Structure and properties of regenerated cellulose fibers from aqueous NaOH/thiourea/urea solution

Regenerated cellulose fibers were successfully prepared through dissolving cotton linters in NaOH/thiourea/urea aqueous solution at ?2 °C by a twin-screw extruder and wet-spinning process at varying precipitation and drawing conditions. The dissolution process of an optimized 7 wt% cellulose was controlled by polarizing microscopy and resulted in a transparent and stable cellulose spinning dope. Rheological investigations showed a classical shear thinning behavior of the cellulose/NaOH/thiourea/urea solution and a good stability towards gelation. Moreover, the mechanical properties, microstructures and morphology of the regenerated cellulose fibers were studied extensively by single fiber tensile testing, X-ray diffraction, synchrotron X-ray investigations, birefringence measurements and field-emission scanning electron microscopy. Resulting fibers demonstrated a smooth surface and circular cross-section with homogeneous morphological structure as compared with commercial viscose rayon. At optimized jet stretch ratio, acidic coagulation composition and temperature, the structural features and tensile properties depend first of all on the drawing ratio. In particular the crystallinity and orientation of the novel fibers rise with increasing draw ratio up to a maximum followed by a reduction due to over-drawing and oriented crystallites disruption. The microvoids in the fiber as analysed with SAXS were smaller and more elongated with increasing drawing ratio. Moreover, a higher tensile strength (2.22 cN/dtex) was obtained in the regenerated fiber than that of the viscose rayon (2.13 cN/dtex), indicating higher crystallinity and orientation, as well as more elongated and orientated microvoid in the regenerated fiber. All in all, the novel extruder-based method is beneficial with regard to the dissolution temperature and a simplified production process. Taking into account the reasonable fiber properties from the lab-trials, the suggested dissolution and spinning route may offer some prospects as an alternative cellulose processing route.     

Xylan enriched viscose fibers

In this study, a new xylan enriched viscose fiber was developed. A high molecular weight xylan with a degree of polymerization of 150–200 was added during a late stage of the viscose production process. The xylan deriving from a cold caustic extraction (CCE) of an eucalypt paper pulp was introduced to the process after xanthation and thus neither objected to any degradation conditions during alkalization nor to the xanthation step. About 90 % of the added xylan was transferred to the final fiber. A xylan content of up to 7.5 % was achieved. Fiber properties like strength showed a comparable level to the reference fibers while the water retention value was clearly raised due to the higher content of hemicelluloses. The hemicellulose distribution over the fiber cross section was investigated by enzymatic peeling. Even though a segregation of the different polysaccharides was observed, the goal of a good blending of CCE-xylan into cellulosic fibers with new interesting features was achieved.     

Preparation and Properties of Alginate/Water‐Soluble Chitin Blend Fibers

Water‐soluble chitin (half‐deacetylated chitin) was prepared from chitosan by N‐acetylation with acetic anhydride. Alginate/water‐soluble chitin blend fibers were prepared by spinning their mixture solution through a viscose‐type spinneret into a coagulating bath containing aqueous CaCl₂ and ethanol. The structure and properties of the blend fibers were studied with the aids of infrared spectra (IR), X‐ray diffraction (XRD) and scanning electron microscopy (SEM). structure analysis indicated good miscibility existed between alginate and water‐soluble chitin, due to the strong interaction from the intermolecular hydrogen bonds and electrostatic interactions. Best values for the dry tensile strength and breaking elongation were obtained when the water‐soluble chitin content was 30 wt%. The wet tensile strength and breaking elongation decreased with the increase of water‐soluble chitin content. The introduction of water‐soluble chitin in the blend fiber can improve the water‐retention properties of the blend fiber compared to pure alginate fiber. The fibers treated with aqueous solution of silver nitrate have good antibacterial activity to Staphylococcus aureus.     

Thermal behavior and the compensation effect of vegetal fibers

The thermal degradation behavior and the Arrhenius parameter of curaua, kenaf, and jute vegetal fibers were studied using X-ray diffraction (XRD), Fourier-transform infrared (FTIR) spectroscopy, and thermogravimetry analysis. XRD showed that the crystallite sizes in the (200) plane were in the order: curaua < jute < kenaf, and similar results were obtained for basal spacing. FTIR spectroscopy corroborated the XRD results. The thermal behavior of the fibers was analyzed by identifying the cellulose and hemicellulose content using independent parallel first-order models. The results were not very consistent with the kinetic degradation models of Kissinger, Friedman, and Flynn–Wall–Ozawa (taking into account the standard errors), which were used to determine the apparent activation energy of the fibers. In addition, the frequency factor (pre-exponential parameter) was observed to be independent of the heating rate. The fibers exhibited a compensation effect; i.e., higher apparent activation energies led to higher frequency factors. Finally, the solid-state degradation mechanism of all fibers was found to comprise diffusion and random nucleation followed by instantaneous growth of nuclei.     

Extraction and Characterization of Cellulose Nanowhiskers from Balsa Wood

Summary: In this study cellulose nanowhiskers were obtained from balsa wood. For this purpose, fibers of balsa wood were exposed to hydrolysis reactions for lignin and hemicellulose digestion and acquisition of nano-scale cellulose. Transmission electron microscopy (TEM) results demonstrated that the obtained cellulose nanocrystals had average length and thickness of 176 (±68 nm) and 7.5 (±2.9 nm), respectively. Infrared spectroscopy (FTIR) and wide angle x-ray diffraction (WAXD) showed that the process for extracting the nanowhiskers digested nearly all the lignin and hemicellulose from the balsa fiber and still preserved the aspect ratio and crystallinity satisfactory enough for future application as nanofillers in polymer nanocomposites. The thermogravimetric analysis (TGA) showed that the onset temperature of thermal degradation of the cellulose nanocrystals (226 °C) was higher than the onset temperature of the balsa fiber (215 °C), allowing its use in molding processes with polymers melts.     

Thermal analysis of less common lignocellulose fibers

The thermal behavior of four unusual lignocellulose fibers — namely Caroa, Curaua, Piassava and Sponge gourd — is described. Caroa and Curaua fibers showed a more homogeneous thermal degradation, with a single peak dominating in the DTG curve. Piassava and Sponge gourd showed two separated peaks, revealing the more pronounced amounts of hemicellulose present at these fibers. All four fibers are, however, thermally stable up to temperatures of around 200°C. The activation energies for the thermal degradation of the fibers were similar, except for the Caroa fiber. The lower activation energy associated to this fiber was attributed to its higher hemicellulose to cellulose ratio.     

Comparison of the degradation behavior of cotton, linen, and kozo papers

The long term degradation behavior of cotton, linen, and kozo papers was studied to compare changes to the chemical and physical properties with time. The elemental composition, α-content, β-content, γ-content, and lignin content (K number) of the three unaged controls were determined. The papers were then degraded at 90 °C and 50 % relative humidity for several thousand hours. Changes to the pH, carbonyl content, yellowness index (YI), moisture content, molecular weight, and tensile strength with aging were monitored. The general trends in degradation behavior of linen and kozo papers were similar to cotton in that all three showed decreases in pH, molecular weight, and strength as well as increases in carbonyl content and YI during hydrolysis. However, the kinetics of degradation differed between the three papers. The cellulose component of all three papers dominated measured changes to the molecular weight while the presence of hemicellulose in the linen and kozo papers led to unique measured moisture contents, carbonyl group, and YI values relative to cotton after the same amount of degradation had occurred.     

Ionic liquid extraction method for upgrading eucalyptus kraft pulp to high purity dissolving pulp

High purity cellulose from wood is an important raw material for many applications such as cellulosic fibers, films or the manufacture of various cellulose acetate products. Hitherto, multi-step refining processes are needed for an efficient hemicellulose removal, most of them suffering from severe cellulose losses. Recently, a novel method for producing high purity cellulose from bleached paper grade birch kraft pulp was presented. In this so called IONCELL process, hemicelluloses are extracted by an ionic liquid–water mixture and both fractions can be recovered without yield losses or polymer degradation. Herein, it is demonstrated that bleached Eucalyptus urograndis kraft pulp can be refined to high purity acetate grade pulp via the IONCELL process. The hemicellulose content could be reduced from initial 16.6 to 2.4 wt% while persevering the cellulose I crystal form by using an optimized 1-ethyl-3-methylimidazolium dimethylphosphate-water mixture as the extraction medium. The degree of polymerization was then reduced by a sulfuric acid treatment for subsequent acetylation of the pulp, resulting in a final hemicellulose content of 2.2 wt%. When pre-treating the pulp enzymatically with endoxylanase, the final hemicellulose content could be reduced even to 1.7 wt%. For comparison, the eucalyptus kraft pulp was also subjected to cold caustic extraction and the same subsequent acid treatment which led to 3.9 wt% of residual hemicelluloses. The performance in acetylation of all produced pulps was tested and compared to commercial acetate grade pulp. The endoxylanase-IONCELL-treated pulp showed superior properties. Thus, an ecologically and economically efficient alternative for the production of highest value cellulose pulp is presented.     

Formation of a large‐scale shish‐kebab structure of polyoxymethylene in the melt spinning and the crystalline morphology evolution after hot stretching

Polyoxymethylene (POM) fiber was produced by melt spinning with a high take‐up speed, which imposed a strong flow field. An unexpected formation of a shish‐kebab morphology with multiple shish of POM fibers was reported for the first time. This morphology is a large‐scale shish kebab with a diameter of 10.5 µm. Further orientation of the POM fiber was obtained by hot stretching twice at 160°C. Two crystalline morphology evolution processes were also observed: (i) the process from the large‐scale shish‐kebab to the deformed small shish‐kebab and (ii) the process from the deformed small shish‐kebab to the perfect whiskers. Compared with the melt spinning fiber, fiber tensile strength with first and second hot stretching increased by 976% and 1705%, respectively. The crystalline melting behavior of fibers significantly changes after the first and second hot stretching. The flow field induces a large number of extended chain crystals. Copyright © 2014 John Wiley & Sons, Ltd.     

Key role of the hemicellulose content and the cell morphology on the nanofibrillation effectiveness of cellulose pulps

The effect of the hemicellulose content and that of the fibre morphology on the nanofibrillation behaviour of delignified cellulose pulps were studied. For this purpose, pulps from two non-woody plants, alfa (Stipa tenacissima) and sunflower (Helianthus annuus), were delignified using NaClO₂/acetic acid and the NaOH pulping processes to obtain fibres with different hemicellulose contents. The ensuing fibres were characterized by chemical analysis, SEM, FTIRS and X-ray diffraction. The fibres were then disintegrated into nanofibrillated cellulose (NFC) using either a high pressure homogenizer or a domestic blender. The degree of fibrillation and the morphology of the nanofibrillated fractions were evaluated by centrifugation and Field-emission scanning electron microscopy. Pulps containing the highest hemicellulose content showed higher yields of the nanofibrillated fraction and a better aptitude for the individualization of the microfibrils. Furthermore, it was shown that fibres from sunflowers exhibiting a thinner cell wall were easier to fibrillate and could be disintegrated into NFC by just using a simple domestic-blender once deliginification process was carried out using the NaClO₂/acetic acid method. Eucalyptus fibres were also used to further confirm the key role of hemicelluloses in the nanofibrillation process of woody plants.     

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.     

Extraction,modification, and characterization of natural ligno-cellulosic fiber strands from napier grass

Napier grass is a high-productivity perennial grass that is a very important forage for animals in the tropics. In this research work, fiber strands from Napier grass were extracted and the effect of acetic acid treatment on their chemical composition, morphological and structural changes, and tensile and thermal properties was studied. The acid treatment was carried out using glacial acetic acid solution at three different concentrations (5, 10, and 15%) for 2 h. Chemical analysis indicated lowering of amorphous hemicellulose content on acid treatment. FT-IR spectroscopic studies revealed variation of functional groups on acid treatment. Scanning electron micrographs indicated roughening of the surface of the fiber strands due to the removal of the hemicellulose layer on acid treatment. X-ray diffraction analysis indicated an increase in crystallinity of the fiber strands on acid treatment. The thermal stability and tensile properties of the fiber strands increased on acid treatment. This fiber has competitive advantages when evaluated with other natural fibers and can be developed further as a potential reinforcement in polymer matrix composites.     

Pretreatment of corn stover with acidic electrolyzed water and FeCl3 leads to enhanced enzymatic hydrolysis

Pretreatment has been viewed as the most efficient strategy for lignocellulosic biomass-to-fermentable sugars conversion. In this study a novel pretreatment with acidic electrolyzed water (AEW) and FeCl₃ was proposed and tested to deconstruct the recalcitrance of corn stover and enhance its subsequent cellulose-to-sugar conversion. The effects of AEW pH and FeCl₃ concentration on hemicellulose degradation were investigated, and the results showed the highest hemicellulose removal (93.40 %) and recovery (93.04 %) were achieved at AEW pH 2.30 and FeCl₃ concentration 0.05 mol/L. Further research on the properties of AEW solutions with FeCl₃, including their pH, ORP, and DO revealed the synergistic effects of strong acidity and high oxidizing capacity of the solution could boost hemicellulose breakup and enhance the enzymatic hydrolysis of cellulose (92.00 %) by removing most of hemicellulose and increasing the accessibility and digestibility of cellulose. Therefore, these studies prove AEW coupled with FeCl₃ pretreatment is an effective and promising approach in biomass-to-biofuel process.     

A rapid feedback characterization technique for polymeric hollow fiber membranes using disperse dyes

The long time lag between fiber spinning and the availability of characteristic data for process evaluation currently complicates research in hollow fiber membrane formation. This lag time is due to the down-stream processing required before traditional gas based permeation measurements can be made on the spun fiber. A rapid feedback characterization technique, based on commercially available disperse dyes, is described here for polymeric hollow fiber membrane spinning applications. This technique involves dyeing wet hollow fibers, immediately after spinning, in an aqueous dye bath. In the present work, polysulfone fibers are shown to be characterizable using this method before lengthy down-stream processing (i.e. solvent exchange, drying, and post-treatment). Dye uptake in the hollow fibers is a function of skin porosity, thereby allowing quick evaluation of permeation characteristics. Dye uptake was measured using UV-visible spectrophotometry. Examples of fibers characterized using this technique and relationships between dye uptake and post-treated permselectivity are shown and discussed.     

Short cellulose nanofibrils as reinforcement in polyvinyl alcohol fiber

Short cellulose nanofibrils (SCNF) were investigated as reinforcement for polyvinyl alcohol (PVA) fibers. SCNF were mechanically isolated from hard wood pulp after enzymatic pretreatment. Various levels of SCNF were added to an aqueous PVA solution, which was gel-spun into continuous fibers. The molecular orientation of PVA was affected by a combination of wet drawing during gel spinning and post-hot-drawing at a high temperature after drying. A maximum total draw ratio of 27 was achieved with various SCNF contents investigated. The PVA crystal orientation increased when small amounts of SCNF were added, but decreased again as the SCNF content was increased above about 2 or 3 %, likely due to SCNF percolation resulting in network formation that inhibited alignment. SCNF fillers were effective in improving PVA fiber tensile properties (i.e., ultimate strength and elastic modulus). For example, the ultimate strength and modulus of PVA/SCNF composite fiber with a SCNF weight ratio of 6 were nearly 60 and 220 % higher than that of neat PVA. Shifts in the Raman peak at ~1,095 cm^?1, which were associated with the C–O–C glycosidic bond of SCNF, indicated good stress-transfer between the SCNF and the PVA matrix due to strong interfacial hydrogen bonding. Cryogenic fractured scanning electron microscopy images of filled and unfilled PVA fibers showed uniform SCNF dispersion.     

Physico-chemical and anatomical characterization of residual lignocellulosic fibers

Anatomical and physico-chemical properties of residual natural fibers (sugarcane bagasse, coconut fibers and peanut hulls) were characterized in order to evaluate their potential for use in the production of particleboard. The bulk density was determined by helium pycnometer and the chemical characteristics by using an electronic pH meter (for pH determination) on fibers dissolved in acidic and neutral detergents (to determine the levels of cellulose, hemicellulose and lignin). The anatomical characteristics were established using scanning electron microscopy coupled with an X-ray detector system, as well as energy dispersive X-ray spectroscopy. Results indicated similarities and differences between physico-chemical and anatomical characteristics of the residual lignocellulosic fibers when compared with the Pinus sp. wood commercially employed in particleboard production. Bulk density and pH for residual lignocellulosic fibers and Pinus sp. wood presented analogous values. Similar amounts of cellulose and lignin were identified between waste fibers and Pinus sp. wood. The presence of silica was identified in coconut fiber, peanut hull and sugarcane bagasse waste fibers, and may affect the mechanical characteristics of panels. Coconut and sugarcane bagasse fibers show surface pores with diameters ranging from 1.2 to 2.1 μm, below the 5 μm identified for Pinus sp. wood. Both fibers present pores distributed over their entire surface, whereas peanut hull fibers have no pores on their surface. This characteristic contributes to resin dispersion among particles, reflecting positively on the physical–mechanical properties of the panels. Particleboards produced with residual lignocellulosic fibers present similar physical–mechanical properties to those of Pinus sp. wood panels.     

The Effects of Demineralization Process on Diameter,Tensile Properties and Biodegradation of Chitosan Fiber

Chitosan fiber is one of the potential fibers that can be used as absorbable monofilament suture in biomedical application. In chitosan synthesis, aside from deproteination and deacetylation, demineralization is a crucial step where the major minerals within crustacean shells are removed. This demineralization process is carried out with two parameters, i.e. time and temperature. This research studies the influence of demineralization time on the diameter, tensile properties and biodegradability of chitosan fibers. Chitosan was synthesized from shrimp shells using 1 × 2 h and 3 × 2 h demineralization process. Chitosan fibers were produced by means of wet spinning. The chemical properties of chitosan fibers were characterized by means of Fourier Transform Infrared (FTIR) spectroscopy and X-Ray Diffractometry (XRD) technique. Physical properties characterization was carried out to measure the fibers’ diameter, density and viscosity. Tensile properties were evaluated by means of tensile test. The results were compared to standard of absorbable suture from the United States Pharmacopoeia (USP). Furthermore, in vitro degradation testing was also performed for analyzing biodegradation properties. Chitosan fibers were successfully made with diameter and maximum tensile force of chitosan fibers in a range of 364 - 460 μm and 5.6 - 8.3 N, respectively. The results of this research pointed that adding demineralization time would increase the diameter of chitosan fiber. However, the degradation occurred in prolonged demineralization process broke the bonds within the fiber which lead to a decrease in fiber's density. It is due to the degradation of chitosan occurred during extended demineralization process, which leads to degree of crystallinity reduction. Extensive demineralization process has been found to lower fibers’ tensile strength from 80.4 MPa to 38.4 MPa (52.2%), but increase their biodegradability by 17% and maximum elongation from 6.9% to 16.2% (136%). Despite that extensive demineralization process lowered chitosan fiber's tensile strength, both fibers made could still fit the standard for synthetic absorbable suture from USP number 0 and 1.     

Electrochemical synthesis and characterization of solid-phase microextraction fibers using conductive polymers: application in extraction of benzaldehyde from aqueous solution

In this work, polyaniline, polypyrrole, and polyaniline/polypyrrole composite fibers were synthesized in the absence and presence of oxidized multiwalled carbon nanotubes using electrochemical cyclic voltammetry with CF₃COOH as dopant. Thermal stability of these fibers was studied by differential scanning calorimetry. Then, headspace solid-phase microextraction process coupled with gas chromatography and flame ionization detector was used for comparing extraction capability of benzaldehyde from aqueous solution. Since polyaniline fiber showed better extraction efficiency than the other fibers, its preparation conditions including acid concentration, aniline concentration, scan rate, and amount of multiwalled carbon nanotubes were studied by means of the “one-factor-at-a-time method”. The analytical performance of polyaniline fibers were investigated to determine benzaldehyde from the aqueous solution. The morphology and texture of polyaniline fibers were examined by field emission scanning electron microscopy and Fourier transform infrared spectroscopy analyses. The attained results revealed that the perfect conditions for acid concentration, aniline concentration, scan rate, and multiwalled carbon nanotubes content were 0.5 M, 0.2 M, 25 mV s^?1, and 0.02 wt%, respectively. The limit of detection for the proposed polyaniline fiber was 15 ng ml^?1.     

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.     

含磷聚酰亚胺纤维的制备与性能

合成了一种含磷二胺单体, 二(4-胺基苯氧基)苯基膦氧(DAPOPO). 该单体与4,4'-二胺基二苯醚(ODA)、 均苯四酸二酐(PMDA)和3,3',4,4'-联苯四酸二酐(BPDA)共聚得到聚酰胺酸溶液, 通过干喷湿纺法纺丝得到聚酰胺酸纤维, 聚酰胺酸纤维经过热亚胺化和热牵伸得到含磷的聚酰亚胺纤维. 利用纤维强度仪、 扫描电子显微镜、 热失重分析仪和氧指数测定仪等研究了含磷聚酰亚胺纤维的力学性能、 形貌、 热稳定性能和阻燃性能. 结果表明, 随着含磷量的增加, 纤维的热稳定性明显提高, 而极限氧指数从35上升到了45, 说明纤维的阻燃性能得到很大提高.