Cadoxen Solution Research Articles

Contribution of xylan to the brightness development and stability in the final ECF bleaching of eucalypt (Eucalyptus globulus Labill.) kraft pulp

Abstract Xylans isolated from eucalypt kraft pulps have been characterized by modern analytical methods. The pulps were partially bleached (DEOPD) and fully bleached with either a final ClO2 (DEOPDD) or an alkaline H2O2 (DEOPDP) bleaching stage. Alternatively, xylan isolated from the DEOPD pulp was treated with ClO2 or with H2O2 under the same conditions as pulps in a final bleaching stage and were further characterized. 1H nuclear magnetic resonance, size exclusion chromatography, UV-vis spectroscopy in cadoxen solution, and UV-resonance Raman spectroscopy were applied as analytical methods. The final ClO2 stage generated new unsaturated moieties in xylan, whereas H2O2 was very effective in the removal of xylan-related chromophores. The role of xylan to the delay of brightness development in the final ClO2 stage was highlighted by means of a pretreatment with xylanase Pulpzyme HC before the final bleaching stage. By this approach, the final bleachability of the pulp was boosted and the brightness stability of the fully bleached pulp was improved.

Characterization of the extracellular polysaccharide of Porphyridium sp.: molecular weight determination and rheological properties

The molar mass of the extracellular polysaccharide produced by the red microalga Porphyridium sp. was determined by gel permeation chromatography (GPC) followed by multiangle laser light scattering (MALLS). Two different disaggregation treatments were used prior to the measurement: (1) sonication and (2) incubation in an aqueous solution of tris(ethylenediamine)cadmium dihydroxide (cadoxen) followed by GPC analysis using a 50% cadoxen solution in the chromatographic mobile phase. The average molar mass was found to be 2.3×10 6 g/mol with the size distribution lying between 2×10 5 and 4×10 6 g/mol. The viscoelastic properties of aqueous solutions of the polysaccharide before and after sonication were evaluated by rheological methods. It was found that the viscosity of the solutions decreased dramatically with increasing sonication time. Changes in the mechanical spectra of aqueous polysaccharide solutions as a result of sonication over a range of frequencies were reflected in the inversion of the ratio of the storage modulus G′ to the loss modulus G″, which indicated a shift from a ‘weak gel’ to a liquid-like state.

Molecular weight and aggregation behaviour in solution of β- d-glucan from Poria cocos sclerotium

The weight-average molecular weights M w and intrinsic viscosities [ν] of linear β-(1 → 3)- d- glucan (PC3), a major polysaccharide in Poria cocos sclerotium were studied by light scattering and viscometry. The M w values of glucan PC3 fractions in 20% cadoxen solution and in cadoxen were 20.6 × 10 4 and 8.93 × 10 4, respectively. The [ν] values of glucan PC3 in water-cadoxen mixtures underwent an almost discontinuous decrease in the range from 20 to 30% cadoxen. The data ( M w ,[ ν]) of the unfractionated PC3 and of two fractions in 20% cadoxen and in cadoxen showed that glucan PC3 forms aggregates in 20% cadoxen solution, and dissociates to single chains in cadoxen. The change of aggregation and disaggregation in water-cadoxen mixtures are reversible.

Determination of Degree of Polymerization of Cellulose in Ligneous Papers

ABSTRACTIn the past, many attempts have been made to determine the degree of polymerization (DP) of cellulose in ligneous pulps or papers. Frequently, the methods employed caused severe depolymerization of the cellulose.The present paper provides a detailed procedure of DP determination of cellulose for both lignin-free and ligneous papers. The proposed method is based on viscosity measurements of cadoxen solutions of cellulose. Prior to dissolution in cadoxen, ligneous samples are partially delignified by a modified chlorite method, under conditions preventing any substantial depolymerization of cellulose. Results of preliminary experiments carried out on groundwood newsprint papers provide strong evidence of reliability of DP values so determined.

Flow birefringence and viscosity of cellulose solutions in semi‐dilute regime

AbstractAn attempt was made to study the flow birefringence and the viscosity of the systems of cellulose in aqueous sodium hydroxide and cadoxen solutions. For this purpose alkali‐soluble cellulose samples with crystal form I (simply denoted as cellulose I sample), prepared from conifer wood pulp by the steam‐explosion method, and alkali‐soluble cellulose samples with crystal form of cellulose II (cellulose II sample), regenerated from cuprammonium cellulose solution under specific conditions, were used. The extinction angle χ of aqueous alkali solutions of the cellulose I sample is significantly less shear rate (γ) dependent as compared with that of the cellulose II sample. In the latter system the χ versus γ relations for a given cellulose sample shifted to the higher γ side with decrease in the average molecular weight. The viscosity of the cellulose II sample in aqueous sodium hydroxide solutions is approximately twice that of the cellulose I sample in the same solvent if compared at the same molecular weight, same concentration, and same temperature. The latter solution showed a non‐Newtonian property at relatively smaller γ than the former solution did. Spin‐lattice relaxation time T1 (by 13C‐NMR) of cellulose in cadoxen solution was smaller in cellulose I, suggesting the existence of intra‐ and intermolecular hydrogen bondings at the C6 position of cellulose molecules in cellulose I solution. A dynamic light scattering study on cellulose in cadoxen showed that in a 5 wt % solution of cellulose I cellulose particles are dispersed with time into smaller particles and the larger particles could be excluded by ultracentrifuge and in cellulose II solutions the cellulose particles had almost the same size during storage. The above findings indicate that in 5 wt% cellulose I solutions in aqueous alkali or in cadoxen, cellulose I is not dissolved molecularly, but a supra‐molecular structure of the solid is at least partly reserved in the above solutions.

Characterization of nonderivatized cellulose by gel permeation chromatography

AbstractThe development of a gel permeation chromatography (GPC) system for the analysis of nonderivatized cellulose in the DP range of technical cellulose products is reported. In contrast to traditional GPC, where cellulose derivatives have to be prepared, in this work the cellulose solvent cadoxen was applied for the determination of the molecular weight distribution using a special analysis system. Nuclear magnetic resonance studies of cadoxen solutions indicated no complex formation between cadoxen and cellulose. Therefore, to avoid precipitation of cellulose from the prepared solution, cadoxen was also used as eluent in the chromatographic system. For this reason a stationary phase had to be found which is stable under the given strong alkaline conditions. The utilization of Fractogel TSK as column material resulted in the separation of dissolved cellulose showing a DPv between 400 and 2000 with good reproducibility. The application of very sensitive detectors together with a GPC program allows the characterization of unknown cellulose samples of different origin within a few hours.

Selective adsorption to cellulose in cadoxen solution

AbstractRefractive index and density increments at constant composition and also at constant chemical potential have been measured on solutions of cellulose in alkaline aqueous cadoxen. Apparent and true molecular weights of cellulose in this solvent have been determined by light scattering. The findings indicate that [Cd(en)3]2+ ions are preferentially adsorbed to the polymer to the average extent of two ions per three anhydroglucose subunits. Molecular models have shown that this effect is feasible sterically. In cadoxen alone the specific conductance increased with increasing concentration of cadmium and, for a fixed cadmium concentration, the specific conductance was observed to decrease with increasing concentration of dissolved cellulose. This was attributed to reduced overall ionic mobility resulting from selective adsorption of complex cadmium ions to the polymer chain. An analysis has been proposed to quantify this interaction.

Purification and properties of endo-(1→4)-β-d-glucanase from Ruminococcus albus

An enzyme active against O-(carboxymethyl)cellulose (CMC) was purified from a synthetic medium containing ball-milled cellulose wherein Ruminococcus albus had been cultivated for 70 h. After 570-fold purification, a homogeneous enzyme was obtained in a yield of 3%. The enzyme degraded CMC (molecular weight, 180,000; degree of substitution, 0.6) to a smaller polymer having a molecular weight of ∼20,000, and generated a small proportion of glucose, but negligible proportions of such cello-saccharides as cellobiose, cellotriose, cellotetraose, or cellopentaose. The fact that the enzyme could produce water-insoluble fragments was discovered by dissolving substrate and products in Cadoxen solution. No water-soluble cello-oligomers were detected by thin-layer chromatography after degradation of water-insoluble cellulose by the purified enzyme. Therefore, the enzyme was classified as an endo-(1→4)-β-d-glucanase.

Light Scattering and Viscometric Study of Cellulose in Aqueous Lithium Hydroxide

An attempt was made to determine molecular parameters of cellulose dissolved in simple solvents. Cellulose regenerated from a cuprammonium solution of acid-hydrolized cotton linters was found to dissolve molecularly, without suffering molecular degradation, into 6 wt% aqueous LiOH solution by choosing an adequate condition. The apparent weight-average molecular weight Mw*, of cellulose obtained by light scattering in a non-dialyzed aqueous LiOH, was converted into the correct weight-average molecular weight Mw with the aid of the data on Mw* and Mw for a dialyzed cadoxen solution of cellulose. The Mark–Houwink–Sakurada equation for cellulose in aq LiOH was [η]=2.78×10−2 Mw0.79 at 25°C {[η]; limiting viscosity number}. The Flory’s viscosity parameter Φ for this system was significantly smaller than the theoretical value for unperturbed chains at non-draining limit, showing a molecular weight dependence. The linear expansion factor for the radius of gyration was always below 1.04 as estimated from the penetration function. The unperturbed chain dimensions were estimated by various methods using the light scattering and/or viscometric data. Cellulose was found to be semiflexible in aq LiOH.

Double-Stranded Helix of Xanthan: Dissociation Behavior in Mixtures of Water and Cadoxen

A sodium salt xanthan sample dissolved directly in mixtures of water and cadoxen was investigated by elastic light scattering and viscometry at 25°C. With the increase in weight fraction wcad of cadoxen in the mixed solvent, the weight-average molecular weight, z-average radius of gyration ‹S2›z1/2, and intrinsic viscosity [η] of the sample fairly sharply decreased from the values for the double-helical dimer (in 0.1 M aqueous NaCl) to those for the single random coil (in pure cadoxen) in a range of wcad from 0.3 to 0.8. It was found that these data can be explained if it is assumed that only these two species coexist in the mixed solvent and if care is taken of the fact, found from measurements on cadoxen solutions diluted with water, that ‹S2›z and [η] of the single chain species markedly increase with decreasing wcad from 1.0 to 0.6. Thus, it was concluded that xanthan double helices in water-cadoxen mixtures dissociate into single chains directly, i.e., without passing through their partial melting. The expansion of the single chain species was attributed to the formation of intramolecular hydrogen bonds.

Phase transitions in cellulose solutions. The kinetics of precipitation of cellulose from diluted cadoxen solutions

AbstractSolutions of cellulose (degree of polymerization: 296 ± 16) in tris(ethylenediamine)cadmium(II)hydroxide‐ethylenediamine‐water (cadoxen), 1.015% (weight per volume) were diluted 1:1.5 with water. The ensuing isothermal precipitations were followed dilatometrically at temperatures ranging from 27.50 to 48.45°C. The precipitation data were characterized by a positive temperature coefficient. They generally conformed to a one‐dimensional nucleation rate law; the Avrami exponents were close to unity. Alternatively, they fit a first‐order reaction rate expression with respect to cellulose concentration. The low crystallinity of the precipitated cellulose leads to the interpretation of the kinetics in terms of the dissociation of a cellulose‐cadoxen complex, rather than phase separation, as the rate‐determining step. The nucleation rate law suggests a one‐dimensional nonrandom cooperative chemical process, while the first‐order rate law suggests a random process.

Spectroscopic investigation of some derivatives of oxycellulose in cadoxen solution

AbstractCondensation methods for the estimation of carbonyl groups in oxycellulose are briefly reviewed. The u.v. absorption spectra of solutions of oxycellulose and some of its derivatives in cadoxen have been examined. The results show that solutions of oxycellulose, its semicarbazide derivative and its thiosemicarbazide derivative are unsatisfactory for the spectrophotometric determination of carbonyl content, whereas the phenylhydrazine derivative may be used for an approximate determination; p‐nitrophenylhydrazine however is shown to be an excellent reagent for this determination.

Spectroscopic investigation of some derivatives of oxycellulose in cadoxen solution

Condensation methods for the estimation of carbonyl groups in oxycellulose are briefly reviewed. The u.v. absorption spectra of solutions of oxycellulose and some of its derivatives in cadoxen have been examined. The results show that solutions of oxycellulose, its semicarbazide derivative and its thiosemicarbazide derivative are unsatisfactory for the spectrophotometric determination of carbonyl content, whereas the phenylhydrazine derivative may be used for an approximate determination; p-nitrophenylhydrazine however is shown to be an excellent reagent for this determination.

Molecular weight distribution of cellulose by fractionation in cadoxen solutions

The fractionation of cellulose in cadoxen solutions has been carried out by precipitation with aqueous propanol. The reproducibility of the method has been tested by means of parallel fractionations, and shown to be good, for both research and routine work. The fractionation data have been analysed using Beall and Schulz methods, and the results compared.

Spectroscopic investigation of hydrocellulose phenylosazones in cadoxen solution

AbstractSolutions of hydrocellulose phenylosazone in cadoxen are stable when oxygen is excluded. In the presence of oxygen, the absorption spectrum changes, but the change is partially reversible when nitrogen is bubbled through the oxidized solution. It is probable that a hydroperoxide of the hydrocellulose phenylosazone is formed initially and is then decomposed by the basic solvent. The work indicates the importance of using deoxygenated solvents and working in an oxygen‐free atmosphere when preparing cadoxen solutions of hydrocellulose phenylosazone.

Spectroscopic investigation of cellulose degraded celluloses, and their phenylhydrazine derivatives in relation to assessment of degradation

AbstractThe ultraviolet absorption spectra of Cadoxen solutions of hydrocellulose and hydrocellulose phenylosazones are described. With solutions of hydrocellulose no simple relationship between D.P. and absorbance was found. Solutions of hydrocellulose phenylosazone in Cadoxen show well‐defined maxima at 277 nm and 390 nm and do not change over 1 hr when oxygen is excluded. The absorbance of the phenylosazone at 390 nm may be used to determine the D.P. of the hydrocellulose samples.

An x‐ray study of crystalline orientation and mechanical properties of swollen cotton fibers using cadoxen solution as swelling agent

AbstractBundles of cotton fibers were given swelling and stretching treatment using Cadoxen solution containing 3.58% cadmium. The fibers were stretched from −2% to +8% in steps of 2%. The crystallite orientation and mechanical properties of treated fibers are markedly improved. Results clearly indicate that the swelling of cotton in Cadoxen solution is intercrystalline and the swollen fiber has retained the cellulose I structure.

The effect of crosslinking on the swelling of cotton in solutions of sodium hydroxide and cadoxen

AbstractThis paper describes the effects of prior crosslinking in dimethylol ethyleneurea (DMEU) on the swelling of cotton fiber in aqueous solutions of sodium hydroxide and in cadoxen solutions (solutions of cadmium oxide in mixtures of ethylenediamine and water). The degree of swelling in the weaker swelling solutions is markedly reduced by the crosslinking, but in the stronger solutions (particularly in concentrated sodium hydroxide) the effect of prior crosslinking is only small; this is accounted for in terms of a fibril‐tearing mechanism in these stronger solutions. Crosslinking cotton reduces the mercerizing effect of strong alkali solutions (i.e., the disordering and the cellulose I → II lattice change), and also reduces the solubility of the fiber in solutions of cadoxen and cuprammonium hydroxide.

The swelling of cotton in cadoxen, ethylenediamine, and cuprammonium hydroxide

AbstractThis paper describes the swelling of cotton fiber in solutions of cadoxen, ethylenediamine, and cuprammonium hydroxide. The absorption of swelling agent and the increase in width of the fiber were measured. The degree of swelling in cadoxen solutions, in relation to the composition of these solutions, is complex; very high degrees of swelling can be attained. The effects of these swelling treatments on the fine structure of cotton, as measured by the infrared‐deuteration method, density, acid hydrolysis, and an acetylation technique, are described and discussed in relation to the swelling behavior.