scanning electron microscope was used to evaluate the fiber morphology, and thereby spinnability. Zero shear viscosity as a function of cellulose concentration show that all the solutions in this study are in the entangled semi‐dilute regime; where the polymer concentration is large enough for significant overlap necessary for chain entanglement. However, within the intervals studied, neither cellulose concentration nor molecular weight seems to be decisive for if a solution can be electrospun into fibers or not. It is rather the viscosity of the solution that is decisive for electrospinnability, even though the solution is in the entangled semi‐dilute regime. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 2303–2310, 2013     

The influence of electrospinning parameters on the structural morphology and diameter of electrospun nanofibers

Electrospinning is a simple method of producing nanofibers by introducing electric field into the polymer solutions. We report an experimental investigation on the influence of processing parameters and solution properties on the structural morphology and average fiber diameter of electrospun poly ethylene oxide (PEO) polymer solution. Experimental trials have been conducted to investigate the effect of solution parameters, such as concentration, molecular weight, addition of polyelectrolyte in PEO solution, solvent effect, as well as governing parameter, such as applied voltage. The concentration of the aqueous PEO solution has shown noteworthy influence on the fiber diameter and structural morphology of electrospun nanofibers. At lower concentrations of PEO polymer solution, the fibers showed irregular morphology with large variations in fiber diameter, whereas at higher concentrations, the nanofibers with regular morphology and on average uniform fiber diameter were obtained. We find that the addition of polyelectrolytes, such as sodium salt of Poly acrylic acid (PAA) and Poly allylamine hydrochloride (PAH), increases the conductivity of PEO solutions and thereby decreases the bead formation in electrospun nanofibers. The increase in applied voltage has been found to affect the structural morphology of nanofiber while the addition of ethanol in PEO solution diminishes the bead defects. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Structural studies of electrospun cellulose nanofibers

Non-woven mats of submicron-sized cellulose fibers (250-750 nm in diameter) have been obtained by electrospinning of cellulose solutions. Cellulose are directly dissolved in two solvent systems: (a) lithium chloride (LiCl)/N,N-dimethyl acetamide (DMAc) and (b) N-methylmorpholine oxide (NMMO)/water, and the effects of (i) solvent system, (ii) the degree of polymerization of cellulose, (iii) spinning conditions, and (iv) post-spinning treatment such as coagulation with water on the miscrostructure of electrospun fibers are investigated. The scanning electron microscope (SEM) images of electrospun cellulose fibers show that applying coagulation with water right after the collection of fibers is necessary to obtain submicron scale, dry and stable cellulose fibers for both solvent systems. X-ray diffraction studies reveal that cellulose fibers obtained from LiCl/DMAc are mostly amorphous, whereas the degree of crystallinity of cellulose fibers from NMMO/water can be controlled by various process conditions including spinning temperature, flow rate, and distance between the nozzle and collector. Finally, electrospun cellulose fibers are oxidized by HNO₃/H₃PO₄ and NaNO₂, and the degradation characteristics of oxidized cellulose fibers under physiological conditions are presented.     

Air gap spinning of a cellulose solution in [DBNH][OAc] ionic liquid with a novel vertically arranged spinning bath to simulate a closed loop operation in the Ioncell® process

A novel, small-volume vertically arranged spin bath was successfully developed for an air gap lyocell-type spinning process. A maximum regeneration bath length with a minimum free volume characterizes the concept of the new spin bath. Using the ionic liquid (IL) 1,5-diazabicyclo[4.3.0]non-5-enium acetate [DBNH][OAc], the spin bath showed very good spinning performances of IL-cellulose dopes at high draw ratios and spinning duration for single filament spinning experiments. Using this new device, it was possible to get a step further in the optimization of the Ioncell® process and simulate a process closed loop operation by performing single filament spinning in IL/H₂O mixtures. Good dope spinnability and preserved fibers mechanical properties were achieved in a coagulation bath containing up to 30 wt% IL. It is only at 45 wt% of IL in the bath that the spinnability and fibers mechanical properties started to deteriorate. The fibers fibrillar structure was less pronounced in IL-containing spinning bath in comparison to a pure water bath. However, their crystallinity after washing was preserved regardless of the spinning bath composition. The results presented in this work have a high relevance to the upscaling of emerging IL-based cellulose dissolution and spinning processes.     

X-ray studies of regenerated cellulose fibers wet spun from cotton linter pulp in NaOH/thiourea aqueous solutions

Regenerated cellulose fibers were fabricated by dissolution of cotton linter pulp in NaOH (9.5 wt%) and thiourea (4.5 wt%) aqueous solution followed by wet-spinning and multi-roller drawing. The multi-roller drawing process involved three stages: coagulation (I), coagulation (II) and post-treatment (III). The crystalline structure and morphology of regenerated cellulose fiber was investigated by synchrotron wide-angle X-ray diffraction (WAXD) and small-angle X-ray scattering (SAXS) techniques. Results indicated that only the cellulose II crystal structure was found in regenerated cellulose fibers, proving that the cellulose crystals were completely transformed from cellulose I to II structure during spinning from NaOH/thiourea aqueous solution. The crystallinity, orientation and crystal size at each stage were determined from the WAXD analysis. Drawing of cellulose fibers in the coagulation (II) bath (H₂SO₄/H₂O) was found to generate higher orientation and crystallinity than drawing in the post-treatment (III). Although the post-treatment process also increased crystal orientation, it led to a decrease in crystallinity with notable reduction in the anisotropic fraction. Compared with commercial rayon fibers fabricated by the viscose process, the regenerated cellulose fibers exhibited higher crystallinity but lower crystal orientation. SAXS results revealed a clear scattering maximum along the meridian direction in all regenerated cellulose fibers, indicating the formation of lamellar structure during spinning.     

Nanoindentation study of individual cellulose nanowhisker-reinforced PVA electrospun fiber

Electrospun poly(vinyl alcohol) (PVA) fiber and its composites have been widely studied recently. However, most physical properties reported in literature are measured from a nanofiber web. In this study, for the first time, the mechanical properties of individual electrospun fiber, rather than fiber web, of cellulose nanowhisker-reinforced poly(vinyl alcohol) was studied using nanoindentation technique. The modulus is 2.1 GPa for a pure PVA electrospun fiber, and 7.6 GPa for 20.0 wt% cellulose nanowhisker-reinforced PVA electrospun fiber, respectively. The modulus of PVA/cellulose nanowhisker electrospun fibers increases linearly with increasing loading ratio of cellulose nanowhiskers up to 20.0 wt%. The experimental results were compared with that calculated using isotropic and longitudinal Halpin–Tsai models. The modules of the cellulose nanowhiskers are 60–80 % higher than the isotropic model predictions but lower than longitudinal model prediction, suggesting the nanowhiskers are partially aligned to the electrospun fiber direction.     

Microstructure and characterization of electrospun poly(vinyl alcohol) nanofiber scaffolds filled with graphene nanosheets

Graphene nanosheets (GNSs) have attracted significant scientific attention because of their remarkable features, including exceptional electron transport, excellent mechanical properties, high surface area, and antibacterial functions. Poly(vinyl alcohol) (PVA) solutions filled with GNSs were prepared for electrospinning, and their spinnability was correlated with their solution properties. The effects of GNS addition on solution rheology and conductivity were investigated. The as‐spun fibers were characterized via scanning electron microscopy (SEM), transmission electron microscopy (TEM), wide‐angle X‐ray diffraction (WAXD), and differential scanning calorimetry (DSC). The results revealed the effects of GNS on the microstructure, morphology, and crystallization properties of PVA/GNS composite nanofibers. The addition of GNSs in PVA solution increased the viscosity and conductivity of the solution. The electrospun fiber diameter of the PVA/GNS composite nanofiber was smaller than that of neat PVA nanofiber. GNSs were not only embedded at the fibers but also formed protrusions on the fibers. In addition, the crystallinity of PVA/GNS fiber decreased with higher GNS content. The possible application of PVA/GNS fibers in tissue engineering was also evaluated. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41891.     

改性酪蛋白/羧甲基纤维素钠共混纤维制备与性能

采用湿法纺丝,以乙醇、氯化钙和盐酸的混合溶液为凝固浴制备了改性酪蛋白(CLC)/羧甲基纤维素钠(CMC-Na)共混纤维。通过测试纺丝液流动性以及纤维的红外光谱、表面形态和力学性能,研究了CLC和CMC-Na不同配比与纺丝溶液pH改性后酪蛋白纤维的力学性能增加,纺丝溶液的流动性与CMC-Na维的红外光谱分析表明CLC与CMC-Na之间有良好的相互作用。CMC-Na质量分数为30%(相对于改性酪蛋白)的共混纤维性能较好,纤维表面较致密,有沿着纤维轴向取向的明显条纹,其断裂强度为341.19MPa。     

离子液体法再生纤维素纤维制造技术及发展趋势

首先概述了再生纤维素纤维制造技术的发展历史,总结了以天然纤维素为原料的黏胶纤维、Lyocell纤维和离子液体纤维（Ioncell）及其技术发展现状。重点介绍了这三种再生纤维素纤维的性能、应用领域及市场前景,并比较了其生产工艺,包括纺丝原液的制备、纺丝工艺、溶剂回收等。与黏胶纤维相比,Lyocell 纤维和Ioncell纤维在溶解纤维素及干喷湿纺纺丝方面具有独特的优势。进一步对该类技术的重点和难点,如纺丝原液的连续制备和溶剂的高效回收进行了分析。与Lyocell纤维使用的NMMO溶剂相比,Ioncell纤维使用的离子液体具有离子液体可设计等优点,可根据纤维素原料的不同来源,设计合成对纤维素具有更好的溶解能力而无降解特征且环境友好的离子液体溶剂,同时对温度、金属离子具有很好的稳定性,为发展新一代纤维素绿色制造技术提供了新途径。另外,对Ioncell纤维存在的问题也进行了详细的分析,提出了未来拟开展的重点研究方向和拟解决的关键难题。     

New class of cellulose fiber spun from the novel solution of cellulose by wet spinning method

A novel cellulose solution, prepared by dissolving an alkali-soluble cellulose, which was obtained by the steam explosion treatment on almost pure natural cellulose (soft wood pulp), into the aqueous sodium hydroxide solution with specific concentration (9.1 wt %) was employed for the first time to prepare a new class of multifilament-type cellulose fiber. For this purpose a wet spinning system with acid coagulation bath was applied. The mechanical properties and structural characteristics of the resulting cellulose fibers were compared with those of regenerated cellulose fibers such as viscose rayon and cuprammonium rayon commercially available. X-ray analysis shows that the new cellulose fiber is crystallographically cellulose II, and its crystallinity is higher but its crystalline orientation is slightly lower than those of other commercial regenerated fibers. The degree of breakdown of intramolecular hydrogen bond at C₃[X_am(C₃)] of the cellulose fiber, as determined by solid-state cross-polarization magic-angle sample spinning (CP/MAS) ¹³C NMR, is much lower than other, and the NMR spectra of its dry and wet state were significantly different from each other, indicating that cellulose molecules in the new cellulose fiber are quite mobile when wet. This phenomenon has not been reported for so-called regenerated cellulose fibers.     

The morphology of electrospun polystyrene fibers

Electrospinning is a process of electrostatic fiber formation which uses electrical forces to produce polymer nanofibers from polymer solution. The electrospinning system consists of a syringe feeder system, a collector system, and a high power supplier. The important parameters in the morphology of electrospun polystyrene fibers are concentration, applied voltage, and solvent properties. Higher concentrations of the polymer solution form thicker fibers and fewer beads. When the concentration is 7 wt%, electrospun fibers have an average diameter of 340 nm, but as the concentration of PS increases to 17 wt%, the fiber diameter gradually thickens to 3,610 nm. The fiber morphology under different solvent mixture ratios and solvent mixtures has also been studied.     

Electrospinning of thermoplastic polyurethane microfibers and nanofibers from polymer solution and melt

Electrospinning technique was used to produce ultrafine fibers from thermoplastic polyurethane (TPU). A direct comparison between melt and solution electrospinning of TPU was provided for the evaluation of process–structure relationship. It was found that the deposition rate of melt electrospinning (0.6 g h^?1) is four times higher than that of solution electrospinning (0.125 g h^?1) for TPU under the same processing condition. However, the average fiber diameters of solution electrospun TPUs (220–280 nm) were much lower than those of melt electrospun TPUs (4–8 μm). The effect of processing variables including collection distance and electric field strength on the electrospun fiber diameter and morphology was also studied. The findings indicate that increasing the electric field strength yielded more electrical forces acting on polymer jet and resulted in a decrease in fiber diameter as a result of more fiber drawing in both solution and melt electrospun fibers. It was also demonstrated that increasing the collection distance led to an improvement in the solidification of melt electrospun fibers and thus less fused fibers were obtained. Finally, a close investigation of fiber structures revealed that melt electrospun TPU fibers had smooth surface, whereas solution electrospun TPU fibers showed high intensity of cracks on the fiber surface. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Processing of Cellulose Using Ionic Liquids

The processing of cellulose dissolved in ionic liquids (ILs) enables the development of new materials. Besides the established production of cellulosic fiber products, interesting technical applications are developed like super micro filament fibers, cellulose/chitin blend fibers, precursors for carbon fibers, and all‐cellulose composites. This review provides a detailed summary of these new developments and describes how ILs are selected for the processing of cellulose with a particular emphasis on industrial realization. State‐of‐the‐art spinning processes are reviewed and it is illustrated how uniquely selected ILs can be used not only for established fiber spinning but for the development of new cellulose‐based materials.     

聚醚砜的静电纺丝研究

采用聚醚砜(PES)的良溶剂二甲基甲酰胺(DMF)和非良溶剂丙酮(AC)为共溶剂体系,研究了溶剂组成、纺丝成形条件对静电纺丝PES纤维的形貌及纤维直径的影响。结果表明:DMF/AC的配比对于静电纺丝PES纤维形貌具有直接的调控作用,随着DMF/AC混合溶剂中AC用量的增加,纤维平均直径变大,纤维毡中串珠数目明显减少,纤维均一性变好;随着纺丝液浓度的升高,纺丝电压的增大,纤维的平均直径变大;接收距离的变化对纤维平均直径影响不大;PES最佳纺丝工艺条件为纺丝溶液质量分数13%,纺丝电压15 kV,接收距离10 cm,mDMF/mAC为8.5/1.5,在此条件下,可以获得纤维平均直径为96 nm的PES纤维毡。