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. 相似文献
Cellulose was dissolved rapidly in 9.5 wt% NaOH/4.5 wt% thiourea aqueous solution pre-cooled to −5 °C, as a result of the formation of an inclusion complex (IC) associated with cellulose, NaOH and thiourea, which could bring cellulose to the aqueous system. To clarify the rheological behaviors of the system dissolved at low temperature, this cellulose solution was investigated by dynamic viscoelastic measurement. The shear storage modulus (G′) and loss modulus (G″) as a function of the angular frequency (ω), concentration (c), temperature (T) and weight-average molecular weight (Mw) were analyzed and discussed. The results revealed that gels could form in the cellulose solution at either high temperature or low temperature, or for longer time. Interestingly, 4 wt% cellulose solution having cellulose Mw of 12.0 × 104 remained at liquid state for longer time (12 days) at the temperature ranging from 0 to 5 °C. The gels already formed at elevated temperature were irreversible, i.e., after cooling to lower temperature including the temperature of cellulose dissolution (−5 °C), they could not be dissolved to become liquid. The Arrhenius analysis of the temperature dependence of viscosity in the cellulose solution indicated that a high apparent activation energy (Ea) occurred at 0 to −5 °C, suggesting the relatively stable IC structure. However, the viscosity of the cellulose solution increased slowly with an increase in the temperature at 0-40 °C, leading to the negative Ea values. The results suggested that the cellulose solution in NaOH/thiourea system is complex to differ from normal polymer systems. 相似文献
Summary A series of methylcellulose (MC) samples were successfully synthesized using dimethyl sulphate (DMS) as a methylation reagent
in 7 wt% NaOH/12 wt% urea aqueous solution through controlling the reaction conditions. The MC samples were characterized
with 1H and 13C NMR, gas chromatography (GC), ultraviolet spectroscopy, viscometry and solubility measurement. Analysis of GC showed that
there were no unsubstituted anhydroglucose units (AGU) and few completely substituted AGU along the molecular chains of the
MC samples, and there was a uniform distribution of methyl substitution along the MC molecular chains. The stability of 7 wt%
NaOH/12 wt% urea solution for the methylation of cellulose was investigated for the first time. The results showed 2 wt% cellulose
solution in the 7 wt% NaOH/12 wt% urea solvent was almost stable at room temperature, and little decomposition of the cellulose
molecular chains occurred during the methylation reaction. 相似文献
All-cellulose composites (ACCs) were prepared by partially dissolving cellulose in the filter paper using NaOH/thiourea aqueous solution. The effects of dissolution time, thiourea ratio, and temperature on the properties of ACCs were investigated. ACCs were characterized by scanning electron microscope, attenuated total reflectance Fourier transform infrared spectroscopy, Raman spectroscopy, X-ray diffraction, and tensile tests. The results revealed that the fibers in ACCs were tightly intertwined. The crystalline form of cellulose in ACCs was transformed from type I to type I/II mixture, and the crystallinity decreased from 77.32 to 51.40%. The tensile strength of ACCs was remarkably improved to 23.16 MPa. The results confirmed ACCs had a high potential for practical applications in the packaging field. 相似文献
Conclusions A method has been developed for dissolving cellulose xanthate at a higher NaOH content in the first period of solution. The optimum NaOH content for this purpose is 9–9.6%.All-Union Synthetic Fibre Research Institute (VNIIV). Translated from Khimicheskie Volokna, No.2, pp. 60–61, March–April, 1969. 相似文献
We investigated effects of ozone treatment on solubility of cellulose and chemical composition in cellulose extracted from palm fiber. The initial holocellulose, α-cellulose, and lignin contents of the extracted cellulose were 88.0, 81.9, and 8.75%, respectively. The extracted cellulose was treated with ozone and NaOH solution. Ozone treatment for 5 hr at 40°C using 3% citric acid decreased the lignin content from 8.75 to 2.71%. Under these conditions, the degree of polymerization (DP) of the cellulose decreased to 29 from 160 and the carboxyl content increased to 2.05 mmol/g. When the solid phase was treated with NaOH after ozone treatment, the mass of the solid phase decreased as the ozone treatment time increased. The lowest mass was 0.43 g. Additionally, the mass of cellulose regenerated from the liquid phase increased with increasing treatment time. The highest mass of regenerated cellulose was 0.54 g. The masses of the solid phase and regenerated cellulose obtained without ozone treatment under the same conditions were 0.76 and 0.18 g, respectively. These results suggest that ozone treatment improves the solubility of cellulose by converting hydroxyl groups in the cellulose to carboxyl groups and reducing the DP. 相似文献
Summary: Novel inorganic‐organic hybrid materials composed of cadmium sulfide (CdS) semiconducting nanocrystals and regenerated cellulose (RC) were prepared by using in situ synthesizing method. Cellulose was dissolved in a 6 wt.‐% NaOH/4 wt.‐% urea/thiourea aqueous solution at low temperature followed by addition of cadmium chloride (CdCl2), resulting that the CdS nanocrystals were successfully grown in situ in the cellulose solution. Nanocomposite films containing homogeneous CdS nanoparticles were obtained by casting the resulting solution. Their structure and optical properties were characterized by X‐ray photoelectron spectroscopy, wide‐angle X‐ray diffraction, thermogravimetry analysis, dynamic mechanical analysis, atomic force microscopy, transmittance electronic microscope, UV‐vis spectroscopy, and photoluminescence spectroscopy. The experimental results confirmed that the CdS nanocrystalline existed in the composite films, and cellulose matrix provided a confined medium for CdS particle growth in uniform size. The CdS/RC composites showed narrow emission in photoluminescence spectra, and their optical absorbance in the UV range was higher than that of the cellulose film without CdS. This work provided a simple method to prepare cellulose functional materials in NaOH/urea aqueous solution.
Photoluminescence of CdS/RC nanocomposites and TEM image of CdS nanocrystals dispersed in RC matrix. 相似文献
Treatment of cotton fabric with carbon disulphide in presence of NaOH resulted in cellulose thiocarbonate. The latter formed a complex when treated with ceric ammonium nitrate (CAN). After being thoroughly washed, the CeIV cellulose thiocarbonate was capable of initiating vinyl graft polymerization onto cotton fabric without homopolymer formation. The graft yield obtained with methyl methacrylate was found to increase by increasing CAN from zero to 50 mmol/l at temperatures from 60 to 80°C. Grafting was greatly favoured at pH 2; alkaline pH offset grafting. Incorporation of up to 7% of methanol, ethanol, or isopropanol in the aqueous polymerization medium enhanced grafting significantly with the certainty that the highest graft yield was obtained with isopropanol; using higher alcohol percentages decreased grafting. The rate of grafting showed an initial fast rate followed by a slower rate; 60 minutes reaction time proved appropriate for grafting irrespective of the condition used. In addition to methyl methacrylate the ability of CeIV-cellulose thiocarbonate to induce grafting of acrylonitrile and acrylamide was also examined. The rate of grafting followed the order methyl methacrylate > acrylonitrile > acrylamide. 相似文献