Application of enzymes in producing bleached pulp from wheat straw

Crude enzymes produced by different strains were used in the production of bleached wheat straw pulp. Pre-treatment with enzymes from Penicillium A10 and Aspergillus L22 at a xylanase dosage of 4 IU/g prior to pulping decreased pulp kappa number by 6.29% and 12.07% respectively as compared to the control. High cellulase activity in crude enzymes has a negative influence on pulping. Xylanase pre-bleaching reduced chlorine charge by 20-30%, or increased final brightness by approximately 4-5% ISO, and improved the pulp strength properties. Xylanase could substitute for alkali extraction in CEH sequence, and be used for treating chemical-bleached pulp, which resulted in higher strength properties for bleached pulp. Modification of bleached pulp with enzymes of 3 IU/g (on xylanase) increased pulp brightness and breaking length by 3-6% ISO and 160-790 m respectively, and decreased post color number and beating degree of pulp by 29-36% and 2.5-5.5 degrees SR respectively, as compared to the original pulp.     

Effect of hot-water extraction on alkaline pulping of bagasse

The effect of hot-water extraction on alkaline pulping was investigated. The properties of black liquor and pulp strength of bagasse were analyzed. The extraction was conducted at 160 °C for 30 min where 13.2% of the mass was dissolved in the extraction liquor. Untreated bagasse and extracted bagasse were digested by soda and soda-AQ processes at 17% and 15.5% (with 0.1% AQ) alkali charge (NaOH). Cooking temperatures were 160 °C and 155 °C respectively. The pulp from extracted bagasse had a lower Kappa number and a higher viscosity compared to the pulp from the untreated bagasse. The black liquor from pulping extracted bagasse had a lower solid content, a lower viscosity and a lower silica content, but a higher heating value than that from pulping of untreated bagasse. Hot-water extraction resulted in a significant decrease in bleaching chemical consumption and the formation of chlorinated organics. Pulp strength properties such as the tensile index and the burst index were found to be lower, but the tear index, bulk, opacity and pulp freeness were found to be higher when hot-water extraction was applied.     

Arundo donax L. reed: new perspectives for pulping and bleaching. Part 4. Peroxide bleaching of organosolv pulps

A comparative study on TCF (totally chlorine-free) bleachability of organosolv pulps from the annual fibre crop Arundo donax L. (giant reed) was carried out using a simple three-stage peroxide bleaching sequence without oxygen pre-bleaching. ASAM (alkali-sulfite-anthraquinone-methanol), Organocell (alkali-anthraquinone-methanol) and ethanol-soda organosolv pulps were bleached and compared with kraft pulp, as a reference. The final brightness of 76-78% ISO was attained for all tested pulps. The chemical charge required to reach this level of brightness varied for different pulps (despite the equal initial content of the residual lignin) and directly related to starting brightness values. No direct correlation between brightness improvement and lignin removal during bleaching was found, indicating the influence of the specific pulp properties introduced by pulping process on bleaching chemistry. The general higher bleaching response of organosolv pulps from A. donax was noted in comparison with kraft.     

Influence of dimethyl formamide pulping of bagasse on pulp properties

Organosolv pulping of bagasse was conducted following a central composite design using a two-level factorial plan involving three pulping variables (temperature: 190-210 degrees C, time: 120-180 min, organic solvent charge: 40-60% dimethyl formamide). Responses of pulp properties (yield and holocellulose, alpha-cellulose, kappa number, ash and ethanol-dichloromethane extractives contents) and the pH of the resulting wastewater to the process variables were analyzed using statistical software (MINITAB). Main factor analysis revealed that optimum pulp has the following characteristics: 82.7% (yield), 92.9 (kappa number), 95.84% (holocellulose), 83.53% (alpha-cellulose), 1.403% (ash), 2.562% (ethanol-dichloromethane extractives contents) and 6.39 (pH). These results showed that acceptable properties of pulps could be gained at 200-210 degrees C for 150 min and 40-60% DMF. Based on these results, this method could be used for pulping of bagasse equivalent NSSC concerning high yield at a fixed kappa number. In addition, bagasse could be pulped with ease to approximately 55% yield with a kappa number approximately 31. Numerical analyses showed that cooking temperature had the greatest influence on properties of obtained pulps within the DMF concentrations and cooking time as cooking variables.     

New perspectives for Paulownia fortunei L. valorisation of the autohydrolysis and pulping processes

This paper will consider the influence of the temperature of autohydrolysis or hydrothermal process from Paulownia fortunei L. to obtain a valuable liquid phase and a suitable solid phase to produce pulp. The solid phase resulting of autohydrolysis was subjected to organosolv pulping process and formed paper sheets, analyzing the influence of operational variables (viz., ethanol concentration, temperature and pulping time) on the yield, viscosity, tensile index, burst index, tear index and brightness. Maximum glucose and xylose contents and minimum paper sheets characteristic loss have been obtained at 190 degrees C authohydrolysis temperature. Suitable characteristics of paper sheets and acceptable yield, viscosity and kappa number of pulp could be obtained by operating at 180 degrees C temperature, 30min pulping time and 20% ethanol concentration. Under those conditions sheets paper with 27.4% ISO brightness, 28.87Nm/g tensile index, 1.22kPam(2)/g burst index and 1.23kNm(2)/g tear index could be obtained.     

Assessment of wood-inhabiting Basidiomycetes for biokraft pulping of softwood chips

Wood-inhabiting Basidiomycetes have been screened for various applications in the pulp and paper industry and it is evident that different fungi need to be used to suit the specific requirements of each application. This study assessed the suitability of 278 strains of South African wood-decay fungi for the pre-treatment of softwood chips for kraft pulping. The influence of these fungi on kappa number, yield and strength properties of pulp was evaluated. A number of these strains were more efficient in reducing kappa number than the frequently used strains of Phanerochaete chrysosporium and Ceriporiopsis subvermispora. Six strains of Stereum hirsutum and a strain of an unidentified species were able to reduce the kappa number significantly without a significant influence on the pulp yield. Treatment of wood with two strains of S. hirsutum, one strain of Peniophora sp. and a strain of an unidentified species resulted in paper with improved strength properties.     

Optimization of xylanase production from Aspergillus niger for biobleaching of eucalyptus pulp

A crude endo-xylanase produced by Aspergillus niger BCC14405 was investigated for its potential in pre-bleaching of chemical pulp from eucalyptus. The optimal fermentation conditions on the basis of optimization using response surface methodology included cultivation in a complex medium comprising wheat bran, rice bran, and soybean meal supplemented with yeast extract, glucose, peptone, and lactose with a starting pH of 6.0 for 7 d. This resulted in production of 89.5 IU/mL of xylanase with minor cellulase activity. Proteomic analysis using LC/MS/MS revealed that the crude enzyme was a composite of hemicellulolytic enzymes, including endo-β-1,4-xylanase and other hemicellulolytic enzymes attacking arabinoxylan and mannan. Pretreatment of the pulp at a xylanase dosage of 10 IU/g increased the brightness ceiling after the C-Eop-H bleaching step up to 3.0% using a chlorine charge with a C-factor of 0.16-0.20. Xylanase treatment also led to reduction in chlorine charge of at least 20%, with an acceptable brightness level. The enzyme pretreatment resulted in a slight increase in pulp viscosity, suggesting an increase in relative cellulose content. The crude enzyme was potent in the enzyme-aided bleaching of chemical pulp in an environmentally friendly pulping process.     

Comparative study on application of T.lanuginosus SSBP xylanase and commercial xylanase on biobleaching of non wood pulps

Biobleaching of three non wood kraft pulps (bagasse, rice straw and wheat straw) by Thermomyces lanuginosus SSBP xylanase and commercial xylanase (cartazyme sandoz), was studied in order to investigate their potential and effect on their various properties (reduction sugars, chlorine dioxide, kappa number, brightness and chromophores). In generally, xylanases released chromophores and reducing sugars and decreased kappa number of pulps. These samples gained over six brightness points over controls. Biobleaching of rice straw pulp with xylanase cartazyme (Sandoz) produced chlorine dioxide savings of up to 25% or 3.5-4 kg chlorine dioxide/ton pulp.     

Alkaline pulping of some eucalypts from Sudan

Four eucalypts (Eucalyptus camaldulensis, Eucalyptus microtheca, Eucalyptus tereticornis and Eucalyptus citriodora) grown in Sudan were examined for their suitability for pulping and papermaking with different alkaline methods. Their physical, morphological and chemical characteristics are reported. The pulping trials with E. citriodora and E. tereticornis were carried out using the kraft-AQ, soda-AQ, modified AS/AQ (ASA), ASAM and kraft methods. For the other two species, only the ASAM and the kraft process were applied. ASAM pulping gave the best results in terms of yield, degree of delignification, mechanical and optical pulp properties. The best pulps, obtained in kraft and ASAM cooking of E. citriodora, were bleached to 88% ISO brightness in a totally chlorine free bleaching sequence (OQ1O/PQ2P). The bleached pulps, especially the ASAM pulp, showed good papermaking properties and would be suitable for manufacture of writing and printing grades of paper.     

Biopulping: An overview of developments in an environmentally safe paper-making technology

Abstract: Treatment of wood chips with lignin-degrading fungi prior to pulping has been shown to have great potential for mechanical as well as chemical pulping on a laboratory scale. Ceriporiopsis subvermispora , when grown on aspen or loblolly pine for 4 weeks, was found to be superior to other fungi. On aspen there was an energy savings of 47%, and an increase in burst and tear indices of 22% and 119%, respectively. With loblolly pine, energy savings amounted to 37%, while burst and tear indices increased by 41% and 54%, respectively. The weight loss was only 6%, but a decrease in optical properties had to be accepted. After sulfite cooking of wood chips pretreated for 2 weeks, the Kappa number decreased by 30% with hard- and softwood. Tensile and tear indices decreased by only 10%, while the brightness of unbleached pulp increased by 4% with birch. Information obtained by immunoelectron microscopy and differential staining led to the conclusion that the biopulping effect obtained after 2 weeks of incubation cannot be explained by the direct action of enzymes on lignin or polysaccharides. Instead, a low molecular mass agent is considered to be responsible for the biopulping effect. These results have changed the aims of biopulping from an emphasis on removing the bulk of lignin to an emphasis on a short-term process, lasting 2 weeks and yielding a low mass loss. Data on these kinetics of fungal development and the degree of asepsis will help to scale-up the process. An advanced chip pile is assumed to be the most feasible process design, rather than a controlled enclosed reactor.     

Enzymatic deinking of secondary fibers: cellulases/hemicellulases versus laccase-mediator system

The use of enzymes has been suggested as an environmentally friendly alternative to complement conventional chemical deinking in the recycling of recovered paper. This study compares the use of cellulases/hemicellulases versus the laccase-mediator system for deinking printed fibers from newspapers and magazines. For this purpose, two commercial enzyme preparations with endoglucanase and endoxylanase activities (Viscozyme Wheat from Aspergillus oryzae and Ultraflo L from Humicola insolens, Novozymes) and a commercial laccase (NS51002 from Trametes villosa, Novozymes), the latter in the presence of synthetic or natural (lignin-related) mediators, were evaluated. The enzymatic treatments were studied at the laboratory scale using a standard chemical deinking sequence consisting of a pulping stage; an alkaline stage using NaOH, sodium silicate and fatty acid soap; and a bleaching stage using hydrogen peroxide. The handsheets were then prepared and their brightness, residual ink concentration, and strength properties were measured. Among the different enzymatic treatments assayed, both carbohydrate hydrolases were found to deink the secondary fibers more efficiently. Brightness increased up to 3–4% ISO on newspaper fibers, being Ultraflo 20% more efficient in the ink removal. Up to 2.5% ISO brightness increase was obtained when magazine fibers were used, being Viscozyme 9% more efficient in the ink removal. Regarding the laccase-mediator system, alone or in combination with carbohydrate hydrolases, it was ineffective in deinking both newspaper and magazine fibers, resulting in pulps with worse brightness and residual ink concentration values. However, pulp deinking by the laccase-mediator system was displayed when secondary fibers from printed cardboard were used, obtaining up to 3% ISO brightness increase and lower residual ink concentrations.     

Bioorganosolve pretreatments for simultaneous saccharification and fermentation of beech wood by ethanolysis and white rot fungi

Ethanol was produced by simultaneous saccharification and fermentation (SSF) from beech wood chips after bioorganosolve pretreatments by ethanolysis and white rot fungi, Ceriporiopsis subvermispora, Dichomitus squalens, Pleurotus ostreatus, and Coriolus versicolor. Beech wood chips were pretreated with the white rot fungi for 2-8 weeks without addition of any nutrients. The wood chips were then subjected to ethanolysis to separate them into pulp and soluble fractions (SFs). From the pulp fraction (PF), ethanol was produced by SSF using Saccharomyces cerevisiae AM12 and a commercial cellulase preparation, Meicelase, from Trichoderma viride. Among the four strains, C. subvermispora gave the highest yield on SSF. The yield of ethanol obtained after pretreatment with C. subvermispora for 8 weeks was 0.294 g g(-1) of ethanolysis pulp (74% of theoretical) and 0.176 g g(-1) of beech wood chips (62% of theoretical). The yield was 1.6 times higher than that obtained without the fungal treatments. The biological pretreatments saved 15% of the electricity needed for the ethanolysis.     

Potential of xylanase from thermophilic Bacillus sp. XTR-10 in biobleaching of wood kraft pulp

An extracellular xylanase produced under optimal conditions by a thermophilic strain of Bacillus sp. XTR-10 was evaluated for its potential application in biobleaching of wood kraft pulp. Spectrophotometric analysis showed considerable release of lignin derived compounds and chromophoric material by the xylanase treated pulp samples. Xylanase was found to be effective in the liberation of reducing sugars in the pulp filtrates with increment in enzyme dose and reaction time. Eight hours pretreatment with 40 IU of xylanase/g of dry pulp resulted in 16.2% reduction of kappa number with 25.94% ISO increase in brightness as compared to the control. The same treatment slightly lowered the tensile strength and burst index, however. Enzyme pretreatment of the pulp saved 15% active chlorine charges in single step and 18.7% in multiple steps chemical bleaching with attainment of brightness at the level of the control. These results indicate the potential of enzymatic pretreatment of pulp for reduction in environmental discharge of hazardous waste from the pulp and paper industry.     

A comparison of kraft, PS, kraft-AQ and kraft-NaBH4 pulps of Brutia pine

The aim of this work was to study the effect of adding PS, AQ and NaBH(4) into kraft pulping with special attention given to NaBH(4). Kraft, kraft-AQ, PS, and kraft-NaBH(4) pulps were produced under the same cooking conditions and the pulps produced were compared in terms of pulp and paper properties. Kraft method was modified by adding 0.1% AQ, 4% PS and 2% and 4% NaBH(4) and the resultant pulps displayed an increase in pulp yield and reduction in both kappa number and screening rejects. On the other hand, there observed an increase in both pulp yield and kappa number when the kraft was modified to PS method. The benefits of NaBH(4) addition into kraft pulping was a significant reduction in kappa number and screening rejects and a significant increase in pulp yield. The most notable outcome of NaBH(4) was 66.6% increase in pulp brightness when 4% NaBH(4) was added into kraft pulping. Of unrefined pulps, unrefined kraft pulp displayed the highest strength of pulp, which is described as tear index at a constant tensile index. Of refined pulps, kraft-AQ showed the highest pulp strength when refined to 6000 and 12,000 revs in PFI mill.     

High level expression of a recombinant xylanase by Pichia pastoris NC38 in a 5 L fermenter and its efficiency in biobleaching of bagasse pulp

A genetically modified XynA gene from Thermomyces lanuginosus was expressed in Pichia pastoris under the control of GAP promoter. P. pastoris expressed greater levels of xylanase (160 IU ml(-1)) on BMGY medium without zeocin after 56 h. The xylanase production by recombinant P. pastoris was scaled up in a 5L fermenter containing 1% glycerol and the highest xylanase production of 139 IU ml(-1) was observed after 72 h. Further studies carried out in fermenter under controlled pH (5.5) yielded a maximum xylanase production of 177 IU ml(-1) after 72 h. The biobleaching efficacy of crude xylanase was also evaluated on bagasse pulp and a brightness of 47.4% was observed with 50 IU of crude xylanase used per gram of pulp, which was 2.1 points higher in brightness than the untreated samples. Reducing sugars (24.8 mg g(-1)) and UV absorbing lignin-derived compounds values were considerably higher with xylanase treated samples.     

Biobleaching of wheat straw pulp with recombinant laccase from the hyperthermophilic <Emphasis Type="Italic">Thermus thermophilus</Emphasis>

The recombinant laccase from Thermus thermophilus was applied to the biobleaching of wheat straw pulp. The best bleaching effect was when the pulp was treated with 3 U laccase g⁻¹ dry pulp at 90°C, pH 4.5, 8% consistency for 1.5 h. Under these conditions, the pulp brightness was increased by 3.3% ISO, and the pulp kappa number was decreased by 5.6 U. Enzymatic treatment improved the bleachability of wheat straw pulp but caused no damage to the pulp fibers. The use of enzyme-treated pulp saved 25% H₂O₂ consumption in subsequent peroxide bleaching without decreasing the final brightness. Pulp biobleaching in the presence of 5 mM ABTS further increased the pulp brightness by 1.5% ISO. This is the first report on the application of laccase from T. thermophilus in the pulp and paper sector.     

Oxalic acid extraction as a posttreatment to increase the brightness of kraft pulps bleached by white-rot fungi

Pulp brightness gains obtained by fungal biobleaching are often decreased by dark MnO₂ deposits which are formed by the biologically-mediated oxidation of Mn(II). Oxalic acid extraction of O₂-delignified kraft pulps bleached by several white-rot fungi was found to increase pulp brightness by up to 9.7 ISO points due to MnO₂ dissolution. These results indicate that pulp extraction with oxalic acid can be used in order to accurately assess the net brightness gains achieved by fungal biobleaching.     

Xylanase-induced reduction of chlorine dioxide consumption during elemental chlorine-free bleaching of different pulp types

The potential of crude xylanase from Thermomyces lanuginosus and Xylanase P (a commercial xylanase) was evaluated in bleaching of various paper pulp types. Xylanases released chromophores and reducing sugars and decreased kappa number of pulps. Chlorine-bleached, alkali-extracted bagasse and post-oxygen kraft pulps, pretreated with enzymes, gained over 5 brightness points over controls. Biobleaching of soda-aq pulp with Xylanase P produced chlorine dioxide savings of up to 30% or 4.5 kg chlorine dioxide t^–1 pulp.     

重组极耐热木聚糖酶和重组极耐热漆酶协同漂白麦草浆

利用来自海栖热袍茵的重组极耐热木聚糖酶XynB和来自嗜热栖热菌Thermus thermophilus HB27的重组极耐热漆酶Tth-laccase对麦草浆进行协同漂白。结果表明,当未漂浆经XL漂序处理(X:重组木聚糖酶用量20 U/g绝干浆,pH 5.8,温度90℃,浆浓8%,处理时间2 h;L:重组漆酶用量3 U/g绝干浆,pH 4.5,温度90℃,浆浓8%,处理时间1.5 h),可获得最佳漂白效果。与对照浆比较,XL处理使浆料白度提升11.5%ISO,卡伯值降低6.9。双酶协同处理在改善浆料可漂性的同时,对纸浆纤维强度无负面影响。在后续过氧化氢漂白段中,当漂终白度相近时,XL预处理浆可节省约50%H_2O_2消耗量。     

Effect of pulping variables with dimethyl formamide on the characteristics of bagasse-fiber

Organosolv pulping of bagasse was conducted following a central composite design using a two-level factorial plan involving three pulping variables (temperature: 190-210 degrees C, time: 120-180 min, organic solvent ratio: 40-60% dimethyl formamide). Responses of pulp and handsheets properties to the process variables were analyzed using statistical software (MINITAB 14). Using values of the independent variables the variation ranges considered provided the following optimum values of the dependent variables: 82.7% (yield), 92.9 (kappa number), 1.403% (ash), 370 ml (freeness), 6290 m (breaking length), 9.4 (folding endurance), 5.955 mN m2 g(-1) (Tear index) and 2.811 kN g(-1) (Burst index) for pulps and handsheets. Results showed that acceptable physical and mechanical properties of pulps and papers similar the pulp used for bleaching could be achieved at 210 degrees C for 150 min and 50% DMF. These are the most suitable conditions for obtaining paper sheets with a high breaking length, tear and burst indices. Also bagasse could be pulped with ease to about 55.72% yield with kappa number approximately 35. The cooking temperature was a significant factor while the DMF ratio and cooking time were not as important in term of the properties of the resultant pulps and papers.