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. 相似文献
O-Methylation is of outstanding importance in structural polysaccharide chemistry. A novel method for the methylation of polysaccharides using microwave (MW) irradiation is described. Seed gum from Cyamopsis tetragonolobus (Guar) was fully methylated with dimethyl sulphate and sodium hydroxide using 100% microwave power for 4 min in 68% yield. The completely methylated seed gum thus obtained was hydrolyzed by 70% formic acid followed by 0.5N H2SO4 under full microwave power for 1.16 and 1.66 min, respectively. The partially methylated monosaccharides were separated and identified. 相似文献
The thermal degradation of graft copolymers of both polysaccharides (guar gum and xanthan gum) showed gradual decrease in
mass loss. Pure guar gum degraded about 95% but pure xanthan gum degraded about 76% up to 1173.15 K, while graft copolymers
of guar gum and xanthan gum degraded only 65–76% up to 1173.15 K. Acrylic acid grafted guar gum and xanthan gum showing two-step
degradation with formation of anhydride and ketonic linkage during heating, same pattern of degradation was found for xanthan
gum-g-methacrylic acid. Guar gum-g-acrylamide degraded in single step and xanthan gum-g-acrylamide started to degrade above 448.15 K and it is a two-stage process and imparts thermal stability due to the formation
of imide linkage with evolution NH3. Guar gum-g-methacrylamide degraded in three steps due to the loss of NH3 and CO2 successively. 4-vinyl pyridine grafted both polysaccharides show single step degradation due to loss of pyridine pendent.
N-vinyl formamide grafted guar gum and xanthan gum started to degrade at about 427.15 K, showed two-stage degradation process
with the evolution of CO and NH3 molecules while guar gum-g-(N-vinyl-2-pyrrolidone) degraded into two steps by the loss of pyrrolidone nucleus. Gum-g-2-acrylamido-2-methyl-1-propane sulfonic acid (AMPS) showed two-step degradation processes in two successive degradation
steps, while xanthan gum-g-AMPS has started degradation at about 427.15 K and completed in five degradation steps. Overall, it was found that the grafted
polysaccharides are thermally more stable than pure polysaccharides. 相似文献
Guar gum was chemically modified by sulphonation using chlorosulphonic acid (ClSO3H) as a reagent. Effects of molar ratio of ClSO3H to glucopyranosic unit (ClSO3H/GU), reaction time and reaction temperature on the degree of sulphonation (DS) and molecular weight (Mw) of products were studied. The structures of guar gum sulphate were investigated by GPC, FT‐IR and UV‐Visible spectroscopy. Activated partial thromboplastin time (APTT) assay showed that the guar gum sulphate could inhibit the intrinsic coagulant pathway. The anticoagulant activity strongly depended on the DS and Mw of polysaccharides. DS>0.56 was essential for anticoagulant activity. The guar gum sulphate with the DS of 0.85 and the Mw of 3.40×104 had the best blood anticoagulant activity. 相似文献
The synthesis of cashew gum-g-polyacrylamide was carried out at 60 °C by a radical polymerisation using potassium persulphate as the redox initiator under N2 atmosphere. A series of graft copolymers, varying in acrylamide concentration and keeping the concentration of the initiator and polysaccharide constant, was prepared. These graft copolymers were characterised by elemental analysis, infrared and 13C NMR spectroscopy, rheological studies, differential scanning calorimetry and thermogravimetric analysis. Comparisons amongst grafting parameters of the reaction of various natural polysaccharides with polyacrylamide (PAM) were carried out. High percentages of acrylamide conversion (%C) and grafting efficiency (%E) were obtained for cashew gum (CG), even with a low acrylamide/gum ratio. All copolymers had intrinsic viscosity and thus the hydrodynamic volume much higher than the CG value and closer to the PAM. The CG-g-PAM solution had an absolute viscosity at 2.5% concentration (wt./vol.) up to 33 and 3.3 times the CG and PAM values, respectively. Grafting of PAM chains onto the polysaccharide enhances its thermal stability. 相似文献
The reaction of cellulose phosphonate and N-vinyl-2-pyrrolidone in ethanol in the presence of sodium ethoxide was investigated and thermal stabilities and flame-retardant properties for cellulose phosphonate modified with N-vinyl-2-pyrrolidone were discussed. The results in this study point out the following important aspects of flame retardation of cellulose fabrics: (1) The reaction of cellulose phosphonate and N-vinyl-2-pyrrolidone in the presence of sodium ethoxide results in graft polymerization of N-vinyl-2-pyrrolidone at P? H sites in cellulose phosphonate; an average chain length of the graft polymer is about five units of vinylpyrrolidone. (2) The graft polymerization of N-vinyl-2-pyrrolidone can improve both stabilities, especially the flame-retardant properties of cellulose fabrics. (3) Amides, whether noncyclic or cyclic, are suitable for nitrogen compounds that can effectively operate as synergists. 相似文献
We have examined the relationships between primary, secondary, and tertiary structures of polysaccharides exhibiting the rheological property of friction (drag) reduction in turbulent flows. We found an example of an exopolysaccharide from the yeastCryptococcus laurentii that possessed high molecular weight but exhibited lower than expected drag reducing activity. Earlier correlations by Hoyt (8,10) showing that β1 → 3, β→4, and αl → 3 linkages in polysaccharides favored drag reduction were expanded to include correlations to secondary structure. The effect of sidechains in a series of gellan gums was shown to be related to sidechain length and position. Disruption of secondary structure in drag reducing polysaccharides reduced drag reducing activity for some but not all exopolysaccharides. The polymer fromC. laurentii was shown to be more stable than xanthan gum and other exopolysaccharides under the most vigorous of denaturing conditions. We also showed a direct relationship between extensional viscosity measurements and the drag reducing coefficient for four exopolysaccharides.
Xyloglucans are the principal polysaccharides coating and crosslinking cellulose microfibrills in the majority of land plants.
This review summarizes current knowledge of xyloglucan structures, solution properties, and the mechanism of interaction of
xyloglucans with cellulose. This knowledge base forms the platform for new biomimetic methods of cellulose surface modification
with applications within the fields of textile manufacture, papermaking, and materials science. Recent advances using the
enzyme xyloglucan endo-transglycosylase (XET, EC 2.4.1.207) to introduce varied chemical functionality onto cellulose surfaces are highlighted. 相似文献
The columnar cactusCereus peruvianus provides various compounds of interest that account for most of its 10% dry wt content. Included are acidic gum and cellulose as the highly polymerized carbohydrate components, and a complex waxy lipid fraction. The major gum fraction (1.5 g% of the fresh phytobiomass on single aqueous extraction) is an uronylated rhamnoarabinogalactan whose intrinsic viscosity may exceed 1000 mL/g. Its rheological behavior is, in part, influenced by the nativeo-acetyl and cation components, mainly Ca2+. A pigment-free powdered gum was obtained by precipitating and washing the fresh mucilage with 2–3 vol of ethanol. The almost protein-free polysaccharide forms viscous solution upon redissolution. The possible uses to be investigated for the pretreated cactus gum will be as an adjuvant in the flocculation of water impurities and in formulation of cosmetics.
Specific modification of the reducing end group of dextran has been achieved using the reductive amination procedure and solvent systems designed to optimize polymer reactivity. Dextran fraction (with Mw ranging from 10,000 to 500,000 daltons) were derivatized with [14C]-octadecylamine in yields of up to 60% to afford the corresponding alkyl dextrans which are of interest as affinity ligands. Reactive dextran intermediates with terminal amine, carboxyl, and aldehyde functions were prepared using sodium cyanoborohydride and ammonium acetate, glycine, and glucosamine, respectively. The dextran glucosamine derivative was further modified by reductive amination with octadecylamine. Similarly, condensation of dextran with streptomycin produced a new type of cationic derivative bearing a terminal, branched saccharide residue. Other reducing-end modifications included nitroxide-spin labelling, covalent attachment to aminopropyl-activated glass beads, and a carbodiimide-mediated amidation of carboxyl—dextran. The reductive amination method was also applied to guar gum and locust bean gum. 相似文献
The effect of 13 viscosity modifying admixtures (VMA) on the Portland cement hydration was studied in this paper. In this purpose, thermal analyses (DTA and TG) were performed after 1, 7 and 28 days of hydration on cement pastes containing 0.01–0.5 % from the following VMA: diutan gum, welan gum, polygalactomannane ether, natural cellulose fibres, modified polysaccharide, polyacrylamide, high-molecular mass synthetic copolymer, hydroxypropyl starch and a chemically modified starch. It was noticed that the proportion of Ca(OH)2 from the samples containing polygalactomannane ether and modified polysaccharide was smaller than in the reference sample, which proved their effect of cement hydration delay. For the other VMA, this effect was not detected, on the contrary, the amount of Ca(OH)2 was higher than in the reference sample. 相似文献
Two cellouronic acids [sodium (1 → 4)-β-polyglucuronates, CUAs] and one 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO)-oxidized wood cellulose (TOC) became soluble in 8 % lithium chloride/N,N-dimethylacetamide (LiCl/DMAc) after the methylation of C6 carboxyl groups in these samples using trimethylsilyldiazomethane (TMSD). The obtained solutions were diluted to 1 % LiCl/DMAc and subjected to size-exclusion chromatography combined with multi-angle laser-light scattering (SEC-MALLS). Neither depolymerization nor side reactions took place during methylation; this was confirmed by SEC-MALLS and nuclear magnetic resonance analyses, using CUAs as models. The SEC-MALLS analysis of the original wood cellulose and the carboxyl-methylated TOC prepared from it, using 1 % LiCl/N,N-dimethyl-2-imidazolidinone and 1 % LiCl/DMAc, respectively, as eluents, showed that the weight-average degree of polymerization of the original wood cellulose decreased from 3,100 to 2,210 through TEMPO-mediated oxidation. The molecular-mass distributions of the original wood cellulose and the TOC both consisted of one large peak with a small shoulder, indicating that some of the oxidized hemicelluloses remained in the TOC. The combination of methylation of carboxyl groups in polysaccharides using TMSD and subsequent SEC-MALLS analysis using 1 % LiCl/DMAc as an eluent may be applicable not only to TOCs, but also to other polysaccharides with carboxyl groups, for evaluation of their molecular-mass parameters. 相似文献
All-cellulose composites were prepared by partly dissolving microcrystalline cellulose (MCC) in an 8.0 wt% LiCl/DMAc solution,
then regenerating the dissolved portion. Wide-angle X-ray scattering (WAXS) and solid-state 13C NMR spectra were used to characterize molecular packing. The MCC was transformed to relatively slender crystallites of cellulose
I in a matrix of paracrystalline and amorphous cellulose. Paracrystalline cellulose was distinguished from amorphous cellulose
by a displaced and relatively narrow WAXS peak, by a 4 ppm displacement of the C-4 13C NMR peak, and by values of T2(H) closer to those for crystalline cellulose than disordered polysaccharides. Cellulose II was not formed in any of the composites
studied. The ratio of cellulose to solvent was varied, with greatest consequent transformation observed for c < 15%, where c is the weight of cellulose expressed as % of the total weight of cellulose, LiCl and DMAc. The dissolution time was varied
between 1 h and 48 h, with only small additional changes achieved by extension beyond 4 h. 相似文献
Thermal denaturation and renaturation of soybean trypsin (Kunitz) inhibitor (STI) were studied by high-sensitivity differential scanning calorimetry in the presence of polysaccharides (dextran, ι- and κ-carrageenans, gum arabic, pectins and dextran sulfate). This study was carried out under conditions of both thermodynamic incompatibility and complex formation of STI and polysaccharides. The presence of polysaccharides did neither influence the denaturation temperature nor the denaturation enthalpy of STI under conditions of their incompatibility with the protein. No polysaccharide (except gum arabic) affected the ability of STI to renature and recover its inhibitory activity after thermal denaturation. At acidic pH values, the protein was shown to form electrostatic complexes with pectins and dextran sulfate. Substantial destabilisation of STI bound to dextran sulfate was observed. In the case of STI/pectin complexes, either a decrease or increase in the stability of STI was observed depending on the complex composition and esterification degree of pectin. The mechanism behind the changes in stability of STI bound to the polysaccharide matrix is discussed. Thermal denaturation of STI in complexes with dextran sulfate and pectin was completely irreversible. This observation indicates a possibility of suppressing antinutritional activities of trypsin inhibitors in soy products.
In a previous study, the nematic ordered cellulose (NOC) templates successfully induced biodirected epitaxial nanodeposition
of cellulose nanofibers secreted by Gluconacetobacter xylinus along the orientation of the molecular tracks (Kondo et al. 2002). As an extended concept for the NOC, this article attempts to propose a sort of biomimic mineralization using the template.
It combines morphologically controlling process with synthesis of the calcium phosphate as a major component of bones. This
process was initially mediated by the modified NOC template having a pair of roles of the ion supply sources and scaffolds
for 3D-ordering architecture of the calcium phosphate as a biomineral in the key functions for biomineralization. The successful
establishment of such an ordered deposition of the inorganic on the template was confirmed by several surface characterizations
such as atomic force microscopy, X-ray photoelectron spectroscopy, scanning electron microscopy, and so on. Moreover, similarly
to human bones, the obtained major assemble states of the calcium phosphates exhibited amorphous. The above process using
the bifunctional cellulose template can be considered as a biomimic mineralization, which also opens pathways toward preparation
of potentially versatile organic–inorganic order-patterned composites under a less energy consumption. 相似文献
Two different polysaccharides with anticoagulant activities, heparin and chondroitin sulfate, were used to modify the surface of sodium-selective electrodes based on asymmetric cellulose triacetate (CTA) membranes. The membranes were formulated with sodium ionophore X, anionic additive, and o-nitrophenyl octyl ether. The response behavior of the surface-modified sodium electrodes was compared with that of control CTA, as well as poly(vinyl chloride) (PVC)-based sodium-selective electrodes. It was found that the selectivity coefficients obtained with the surface modified CTA membrane electrodes were slightly higher than those of the control, but in the case of heparin-modified electrodes they still met the requirements for analysis of sodium in physiological fluids within an error of <1%; the corresponding error for chondroitin sulfate-modified electrodes was also <1% except for the case of potassium ion in which the error was 1.3%. Likewise, it was found that other response characteristics, such as detection limit, linear range, slope of the response plot, selectivity pattern, and response time were comparable in both the control and the polysaccharide-modified electrodes. Therefore, the surface modification does not significantly alter the response behavior of the sensors. 相似文献