Effect of sodium hydroxide pre-treatment on the optical and structural properties of lyocell

Lyocell is a type of regenerated cellulose. Fibres spun from cellulose solution in N-methylmorpholine-N-oxide hydrate consist of crystalline cellulose II and amorphous cellulose. Lyocell fabrics were treated with aqueous sodium hydroxide solution (NaOH) to study the influence of alkali on optical and structural properties. It was observed that sodium hydroxide treatment causes the density, orientation and crystallinity of lyocell fibre to decrease with increasing sodium hydroxide concentration, a corresponding decrease in tensile strength is also observed. The greatest change in fibre properties occurs between 3.0 and 5.0 mol dm⁻³ NaOH. This is attributed to the onset of formation of Na-cellulose II at 3.0 mol dm⁻³ NaOH; a fully formed Na-cellulose II structure is expected above 6.8 mol dm⁻³ NaOH. Formation of Na-cellulose II causes plasticization of the lyocell fibres as both inter- and intra-molecular hydrogen bonds are broken by these higher sodium hydroxide concentrations.     

Influence of extrusion ratio on the thermal properties and morphology of ultradrawn high-density polyethylene

Solid-state extrusion of high-density polyethylene (HDPE) has received considerable attention. It has been shown that extrudate may have high values of optical clarity, tensile modulus (～70 GPa = 7 × 10¹¹ dyn/cm²), and c-axis orientation. The effects of extrusion conditions on the properties of the resultant fibers have, however, not yet been clarified. A systematic study has thus been made here to evaluate extrusion pressure, temperature, and extrusion (draw) ratio, and the molecular weight of extruded HDPE. The effects of extrusion ratio on the degree of crystallinity, melting behavior, crystal orientation, and dimensional change along the extrusion direction are reported.     

Morphology of polysaccharide blend fibers shaped from NaOH, <Emphasis Type="Italic">N</Emphasis>-methylmorpholine-<Emphasis Type="Italic">N</Emphasis>-oxide and 1-ethyl-3-methylimidazolium acetate

The aim of this study was to find newly structured biopolymer blends bearing those adjustable features able to produce innovative materials. Apart from cellulose derivatives (cellulose carbamate and carboxymethyl cellulose), mannans (guar gum, locust bean gum, and tragacanth gum), xylan, starch (cationized), ι-carrageenan, and xanthan were chosen as blend polysaccharides for cellulose as matrix. In order to study their integration into the cellulose skeleton, fibers were shaped from three different solvents: NaOH by a special wet-spinning process, as well as N-methylmorpholine-N-oxide (NMMO) and 1-ethyl-3-methylimidazolium acetate (EMIMac) via Lyocell technology. The structure and morphologies of the fibers were analyzed by X-ray wide-angle scattering and atomic force microscopy. Hydrophilic/hydrophobic properties were determined by means of a contact angle, as well as moisture content and water retention values, while the surface properties throughout zeta-potential measurements. Being very different processes, the wet spinning in NaOH solution and the dry–wet spinning are deeply impacted by the types of solvent and polysaccharide. The X-ray results for NMMO fibers revealed the highest orientation compared with EMIMac having the lowest orientation of NaOH fibrous types. AFM images also show the lowest surface roughnesses for NMMO and EMIMac fibers. The moisture content and water retention values support these trends, while the water contact angle results show insignificant differences between the samples from EMIMac and NaOH, even though the values calculated for NMMO fibers were the lowest.     

Synthesis of antibacterial cellulose materials using a “clickable” quaternary ammonium compound

Development of advanced functional materials from naturally abundant polymers such as cellulose are of significant importance. Of particular interest is embedding antibacterial functionality to cellulose materials to make permanent antibacterial materials and devices. In the present research, a “clickable” quaternary ammonium compound, N-(2-ethoxy-2-oxoethyl)-N,N-dimethylprop-2yn-1-aminium bromide (EdMPABr) was synthesized via a simple reaction with nearly stoichiometric yield and well characterized with 1D (¹H, ¹³C) and 2D (COSY, HSQC) NMR and ATR-FTIR. EdMPABr can be covalently bonded to many molecules containing an azido group to form non-leaching antibacterial materials via the simple Cu(I)-catalyzed alkyne-azide [2 + 3] cycloaddition reaction. As an example, EdMPABr was attached to our previously reported 3-O-azidopropoxypoly(ethylene glycol)-2,6-di-O-thexyldimethylsilyl cellulose (3-N₃PEG-2,6-TDMS cellulose, DS = 0.54 at C3 determined by ¹H NMR). Significant antibacterial activity of the synthesized 3-O-quaternary ammonium-2,6-di-O-thexyldimethylsilyl cellulose (3-QA-2,6-TDMS cellulose, DS = 0.30 at C3 determined by using N content from elemental analysis) was confirmed by testing against the representative bacteria Escherichia coli. By linking the EdMPABr to the honeycomb film of 3-N₃PEG-2,6-TDMS cellulose, the formed honeycomb film exhibited both antibacterial and antifouling properties. This research provides a simple and robust route towards the development of permanent antibacterial materials and biomedical devices.     

Synthesis and properties of novel polyimide fibers containing phosphorus groups in the side chain (DATPPO)

A series of polyamic acid copolymers(co-PAAs) containing phosphorous groups in the side chains were synthesized from [2,5-bis(4-aminophenoxy) phenyl] diphenylphosphine oxide(DATPPO) and 4,4′-oxydianiline(ODA) with 3,3′,4,4′-biphenyltetracarboxylic dianhydride(s-BPDA) through the polycondensation in N,N′-dimethyacetamide(DMAc). The co-PAA solutions were spun into fibers by a dry-jet wet spinning process followed by thermal imidization to obtain co-polyimide(co-PI) fibers. FTIR spectra and elemental analysis confirmed the chemical structure of PI fibers. SEM results indicated that the resulting PI fibers had a smooth and dense surface, a uniform and circle-shape diameter. The thermogravimetric measurements showed that with the increase of DATPPO content, the resulting PI fibers possessed high decomposition temperature and residual char yield, indicating that the PI fibers had good thermal stability. The corresponding limiting oxygen index(LOI) values from the experiment results showed that the co-PI fibers possessed good flame-retardant property. Furthermore, the mechanical properties of the co-PI fibers were investigated systematically. When the DATPPO content increased, the tensile strength and initial modulus of the co-PI fibers decreased. However, the mechanical properties were improved by increasing the draw ratio of the fibers. When the draw ratio was up to 2.5, the tensile strength and initial modulus of the co-PI fibers reached up to 0.64 and 10.02 GPa, respectively. The WAXD results showed that the order degree of amorphous matter increased with increased stretching. In addition, the SAXS results displayed that valuably drawing the fibers could eliminate the voids inside and lead to better mechanical property. WAXD revealed that the orientation of the amorphous polymer influenced the mechanical properties of the fibers.     

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.     

Studies on the Stabilization of Modified Lyocell Solutions

Additives with functional properties makes the Lyocell process a versatile tool for the creation of new innovative materials beyond the textile sector. Occupying functional groups or active surfaces the additives emphasize the suitability of Lyocell fibers, but simultaneously enhance the complexity of chemical reactions in cellulose/N-methylmorpholine-N-oxide (NMMO) solutions, respectively. Concerning to the concentration acidic ion exchange resins, activated charcoals, carbon black etc. shift the start of decomposition to lower temperatures, decrease the viscosity, enhance the formation of amines as the main degradation products or cause autocatalytic reactions. New routes in stabilization of modified Lyocell solutions applying a polymeric stabilizer system are described. Using calorimetric, UV/VIS, ESR and HPLC analysis the degradation processes and thermal stability of modified Lyocell solutions compared to the unstabilized were studied. Moreover, as kinetic investigations show a distinguished behavior for modified solutions autocatalytic reactions can be suppressed by the stabilizing system. ESR kinetic study of radicals reveals that formation and recombination rates of radical reactions depend on cellulose concentration in Lyocell solutions and additional ingredients.     

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.     

Oriented cellulose films and fibers from a mesophase system

Cellulose mesophases were obtained by preparing concentrated solutions of cellulose (20–55%) in a mixture of N-methyl-morpholine N-oxide (MMNO) and water. The anisotropy depends on four interconnected parameters: the temperature of the solution which, in general, must be lower than 90°C; the concentration of cellulose which must exceed 20%; a water content such that the mole ratio water/anhydrous MMNO is smaller than unity; and the degree of polymerization of the dissolved cellulose. The anisotropic cellulose solutions can readily be oriented during extrusion or casting thus giving fibers or films which upon regeneration exhibit high orientation.     

Mesoporous structures in never-dried softwood cellulose fibers investigated by nitrogen adsorption

Nitrogen adsorption was used to characterize mesoporous structures in never-dried softwood cellulose fibers. Distinct inflections in desorption isotherms were observed over the relative vapor pressure (P/P₀) range of 0.5–0.42 for never-dried cellulose fibers and partially delignified softwood powders. The reduction in N₂ adsorption volume was attributed to cavitation of condensed N₂ present in mesopores formed via lignin removal from wood cell walls during delignification. The specific surface areas of significantly delignified softwood powders were ~150 m² g^?1, indicating that in wood cell walls 16 individual cellulose microfibrils, each 3–4 nm in width, form one cellulose fibril bundle surrounded with a thin layer of lignin and hemicelluloses. Analysis of N₂ adsorption isotherms indicates that mesopores in the softwood cellulose fibers and partially delignified softwood powders had peaks ranging from 4 to 20 nm in diameter.     

Antibacterial modification of cellulose fibers by grafting β-cyclodextrin and inclusion with ciprofloxacin

Antibacterial-modified cellulose fiber was prepared by covalently bonding β-cyclodextrin (β-CD) with cellulose fiber via citric acid (CA) as crosslinking agent, followed by the inclusion of ciprofloxacin hydrochloride (CipHCl) as antibiotic. Effects of reaction time, temperature, concentration of β-cyclodextrin citrate (CA-β-CD) and pH on the grafting reaction were investigated, and the grafting ratio of β-CD onto cellulose fibers was 9.7 % at optimal conditions; the loading and releasing behaviors of CipHCl into/from β-CD grafted cellulose fibers were also revealed, the load amount of CipHCl into grafted cellulose fibers increased remarkably, and the release of CipHCl from the grafted cellulose fibers was prolonged. The microstructure, phase and thermal stability of modified cellulose fibers were characterized by FT-IR, ¹³C CPMAS NMR, X-ray diffraction and TGA. Considerably longer bacterial activity against E. coli and S. aureus was observed for grafted fibers loading CipHCl compared to virgin ones. Optical and mechanical properties of the paper sheets decreased generally with more antibacterial-modified fibers added.     

Physical and mechanical properties of ultra-oriented high-density polyethylene fibers

Ultra-oriented high-density polyethylene fibers (HDPE) have been prepared by solid-state extrusion over 60–140°C range using capillary draw ratios up to 52 and extrusion pressures of 0.12 to 0.49 GPa. The properties of the fibers have been assessed by birefringence, thermal expansivity, differential scanning calorimetry, x-ray analysis, and mechanical testing. A maximum birefringence of 0.0637 ± 0.0015 was obtained, greater than the calculated value of 0.059 for the intrinsic birefringence of the orthorhombic crystal phase. The maximum modulus obtained was 70 GPa. The melting point, density, crystallinity, and negative thermal expansion coefficient parallel to the fiber axis all increase rapidly with draw ratio and at draw ratios of 20–30 attain limiting values comparable with those of a polyethylene single crystal. The properties of the fibers have been analyzed using the simple rule of mixtures, assuming a two-phase model of crystalline and noncrystalline microstructure. The orientation of the noncrystalline phase with draw ratio was determined by birefringence and x-ray measurements. Solid-state extrusion of HDPE near the ambient melting point produced a c-axis orientation of 0.996 and a noncrystalline orientation function of 0.36. Extrusion 50°C below the ambient melting point produced a decrease in crystallinity, c-axis orientation, melting point, and birefringence, but the noncrystalline orientation increased at low draw ratios and was responsible for the increased thermal shrinkage of the fibers.     

Mechanistic aspects for the oxidation of brilliant green dye by chloramine-T in the presence of perchloric acid: a spectrophotometric kinetic approach

The kinetics of a triarylmethane dye, brilliant green (BG), by sodium N-chloro-p-toluenesulfonamide or chloramine-T (CAT) was studied spectrophotometrically in HClO₄ media at 303 K. Under identical experimental conditions, the rate law was ?d [BG]/dt = k [BG] [H⁺]. Variations in ionic strength (μ) of the medium had no effect on the oxidation velocity. Addition of p-toluenesulfonamide, the reduction product of CAT and Cl^?, had no significant effect on the rate of reaction. The values of rate constants observed at five different temperatures (298, 303, 308, 313, and 318 K) were utilized to calculate the activation parameters. The observed results have been explained by a general mechanism and the related rate law has been obtained. The process demonstrated in this study is cost effective, which holds great promise in potential application for pollutant control.     

Anisotropy of the elastic properties of crystalline cellulose Iβ from first principles density functional theory with Van der Waals interactions

In spite of the significant potential of cellulose nanocrystals as functional nanoparticles for numerous applications, a fundamental understanding of the mechanical properties of defect-free, crystalline cellulose is still lacking. In this paper, the elasticity matrix for cellulose I_β with hydrogen bonding network A was calculated using ab initio density functional theory with a semi-empirical correction for van der Waals interactions. The computed Young’s modulus is found to be 206 GPa along [001] (c-axis), 98 GPa along [010] (b-axis), and 19 GPa along [100] (a-axis). Full compliance matrices are reported for 1.0, 1.5 and 2.0 % applied strains Color contour surfaces that show variations of the Young’s modulus and average Poisson’s ratio with crystallographic direction revealed the extreme anisotropies of these important mechanical properties. The sensitivity of the elastic parameters to misalignments in the crystal were examined with 2D polar plots within selected planes containing specific bonding characteristics; these are used to explain the substantial variability in the reported experimental Young’s moduli values. Results for the lattice directions [001], [010] and [100] are within the range of reported experimental and other numerical values.     

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.     

Cellulose fibers modified by Eu3+-doped yttria-stabilized zirconia nanoparticles

This paper describes a method for manufacturing luminescent cellulose fibers. Good optical properties of cellulose fibers under UV-C illumination were achieved by incorporating ZrO₂ (0.5?mol% of Eu³⁺) stabilized by Y₂O₃ (7?mol%) into the fiber structure’s particles. Fibers were obtained from 8?wt% cellulose solution in N-methylmorpholine N-oxide (NMMO) with the addition of a luminescent modifier in the range between 0.5 and 10?wt%. The physico-chemical and mechanical parameters and the structure of these fibers were examined.     

Double crystallization behavior in dry-jet wet spinning of cellulose/N-methylmorpholine-N-oxide hydrate solutions

The structure and resultant mechanical properties of fibers in the dry-jet wet spinning process of cellulose solutions in N-methylmorpholine-N-oxide (NMMO) hydrates were investigated in terms of molecular weight of cellulose, concentration, and hydration number (n) of NMMO hydrate. The value of n had an effect on the crystallization behavior of the cellulose solution system, which influenced the resultant fiber structure. Increasing cellulose concentration and decreasing the value of n retarded crystallization because of the increased interactions between cellulose and NMMO hydrate. Reducing the value of n from 1 to 0.72 produced more highly oriented cellulose fibers. However, incorporating n-propyl gallate, an antioxidant, had little effect on the fiber structure. When n=0.72 a double crystallization behavior was observed in the fiber spinning process irrespective of molecular weight of cellulose and concentration over the experimental ranges examined. It should be noted that such a double crystallization took place in the absence of foreign additives. The double crystallization behavior was more noticeable when the aspect ratio of spinning nozzle was greater. The double layer structure had a positive effect on the mechanical strength.     

NMR spectroscopic studies on dissolution of softwood pulp with enhanced reactivity

N-methylmorpholine N-oxide (NMMO) is a known cellulose solvent used in industrial scale (LyoCel process). We have studied interactions between pretreated softwood pulp fibers and aqueous NMMO using nuclear magnetic resonance (NMR) spectroscopic methods, including solid state cross polarisation magic angle spinning (CP-MAS) ¹³C and ¹⁵N spectroscopies, and ¹H high resolution MAS NMR spectroscopy. Changes in both cellulose morphology and in accessibility of solvents were observed after the pulp samples that were exposed to solvent species were treated at elevated temperature. Evidence about interactions between cellulose and solvent components was observed already after a heat treatment of 15 min. The crystalline structure of cellulose was seen to remain intact for the first 30 min of heat treatment, at the same time there was a re-distribution of solvent species taking place. After a 90 min heat treatment the crystalline structure of cellulose had experienced major changes, and potential signs of regeneration into cellulose II were observed.     

Quantitative evaluation of the biosynthetic pathways leading to δ-aminolevulinic acid from the Shemin precursor glycine via the C5 pathway in Arthrobacter hyalinus by analysis of 13C-labeled coproporphyrinogen III biosynthesized from [2-13C]glycine, [1-13C]acetate, and [2-13C]acetate using 13C NMR spectroscopy

The biosynthetic pathways leading to δ-aminolevulinic acid (ALA) from the Shemin precursor glycine via the C5 pathway in Arthrobacter hyalinus were quantitatively evaluated by means of feeding experiments with [2-¹³C]glycine, sodium [1-¹³C]acetate, and sodium [2-¹³C]acetate, followed by analysis of the labeling patterns of coproporphyrinogen III (Copro’gen III) (biosynthesized from ALA) using ¹³C NMR spectroscopy. Two biosynthetic pathways leading to ALA from glycine via the C5 pathway were identified: i.e., transformation of glycine to l-serine catalyzed by glycine hydroxymethyltransferase, and glycine synthase-catalyzed catabolism of glycine to N ⁵,N ¹⁰-methylene-tetrahydrofolic acid (THF), which reacts with another molecule of glycine to afford l-serine. l-Serine is transformed to acetyl-CoA via pyruvic acid. Acetyl-CoA enters the tricarboxylic acid cycle, affording 2-oxoglutaric acid, which in turn is transformed to l-glutamic acid. The l-glutamic acid enters the C5 pathway, affording ALA in A. hyalinus. A ¹³C NMR spectroscopic comparison of the labeling patterns of Copro’gen III obtained after feeding of [2-¹³C]glycine, sodium [1-¹³C]acetate, and sodium [2-¹³C]acetate showed that [2-¹³C]glycine transformation and [2-¹³C]glycine catabolism in A. hyalinus proceed in the ratio of 52 and 48 %. The reaction of [2-¹³C]glycine and N ⁵,N ¹⁰-methylene-THF, that of glycine and N ⁵,N ¹⁰-[methylene-¹³C]methylene-THF generated from the [2-¹³C]glycine catabolism, and that of [2-¹³C]glycine and N ⁵,N ¹⁰-[methylene-¹³C]methylene-THF transformed the fed [2-¹³C]glycine to [1-¹³C]acetyl-CoA, [2-¹³C]acetyl-CoA, and [1,2-¹³C₂]acetyl-CoA in the ratios of 42, 37, and 21 %, respectively. These labeled acetyl-CoAs were then incorporated into ALA. Our results provide a quantitative picture of the pathways of biosynthetic transformation to ALA from glycine in A. hyalinus.     

Facile radiosynthesis of <Superscript>18</Superscript>F-labeled β-glutamic acid as a new PET tracer for imaging lung cancer

In this paper, N-(2-[¹⁸F]fluoropropionyl)-β-glutamic acid 8 ([¹⁸F]FP-β-Glu), a new N-substituted ¹⁸F-labeled amino acid tracer, was synthesized from the precursor 4 (diethyl 3-(2-bromopropanamido)pentanedioate) via a two-step reaction on the modified FDG synthesizer. The radiochemical yield was 20 ± 5% (n = 10, decay-corrected) from [¹⁸F]fluoride within 40 min, the radiochemical purity was 98%. Moreover, microPET studies showed that [¹⁸F]FP-β-Glu 8 exhibited rapid tumor uptake and good tumor-to-lung ratio in SPC-A-1 tumor-bearing mice. A high accumulation of radioactivity was found in the kidneys and bladder, which suggested that the tracer was mainly eliminated through the urinary system.