IMPROVING DRAINAGE CHARACTERISTICS OF PULPS USING COMMERCIAL AND ISOLATED FUNGAL ENZYMES

Abstract

In papermaking, the drying process at dryer section is the most energy consuming unit operation. One of the most influential problems with nonwood as well as recycled pulp is the slow drainage in different processes during papermaking. This can be the cause of slow dewatering on the wire and press sections of the paper machine leading to low production. By the improvement in pulp drainage, paper machine speed could be significantly increased along with steam savings. This research work presents a possible action of endoglucanase (EG) and cellobiohydrolase (CBH) components of cellulases on cellulosic pulps having high fines content. It covers the understanding whether the effectiveness or strength loss depends on a specific type of enzyme activity (EG or CBH). Better understanding of the enzyme−fines interaction will improve the selection of enzymes for drainage improvement of recycled and wheat straw pulps with high fines content. The objectives of the present study are as follows.  Evaluation of different commercial cellulase enzymes for improvement in pulp drainage and impact on pulp and paper properties  Evaluation of enzymes and polymeric drainage aid (sequential treament) for improvement in pulp drainage and impact on pulp and paper properties  Lab scale production of endoglucanase enzymes and their application for drainage improvement of pulps Based on these objectives, the research work has been distributed in seven chapters. Chapter 1 Introduction Poor drainability i.e. less drainage of water during paper formation process is one of the major problems with recycled and wheat straw pulps. It is due to the higher relative surface area of secondary fibre fines than virgin fibre fines. The fibre fines causing lower drainage rate in recycled and wheat straw pulps are reported to consist of amorphous cellulose (Dienes et al. 2004). Dewatering properties of the pulp strongly affect the energy efficiency of paper machine and thus the cost efficiency of papermaking. Conventionally, dewatering is increased in a paper machine by using drainage aids in the wet-end section and/or more intense wet pressing in the press section. But use of drainage aids can worsen formation, and high wet press levels decrease the bulk of the end-product (Oksanen et al. 2011). Therefore, novel pulp modification and dewatering innovations are required with new high speed paper machines. Chapter 2 Literature review The fines content in recycled pulps and wheat straw ranging from 20 to 45% has already been reported in the literature (Dienes et al. 2004, Rousu and Hytonen 2007). Recent studies have shown that removal of fines from recycled and wheat straw pulps either by conventional viii methods such as fractionation or other methods can improve not only the drainability of the pulp suspension but also the mechanical and optical properties of the paper sheet due to the fines acting as a filler, with less contribution in bonding properties of the paper sheet. Jackson et al. (1993) reported that enzymes can either flocculate or hydrolyze fines and remove fibrils from the surface of large fines. The probable explanation for an increased drying rate is a more bulky and porous fibre network with enzymatic treated pulp. Reduced shrinkage forces due to hydrolysis of fines and surface hemicelluloses are a probable explanation for the increase in bulk with enzymatic treated pulps (Oksanen et al. 2011a). Cellulose has both crystalline and amorphous regions and it is easier to hydrolyze amorphous regions in comparison to crystalline regions (Zuhair 2007). In this study, the concept of monocomponent cellulase treatment of recycled-newsprint (NP), recycled- writing printing (WP) and wheat straw (WS) mill pulps, for improvement in drainage as a result of selective and controlled hydrolysis is demonstrated. Chapter 3 Materials and methods Bleached recycled-NP, recycled-WP and wheat straw pulps were procured from different paper mills in India. Different enzyme activities of different commercial enzymes were determined using standard assay procedures. The enzyme based products were added to pulp at varying doses ranging from 0.010 to 0.025% on dry pulp. The drainage time of the untreated and enzyme treated pulps was measured on modified °SR tester. The fines content and fibre length distributions of untreated and enzyme treated pulps were determined using Bauer McNett fibre classifier and L&W fibre tester, respectively. The pulp was also characterized for several other pulp properties such as drainage time, Canadian standard freeness, water retention value and viscosity. The thickness, tensile index, tear index, bendtsen roughness of paper was determined on L&W instruments as per different TAPPI test methods. The extreme effects of different enzyme treatments on pulps were evaluated using Field emission scanning electron microscope (FE-SEM). The effect of different enzymes on the crystallinity of treated pulps was also studied by X-ray diffraction. Two cellulase producing fungal strains, Pycnoporus sanguineus (PVYA07 NFCCI 3628) and Alternaria gaisen (PVYA11 NFCCI 3629) were isolated. Different nutritional factors (carbon sources, nitrogen sources, and different surfactants) and environmental factors (initial pHs, inoculum size, incubation days, incubation temperature of the fermentation medium) were analyzed for enzyme production by both the fungal isolates individually. Chapter 4 Drainage improvement by commercial cellulase enzymes The increased solubilization of amorphous cellulose mediated by endoglucanase treatments consequently improved the drainability of recycled pulp-NP, recycled pulp-WP and wheat straw pulp-WS in the range of 15.5 to 20.7%, along with better paper properties such as tensile ix index and smoothness. The proportion of longer fibres (greater than 1 mm) was increased and that of shorter fibres was decreased. FE-SEM studies displayed more damage to the fibres in enzyme Fibrecare R treated fibres when compared to endoglucanase treated fibres at high enzyme dose. Treatment with the enzyme Fibercare D resulted in extensive fibre wall peeling, fibre collapse and increased fibre flexibility. X-ray diffraction studies also supported the finding that endoglucanases can improve the pulp drainage by hydrolyzing the most accessible parts of cellulose i.e. fines containing amorphous cellulose and other dissolved and colloidal substances and hemicellulose present in the fibres. The crystallinity was observed to be increased in case of endoglucanase Fibrecare D treated samples due to more action on amorphous cellulose. Chapter 5 Drainage improvement by combined treatment of commercial cellulases and polymeric drainage aid The interaction of various types of cellulases (Fibercare D and Fibercare R) and polymeric drainage aid for enhancing the freeness of recycled and wheat straw pulps were also explored. Polymer treatments alone were found to increase the drainage in the range of 12 to 25% at various doses but formation was adversely affected due to flocculation. It was observed that endoglucanase Fibercare D, in combination with polymeric drainage aid (P) at optimized dose levels, further enhances the freeness of recycled and wheat straw pulps by 25 to 28%. It was further concluded that by using enzyme with lower levels of polymeric drainage aid, a potentially more uniform sheet can be produced with even better pulp drainability than the enzymes alone. Chapter 6 Lab scale production of endoglucanase enzymes and their application for drainage improvement of pulps This chapter describes the isolation, screening and identification of two cellulase producing fungus i.e. Pycnoporus sanguineus PVYA07 NFCCI-3628 and Alternaria gaisen (PVYA11 NFCCI-3629) from 54 different fungal isolates. It also covers the production and purification of isolated endoglucanase enzymes and their evaluation of for improvement in pulp drainage. The cultures were identified based on sequencing of the genomic deoxyribonucleic acid (DNA), and deposited at National Fungal Culture Collection of India (NFCCI), Pune, India with accession numbers. Purified cellulosic substrates such as carboxymethyl cellulose (CMC) and Avicel were found to be suitable for cellulase production. Yeast extract (YE) followed by urea were found to be the suitable nitrogen source for cellulase production by Pycnoporus sanguineus and Alternaria gaisen. Tween 80 assisted to release the cellulase complex in the medium. The endoglucanase enzymes were purified to homogeneity from the culture filtrates of Pycnoporus sanguineus and Alternaria gaisen via ammonium sulfate fractionation, Sephadex G-100, and Q-Sepharose column chromatography. The molecular weights of the x enzymes from 2 different fungal strains were determined by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS PAGE). The effect of enzymes produced at lab scale on pulp drainage and other pulp and paper properties was also analyzed. Pulp drainage was observed to be improved by 10.1 to 19.5% using the purified enzymes from two fungal isolates. Significant improvement in tensile index and smoothness was also observed in handsheets prepared from enzyme treated pulps. Chapter 7 Conclusions and recommendations for future work The carried out investigations on endoglucanase treatments showed an opportunity for significant improvement in dewatering of different pulps at different enzyme doses. Significant improvement in tensile index and smoothness was also observed. The results indicated that applying specific cellulase component, i.e. endoglucanase, may be more effective for improving the drainage of pulps with high fines content, by selective hydrolysis of excess fibre fines and other dissolved colloids. The established effect of mono component endoglucanases for improving pulp drainage can be utilized for enhancing the paper productivity (increased machine speed) and decreasing the dryer steam consumption. Further research efforts in this direction should be carried out to demonstrate the commercial utility of the endoglucanase enzymes for drainage improvement at mill scale.