Enzymatic Modification of Paper Fibres

The enzymatic mode of action in paper fibre upgrading is still uncertain. In an attempt to clarify how enzymes modify pulp and paper properties, several parameters were analysed in the present work: (i) thermal analysis of the water-solid surface interactions; (ii) fibre cake permeability; (iii) particle size analysis. The results obtained suggest that enzymes modify the interfacial properties of fibres, increasing the water affinity, which in turn change the technical properties of pulp and paper, such as drainability and strength. The modification of paper and pulps following a treatment with cellulose-binding domains further supports this hypothesis.     

Use of cellulases and recombinant cellulose binding domains for refining TCF kraft pulp

The modular endoglucanase Cel9B from Paenibacillus barcinonensis is a highly efficient biocatalyst, which expedites pulp refining and reduces the associated energy costs as a result. In this work, we set out to identify the specific structural domain or domains responsible for the action of this enzyme on cellulose fibre surfaces with a view to facilitating the development of new cellulases for optimum biorefining. Using the recombinant enzymes GH9–CBD3c, Fn3–CBD3b, and CBD3b, which are truncated forms of Cel9B, allowed us to assess the individual effects of the catalytic, cellulose binding, and fibronectin‐like domains of the enzyme on the refining of TCF kraft pulp from Eucalyptus globulus. Based on the physico‐mechanical properties obtained, the truncated form containing the catalytic domain (GH9–CBD3c) has a strong effect on fibre morphology. Comparing its effect with that of the whole cellulase (Cel9B) revealed that the truncated enzyme contributes to increasing paper strength through improved tensile strength and burst strength and also that the truncated form is more effective than the whole enzyme in improving tear resistance. Therefore, the catalytic domain of Cel9B has biorefining action on pulp. Although cellulose binding domains (CBDs) are less efficient toward pulp refining, evidence obtained in this work suggests that CBD3b alters fibre surfaces and influences paper properties as a result. © 2010 American Institute of Chemical Engineers Biotechnol. Prog., 2010     

Enzymatic treatment of mechanical pulp fibers for improving papermaking properties

Three enzyme preparations (crude cellulase, laccase, and proteinase) were evaluated for their potential to improve the papermaking properties of mechanical pulp. After treating a long fibre-rich fraction of the pulp with enzyme, the fibres were recombined with untreated fines for handsheet making and testing. None of the enzymes altered the retention of fines or the consolidation of the furnish mix during handsheet formation. All three enzymes increased tensile stiffness index, which is a measure of the initial resistance of the handsheets to strain. Only the laccase preparation, an enzyme that modifies pulp lignin, consistently increased fibre bonding to enhance other strength properties of the handsheets.     

Xylanases in bleaching: From an idea to the industry

Abstract: The utilization of hemicellulases in bleaching of kraft (sulphate) pulp is considered as one of the most important new large-scale industrial applications of enzymes. This is partly due to the great potential of an environmentally safe method. This method has in a short period also proven to be economically realistic. The main enzymes needed in the enzyme-aided bleaching have been shown to belong to the group of endo-/gb-xylanases. Xylanases act mainly on the relocated, reprecipitated xylan on the surface of the pulp fibres. Enzymatic hydrolysis of this specific type of xylan renders the structure of the fibres more permeable. The hydrolysis of xylan or mannan in the inner fibre layers may also enhance the bleachability. In practical process conditions, properties of the enzymes such as substrate specificity and the pH and temperature optima are of utmost importance. The benefits obtained by enzymes are dependent on the chemical bleaching sequence used as well as on the residual lignin content of pulp. The main goals in the enzyme-aided bleaching of kraft pulps have been the reduction of consumption of chlorine chemicals in the bleaching process and consequently lowering the AOX of the effluents. Enzymes have been applied as a pretreatment both in conventional (C/D)EDED and in ECF (elementary chlorine-free) bleaching sequences. In the production of TCF (totally chlorine-free) pulps, enzymes have also been successfully used for increasing the brightness of pulp.     

Water hyacinth — A potential source of raw material for greaseproof paper

The potential use of water hyacinth as a pulp material for producing greaseproof paper was investigated. The proximate chemical analyses of the raw materials, the morphology of the water hyacinth stalk and fibre, pulp characteristics, and data on the physical properties of the paper hand-sheets formed from water hyacinth and bamboo pulps and their blends are presented. A comparative study of the pulp freeness (°SR) and drainage properties of water hyacinth and bamboo pulps showed that with a high freeness value of the pulps the drainage time increased. Blending of water hyacinth and bamboo pulps increased the physical strength. Paper hand-sheets made with a blend of water hyacinth pulp (75°SR) and bamboo pulp (80°SR), at 75:25 proportion, gave a tear index of 4·90 mN m² g⁻¹, tensile index of 51·10 N mg⁻¹ and burst index of 7·25 kPa m² g⁻¹. These were higher than the values obtained from sheets made with pulp blends (water hyacinth:bamboo) of 80:20 or 90:10. The pulp sheets at a blend proportion of 75:25 also gave satisfactory greaseproof properties.     

Pyrolytic characteristics of microalgae as renewable energy source determined by thermogravimetric analysis

This paper describes the fibre morphology of switchgrass (Panicum virgatum L.) and its pulping characteristics using sodium hydroxide and a combination of sodium hydroxide and sodium sulphite as the cooking agents. It was found that the fibre length of switchgrass is similar to that of poplar despite its high population of short fibre elements (< 0.2 mm). The switchgrass used in this study had a lignin content comparable to that of poplar, but a particularly high content of extractable materials. The soda pulp from switchgrass showed excellent mechanical properties and showed a great potential as a reinforcement component in newsprint making.     

Easily available enzymes as natural retting agents

Easily available commercial enzymes currently have great potential in bast fibre processing and can be modified for different end uses. There are several new technologies using enzymes that are able to modify fibre parameters, achieve requested properties, improve processing results and are more beneficial to the ecology in the area of bast fibre processing and fabrics finishing. Enzymatic methods for retting of flax, "cottonisation" of bast fibres, hemp separation, and processing of flax rovings before wet spinning, etc., fall into this group of new technologies. Such enzymatic biotechnologies can provide benefits in textile, composite, reinforced plastic and other technical applications. Laboratory, pilot and industrial scale results and experiences have demonstrated the ability of selected enzymes to decompose interfibre-bonding layers based on pectin, lignin and hemicelluloses. Texazym SER spray is able to increase flax long fibre yields by more than 40%. Other enzymes in combination with mild mechanical treatment can replace aggressive and energy-intensive processing like Laroche "cottonisation". Texazym SCW and DLG pretreatments of flax rovings are presented.     

Composition of citrus pulp

Eight groups of citrus varieties grown in Spain were included in this study. Citrus pulp composition was (dry matter basis) 60–65% peel, 30–35% segment pulp and 0–10% seeds. Citrus seeds had a high percentage of protein, ether extract and crude fibre. Segment pulp contained slightly less fibre than citrus pulp. The proximate composition of citrus pulp was similar to that of the peel fraction and did not differ from previous results. Significant differences in fibre and acid detergent lignin of the dried citrus pulp samples were found between varieties.The drying process was studied. Temperatures over 130°C and the addition of calcium hydroxide affected some fractions of the pulp, mainly by increasing ash and fibre contents.     

Differential and synergistic effects of xylanase and laccase mediator system (LMS) in bleaching of soda and waste pulps

AIMS: Investigation of waste pulps and soda pulp bleaching with xylanase (X) and laccase mediator system (LMS) alone and in conjunction (one after the other) (XLMS). METHODS AND RESULTS: Soda and different grades of waste pulp fibres [used for making three-layered duplex sheets - top layer (TL), protective layer (PL) and bottom layer (BL)] when pretreated with either xylanase (40.0 IU g(-1)) or LMS (up to 200.0 U g(-1)) alone and in combination (one after the other) (XLMS) exhibited an increase in release of reducing sugars [up to 881.0% soda pulp; up to 736.6% (TL), up to 215.7% (PL) and up to 198.0% (BL) waste pulp], reduction in kappa number [up to 17.6% soda pulp; up to 14.0% (TL), up to 25.3% (PL) and up to 10.9% (BL), waste pulp], improvement in brightness [up to 20.4% soda pulp; up to 23.6% (TL), up to 8.6% (PL) and up to 5.0% (BL), waste pulp] when compared with the respective controls. The usage of XLMS along with 15% reduced level of hypochlorite at CEHHXLMS/EHHXLMS bleaching stage reduced kappa number [5.5% soda pulp; 11.4% (TL), 7.9% (PL), waste pulp] and improved brightness [1.0% soda pulp; 0.9% (TL), 1.4% (PL) waste pulp] when compared with the controls. Scanning electron microscopic studies revealed development of cracks, flakes, pores and peeling off the fibres in the enzyme-treated pulp samples. These modifications of the fibre surface during enzymatic bleaching in turn indicated the removal of lignin and derived compounds from the fibre cell wall. CONCLUSIONS: The work describes synergistic action of xylanase with LMS for bleaching of waste and nonwood pulps for eco-friendly production of paper and thus reveals a new unexploited arena for enzyme-based pulp bleaching. SIGNIFICANCE AND IMPACT OF THE STUDY: The drastic improvement in pulp properties obtained after xylanase and LMS treatment would improve the competitiveness of enzyme-based, environmentally benign processes over chemicals both economically and environmentally.     

Surface character of pulp fibres studied using endoglucanases

The endoglucanase Cel5A from Trichoderma reesei and an endoglucanase from Aspergillus sp. (Novozym 476 from Novozyme A/S) were evaluated as probes for the surface properties of soft- and hardwood chemical pulp fibres. The hydrolysis time curves were in accordance with a two-phase degradation model described by a biexponential function. The kinetic parameters corresponding to the amount of fast and slow degraded parts of the substrate correlated to tensile index, relative bonded area and z-strength of the paper. All paper properties showing a correlation with enzyme kinetic parameters were related to fibre-fibre interactions. Fluorescence labelling of the reducing end groups in pulp fibres followed by enzyme treatment indicated that the fast substrate class corresponds to the population of "loose" cellulose chain ends not tightly associated with the bulk cellulose. The correlation between the parameters of enzyme kinetics and mechanical properties of the paper produced from the corresponding pulp found in this study should allow a rapid evaluation of the raw fibre material used in paper making process.     

Family-10 and Family-11 xylanases differ in their capacity to enhance the bleachability of hardwood and softwood paper pulps

Enzyme-aided bleaching of softwood and hardwood kraft pulps by glycosyl hydrolase family-10 and -11 xylanases and a family-26 mannanase was investigated. The ability to release reducing sugar from pulp xylan and to enhance bleachability is not a characteristic shared by all xylanases. Of the six enzymes tested, two xylanases belonging to family 11 were most effective at increasing bleachability and improving final paper brightness. None of the enzymes had a deleterious effect on pulp fibre integrity. The efficiency of individual xylanases as bleach enhancers was not dependent on the source microorganism, and could not be predicted solely on the basis of the quantity or nature of products released from pulp xylan. Cooperative interactions between xylanase/xylanase and xylanase/mannanase combinations, during the pretreatment of softwood and hardwood pulps, were investigated. Synergistic effects on reducing-sugar release and kappa number reduction were elicited by a combination of two family-10 xylanases. Pretreatment of kraft pulp with mannanase A from Pseudomonas fluorescens subsp. cellulosa and any one of a number of xylanases resulted in increased release of reducing sugar and a larger reduction in kappa number than obtained with the xylanases alone, confirming the beneficial effects of family-26 mannanases on enzyme-aided bleaching of paper pulp. Received: 6 January 1997 / Received revision: 10 April 1997 / Accepted: 19 April 1997     

Cynara cardunculus L. alkaline pulps: alternatives fibres for paper and paperboard production

The pulping of Cynara cardunculus L. (cardoon) was performed under conditions for kraft, kraft-AQ and soda-AQ processes. The best results in terms of delignification degree, expressed as kappa number, pulp viscosity and screened yield, were obtained for the kraft-AQ process with 0.20% of anthraquinone (AQ). The papermaking potential of the selected pulp was studied attending to biometric fibre characterisation, refining aptitude, optical and strength properties. All properties were compared against a Eucalyptus globulus pulp at different refining degrees. The cardoon pulp was also evaluated concerning its potential to board manufacture, alone and in mixtures with pine pulp, giving rise to promising results for liner manufacture.     

Activity of laccase on unbleached and bleached thermomechanical pulp

The introduction of value-added properties to pulp fibres is an attractive proposition. One interesting option is targeted modification of fibre surfaces by enzymatic activation. In this work, the activity of laccase on pulp and pulp fractions from thermomechanical pulp (TMP) and peroxide bleached TMP was studied on the basis of consumption of the co-substrate oxygen in the reaction and by studying the formation of radicals in the pulp material as analysed by electron paramagnetic resonance spectroscopy (EPR). Laccases obtained from Trametes hirsuta and Myceliophthora thermophila were used in the study. Laccases were found to be active on pulp material of unbleached TMP, whereas only fines from bleached TMP reacted in laccase treatment. Dissolved and colloidal substances (DCS) were assumed to have a mediating role in the laccase-catalysed oxidation of the fibre-bound material.     

Cellulase-assisted refining of chemical pulps: Impact of enzymatic charge and refining intensity on energy consumption and pulp quality

Paper production requires fibres to be refined, meaning mechanically treated to present sufficient bonding potential. As it is a highly energy consuming stage, various charges of cellulase as a pre-treatment were investigated to reduce the energy consumption and improve paper properties. The enzyme was added during pulp slushing and conditions of treatment were chosen to be compatible with an industrial application. Results obtained after low consistency disc refining of a softwood bleached kraft pulp were compared at a given drainage index. Enzymatically-treated samples showed a better development of fibrillation leading to a stronger paper. Moreover, fibre swelling was significantly improved. The impact of cellulase charge added to the pulp was identified. However, for all cellulase charges tested, fibre intrinsic resistance was lowered. Consequently fibres became shorter and tear index dropped. A solution was found by applying a milder treatment consisting in reducing refining intensity. This was a way to limit the intense fibre cutting at high refining levels. Moreover, by treating pulp with cellulase, it became possible to reduce refining intensity by 33%, keeping breaking length similar to control.     

Polymorphism of myofibrillar proteins in histochemically identified myotomal muscle fibre types of Heteropneustes fossilis (Bloch) and Labeo rohita (Hamilton)

Myofibrillar proteins in the myotomal muscle fibre types of two freshwater teleosts, Heteropneustes fossilis (Bloch) and Labeo rohita (Hamilton), were investigated. The fibre types were identified histochemically based on the reactivities of the enzymes SDH and m -ATPase. Electrophoretic analysis revealed distribution patterns of myosin light chains, tropomyosin, troponin, c - and m -protein; specific to the muscle fibre types. The results correlate well with the general pattern of myofibrillar protein distribution found in the skeletal muscles of higher vertebrates. The significance of the present findings are discussed with regard to histochemical, biochemical as well as functional properties of the muscle fibre types.     

Effects of fibre-degrading enzymes in combination with different fibre sources on ileal and total tract nutrient digestibility and fermentation products in pigs

ABSTRACT

The study was conducted to determine effects of a complex of fibre-degrading enzymes (xylanase, cellulase and β-glucanase) on nutrient digestibility, fibre fermentation and concentrations of short chain fatty acids (SCFA) at different parts of digestive tract in pigs fed different fibre-rich ingredients. A total of 36 barrows fitted with T-cannulas in the distal ileum (initial body weight of 41.1 ± 2.7 kg) were randomly allotted to six dietary treatments with three different high-fibre diets including maize bran (MB), sugar beet pulp (SBP) and soybean hulls (SH) with or without supplementation of fibre-degrading enzymes. Enzyme supplementation improved (p < 0.05) apparent ileal digestibility (AID) of dietary gross energy (GE), crude protein, dry matter (DM), organic matter (OM), total dietary fibre (TDF), neutral detergent fibre (NDF) and apparent total tract digestibility (ATTD) of dietary GE, DM, OM, TDF, insoluble dietary fibre (IDF) when pigs were fed MB, SBP or SH diets. When compared to the SBP and SH diets, the AID of GE, DM, ash, OM and NDF in diet MB was higher (p < 0.05), but the hindgut disappearance and ATTD of nutrients, except for ether extract and crude ash, were lower (p < 0.05). Enzyme supplementation increased acetate and total SCFA concentrations in ileal digesta and faeces of pigs. In conclusion, enzyme addition improved IDF fermentation and SCFA concentration in the whole intestine of pigs, and there was a large variation of digestibility of fibre components among MB, SH and SBP owing to their different fibre composition. Therefore, fibre-degrading enzymes should be applied to fibrous diets to improve efficient production of swine, especially considering low fibre digestibility of fibre-rich ingredients.     

Micromechanical understanding of the cell-wall structure

For improving properties of pulp fibres, a better understanding of the relationships between its macroscopic mechanical properties, fibre ultrastructure, and properties of the wood polymers is important. This paper discusses such relations between elastic properties of fibres, their matrix structure and the wood polymer elastic constants. It is argued that an orientation of all of the wood polymers in the direction of the cellulose microfibrils is most likely. The elastic longitudinal modulus of cellulose is well described by the value of 134 GPa dominating the longitudinal fibre properties. In the transverse direction the amorphous polymers play a more important role.     

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.     

Investigation of lignin-carbohydrate complexes in kraft pulps by selective enzymatic treatments

The occurrence of covalent bonds between residual lignin and polysaccharides in birch and pine kraft pulps was investigated by specific enzymatic treatments. Pure enzymes degrading cellulose, xylan and mannan were used both separately and in combination. Comparison of the molar masses of polysaccharides and lignin in the orginal pulps and in the residual pulps after enzymatic treatments showed that residual lignin in birch kraft pulp is linked at least to xylan. A minor portion may also be linked to cellulose. In pine kraft pulp some of the residual lignin appears to be linked to cellulose, glucomannan and xylan. The linkages between lignin and cellulose and hemicelluloses may be either native or formed during pulp processing. The results also provided new information on the synergistic action of cellulose- and hemicellulose-degrading enzymes on pulp fibres. The synergism appears to be mainly due to the structure of the pulp fibres, with different layers of cellulose sheets, hemicelluloses and lignin. On the other hand the results also provided information about fibre structure. The degradation of xylan clearly enhanced the action of enzymes on cellulose, suggesting that xylan partially covers the cellulose. A similar phenomenon was not observed in the simultaneous hydrolysis of glucomannan and cellulose. However, the results suggest that glucomannan does interact with cellulose, possibly by non-covalent linkages. Received: 8 July 1998 / Received revision: 7 October 1998 / Accepted: 11 October 1998     

Influence of different fibre sources on digestibility and nitrogen and energy balances in growing pigs

The present study was undertaken to investigate how three different fibre sources, sugar beet pulp, soya bean hulls and pectin residue, constituting 15% of diets for growing pigs, influenced daily body gain, feed conversion, apparent faecal digestibility and nitrogen and energy balances. Eight castrated crossbreed pigs (30-80 kg live weight) were used in a replicated 4 x 4 Latin-square design with one control diet and three fibre containing diets. Daily body weight gain and feed conversion were not affected by the dietary treatments. The apparent faecal digestibility of organic matter (OM) and energy were significantly lower for the fibre diets (OM: 0.81-0.85; energy: 0.78-0.83) compared to the control diet (OM: 0.88; energy: 0.86). The apparent faecal digestibility of crude protein (CP) was lower for the fibre diets (0.71-0.78) compared to the control diet (0.83), although it was only significantly lower for the sugar beet pulp and pectin residue diets. The pectin residue diet, which contained the highest amount of dietary fibre, lignin and insoluble non-starch polysaccharides, had the lowest digestibility of OM, CP and energy. There was a tendency (p = 0.07) for a diet effect on retained nitrogen in proportion to digested nitrogen, where the sugar beet pulp and pectin residue diets had numerically the highest values. Heat production and retained energy in proportion to metabolizable energy intake were not affected by fibre inclusion. It was concluded that the inclusion of sugar beet pulp, soya bean hulls and pectin residue in diets for growing pigs decreased the apparent faecal digestibility and in the diets with sugar beet pulp and pectin residue higher utilization of digested nitrogen for retention compensated for the lower amount of digested nitrogen.