Properties of spruce sulfite pulp and birch kraft pulp after sorption of cationic birch xylan

In this study, correlations between the charge density of adsorbed cationic xylans and the mechanical properties of selected pulps are discussed. Hand-sheet experiments were carried out using birch sulfate pulp and spruce sulfite pulp after the adsorption of 2-hydroxypropyl-trimethylammonium-4-O-methylglucuronoxylans (HPMAGXs) with different molar degrees of substitution (MS) in the range of 0.06–0.19. The charge density of the HPMAGX in water was determined by polyelectrolyte titration. Properties such as the tensile and burst index increased after HPMAGX addition and showed an optimum depending on the MS, which was 0.1 for both pulps. Other properties like the tear-index or the specific volume changed depending on the pulp. Beating experiments were also performed and showed an increasing tensile index of birch kraft pulp in the range of 53.7 to 85.7 N m g⁻¹ for a beating time of 10 min. The adsorption of HPMAGXs with different MS onto thiol-based self-assembled monolayers (SAMs) on gold and regenerated cellulose surfaces were studied using surface plasmon resonance (SPR). Electrostatic interactions were found to be the most important factors affecting HPMAGX adsorption, and a strong correlation between HPMAGX adsorption onto carboxyl-terminated SAMs (SAM-COOH) and paper strength when HPMAGX was used as a papermaking additive was observed.     

Surface selective removal of xylan from refined never-dried birch kraft pulp

In this study, the effect of enzyme treatment on refined, never-dried bleached birch kraft pulp was investigated, using an endo-1,4-β-xylanase, that is substantially free from cellulase activity. The xylanase treatment of refined never-dried pulp revealed a rapid initial hydrolysis rate with a time-dependent saturation level in the amount of hydrolyzed pulp carbohydrates. Surprisingly short xylanase treatment times were found to have an impact on the fiber surface structure and on the physicochemical properties of kraft pulp fibers. Xylanase treatment led to mild microscopic differences in the ultrastructure of a never-dried fiber, whereas local topographical differences were distinguishable with atomic force microscopy. Results from the analysis of dissolved carbohydrates and the interfacial properties of the xylanase-treated never-dried fibers thus confirm a selective removal of xylan from the fiber surfaces. The zeta-potential charge and dewatering properties of the pulp slurry, fiber morphology, and strength properties of the paper were affected, which is a concomitant of xylanase treatment. However, the papermaking properties of the fibers were mainly preserved with simultaneous improvement in the dewatering rate of the pulp. Thus, optimized xylanase treatment of refined bleached kraft pulp provides a fiber for papermaking or fiber modification purposes with a selectively modified chemical composition of the fiber surface layer.     

On the accessibility and structure of xylan in birch kraft pulp

The structure of -(14)-xylan, both in isolated form and as a component of bleached birch kraft pulp, was studied employing CP/MAS ¹³C NMR spectroscopy. Bleached birch kraft pulp was treated with xylanases or alkali in order to distinguish between accessible and inaccessible xylan. In xylan which was alkali-extracted from bleached birch kraft pulp, the relative contents of xylose and 4-O-methylglucuronic acid were 99.4 and 0.6 weight %, respectively, and the degree of polymerization was 70. The supermolecular structure of xylan is very sensitive to the surrounding environment. All extracted xylan chains were accessible to water and methanol and the solvent molecules easily exchanged. In bleached birch kraft pulp, cellulose fibrils interact with xylan chains, causing these to adopt a conformation similar to one of the configurations observed for dry xylan. In birch pulp, about 1/3 of the xylan was found to be accessible to digestion by xylanases or extraction with 5% w/w potassium hydroxide (aq). A signal at 81.7ppm in the C-4 region of the CP/MAS ¹³C NMR spectrum of bleached birch kraft pulp originated from xylan at the accessible fibril surfaces. A portion of a broad signal at 83.5ppm reflected inaccessible xylan, which is probably present as co-aggregates with cellulose fibril aggregates.     

Bleaching of kraft pulp with commercial xylanases

The perform ance of commercial xylanases in totally chlorine-free bleaching of kraft pulp from conifer was tested with Pulpzyme HC (Novo Nordisk) and Cartazyme NS-10 (Sandoz/Clariant), at 500 U/kg of dry pulp, respectively. The treatment with Pulpzyme (X_p) or Cartazyme (X_c) has been combined with stages of bleaching using: oxygen (O), sulfuric acid (A), and extraction with hydrogen peroxide (E_op). The following sequences have been tested: OXpAE_op, OXcAE_op, XpOAE_op, XcOAE_op and OAE_op, Kraft pulp bleached at the Klabin industrial plant using the sequence, CEH (chlorine, alkaline extreaction, and hypochlorination) was, used for comparison. The following average values were obtained: 1. Kappa number: OX_pAE_op, 4.8; OX_cAE_op, 4.9; XpOAE_op, 5.0; XcOAE_op, 4.9; OAE_op, 5.6, and CEH, 1.9; 2. Brightness (% ISO values): OX_pAE_op, 68.4; OX_cAE_op, 70.1; X_pOAE_op, 67.9; X_cOAE_op, 26.9; X_pOAE_op, 23.4; X_cOAE_op, 23.1; OAE_op, 25.4, and CEH, 25.2. Pulps that were treated with xylanases, before or affer the delignification with oxygen, have shown reduced kappa number and higher brightness than the pulp OAE_op, Enzyme treatment before delignification with oxygen reduces pulp viscosity. Brightness obtained for pulp produced with bleaching sequences containing the enzymatic treatment, when compared with the control, CEH, shows that the xylanases enhance the action of the bleaching agents.     

Clean and selective oxidation of alcohols catalyzed by ion-supported TEMPO in water

Three different types of ion-supported TEMPO catalysts are synthesized and their catalytic activity in the chemoselective oxidation of alcohols is investigated. These new catalysts show high catalytic activity in water and can be reused for the next run by extraction of products. Recycling experiments exhibit that ion-supported TEMPO can be reused up to five times without loss of catalytic activity. This system offers a very clean, convenient, environmentally benign method for the selective oxidation of alcohols.     

A comparison of softwood and birch kraft pulp fibers as raw materials for production of TEMPO-oxidized pulp, MFC and superabsorbent foam

This study compares the suitability of using birch kraft pulp or softwood kraft pulp in the preparation of TEMPO-oxidized pulp, MFC and superabsorbent foam. TEMPO oxidation was performed using five different dosages of primary oxidant. The time of disintegration treatment was varied to study its influence on the properties of the produced MFCs and foams. Both the birch and the softwood pulps could be used for producing superabsorbent foams, depending on the process conditions, the absorption capacities were about the same for the two pulps and varied between 25 and 55 g saline solution/g absorbent. The foams based on birch pulp had, however, on average, 30 % higher retention capacity than the foams based on softwood pulp. The maximum retention capacity obtained was 16.6 g saline solution/g absorbent. The greater retention capacity of birch-based foams is not fully understood, but a smaller pore size may be the reason, which in turn would generate greater capillary forces. In addition to this, it was found that birch pulps, contrary to softwood pulps, had a substantial amount of fibers that were relatively unaffected by the disintegration treatment. These oxidized fibers are likely to reinforce the foam, thereby making the foam more resistant to external pressures, which is in accordance with earlier findings.     

Sorption of dissolved galactoglucomannans and galactomannans to bleached kraft pulp

Sorption of mannans onto bleached kraft pulp (BKP) was investigated withreference to other interactions of mannans in mechanical pulping andpapermaking. O-Acetyl galactoglucomannans (GGM) isolated from thermomechanicalpulp (TMP), as well as enzymatically modified guar gum galactomannans (GM) wereused in the study. The results showed that deacetylation of TMP GGMs, alsooccurring during peroxide bleaching of TMP, dramatically increased thesorption.A higher sorption was also achieved after salt addition, while temperature hadno effect. Sorption of guar gum GMs onto BKP fibres was, on the other hand,quite unaffected by external conditions such as temperature, pH and saltaddition. The degree to which the pulp was beaten did not notablyinfluence the sorption either – only unbeaten pulp gave a clearly lower mannansorption. A lower number of galactose side groups, however, strongly affectedsorption – the lower the number of side groups, the higher the sorption.The molar mass did not seem to affect the rate of sorption to any higher extentat ambient temperature. At higher temperatures the rate of sorption of smallerGM polymers was, nevertheless, slightly increased. Low-molar-mass GMs alsosorbed at a higher rate onto unbeaten pulp compared to high-molar-mass mannans.GM sorption appeared to be virtually irreversible.     

Aerobic selective oxidation of alcohols to aldehydes or ketones catalyzed by ionic liquid immobilized TEMPO under solvent-free conditions

A selective ionic-liquid immobilized TEMPO/CuCl catalyzed oxidation procedure of alcohols to the corresponding aldehydes and ketones with molecular oxygen under solvent-free conditions was developed. The catalyst was easily recovered and reused in the reaction. Correspondence: Yun-Yang Wei, School of Chemical Engineering, Nanjing University of Science and Technology, 210094 Nanjing, P.R. China.     

Fiber properties of eucalyptus kraft pulp with different carboxyl group contents

Fiber properties (fiber swelling ability, crystal structure of cellulose, fiber surface morphology, and etc.) of eucalyptus kraft pulp with different contents of carboxyl group in Na-form were studied. There was a direct proportional relationship between water retention value and carboxyl content of pulp. When the carboxyl content increased from 35.6 to 315.7 mmol/kg, tensile index and burst index increased by 56.1 and 117.8 %, respectively, and crystallinity of cellulose decreased by 11.8 %. Environmental scanning electron microscope showed that more fibrillation was observed on the carboxymethylated fiber surface, compared with the control sample. The results from Fourier transform infrared spectra analysis suggested that the relative intensity of the band at 1,633/cm was increased after carboxymethylation treatment, which showed that the carboxyl content increased. The increase in the carboxyl content not only could increase the fiber strength properties, but also could increase the recycling times of the fiber.     

Diepoxide treatment of softwood kraft pulp: influence on absorption properties of fibre networks

Many different approaches to the introduction of intra-fibre cross-links in fibres for use in absorption products are described in the patent literature, but relatively little has been done in terms of academic research. In this study, the long fibre fraction of a Scandinavian softwood kraft pulp has been cross-linked with the diepoxide 1,4-butanediol diglycidyl ether (BDDE). The fibre properties and the performance of the pulp in low density fibre networks were analyzed. In experiments, the cross-linking agent (BDDE) was dissolved in acetone and then mixed with the pulp. It was shown that a prior wash with NaOH (0.1 M) activates the polysaccharides and increases the extent of cross-linking, detected as a decrease in the water retention value. Chemical analysis of modified fibres also gave a clear indication of that cross-linking reactions actually occurred. The pulp properties could furthermore be influenced by varying time, temperature and the amount of BDDE in the reaction. It was also shown that it is possible to use water as a solvent for the cross-linking agent, even though the reactivity of water towards diepoxide must be considered to be high. The cross-linked pulps showed wet bulk under load comparable to that of the mechanical pulps and enhanced properties than unmodified Scandinavian softwood kraft pulp. It was also observed that fibre network test pads of the cross-linked pulp fibres, after being tested in the wet state, regained a substantially large part of their low-density structure when air-dried.     

Highly chemoselective oxidation of 1,5-diols to δ-lactones with TEMPO/BAIB

The selective oxidative conversion of a variety of highly functionalized 1°,2°-1,5-diols into the corresponding δ-lactones has been effected simply and efficiently using a reagent system comprised of catalytic 2,2,6,6-tetrmethylpiperidinooxy (TEMPO) and excess bis-acetoxyiodobenzene (BAIB).     

Selective aerobic oxidation of alcohols catalyzed by iron chloride hexahydrate/TEMPO in the presence of silica gel

An environmentally friendly and efficient process whereby FeCl₃?6H₂O/2,2,6,6‐tetramethylpiperidine N‐oxyl (TEMPO)‐catalyzed oxidation of alcohols to the corresponding aldehydes and ketones is accomplished in the presence of silica gel using molecular oxygen or air as the terminal oxidant. The electron‐deficient benzyl alcohol was smoothly oxidized to the corresponding aldehydes with up to 99% isolated yield. It was found that silica gel not only could enhance the catalytic reaction rate but also increase the selectivity for the product. The high performance of FeCl₃?6H₂O/TEMPO catalyst system in the presence of silica gel might be attributed to the surface silanol groups. UV–visible spectra analysis showed that the Fe (III)–TEMPO complex could serve as the active intermediate species in the present catalytic system. A plausible mechanism of the catalytic system is proposed. Copyright © 2012 John Wiley & Sons, Ltd.     

Comparison of TEMPO and its derivatives as mediators in laccase catalysed oxidation of alcohols

A series of TEMPO (2,2′,6,6′-tetramethylpiperidinyl-1-oxy) derivatives were studied as mediators of laccase (from Trametes versicolor) in the oxidation of benzyl alcohol and 1-phenylethyl alcohol. TEMPO (1), 4-hydroxy-TEMPO (2) and 4-acetylamino-TEMPO (4) turned out to be the most active mediators for laccase. In addition, 4-acetylamino-TEMPO and 4-hydroxy-TEMPO were more active in the oxidation of 1-phenylethanol compared to TEMPO. For these mediators kinetic isotope effects in the range of 2.1-3.2 were observed for α-monodeutero-p-methylbenzyl alcohol oxidation. These values are consistent with a mechanism involving oxoammonium intermediacy. Competition experiments between benzyl alcohol and 1-phenylethanol showed that TEMPO and its derivatives react faster with primary alcohols than with secondary alcohols, also in line with the proposed mechanism.     

Kinetics and mechanism of the oxidation of amaranth with hypochlorite

The reaction mechanism of the oxidation of Amaranth dye (2-hydroxy-1-(4-sulfonato-1-naphthylazo) naphthalene-3,6-disulfonate) with hypochlorite under varied pH conditions was elucidated by a kinetic approach. Under excess concentration of oxidant, the reaction followed pseudo-first-order kinetics with respect to Amaranth, and the oxidation was found to occur through two competitive reactions, initiated by hypochlorite and hypochlorous acid. The reaction order with respect to both OCl(-) ion and HOCl was unity. While the latter reaction was fast, the significance of the oxidation paths depended on the relative concentration of the two oxidizing species, which was dictated by the reaction pH. The role of the H(+) ion in the reaction was established. For the hypochlorite ion and hypochlorous acid facilitated reactions, the second-order rate coefficients were 1.9 and 23.2 M(-1) s(-1), respectively. The energy parameters were E(a) = 33.7 kJ mol(-1), ΔH(?) = 31.2 kJ mol(-1) and ΔS(?) = -190.6 J K(-1) mol(-1) for the OCl(-) ion-driven oxidation, and E(a) = 26.9 kJ mol(-1), ΔH(?) = 24.3 kJ mol(-1) and ΔS(?) = -222.8 J K(-1) mol(-1) for the reaction with HOCl-initiated oxidation. The major oxidation products for both the pathways were 3,4-dihydroxy naphthalene-2,7-disulfonic sodium salt (P(1)), dichloro-1,4-naphthoquione (P(2)) and naphtha(2,3)oxirene-2, 3-dione (P(3)). On the basis of the primary salt effect and other kinetic data, the rate law for the overall reaction and probable reaction mechanism was elucidated. The proposed mechanism was validated by simulations using Simkine-2.     

Allylic oxidation: easy synthesis of alkenones from activated alkenes with TEMPO

Activated alkenes and dienes are converted into the corresponding alkenone in excellent yields (>90%). In aqueous acetonitrile, the transformations are catalyzed by 2,2,6,6-tetramethyl-1-oxopiperidinium (TEMPO⁺) in the presence of water and 2,6-lutidine. TEMPO⁺ cations were regenerated electrochemically from the radical parent (TEMPO) at a vitreous carbon anode.     

Biobleaching of hardwood kraft pulp with cellulasedeficient mutant from hyper ligninolytic fungus izu- 154

Protoplasts of the monokaryotic strain from hyperligninolytic fungus IZU-154 were treated with UV irradiation, and the regenerants were screened for their inability to degrade Walseth cellulose (WC) and carboxymetylcellulose (CMC) on an agar plate. From 2700 regenerants, cellulase deficient and noncellulase mutants were isolated and designated Cel-139 and Cel-145, respectively. Cel-139 showed 15% Avicelase, 60% CMCase, and 10% β-glucosidase activities; however, it retained the same level of lignin degrading capability and manganese peroxidase (MnP) production when compared with wild-type IZU-154. On the other hand, Cel-145 showed deterioration in lignin-degrading capability, despite a substantial level of MnP production. Furthermore, biobleaching of hardwood kraft pulp (HWKP) by wild-type IZU-154 and Cel-139 in the solidstate fermentation system, without supplemental nutrients, were investigated. After 5 d of treatments with both fungi, pulp brightness increased from 33 to 65% ISO brightness, and Kappa number decreased from 13.9 to 6.0. However, yield loss of biobleached pulp was 20% lower with Cel-139 than with wild-type IZU-154.     

Production of microfibrillated cellulose from unbleached kraft pulp of Kenaf and Scotch Pine and its effect on the properties of hardwood kraft: microfibrillated cellulose paper

This work investigated the effect of using Kenaf bast fibre kraft pulps compared to Scotch Pine kraft pulps for producing microfibrillated cellulose (MFC) and its employment for improving mechanical and physical properties of handsheets made from unbleached kraft hardwood pulp. It was shown that MFC based on Kenaf fibres can be produced at higher consistencies [>5 % (w/w)] compared to when Scotch Pine is employed [≈2 % (w/w)] as raw material. The possibility of using a higher consistency when processing Kenaf is beneficial for the processing in microfluidizers. The rheological properties of the products were shown to be consistent with what is known for MFC-based systems. The studies indicate that the mechanical properties of handsheets from unbleached kraft hardwood pulp can be improved by replacing part of the unbleached kraft hardwood pulp fibres with either unbleached kraft Kenaf pulp or unbleached Scotch Pine kraft pulp. However, the same levels of improvements were obtained when using only a small amount [≈6 % (w/w)] of MFC based on Kenaf or Scotch Pine, when introduced into the system either as a dry strength additive or by coating pre-made handsheets. Finally, it was shown that the incorporation of MFC in handsheets decreases the air-permeability; this effect became amplified when the MFC was applied as a coating onto the handsheets.     

Copper catalyzed oxidation of sulfides to sulfoxides with aqueous hydrogen peroxide

Copper(II) complex 1 catalyzes the oxidation of sulfides to sulfoxides with 30% H₂O₂ in high yields. Addition of a catalytic amount of TEMPO to the reaction mixture enhances the conversion and selectivity. Complex 1 can be recycled without loss of activity.     

TEMPO visible light photocatalysis: The selective aerobic oxidation of thiols to disulfides

TEMPO(2,2,6,6-tetramethylpipe ridine-1-oxyl) is well-established in orangocatalysis that usually work in synergy with transition-metal catalysis or semiconductor photocatalysis.Here,TEMPO was turned into a visible light photocatalyst to conduct the selective aerobic oxidation of thiols into disulfides.With O_2 as an oxidant,a mild and efficient protocol for the selective oxidation of thiols into disulfides including symmetrical and unsymmetrical ones with 5 mol% of TEPMO as a photocatalyst was developed at room temperature under the irradiation of 460 nm blue LEDs.It was found that a complex formed between TEMPO and thiols underpinned the visible light activity and disulfides were obtained in very high isolated yields.This work suggests that TEMPO takes diverse roles in for photocatalytic selective oxidative transformations with O_2 as the oxidant.     

Analysis of cellulose and kraft pulp ozonolysis products by anion-exchange chromatography with pulsed amperometric detection

Efforts to reduce the level of chlorinated organics discharged into the environment have led to interest in ozone bleaching of kraft pulp. In the course of this operation the transformation of cellulose has to be reduced to the minimum. With this aim, the investigation of the cellulose—ozone reaction was carried out from a mechanistic point of view. The initial interest was in the composition of kraft pulp and cellulose ozonation effluents. High-performance anion-exchange chromatography with pulsed amperometric detection was used to separate and partially identify the soluble modified or unmodified carbohydrates of kraft pulp and cellulose ozonolysis. The main results indicate that after ozonation at 0, 25 and 65°C, cellulose gives oligosaccharides, monosaccharides and probably oxidized forms of those products. Formaldehyde was also directly determined under the same conditions as for carbohydrates.