Mercerization and acid hydrolysis of bacterial cellulose

Structural changes in never- dried, disintegrated bacteria l cellulose by treatment with aqueous NaOH were examined by electron microscopy, X-ray diffractometry and acid hydrolysis behaviour and compared with those of cotton cellulose. The microfibril kept its fibrillar morphology after treatment with NaOH solutions of less than 9% (w/w), but changed into irregular aggregates when treated with NaOH above 12% (w/w), corresponding to the crystal conversion to cellulose II. The crystallinity of the resulting cellulose II was very low after a brief alkali treatment, but was increased significantly by elongated treatment (up to 10 days). In contrast, cotton cellulose was converted to cellulose II of fairly high crystallinity by alkali treatment of as little as 3 min duration, and the crystallinity did not change with longer treatments. The leveling-off degree of polymerization (LODP) of bacterial cellulose was decreased from 150 to 50 by 18% (w/w) NaOH treatment, while that of cotton linter decreased from 260 to 70. These characteristic differences between cotton linter cellulose and bacterial cellulose can be ascribed to a basic difference in microfibrillar organization in these materials: the microfibrils in cotton cellulose are in close contact with neighbouring microfibrils having opposite polarity, and in bacterial cellulose are isolated from each other and require chain folding to form the antiparallel cellulose II crystal     

Mercerization of primary wall cellulose and its implication for the conversion of cellulose I→cellulose II

The mercerization of homogenized primary wall cellulose extracted fromsugar beet pulp was investigated by transmission electron microscopy (TEM),X-ray diffraction together with ¹³C CP-MAS NMR, and FT-IR spectroscopy.For samples resulting from acid extraction, mercerization began at 9% NaOH, whereasfor samples purified by alkaline treatment, the mercerization started at 10%NaOH. The change in morphology when going from cellulose I to cellulose II wasspectacular, as all the microfibrillar cellulose morphology disappeared duringthe treatment. This change in morphology was very drastic as soon as the NaOHconcentrations were increased beyond 8 and 9% for the acid and alkalinepreparedsamples, respectively. On the other hand, the conversion was found to be moreprogressive in terms of increasing NaOH concentration when the transformationwas analyzed by X-ray diffraction or spectroscopy. Our observations of themercerization of isolated cellulose microfibrils are consistent with theconceptof cellulose microfibrils made of parallel chains in cellulose I and crystalsofcellulose II consisting of antiparallel chains.     

Hydrogen bonding interactions between adsorbed polymer molecules and crystal surface of acetaminophen

The objective of this work was to investigate whether or not the hydrogen bonding interaction between polymer and crystal surface can be detected by the etching pattern changes in the presence of polymers. The (010) face of acetaminophen single crystal was used as a model solid surface. The etching patterns on the (010) face of acetaminophen crystal by water are in the directions of a- and c-axes, which are the same as the directions of the dominant attachment energies on the (010) face. In the presence of polymer, the hydrogen bonding interactions between adsorbed polymer and crystal surface can affect surface diffusion of acetaminophen molecules and change the etching patterns in the direction of a-axis, i.e., the direction of one hydrogen bond chain. Studies with 2-hydroxyethyl cellulose (HEC), hydroxypropyl cellulose (HPC), hydroxypropyl methylcellulose (HPMC) and poly(vinyl alcohol) (PVA) showed that polymers, which can form hydrogen bonds with acetaminophen crystal surface, can change etching patterns in the direction of a-axis. Study with Dextran suggested that if a polymer cannot form hydrogen bonds with crystal surface due to steric repulsion, it will not change the etching pattern in the direction of a-axis. Studies with poly(ethylene glycol) (PEG) and poly(propylene glycol) (PPG) further confirmed that only if a polymer can form hydrogen bonds with acetaminophen on crystal surface, the etching patterns in the direction of a-axis will be affected. The study results suggest that in the presence of polymers, the etching pattern change in the direction of hydrogen bond chain, the a-axis of acetaminophen crystals, can be used to indicate the existence of the hydrogen bonding interactions between adsorbed polymers and acetaminophen crystal surface.     

Nanofibrillation of dried pulp in NaOH solutions using bead milling

The drying process in typical pulp production generates strong hydrogen bonding between cellulose microfibrils in refined cell walls and increases the difficulty in obtaining uniform cellulose nanofibers. To investigate the efficacy of alkaline treatment for cellulose nanofibrillation, this study applied a bead-milling method in NaOH solutions for the nanofibrillation of dried pulps. NaOH treatments loosened the hydrogen bonding between cellulose microfibrils in dried pulps and allowed preparation of cellulose nanofibers in 8 % NaOH with a width of approximately 12–20 nm and a cellulose I crystal form. Both the nanofiber suspensions prepared in 8 and 16 % (w/w) NaOH were formed into hydrogels by neutralization because of surface entanglement and/or interdigitation between the nanofibers. When the dried pulp was fibrillated in 16 % (w/w) NaOH, the sample after neutralization had a uniquely integrated continuous network. These results can be applied to the preparation of high-strength films and fibers with cellulose I crystal forms without prior dissolution of pulps.     

GRAFTING OF HUMIC ACID ONTO COTTON CELLULOSE (Ⅱ)*

Cotton cellulose reacted with epichlorohydrin under the catalytic action of HClO_4 and H_2O to form 3-chloro-2-hydroxypropyl ether with a substitution degree of 0.61. The chlorine-containing product was treated with aliphatic diamines (ethylenediamine, propylenediamine, etc.) to produce nitrogen-containing cellulose which further reacted with humic acid to give black fiberous graft cellulose. This product contains 27—35% humic acid, 0.90 meq/g acidic groups, possesses 0.49 meq/g Cu~(2+)-complexing capacity and good mechanical strength, and can be used under pH12.     

Adsorption of carboxymethyl cellulose on polymer surfaces: evidence of a specific interaction with cellulose

The adsorption of carboxymethyl cellulose (CMC), one of the most important cellulose derivatives, is crucial for many scientific investigations and industrial applications. Especially for surface modifications and functionalization of materials, the polymer is of interest. The adsorption properties of CMC are dependent not only on the solutions state, which can be influenced by the pH, temperature, and electrolyte concentration, but also on the chemical composition of the adsorbents. We therefore performed basic investigation studies on the interaction of CMC with a variety of polymer films. Thin films of cellulose, cellulose acetate, deacetylated cellulose acetate, polyethylene terephthalate, and cyclo olefin polymer were therefore prepared on sensors of a QCM-D (quartz crystal microbalance) and on silicon substrates. The films were characterized with respect to the thickness, wettability, and chemical composition. Subsequently, the interaction and deposition of CMC in a range of pH values without additional electrolyte were measured with the QCM-D method. A comparison of the QCM-D results showed that CMC is favorably deposited on pure cellulose films and deacetylated cellulose acetate at low pH values. Other hydrophilic surfaces such as silicon dioxide or polyvinyl alcohol coated surfaces did not adsorb CMC to a significant extent. Atomic force microcopy confirmed that the morphology of the adsorbed CMC layers differed depending on the substrate. On hydrophobic polymer films, CMC was deposited in the form of larger particles in lower amounts whereas hydrophilic cellulose substrates were to a high extent uniformly covered by adsorbed CMC. The chemical similarity of the CMC backbone seems to favor the irreversible adsorption of CMC when the molecule is almost uncharged at low pH values. A selectivity of the cellulose CMC interaction can therefore be assumed. All CMC treated polymer films exhibited an increased hydrophilicity, which confirmed their modification with the functional molecule.     

TEMPO-mediated Oxidation of Native Cellulose: SEC–MALLS Analysis of Water-soluble and -Insoluble Fractions in the Oxidized Products

Linter cellulose was suspended in water and oxidized by the NaClO/NaBr/2,2,6,6-tetramehylpiperidine-1-oxy radical (TEMPO) system at pH 10.5 (TEMPO-mediated oxidation), and the oxidized products were separated into several fractions by filtration and centrifugation, depending on their particle sizes and apparent water-solubility. The major fraction (>ca. 80 mass % of the original linter cellulose) is the filter paper-trapped fibers, which can form inter-fiber hemiacetal linkages when handsheets are prepared thereof. Size-exclusion chromatographic analysis with multi-angle laser light scattering detection (SEC–MALLS) of these fibrous fractions dissolved in 0.5% LiCl/N,N-dimethylacetamide (DMAc) showed that some depolymerization occurred on cellulose chains during the TEMPO-mediated oxidation. On the other hand, the apparently water-soluble fractions (<ca. 20 mass % of the original linter cellulose) in the TEMPO-oxidized linter cellulose consisted of small amounts of colloidal particles having the cellulose I crystal structure, which came off from linter cellulose by the TEMPO-mediated oxidation and were mixed in the apparently water-soluble fraction even after filtration using 0.45 μm membrane. The presence of such colloidal cellulose crystals in the water-soluble fractions of the TEMPO-oxidized linter cellulose brings about anomalous bimodal SEC-elution patterns and extremely large molecular-mass values calculated from the SEC–MALLS data. Truly water-soluble cellouronic acid and/or over-oxidized compounds having glucuronic acid and hexeneuronic acid units are also present in the water-soluble fractions.     

Hot Topics in Polysaccharide Chemistry – Selected Examples

Summary: The paper highlights recent developments in polysaccharide chemistry. Cellulose tert-butyl- and thexyldimethylsilyl ethers with degree of substitution up to 2 were accessible and comprehensively characterized by means of NMR spectroscopy. These derivatives enable the preparation of 3-O-functionalized cellulose ethers. Especially the allyl ether as protecting group at position 3 can be used for the synthesis of 2,6-di-O-methyl cellulose. Nucleophilic displacement reactions of cellulose p-toluenesulfonic acid esters with amines afforded deoxyamino celluloses that form stable monolayers on different substrates. Based on 6-deoxy-6-azido cellulose, dendrons with a focal alkyne moiety were bound via the copper(I) catalyzed Huisgen reaction. Moreover, dextran derivatives were synthesized that form stable nanoparticles useful, e.g., for the determination of the pH value in biological systems.     

Preparation of tough cellulose II nanofibers with high thermal stability from wood

Well-dispersed cellulose II nanofibers with high purity of 92 % and uniform width of 15–40 nm were isolated from wood and compared to cellulose I nanofibers. First, ground wood powder was purified by series of chemical treatments. The resulting purified pulp was treated with 17.5 wt% sodium hydroxide (NaOH) solution to mercerize the cellulose. The mercerized pulp was further mechanically nanofibrillated to isolate the nanofibers. X-ray diffraction patterns revealed that the purified pulp had been transformed into the cellulose II crystal structure after treatment with 17.5 wt% NaOH, and the cellulose II polymorph was retained after nanofibrillation. The cellulose II nanofiber sheet exhibited a decrease in Young’s modulus (8.6 GPa) and an increase in fracture strain (13.6 %) compared to the values for a cellulose I nanofiber sheet (11.8 GPa and 7.5 %, respectively), which translated into improved toughness. The cellulose II nanofiber sheet also showed a very low thermal expansion coefficient of 15.9 ppm/K in the range of 20–150 °C. Thermogravimetric analysis indicated that the cellulose II nanofiber sheet had better thermal stability than the cellulose I nanofiber sheet, which was likely due to the stronger hydrogen bonds in cellulose II crystal structure, as well as the higher purity of the cellulose II nanofibers.     

Monovalent Cation–Phenolic Crystals with pH-Driven Reversible Crystal Transformation

The conversion of renewable plant polyphenol to advanced materials with tailorable properties and various functions is desirable and challenging. In this work, monovalent cation-phenolic crystals contained K⁺ or Na⁺ ions were synthesized by using plant polyphenol as an organic source in alkaline solution. The crystal structure was resolved, showing a laminar crystal structure with M⁺ as connecting nodes. The morphologies (e.g., rod-like and spindle-shaped) and chemical compositions of crystals could be tuned by changing the cations. Interestingly, these polymer crystals exhibited a pH-driven reversible crystal transformation. They transformed into their protonated crystalline form under acidic conditions (e.g., pH 2) and went back to the cation-bound crystalline form in alkaline solutions. Furthermore, the crystals proved excellent antioxidants and heavy metal ion adsorbents.     

Substituent effects control the self-association of molecular clips in the crystalline state

We report the X-ray crystal structure of 11 molecular clips and analyze the influence of substituents (e.g., OMe, Me, and NO2) and their location on the observed crystal packing. Molecular clips 3a and 3b form tapelike structures in the crystal due to pi-pi interactions between the aromatic walls. Compounds 3d, 3eC, and 3fC form dimers driven by critical C-H...O interactions and then form tapes driven by pi-pi interactions in the crystal. These two building motifs, pi-pi and C-H...O interactions, can be used to rationalize the enantio- and diastereoselectivity observed in the X-ray crystal structures of the remaining five molecular clips. For example, the C-H...O interactions are found to dictate the formation of homochiral dimers in the structures of (+/-)-3eT and (+/-)-3fT and to control the diastereoselective formation of 6a2-6c2 dimeric motifs with internal p-dimethoxy-o-xylylene walls. Overall, the results suggest that substituent effects that induce even weak intermolecular interactions (e.g., C-H...O) can be used to reliably control crystal packing within glycoluril-based systems.     

Flame retardant finishing of cotton fleece: part VII. Polycarboxylic acids with different numbers of functional group

In our previous research, multifunctional carboxylic acids have been used as flame retardants to reduce the flammability of cotton fleece so that the garment made of cotton fleece can pass the US mandatory requirement specified by the government regulation “Standard for the Flammability of Clothing Textiles” (16 CFR 1610). In this research, we studied and compared the effectiveness of the polycarboxylic acids having different numbers of carboxylic groups as the durable flame retardants for cotton fleece. The cotton fabrics were treated with 1,2,3,4-butanetetracarboxylic acid (BTCA), citric acid (CA), succinic acid (SUA) and malic acid (MLA). We compared the reactivity of those polycarboxylic acids to esterify cotton cellulose and their effectiveness to reduce the flammability of the cotton fleece. The data indicated that the polycarboxylic acids with higher functionalities (BTCA and CA) form more esterlinkages on cotton and are more durable to home launderings than that treated with their bifunctional counter parts (SUA and MLA, respectively). In addition, the cotton fabrics treated with BTCA and CA have higher dimensional stability and higher strength loss. All those differences can be attributed to the fact that only those acids with three or more carboxylic groups, i.e., BTCA and CA, are able to crosslink cotton cellulose whereas the bifunctional acids (SUA and MLA) only form single esterlinkage with cotton.     

氰乙基纤维素/二甲基乙酰胺液晶溶液的研究

本文利用Abbe折射仪,热台偏光显微镜,小角光散射等方法研究了氰乙基纤维素/二甲基乙酰胺液晶溶液的形成,形态结构和某些性质。溶液随浓度的增加,从各向同性态经过两相共存状态,转变成为单一的液晶态。该液晶是胆甾型的。溶液的双折射Δn随浓度的增加或温度的降低而增大。在无外力作用时,液晶相由许多无规分布的取向微区组成。液晶溶液受切应力后形成“条纹结构”,大分子链沿切应力方向取向,并在各条纹中排列有序。     

Properties and Applications of Cellulose Acetate

Cellulose acetate is one of the most important esters of cellulose. Depending on the way it has been processed cellulose acetate can be used for great varies of applications (e.g. for films, membranes or fibers). The properties of the applied cellulose acetates are very important for these applications. A special field for using cellulose acetate is the synthesis of porous, spherical particles, so called cellulose beads. Different types of technical cellulose acetates were used and their ability to form such cellulose beads was characterized. First the different types of cellulose acetates were characterized by means of solubility; turbidity and degree of substitution. In addition the molar mass and the distribution of substituents along the polymeric chain were analyzed. Next, the cellulose beads were synthesized within an emulsion process using these different cellulose acetates. Then the properties (particle size, porosity, morphology) of the cellulose beads were determined. Finally, the relationship between the characteristic of cellulose acetates and properties of cellulose beads was investigated.     

Adsorption and viscoelastic properties of cationic xylan on cellulose film using QCM-D

The adsorption and viscoelastic properties of cationic xylan layers adsorbed from an aqueous electrolyte solution (NaCl 0, 1, 10, 100 mM) on a cellulose model surface were studied using quartz crystal microbalance with dissipation (QCM-D). Three cationic xylans with different charge densities were used (molecular weight, 9,600 g/mol with degrees of substitution, DS = 0.150, 0.191, and 0.259). The influences of the electrolyte concentration and charge density of cationic xylan on its adsorption onto a cellulose surface were investigated. Low charged cationic xylan was substantially more efficient in surface adsorption on cellulose compared to high charged cationic xylan at a low concentration of electrolytes. Adsorption of low charged cationic xylan decreased with increases in electrolyte concentration. However, adsorption of high cationic xylan increased with electrolyte concentration. The conformation and viscoelastic properties of the layers were interpreted by modeling the data under the assumption that the layers can be explained by the a Voigt model. Low charged cationic xylan adsorbed relatively weakly onto the cellulose surface, and formed a thicker, softer layer than high charged cationic xylan. On the other hand, high charged cationic xylan formed a thinner adsorption layer onto the cellulose surface.     

Structural Changes of Cellulose Crystallites Induced by Mercerisation in Different Solvent Systems; Determined by Powder X-ray Diffraction Method

The completeness of mercerisation can be evaluated by investigating the changes in the crystalline regions of cellulose from cellulose I (C-I) to cellulose II (C-II) by the X-ray powder diffraction method. Mercerisation experiments in four different solution systems: ethanol/water, acetone, DMSO and xylene, are reported. Also the effect of some additives, external pressure, treatment time and alkalisation temperature were studied. In two-phase solvent systems, structural changes of cellulose crystallites depended primarily on the distribution and solubility of sodium hydroxide in the solvent phases. The sodium hydroxide concentration in the hydrophilic phase must exceed 7–8 w/w-% before complete crystal change from C-I to C-II can occur. The precipitation of sodium hydroxide due to high concentration prevents the successful use of one-phase ethanol/water system in slurry process. On the contrary, the 2-propanol/water/sodium hydroxide system separates into two layers; to the water-rich lower layer and the 2-propanol-rich upper layer, where the sodium hydroxide remains mainly in the water-rich lower layer. This prevents the precipitation of sodium hydroxide and promotes the alkalisation of cellulose. Ammonium chloride and ammonium hydroxide clearly had a positive effect by promoting the crystal changes, however, the urea concentration used in this study was obviously too small. In the advantageous two-phase 2-propanol/water systems, the alkalisation time was only 15 min when the treatment temperature was kept between 0 and 10 °C. Reduced external pressure was found to have a small but still detectable positive effect on cellulose alkalisation while over-pressure prevented crystal changes.     

Analytical fractionation of trace metals in human serum by means of a chelating ion-exchanger

Conclusions Both, in labile form bound trace metals as well as ionic ones in human serum can selectively be separated on the heavy-metal chelating cellulose HYPHAN under physiological conditions. From the separation kinetics, detailed informations on the binding stability of metal-proteins [e.g., Cu(II), Fe(III), Zn(II)] result. Owing to low blanks, the separation procedure can also be applied to the fractionation of nanogram amounts of other metals [e.g., Al(III), Be(II), Mn(II), Ni(II), Pb(II)] in serum. Furthermore, the coupling with a protein fractionation method (e.g., gelchromatography, isotachophoresis) allows to investigate the binding stability of isolated metal-proteins.

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Analytische Fraktionierung von Schwermetallspuren in Blutserum mittels Chelat-Ionenaustauscher

     

氰乙基纤维素溶致性液晶的研究

氰乙基纤维素在二甲基甲酰胺、二甲基乙酰胺、二甲基亚砜、乙腈以及丙酮等溶剂中可以形成溶致性液晶。随浓度增加,溶液从各向同性状态经两相共存态转变成为完全的液晶态。升高温度到T_c,液晶相消失;降低温度到T′_c,液晶相再生成。T_c总大于T′_c。而且,浓度越高,过冷温度△T=T_c—T′_c越小。在各向同性,两相共存或完全的液晶状态,溶液平均折射率和消光度均与浓度呈线性关系。但在两相间相互转变时,即在C_1~*和C_2~*处,n-C和 A-C 曲线上出现转折点。高聚物与溶剂的相互作用参数X_(12)愈小,临界浓度C_1~*愈小。把描述大分子链柔顺性的参数f与X_(12)联系起来,可用 1956年 Flory的理论定性地解释溶剂对高聚物溶致性液晶形成的影响。     

Crystallization behavior of isotactic propylene‐1‐hexene random copolymer revealed by time‐resolved SAXS/WAXD techniques

The crystallization behavior of isotactic propylene‐1‐hexene (PH) random copolymer having 5.7% mole fraction of hexene content was investigated using simultaneous time‐resolved small‐angle X‐ray scattering (SAXS) and wide‐angle X‐ray diffraction (WAXD) techniques. For this copolymer, the hexene component cannot be incorporated into the unit cell structure of isotactic polypropylene (iPP). Only α‐phase crystal form of iPP was observed when samples were melt crystallized at temperatures of 40 °C, 60 °C, 80 °C, and 100 °C. Comprehensive analysis of SAXS and WAXD profiles indicated that the crystalline morphology is correlated with crystallization temperature. At high temperatures (e.g., 100 °C) the dominant morphology is the lamellar structure; while at low temperatures (e.g., 40 °C) only highly disordered small crystal blocks can be formed. These morphologies are kinetically controlled. Under a small degree of supercooling (the corresponding iPP crystallization rate is slow), a segmental segregation between iPP and hexene components probably takes place, leading to the formation of iPP lamellar crystals with a higher degree of order. In contrast, under a large degree of supercooling (the corresponding iPP crystallization rate is fast), defective small crystal blocks are favored due to the large thermodynamic driving force and low chain mobility. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 26–32, 2010     

Partial crystalline transformation of solvated cellulose IIII crystals, reproduced by theoretical calculations

In hot-water molecular dynamics simulation at 370 K, four cellulose III_I crystal models, with different lattice planes and dimensions, exhibited partial crystalline transformations of (1 ?1 0) chain sheets, in which hydroxymethyl groups were irreversibly rotated from gt into tg conformations, accompanied by hydrogen-bond exchange from the original O3–O6 to cellulose-I-like O2–O6 bonds. The final hydrogen-bond exchange ratio was about 95 % for some of the crystal models after 50 ns simulation. The corrugated (1 ?1 0) chain sheet was converted to a cellulose-I-like flat chain sheet with a slightly right-handed twist. The 3D structures of the three types of isolated chain sheet models were optimized using density functional theory calculations to compare their stabilities without crystal packing forces. The cellulose Iβ (1 0 0) models were more stable than the cellulose III_I (1 ?1 0) models. The optimized structure of cellulose III_I (1 0 0) models deviated largely from the initial sheet form. It was proposed to the crystalline transformation from cellulose III_I to Iβ that conversion of the chain sheet structure first take place, followed by sliding of the chain sheet along the fiber axis.