Acetylation and characterization of xylan from hardwood kraft pulp

Alkaline treatment of eucalyptus hardwood kraft pulp with 10% NaOH yielded 6-8% xylan. The acetylation of the extracted xylan was carried in DMAC/LiCl/pyridine system to obtain a series of xylan acetates with different degrees of substitution (DS). Structure elucidation of xylan and xylan acetate was obtained by ¹H and ¹³C NMR spectroscopy and other homonuclear and heteronuclear 2D-NMR techniques. Inverse-gated ¹³C NMR was employed to determine the DS of xylan acetate. Furthermore, results also revealed equal reactivities at the C-2 and C-3 positions of xylan towards acetylation. Thermal stability, solubility behavior and nanofiber formation of xylan acetate were influenced by its DS values. The mechanical properties of xylan acetate propionate were also investigated.     

Delignification of an unbleached hardwood kraft pulp by Phanerochaete chrysosporium

Summary Culture conditions affecting lignin degradation of an unbleached hardwood kraft pulp by Phanerochaete chrysosporium have been examined. Optimum pH and temperature for lignin degradation (about 33%) were 3.5 and 38°C, respectively. Optimum fungal growth was at a pH of 4.5 and a temperature of around 32°C. Addition of exogeneous glucose to the cultures lessened the degradation of pulp carbohydrates. Lignin degradation was stimulated by oxygen atmosphere and non-agitated cultures. Increased surface to volume ratio (decreased culture depth) enhanced lignin degradation (about 56% at a depth of 1.2 cm). Finally, the correlations: pulp yield vs. residual glucose, ligninase activity vs. mycelium, and extent of delignification vs. residual extracellular H₂O₂ were discussed in light of recent findings of ligninases responsible for ligninolysis.     

Material properties of plasticized hardwood xylans for potential application as oxygen barrier films

Free films based on glucuronoxylan isolated from aspen wood were prepared by casting from aqueous solutions and drying in a controlled environment. Addition of xylitol or sorbitol facilitated film formation and thus examination of the material properties of these films. The mechanical properties of the films were evaluated using tensile testing and dynamic mechanical analysis in a controlled ambient relative humidity. The strain at break increased, and the stress at break and Young's modulus of the films decreased with increasing amounts of xylitol and sorbitol due to plasticization. At high amount of plasticizer, it was found that films with xylitol gave lower extensibility. Wide-angle X-ray scattering analysis showed that xylitol crystallized in a distinct phase, which we believe contributes to the more brittle behavior of these films. The effect of the plasticizers on the glass transition temperature was determined using dynamic mechanical analysis and differential scanning calorimetry. An increased amount of plasticizer shifted the glass transition to lower temperatures. The effect of moisture on the properties of plasticized films was investigated using water vapor sorption isotherms and by humidity scans in dynamic mechanical analysis. Sorption isotherms showed a transition from type II to type III when adding plasticizer. The films showed low oxygen permeability and thus have a potential application in food packaging.     

Changes in the structural composition of hardwood kraft pulp during bleaching

The possibility of using xylanase preparations for hydrolyzing hemicelluloses in a non-bleached kraft pulp in order to facilitate its bleaching was studied. The effects of enzymatic preparations of fungal and bacterial origins were examined, and the optimal conditions for xylanase activity were determined. UV spectroscopy demonstrated that the treatment of kraft pulp with enzymatic preparations containing xylanase facilitated the subsequent removal of lignin and increased the brightness by 5%. The effect of enzymatic treatment was retained in the case of peroxide bleaching. The enzymatic preparations studied are promising for the development of chlorine-free pulp bleaching technologies.     

Biobleaching of Eucalyptus globulus kraft pulps: comparison between pulps obtained from exploded and non-exploded chips

The aim of this work was to evaluate the response to biobleaching of steam exploded kraft pulps and to compare the results with the controls. For this end, a laccase-mediator treatment using commercial laccase (Novozyme 51003) and a natural mediator (acetosyringone) were assayed, followed by alkaline extraction and hydrogen peroxide stages.Our approach resulted in exploded biobleached pulps with lower kappa number and improved optical properties compared to controls, even after subjecting pulps to accelerated ageing. Additionally, use of hydrogen peroxide was reduced. The LMS (laccase-mediator system) had a smaller impact on the properties of the bleached pulps and on hydrogen peroxide consumption than the steam explosion process did.     

Combination of steam explosion and laccase-mediator treatments prior to Eucalyptus globulus kraft pulping

The effect of a pretreatment consisting of steam explosion (SE) followed by a laccase mediator system (LMS) stage on Eucalyptus globulus kraft pulping has been evaluated and compared with fungal pretreatments. Pretreatment with SE and LMS was more efficient than pretreatments using Pycnoporus sanguineus and Trametes sp. I-62. Steam explosion not only improved the enzyme penetration into the wood chips and shortened the pulping process by 60%, but also extracted around 50% of the hemicelluloses which could be converted into value-added products. The optimal conditions for the LMS treatment were 3 h, 3 UA/g and 40 °C. Compared to SE, the SE/LMS treatment yielded an increase in delignification of 13.9% without affecting pulp properties, provided a similar screened kraft yield, and reduced consumption of chemical reagents Na₂S and NaOH by 11.5% and 6.3%, respectively. Therefore, SE/LMS is a promising pretreatment for converting the pulp mill into a forest bio-refinery.     

Kinetics of enzyme action of Cartazyme NS-10 prior to bleaching of kraft pulp

The kinetics of enzyme treatment of hardwood kraft pulp with commercial xylanase Cartazyme NS-10 was investigated. The enzyme treatment process was found to follow closely the topochemical modified equation of Prout–Tompkins. The influence of the initial enzyme concentration was studied and the applicability of the power kinetic equation was established for the initial rate of the process. An equation of practical use was obtained, which provides the temperature function of the amount of the reducing substances, depending on the enzyme initial concentration. This function made it possible to control the process of prior enzyme treatment of unbleached kraft pulp.     

The effects of fungi pre-treatment of poplar chips on the kraft fiber properties

Poplar chips were pre-treated by Trametes versicolor for 1, 2 and 3 weeks. Pre-treated chips, after washing, have been air dried for kraft pulping to achieve pulp kappa number of about 20. Pulp samples have been analyzed by Bauer Mc Nett, Kajaani analyzer and SEM. The results indicated that fungi pre-treatment of chips can degrade lignin and carbohydrates and affect kraft pulping and fiber characteristics. Higher chemical charge in pulping, lower fine and higher long fiber fraction were observed in pre-treated pulp samples in comparison with others. Fiber length, cross sectional area, width, cell wall thickness and volume index were increased by increasing pre-treatment time while fine length, fiber coarseness and curl have been reduced. Based on the study findings, with respect to higher fiber length, lower fine, and lower fiber curl and coarseness, 2-weeks pre-treatment of chips was recommended to produce acceptable overall fiber properties in kraft pulping.     

Co-gasification of hardwood chips and crude glycerol in a pilot scale downdraft gasifier

Seeking appropriate approaches to utilize the crude glycerol produced in biodiesel production is very important for the economic viability and environmental impacts of biodiesel industry. Gasification may be one of options for addressing this issue. Co-gasification of hardwood chips blending with crude glycerol in various loading levels was undertaken in the study involving a pilot scale fixed-bed downdraft gasifier. The results indicated that crude glycerol loading levels affected the gasifier’s performance and the quality of syngas produced. When crude glycerol loading level increased, the CO, CH₄, and tar concentrations of the syngas also increased but particle concentration decreased. Though further testing is suggested, downdraft gasifiers could be run well with hardwood chips blending with liquid crude glycerol up to 20 (wt%). The syngas produced had relatively good quality for fueling internal combustion engines. This study provides a considerable way to utilize crude glycerol.     

Structure of hardwood glucuronoxylans: modifications and impact on pulp retention during wood kraft pulping

The behaviour of different hardwood glucuronoxylans during the kraft pulping process was investigated. Woods and pulps xylans were isolated and characterized by size exclusion chromatography, methylation (linkage) analysis and ¹H NMR. Eucalyptus globulus and Eucalyptus urograndis showed xylan retention significantly higher than that of Betula pendula. The higher retention of Eucalyptus xylans was assigned to (i) their higher average molecular weight (31 against 24 KDa in B. pendula) and to (ii) the presence of O-2 substituted 4-O-methyl--d-glucuronic acid groups ([→2)-GlcpA-(1→]) with galactopyranosyl/glucopyranosyl residues belonging to fragments of galactan/glucan chains that were absent in B. pendula xylans. A significant part of uronic acids, particularly [→2)-GlcpA-(1→] units, remain in fibres until the end of pulping. The acetylation degree and distribution of acetyl groups between Xylp units, in general terms, was similar in the three types of xylans. Unexpectedly, about 20% of the acetyl groups persisted in pulps xylans till the end of pulping.     

Effect of polydimethylsiloxane oxygen carriers on the biological bleaching of hardwood kraft pulp by Trametes versicolor

Summary Improving the availability of oxygen by adding polydimethylsiloxanes (PDMS) oxygen carriers to Trametes versicolor cultures increased pulp brightening. The presence of the oxygen carriers in cultures of T. versicolor with hardwood kraft pulp increased the growth rate of the fungus, but not the ultimate biomass yield. The PDMS also stimulated brightening of hardwood kraft pulp by it T. versicolor immobilized in polyurethane foam. A threefold increase in the oxygen uptake rate in T. versicolor cultures with PDMS was observed. This increase can be explained by elevated oxygen transfer rate and attributed to the surfactant properties of PDMS. Offprint requests to: E. ZiomekIssued as NRCC 32760     

Biological bleaching of hardwood kraft pulp using Trametes (Coriolus) versicolor immobilized in polyurethane foam

Summary Incubation of hardwood kraft pulp (HWKP) in agitated aerated cultures of the white-rot fungus Trametes versicolor increases pulp brightness and decreases its residual lignin content. A consequence of this biobleaching with whole cultures is that the resulting pulp also contains fungal biomass (up to ca. 10% (w/w)). In this report culture conditions for the immobilization of T. versicolor on polyurethane foam and bleaching of HWKP with the immobilized fungus are described. The major advantage of using immobilized fungus to bleach HWKP is that the fungal biomass can be separated from the pulp after treatment, resulting in a biologically bleached pulp free of fungal mycelium. From an analysis of pulp samples bleached with free and foam-immobilized mycelium, we conclude that fungal biomass in pulp treated with free mycelium accounts for up to 25% of the reduction in pulp viscosity (indication of cellulose chain length) whereas the zero span breaking length (indication of fibre strength) is not significantly affected by the presence of the fungus. Immobilization of the fungus on polyurethane foam also allows the repeated use of the same fungal biomass to bleach successive batches of pulp, either immediately or after storage at 4°C. Offprint requests to: I. D. ReidIssued as NRCC no. 30975     

Protein chips: from concept to practice

A series of exciting reports over the past two years has established the usefulness of protein chips and made important advances in preparing protein arrays. However, several technical challenges must still be addressed to make these tools available to the wider community of researchers. Here, we discusses these challenges and survey recent opportunities for creating quantitative assays, preparing and immobilizing large numbers of proteins, using detection methods to analyze the results of chip-based experiments, and using informatics tools to interpret these results.     

Lignin peroxidase is involved in the biobleaching of manganese-less oxygen-delignified hardwood kraft pulp by white-rot fungi in the solid-fermentation system

Biobleaching of manganese-less oxygen-delignified hardwood kraft pulp (E-OKP) by the white-rot fungi Phanerochaete sordida YK-624 and P. chrysosporium was examined in the solid-state fermentation system. P. sordida YK-624 possessed a higher brightening activity than P. chrysosporium, increasing pulp brightness by 13.4 points after seven days of treatment. In these fermentation systems, lignin peroxidase (LiP) activity was detected as the principle ligninolytic enzyme, and manganese peroxidase and laccase activities were scarcely detected over the course of treatment of E-OKP by either fungus. Moreover, a linear relationship between brightness increase and cumulative LiP activity was observed under all tested culture conditions with P. sordida YK-624 and P. chrysosporium. These results indicated that LiP is involved in the brightening of E-OKP by both white-rot fungi.     

Balancing the effect of pretreatment severity on hemicellulose extraction and pulping performance during auto-hydrolysis prior to kraft pulping of acacia wood

When using a combination of pre-extraction and chemical pulping, a high yield of sugar recovery and minimal negative effect on the subsequent pulping step are expected. In this work, the P factor was utilized to investigate the effect of auto-hydrolysis severity on sugar recovery, removal of the main component, and impact on the kraft pulping of acacia wood chips. Using a P factor of 235, 84.34% of the polysaccharides in 14.05 g L⁻¹ of dissolved sugars could be obtained. In addition, the soluble sugars were easily separated with a recovery yield of 3.54 g ·L⁻¹ and Mw of 4,690 g mol⁻¹ by direct precipitation using organic solvents. However, a maximum of 22.14 g L⁻¹ of dissolved sugars was obtained with approximately 72.53% polysaccharides and Mw of 2,198 g mol⁻¹ for a P factor of 601. Moreover, nearly 50% of the degraded carbohydrates remained in the auto-hydrolyzed wood chips. The decrease in the mass of pentosan, holocellulose, and klason lignin was 62, 30, and 8.76%, respectively. With intensifying severity, the screened yield and viscosity of pulps decreased markedly, whileas the Kappa number increased. No significant differences were observed in the morphology of the resultant fibers. Moreover, there was a decrease in the physical strength of the pulps due to the loss of the intrinsic strength of the pulp fibers, which in turn resulted from the cellulose damage. The combustion performance of the resultant pulping black liquor is improved due to the higher lignin content.     

Isolation and characterization of xylans from seed pericarp of Argania spinosa fruit

Hemicellulose-type polysaccharides were isolated from the pericarp of seeds of Argania spinosa (L.) Skeels fruit by sequential alkaline extractions and fractionated by precipitation. Water soluble and water insoluble fractions were obtained, purified and characterized by sugar analysis and 1H and 13C NMR spectroscopy. The water soluble fractions were assumed to be (4-O-methyl-D-glucurono)-D-xylans, with 4-O-methyl-D-glucopyranosyluronic acid groups linked to C-2 of a (1-->4)-beta-D-xylan. The 1H NMR spectrum showed that the water soluble xylans have, on average, one non-reducing terminal residue of 4-O-methyl-D-glucuronic acid for every seven xylose units. The water insoluble fractions consisted of a neutral xylan with linear (1-->4)-beta-D-xylopyranosyl units.     

Pretreatment of eucalyptus wood chips for enzymatic saccharification using combined sulfuric acid-free ethanol cooking and ball milling

A combined sulfuric acid-free ethanol cooking and pulverization process was developed in order to achieve the complete saccharification of the cellulosic component of woody biomass, thereby avoiding the problems associated with the use of strong acid catalysts. Eucalyptus wood chips were used as a raw material and exposed to an ethanol/water/acetic acid mixed solvent in an autoclave. This process can cause the fibrillation of wood chips. During the process, the production of furfural due to an excessive degradation of polysaccharide components was extremely low and delignification was insignificant. Therefore, the cooking process is regarded not as a delignification but as an activation of the original wood. Subsequently, the activated solid products were pulverized by ball-milling in order to improve their enzymatic digestibility. Enzymatic hydrolysis experiments demonstrated that the conversion of the cellulosic components into glucose attained 100% under optimal conditions. Wide-angle X-ray diffractometry and particle size distribution analysis revealed that the scale affecting the improvement of enzymatic digestibility ranged from 10 nm to 1 microm. Field emission scanning electron microscopy depicted that the sulfuric acid-free ethanol cooking induced a pore formation by the removal of part of the lignin and hemicellulose fractions in the size range from a few of tens nanometers to several hundred nanometers.