Fumihiko Onabe

Preparation of low-molecular-weight chitosan using phosphoric acid

Abstract Two types of low degree of polymerisation (DP) chitosan were prepared by homogeneous hydrolysis of chitosan in 85% phosphoric acid at room temperature for 1–6 weeks. The hydrolysates were collected by addition of excess ethanol, and were fractionated by solubility in water. The changes in yields of water-insoluble (higher DP) and water-soluble (lower DP) fractions were determined as a function of hydrolysis time. The hydrolysis proceeded with further deacetylation of chitosan, resulting in degree of deacetylation of more than 90%. The water-insoluble fraction prepared after the hydrolysis for 4 weeks (43% yield) had a weight-average DP ( DP w ) of 16·8, and showed the ‘tendon’ type X-ray diffraction pattern. The water-soluble fraction (12·5% yield) had a DP w of 7·3, and showed the ‘annealed’ type pattern.

Preparation of cellulose-chitosan blend film using chloral/dimethylformamide

Abstract Cellulose-chitosan blend films with varied mixing ratios (0–100%) were prepared by dissolving the polymers in chloral/dimethylformamide followed by casting onto glass plates. X-ray diffraction patterns of the films showed a gradual transition from partially crystalline cellulose to non-crystalline chitosan with increasing chitosan content. The tensile strength and Youngs modulus of the blend films were greater than those calculated by adding the values of the two components according to the blend ratios. Maxima in these properties appeared at chitosan contents of 10–20%. Chitosan in the blend films showed increased resistance to extraction with acetate buffer (pH 4.5). These results suggest the occurrence of specific interactions between cellulose and chitosan molecules, probably based on the structural similarity. Solute permeability in the blend films was greater than that for pure cellulose or chitosan film.

Size-exclusion chromatography of cellulose and chitin using lithium chloride—N,N-dimethylacetamide as a mobile phase

Abstract Distributions of molecular mass of cellulose and chitin were determined by size-exclusion chromatography (SEC) using 5% (w/w) lithium chloride—N,N-di

Acid hydrolysis behaviour of microbial cellulose II

A mutant strain of Acetobacter xylinum produces cellulose of anomalous band-like form (‘native band’), and this material has been found to be cellulose II, presumably having a folded-chain structure (according to recent work by Kuga et al.). In addition to the previous results of electron diffraction, X-ray analysis showed that this band material was composed of virtually pure cellulose II. We have studied the acid hydrolysis behaviour of this material to obtain additional evidence for the proposed structure. When hydrolysed with 1 N hydrochloric acid at 100°C, the degree of polymerization (DP) of the material decreased rapidly from 322 (DPw/DPn = 3.83) to 18.3 (DPw/DPn = 1.19). The latter value (levelling-off DP) corresponds to the observed width (10 nm) of strand-like constituents of the band material. The sample dissolved in and regenerated from 8.75% aqueous sodium hydroxide lost its original characteristic morphology and became irregular-shaped agglomerates. The leveling-off DP of this regenerated sample was 55.2 (DPw/DPn = 2.53), a typical value for common regenerated celluloses. These findings as a whole strongly suggest that the cellulose molecules in the native band are selectively cleaved at sharply folded parts by acid, producing fragments of the length of folding periodicity.

Adsorption behavior of aluminum compounds on pulp fibers at wet-end

Various aluminum compounds were added to pulp suspensions, and the adsorption behavior of their aluminum components on pulp fibers was studied. Aluminum contents in the handsheets were determined using an energy dispersive X-ray analyzer attached to a scanning electron microscope and an X-ray fluorescence analyzer. Although aluminum contents in the handsheets increased with increasing additions of the aluminum compounds, the detailed adsorption patterns varied among the aluminum compounds used. Their chemical structures and the pH values of the pulp suspensions greatly influence the adsorption behavior. When fines are present in the pulp suspensions, the aluminum components are predominantly adsorbed on the fines, probably due to their larger surface areas or the higher carboxyl contents compared to those of coarse fibers. Not only aluminum flocs but also far smaller components such as various aluminum cations seemed to be adsorbed on pulp fibers. Most aluminum flocs, which are formed in pulp suspensions by reacting with OH and entrapped in a fiber matrix by filtration effects, are removable by repeated mechanical agitation of the pulp suspensions.

NMR analyses of polysaccharide derivatives containing amine groups

Amylose, amylopectin, hydroxyethylcellulose, methylcellulose, and cellulose were reacted with diethylaminoethyl chloride HCl salt and 3-chloro-2-hydroxy-propyltrimethylammonium chloride under aqueous alkaline conditions in order to introduce tertiary amine and quaternary ammonium groups into polysaccharides. Degrees of substitution were obtained from 1H- or 13C-NMR spectra of hydrolyzates, and distributions of diethylaminoethyl groups in polysaccharides were measured by 13C-NMR. Since amylose, amylopectin, and hydroxyethylcellulose were soluble in the reaction media, these three polysaccharides had higher reactivity for etherifications than cellulose. Methyl-cellulose, which has hydrophobic methyl groups, had as much reactivity as cellulose. Primary hydroxyl groups, C-6, of polysaccharides had the highest reactivity for diethylaminoethylation.

Kinetic studies on enzymatic hydrolysis of celluloses for evaluation of amorphous structures

Abstract Enzymatic hydrolysis of never-dried, freeze-dried, and oven-dried amorphous celluloses, and crystalline cellulose was studied for evaluation of amorphous structures of cellulosic materials. Hydrolysis rate constants at the initial stage were indirectly measured using a glucose sensor, and Km and Vmax values were obtained from the vo/[S]o versus [S]o plots. The decreasing order of 1/Km values was as follows: never-dried amorphous cellulose ⪢ solvent-exchanged amorphous cellulose ≥ freeze-dried amorphous cellulose > oven-dried amorphous cellulose ≥ microcrystalline cellulose powder. On the other hand, the decreasing order of Vmax was as follows: never-dried amorphous cellulose ≥ solvent-exchanged amorphous cellulose > freeze-dried amorphous cellulose = microcrystalline cellulose powder > oven-dried amorphous cellulose. These observations indicated that 1/Km and Vmax values reflected subtle differences in amorphous structure. Almost no relationship was observed between those values and either crystallinity or specific surface area determined by the nitrogen adsorption method. Thus, kinetic studies of enzymatic hydrolysis of cellulose samples may be applicable for the characterization of non-crystalline regions of cellulose.

Retention behavior of size and aluminum components in handsheets prepared in rosin soap size-alum systems

Handsheets were prepared with rosin soap size and aluminum sulfate under various conditions, and the retention behavior of the rosin size and aluminum components in the handsheets was studied. Pyrolysis-gas chromatography and X-ray fluorescence analysis were used to determine the size and aluminum contents in the handsheets, respectively. When the addition level of rosin soap size varied from 0% to 4% and that of aluminum sulfate was fixed at 2%, the rosin size content increased with the increase in the size addition level, whereas aluminum and calcium contents were roughly constant. Under these conditions, handsheets prepared from fines-free pulp had aluminum contents less than those for the original beaten pulp, probably because the former pulp had a carboxyl content less than that of the latter pulp. Not only the conventional rosin retention mechanism but also mechanism proposed below must exist in the rosin soap size-alum systems. That is, some aluminum compounds originating from aluminum sulfate are adsorbed on pulp fibers immediately after the aluminum sulfate addition. These adsorbed aluminum compounds form cationic sites on pulp fibers, and free rosin acid components with anionic charges are then adsorbed onto the cationic sites of pulp fibers at the wet-end.

Influence of coating properties on paper-to-paper friction of coated paper

Coated paper-to-coated paper friction properties were examined in relation to printing runnability difficulties like erroneous double feeding of paper sheets. Higher ratios of precipitated calcium carbonate (PCC) to clay in mixed pigment coatings resulted in higher static and kinetic coefficients of friction (COFs). Microroughness in the order of pigment particle size is considered to relate to COF, because cube-shaped particles of PCC resist sliding. Calendering decreased COF at larger amounts of PCC, but did not change COF of the sole clay formulation at all. Addition of ground calcium carbonate (GCC) decreased COF. The rate of decrease in kinetic COF with increasing number of sliding for the GCC-rich formulation was higher than that for the PCC-rich formulation, presumably because protruding parts, characteristic of the GCC-rich formulation, on the surface were selectively flattened. Addition of styrene-butadiene (SB)-latex up to 14pph decreased COF, but static COF had the highest value at 18pph. The antislip property (as a rubber) of SB-latex developed only in the static mode. Among lubricants formulated, the wax type decreased COF the most remarkably with more effect on kinetic COF than on static COF.

Studies on interactions between aluminum compounds and cellulosic fibers in water by means of 27 Al-NMR

Interactions between pulp fibers and aluminum compounds in pulp suspensions were studied using fibrous cellulose (FC) and fibrous carboxymethylcellulose (FCMC) powders as models of pulp fibers by X-ray fluorescence analysis and27Al nuclear magnetic resonance. When deionized water was used at pH 4–5, water-soluble cationic aluminum species (Al3+, aluminum oligomer, and polyaluminum species) were adsorbed on the solid FCMC, forming carboxylic acid aluminum salts by cation exchange. The formation of these nondissociated pulp-COOAl type structures in paper sheets may contribute to some decreases in hydrophilic property. On the other hand, the water-soluble cationic aluminum species had nearly no interactions with hydroxyl groups of solid cellulose in the suspensions at pH 4–5. When tap water was used at pH 5–7, some aluminum components were retained on not only FCMC but also the FC sample. Probably, water-insoluble Al(OH)3 flocs are formed in the suspensions at pH 5–7 and retained on the FC sample by simple filtration effect. Therefore, two mechanisms of the aluminum retention (i.e., electrostatic interactions and a simple filtration effect) may exist between pulp fibers and aluminum components in the practical papermaking process.