Chitin/cellulose blend fibers prepared by wet and dry‐wet spinning

We describe the wet and dry‐wet spinning of multifilament cellulosic composite fibers, namely chitin/cellulose fibers. The direct solution process for the two biopolymers based on an ionic liquid as solvent represents an environmentally friendly and alternative technology to the industrially applied viscose and lyocell process. Both cellulose and chitin possess good solubility in 1‐ethyl‐3‐methylimidazolium propionate ([C₂C₁Im][OPr]) and were spun into multifilament composite fibers. Moreover, for the first time, pure chitin multifilament fibers were obtained by dry‐wet spinning. The effect of chitin addition on the filament properties was investigated and evaluated by microscopic, spectroscopic, and mechanical analyses.     

Effect of coagulant temperature and composition on surface morphology and mass transfer properties of cellulose acetate hollow fiber membranes

Cellulose acetate (CA) hollow fibers were spun via the dry‐jet wet spinning technique under various external coagulant compositions and temperatures. The surface morphology of the resulting hollow fiber was examined using field emission scanning electron microscopy (FESEM) and tapping mode atomic force microscopy (TMAFM). The pure water permeability (PWP) and the retention of dextran of the hollow fiber were also measured. The results showed that both the temperature and composition can affect greatly the surface morphology and hence the permeation performance of hollow fiber membranes when the temperature was over 55°C and the dimethyl formamide (DMF) content was higher than 15%. The on‐line draw ratio increased with the coagulant temperature and DMF content (in the range of 0 to 10%) in the external coagulant. The ultimate tensile strength also increased when the fibers were coagulated in 5–10% DMF and at 70°C. The PWP increased with the DMF content in the coagulant and the coagulant temperature. The retention of dextran decreased with the increase of the DMF content in the coagulant and the coagulant temperature. Copyright © 2005 John Wiley & Sons, Ltd.     

Electrospun fiber mats of poly(3‐hydroxybutyrate), poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate), and their blends

Electrospinning of poly(3‐hydroxybutyrate) (PHB), poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) (PHBV), and their blends was first carried out in chloroform at 50 °C on a stationary collector. The average diameter of the as‐spun fiber from PHB and PHBV solutions decreased with increasing collection distance and increased with increasing solution concentration and applied electrical potential. In all of the spinning conditions investigated, the average diameter of the as‐spun pure fibers ranged between 1.6 and 8.8 μm. Electrospinning of PHB, PHBV, and their blends was carried out further at a fixed solution concentration of 14% w/v on a homemade rotating cylindrical collector. Well‐aligned, cross‐sectionally round fibers without beads were obtained. The average diameter of the as‐spun pure and blend fibers ranged between 2.3 and 4.0 μm. The as‐spun fiber mats appeared to be more hydrophobic than the corresponding films and much improvement in the tensile strength and the elongation at break was observed for the blend fiber mats over those of the pure fiber ones. Lastly, indirect cytotoxicity evaluation of the as‐spun pure and blend fiber mats with mouse fibroblasts (L929) indicated that these mats posed no threat to the cells. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 2923–2933, 2006     

A Preliminary Study on Preparation of the Aromatic/Aliphatic Co‐polyurea as Spun Fibers

Aromatic‐aliphatic co‐polyurea has been synthesized from 4,4 prime‐diphenylmethane diisocyanate (MDI), m‐phenylene diamine (m‐PDA), and 1,6‐diaminohexane (HDA) in DMAc by solution polymerization. The chemical structure of the co‐polyurea has been characterized by ¹H‐NMR. The thermal properties of the copolymers were measured by DSC and TGA. The co‐polyurea solutions were spun into fibers by means of wet spinning. The effects of coagulation conditions on the morphologies and mechanical properties of the co‐polyurea as spun fibers are discussed.     

Continuous cellulose fiber-reinforced cellulose ester composites III. Commercial matrix and fiber options

Thermoplastic composites were prepared using two continuous regenerated cellulose fiber types, rayon and lyocell, and with several different commercially-available thermoplastic cellulose esters as matrix. Matrix options included cellulose acetate propionate (CAP), and several cellulose acetate butyrates (CAB) with different butyryl content, having different molecular weights and different methods of plasticization (adipates and very low molecular weight cellulose ester fractions). Choice of cellulose ester type was generally found to have little or no effect on mechanical properties. A significant effect, however, was revealed for fiber type. The lyocell-based composites thereby were reflective of the greater stiffness of a fiber produced from anisotropic solution state. Their modulus consistently exceeded 20GPa whereas the rayon fiber-based composites had moduli between 6 and 8GPa. The latter, however, possessed failure strains that were 3 to 4 times greater than their stiffer counterparts.     

有机蒙脱土改性聚氨酯纺丝研究

无机纳米颗粒如二氧化硅、二氧化钛和有机改性层状硅酸盐添加到聚合物如塑料和橡胶基质中,可以提高复合材料的某些力学性能、使用性能和热学性能,如强度、模量、热变形温度、阻隔性能和阻燃性能等等.近年来,将无机纳米颗粒加入到纤维基质中,以期获得纳米复合纤维也成为国内关注     

Morphology and properties of fibers based on polycarbonate/liquid crystalline polymer blends

Polycarbonate-triad-4–co-polybutylene terephthalate liquid crystalline blends were prepared and spun into fibers. It has been shown that fibrillation of the thermotropic liquid crystalline polymer (TLCP) takes place at the given spinning conditions, forming thus “in situ” reinforcement. Continuous fibrils are formed at concentrations between 2.5 and 5% LCP. A degree of miscibility between two phases was observed. The moduli of both as-spun and cold drawn fibers increase almost linearly with increasing concentration of TLCP. Tensile strength was found to decrease and elongation at break to increase with increasing TLCP content. The structure of the cold drawn fibers was not stable with time, causing a relaxation in the observed properties.     

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.     

Unique crystalline structure and performance of poly(ethylene terephthalate) melt spun fibers

Modification of the threadline dynamics has effected significant alternations in the structure and improvements in the properties of high-speed melt spun poly(ethylene terephthalate) (PET) fibers. Key process parameters extant in the threadline dynamics, such as temperature, tensile stress, and deformation time, were independently controlled through proper implementation of on-line perturbations. The placement of a liquid isothermal bath in close proximity to the spinneret in the melt spinning threadline provided tremendous increase in the spinning stress while at the same time controlled the filament temperature corresponding to development of the desired fiber structure. Characterization of the fiber structure and physical properties has been carried out using birefringence measurements, density, shrinkage, x-ray diffraction, DSC, FTIR spectroscopy, and tensile tests. The results provided sufficient evidence to support the existence of a unique crystalline morphology that led to the significantly improved tensile properties and excellent dimensional stability of the resulting fibers. This unique crystalline morphology was typically characterized by the presence of a larger amount of extended chain segments and an enhanced molecular connectivity. ©1995 John Wiley & Sons, Inc.     

The preparation and characterization of silver‐loading cellulose acetate hollow fiber membrane for water treatment

Silver‐loading asymmetric cellulose acetate (CA) hollow fiber membrane was spun via the dry jet‐wet spinning technique. The spinning solution was prepared by dissolving AgNO₃ and CA in N,N‐dimethylformamide (DMF). The silver ions were reduced in the spinning dope into silver nano‐particles. The morphology of the resulting hollow fibers was examined using a scanning electron microscope and the silver content in the fiber was measured using an inductively coupled plasma atomic emission spectrometer. The antibacterial activities were evaluated. These hollow fibers had a sponge‐like structure and dense inner and outer surfaces. At a 50 k magnification, the pore on the skin layer was not observable, while the nodule size was smaller than 10 nm. The residual silver content of as‐spun hollow fiber was about 60% of the original silver added in the polymer solution. After immersing in water bath for 180 days, the silver content in the bulk of the hollow fibers decreased to 60% and the silver content on the surface reduced to 10%, yet still showed antibacterial activity against Escherichia coli and Staphylococcus aureus. After permeating with water for 5 days, the silver content in the hollow fibers decreased, and did not show antibacterial activity against E. coli and S. aureus. Thus, silver content must be periodically replenished after permeation. The proper range of AgNO₃ in the spinning solution for CA hollow fiber should be about 100–1000 ppm. Copyright © 2005 John Wiley & Sons, Ltd.     

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.     

Centrifugally spun poly(ethylene oxide) fibers rival the properties of electrospun fibers

Centrifugal force spinning (CFS), also known as centrifugal spinning, forcespinning, or rotary jet spinning, provides considerably higher production rates than electrospinning (ES), but the more widespread use of CFS as an alternative depends on the ability to produce fibers with robust thermal and mechanical properties. Here, we report the CFS of poly(ethylene oxide) (PEO) fibers made using a spinning dope formulated with acetonitrile (AcN) as the volatile solvent, and we describe the thermal and mechanical properties of the centrifugally-spun fibers. Even though the formation, diameter, and morphology of electrospun and centrifugally-spun PEO fibers are relatively well-studied, the article presents three crucial contributions: the pioneering use of PEO solutions in AcN as spinning dope, characterization of crystallinity and mechanical properties of the centrifugally-spun PEO fibers, and a comparison with the corresponding properties of electrospun fibers. We find that fiber formation occurrs for the chosen CFS conditions if polymer concentration exceeds the entanglement concentration, determined from the measured specific viscosity. Most significantly, the centrifugally spun PEO fibers display crystallinity, modulus, elongation-at-break, and fiber diameter that rival the properties of electrospun PEO fibers reported in the literature.     

Fiber formation from liquid-crystalline precursors. II. Cellulose in N,N-dimethylacetamide-lithium chloride

Fibers were spun from isotropic and biphasic solutions of regenerated cellulose (DP = 290) in N, N-dimethylacetamide +7.8% LiCl using water as a coagulant. There is an increase in mechanical properties through the isotropic → anisotropic transition with moduli reaching 22 GPa. The problem with this system is that crystallization encroaches on the biphasic region, and a pure mesophase is never observed. However, owing to the slow nucleation rate of the crystals, a biphasic solution is stable for a long time and can be spun to yield high modulus and orientation. The best approach is to use small flow gradients (extrusion rate and pick-up ratio) and to allow long times for homogenization and nucleation of the mesophase.     

All-cellulose nanocomposite fibers produced by melt spinning cellulose acetate butyrate and cellulose nanocrystals

Bio-based continuous fibers were prepared by melt spinning cellulose acetate butyrate (CAB), cellulose nanocrystals (CNC) and triethyl citrate. A CNC organo-gel dispersion technique was used and the prepared materials (2 and 10 wt% CNC) were melt spun using a twin-screw micro-compounder and drawn to a ratio of 1.5. The microscopy studies showed that the addition of CNC in CAB resulted in defect-free and smooth fiber surfaces. An addition of 10 wt% CNC enhanced the storage modulus and increased the tensile strength and Young’s modulus. Fiber drawing improved the mechanical properties further. In addition, a micromechanical model of the composite material was used to estimate the stiffness and showed that theoretical values were exceeded for the lower concentration of CNC but not reached for the higher concentration. In conclusion, this dispersion technique combined with melt spinning can be used to produce all-cellulose nanocomposites fibers and that both the increase in CNC volume fraction and the fiber drawing increased the mechanical performance.     

Nonalkali swelling solutions for regenerated cellulose

Swelling of regenerated cellulose in nonalkali aqueous solutions containing lithium chloride and urea (LiCl/urea/water) was examined. The effect of solution concentration on fiber properties was studied using microscopy, weight gain (swelling), and mechanical strength tests. The regenerated cellulose samples included lyocell fibers, viscose fibers, and fibers spun from alkali. The change in the mechanical properties of treated fibers was smaller than that of fibers treated with alkali to the same level of swelling. The degree of swelling in these solutions was related to the propensity for the formation of Li–cellulose coordination complexes, and these were enhanced by reductions in both urea and water content.     

碳纳米管改性聚苯硫醚熔纺纤维的结构与性能研究

将多壁碳纳米管(MWCNTs)和聚苯硫醚(PPS)经过熔融挤出后制备成复合材料切片,并采用熔融纺丝法制得碳纳米管改性聚苯硫醚复合纤维.采用扫描电镜(SEM)、拉曼光谱、示差扫描量热分析(DSC)、动态机械分析(DMA)以及力学性能测试等表征手段研究了复合纤维中碳管的分散状态,与基体的界面作用,复合纤维的结晶性能以及力学性能,从而探讨了聚苯硫醚/碳纳米管复合纤维体系的微观结构与宏观性能之间的关系.研究表明,聚苯硫醚分子结构与碳纳米管之间具有的π-π共轭作用使碳管较为均匀的分散在基体中,界面结合较为紧密.同时熔融纺丝过程中的拉伸作用使碳管进一步解缠并使碳管沿纤维拉伸方向取向.另一方面,拉曼光谱显示拉伸作用有效地增强了界面作用,有利于外界应力的传递.碳管的良好分散以及强的界面作用使复合纤维力学性能得到大幅度的提高,当碳管含量达到5 wt%时,复合纤维的模量有了明显的提高,拉伸强度较纯PPS纤维提高了近220%.     

Morphological characteristics of the lyotropic and gel phases in the cellulose/NH3/NH4SCN system

Solutions of cellulose in the ammonia/ammonium thiocyanate (24.5/75.5 w/w) solvent form several stable phases. Of particular interest in this work are the temperature-dependent liquid crystalline and gel phases which are stable at cellulose concentrations above 6% w/v. While the temperature-composition conditions yielding these phases are reasonably well established, very little is currently known about the morphological characteristics of lyotropic and gelled cellulose. Polarized light microscopy is employed here to demonstrate that solutions at temperatures above the gel melting point are birefringent, composed of liquid crystals. Field-emission scanning electron microscopy has been used to (i) examine the three-dimensional network in cellulose gels, and (ii) correlate network morphology with cellulose molecular weight and solution concentration. Results obtained from two complementary sample preparation techniques (i.e., critical point drying and freeze drying) are compared to identify and minimize artifacts, and reveal that gel formation occurs as the solutions phase-separate into polymer-rich anisotropic and solvent-rich isotropic phases. The polymer-rich phase is highly interconnected and forms a fibrillar network, with fibrils measuring 20–70 nm in diameter. © 1996 John Wiley & Sons, Inc.     

Structure–properties relationship in spun fibers of poly(ethylene terephthalate): Comparisons between samples obtained by terephthalic acid or dimethyl terephthalate processes

Some properties and structural aspects of fibers obtained by spinning, in a wide range of take-up speed (2,800–4,400 m/min), of commercial samples of PET, produced by dimethyl terephthalate (DMT) and the terephthalic acid (TPA) processes, are compared. For a same take-up speed, the considered fibers from TPA are spun at lower pack pressures and always show higher tenacity and lower ductility than fibers from DMT. X-ray diffraction, density, and birefringence measurements indicate that, for the fibers from the DMT process, an earlier crystallization occurs which prevents the progress of the orientation of the amorphous phase. The lower molecular orientation in the amorphous phase of the fibers from DMT, in turn, accounts for their lower tenacity. The earlier crystallization of the fibers from DMT would be related to their slightly higher melting temperatures and melt viscosities, which could be due to the lower amount of constitutional defects (diethylene glycol content) in the considered PET samples from DMT compared with those from TPA. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35 : 889–896, 1997     

Microstructural investigation of high‐speed melt‐spun nylon 6 fibers produced with variable spinning speeds

The structural details of high‐speed melt‐spun nylon 6 fibers at spinning speeds ranging from 4500 to 6100 m/min were investigated by solid‐state proton nuclear magnetic resonance (¹H NMR) spectroscopy, density and birefringence measurements, differential scanning calorimetry (DSC), and X‐ray diffraction (XRD). The analyses of the proton spin‐lattice relaxation times in the rotating frame and correlation times confirmed the existence of three different phases, the immobile crystalline, intermediate rigid amorphous, and mobile amorphous regions, in the fiber sample. At spinning speeds lower than 5200 m/min, the portion of the crystalline phase increased at the expense of the rigid amorphous region and then reached a plateau afterward, from which the mobile amorphous portion increased. Combined analyses of density and birefringence measurements, DSC, and XRD in conjunction with NMR results indicated that the formation of the γ crystal became predominant compared to that of the α crystal. The orientation factor of the crystalline phase increased slightly with increasing spinning speed, whereas the amorphous orientation factor decreased because of the increase of the purely amorphous region. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 1285–1293, 2000     

Continuous cellulose fiber-reinforced cellulose ester composites. I. Manufacturing options

Thermoplastic fiber composites were prepared using high modulus lyocell (regenerated cellulose) fibers for reinforcement and cellulose acetate butyrate (CAB) as matrix. Choices were made with regard to fiber options (fabric versus continuous tow) and method of matrix deposition (prepregging by powder coating, film stacking, or solution impregnating). The results suggest that solution-prepregged fiber tow consolidated at circa 200°C produced unidirectional consolidated panels with tensile strength, modulus, and strain at failure values of approximately 250MPa,>20GPa and 3–4%, respectively, at fiber volume contents of approximately 60%. Modulus and ultimate tensile strength increased with fiber content, and modulus followed rule-of-mixture behavior. Adequate surface wetting and matrix-fiber adhesion were found with solution-prepregged composites. The unexpectedly low strain at failure (2 to <4%) was attributed to brittle matrix failure, and failure surfaces revealed that the fibers, for the most part, remained intact after the matrix had failed.