Journal of Scientific & Industrial Research Vol. 78, January 2019, pp. 50-54 Reduction in Refining Energy and Improvement in Pulp Freeness through Enzymatic Treatment Lab and Plant Scale Studies S Tripathi 1 *, P Verma 2, O P Mishra 3, N Sharma 4, N K Bhardwaj 5 and R Tandon 6 1,2,3,4,5 Avantha Centre for Industrial Research & Development, Yamuna Nagar, India 6 Central Pulp and Paper Research Institute, Saharanpur, India Received 25 October 2017; revised 03 August 2018; accepted 05 October 2018 Lab as well as plant scale studies were carried out on enzymatic refining of mixed hardwood pulp aiming reduction in refining energy and improvement in fiber freeness. For the study different commercially available enzymes were used. Enzymatic treatment of pulp reduced refining energy by 29.3% in the laboratory scale experiments and by 20% in the plant scale trials conducted at a wood based paper mill. Enzymatic treatment of pulp improved the drainage of pulp by 11.1% in the laboratory scale experiments and improved FPR by 3.0%, FPAR by 3.6% in plant trial. During plant scale trial breaking length of the paper was improved by 14.7-17.4%. Keywords: Refining of Pulp, CMCase, Cellulase, Xylanase, Refining Energy, Drainage of Pulp, Physical Strength Properties Introduction Several studies have been carried out on application of cellulase enzymes for freeness improvement 1, 2 and refining energy reduction 3, 4 in paper industry. Two major types of cellulase are the exocellulases and endocellulases. Exocellulases act on the end of the cellulose chain and on the crystalline part whereas; endocellulases act in the middle of the cellulose chains and on the amorphous part 5, 6. Enzymatic pretreatment of chemical pulps before refining helps in fibrillation; this can reduce the energy requirement in mechanical refiner. Therefore, the cutting of fibres or fines generation reduced during refining. Due to lesser fines in the refined pulp, the drainage rate at the wire increased which required less or no drainage aid chemicals 7, 8. The desired mechanical strength properties of paper can be obtained even with lesser degree of refining (at higher freeness), improving the bulk of the paper. This affects fibre bonding and subsequently, paper strength properties 9. This paper describes the effect of using different commercial cellulase enzymes on refining energy, fiber freeness and morphological properties of pulp and strength properties of paper. Besides the findings of lab scale studies, results of two mill scale trials are also reported. *Author for Correspondence E-mail: sandeep@avantharesearch.org Experimental This study was conducted with different commercial enzymes collected from different national and international enzyme manufacturers. The enzyme samples were randomly marked as Enzyme-1, Enzyme- 2, Enzyme-3, Enzyme-4 and Enzyme-5. Bleached unrefined pulp was collected from an integrated pulp and paper mill in north India. The raw materials furnish used was mixed hardwood and bleaching sequence followed at the mill was C D E OP D 1 D 2. Enzymatic treatment was given in plastic beakers with mild stirring at 4% consistency. Refining of the pulps was carried out in the PFI mill. Hand sheets of refined and unrefined pulps were prepared and tested for different physical strength and surface properties. Analytical techniques Cellulase activity in enzymes was determined as per the method published in Pure & applied chemistry 10. Xylanase activity was determined as per the method described in Journal of biotechnology 11. Drainage of the pulp was measured as per the method described by Litchfield 12. Freeness of pulp was determined as per Tappi Test Method T 227 om-09. Hand sheets of the pulp were made according to Tappi Test Method T 205 sp-06. Laboratory refining of pulp was done as per Tappi Test Method T 248 sp-08. Moisture content of the pulp was determined as per Tappi Test Method T 210 cm-03. Physical strength properties were determined as per Tappi Test Method T 220 sp-06.
TRIPATHI et al.: REDN IN REFINING ENERGY AND IMPROVEMENT IN PULP FREENESS 51 Results and Discussions Enzyme activities in enzymes Table 1, shows various enzyme activities viz. carboxymethyl cellulase (CMC), filter paper activity and xylanase activity at ph 7.0 and 50 o C in commercial enzymes. Enzyme 3 has the highest CMCase and FPase activity whereas Enzyme-2 has the highest xylanase activity as compared to other enzymes. One IU is defined as the amount of enzyme necessary for the production of 1 mol product/minute. Enzymatic treatment of pulp and effect on refining Mixed hardwood pulp was refined to get Canadian standard freeness (CSF) about 490 ml with and without using enzymes prior to refining. With the enzyme pretreatment of pulp refining energy requirement was reduced. Refining energy reduction was the highest with the Enzyme-5 and the lowest with the use of Enzyme-1. Enzymatic treatment of pulp prior to refining was able to reduce refining energy by 29.3%. Detailed results are given in Table 1. Earlier study reported a reduction of 16% in refining energy when the enzyme was added to the unrefined mill bleached mixed hardwood pulp containing acacia and mixed tropical hardwood 2. Enzymatic drainage improvement of pulp For the enzymatic drainage improvement study, second stage enzymatic treatment was given to the pulp after refining. Enzyme-3 and Enzyme-4 were found most effective to improve drainage of pulp by 10.7-11.1%. Detailed results of two stage enzyme treatment are given in Table 1. Jackson et al. 13 proposed a mechanism that cellulases and hemicellulases adhered preferentially to fines rather than to long fibers of pulp thereby protecting the long fibers from the excessive degradation by the cellulases. Degradation of fines and intact long fibers are responsible for improvement in drainage along with improved physical strength properties of paper. Earlier study carried out by Efrati et al. 14 on recycled pulp using cellulose enzyme reported an improvement in drainage by 13.8%. Effect of enzymatic refining of pulp on physical strength properties Physical strength properties of mixed hardwood pulp were determined at about 490 ml CSF with and without using enzymes prior to refining. Tensile and burst strength of the enzymatic refined pulps was marginally improved whereas; tear index of the enzymatic refined pulps was marginally reduced. Smoothness of the paper sheet was improved by 33% and porosity got reduced by 45% with the use of enzymes prior to refining. Detailed results on effect of enzymatic refining of pulp on physical strength properties are given in Table 2. Efrati et al. 14 reported Table 1 Effect of pre and post-refining enzyme treatment on properties of pulp Particulars Control Enzyme-1 Enzyme-2 Enzyme-3 Enzyme-4 Enzyme-5 Different activities of the enzymes at 7.0 ph and 50 C temperature CMC activity (IU/ml) -- 201 289 384 218 220 Xylanase activity (IU/ml) -- 3748 11,406 1429 602 1324 FPase activity (IU/ml) -- 9.7 12.2 22.9 7.3 7.0 1 st Enzyme treatment (Time 60 min, temp. 40 C, ph 7.0) Enzyme dose (g/t) 0 150 150 150 150 150 PFI revolutions to get 490 ml CSF 1400 1150 1050 1050 1050 990 Reduction in refining energy (%) -- 18 25 25 25 29 2 nd Enzyme treatment (Time - 30 min, temp. 40 O C, ph 7.0, Enzyme dose - 75 g/t) CSF(ml) 500 505 510 518 515 490 Difference in CSF(ml) -- 5 15 23 20-10 Drainage time (sec) for 900 ml 47.18 46.11 45.38 41.92 42.12 49.27 Improvement in drainage (%) -- 2.3 3.8 11.1 10.7 -- Table 2 Effect of enzymes on physical strength properties of pulp at about 490 ml CSF Particulars Control Enzyme-1 Enzyme-2 Enzyme-3 Enzyme-4 Enzyme-5 Bulk (cc/g) 1.29 1.32 1.31 1.31 1.29 1.28 Tensile index (N.m/g) 56.2 58.9 61.2 57.5 57.6 56.8 Burst index (kn/g) 4.30 4.40 4.60 4.42 4.60 4.24 Tear index (mn.m 2 /g) 5.3 5.1 4.9 4.8 5.2 4.4 Porosity (sec/100 ml) 14.5 15.2 18.4 18.6 20.7 21.1 Double fold (no.) 77 87 102 91 99 80 Smoothness (ml/min) 112 106 95 74 88 87
52 J SCI IND RES VOL 78 JANUARY 2019 substantial improvement in physical strength properties like tensile index by 9.7%, tear index by 12.4%, burst index by 13.5% and double fold by 2.98% after enzymatic refining of recycled pulp. Effect of enzymes on fibre surface Scanning electron microscope (SEM) micrographs of enzyme treated and untreated mixed hardwood pulps were taken to analyze the effect of enzymes on the surface of pulp fiber. There was no fibrillation as well as delamination of cell wall/ cell wall collapse observed in the unrefined untreated fibers of mixed hardwood pulp fibers (Figure-1). With the mechanical refining of the pulp marginal fibrillation on the surface of fiber as well as delamination of cell wall/ cell wall collapse was observed (Figure-2). Enzymatic refining (Treatment of pulp with enzyme afterwards mechanical refining) of mixed hardwood pulp was resulted to improved fibrillation on the surface of pulp fibers, delamination of cell wall and collapsed cell wall (Figure-3). SEM micrographs reported in earlier studies on enzymatic refining of pulps also showed increased fiber to fiber bonding, more fibre wall dislocation after enzymatic pre treatment of pulp 14, 15. Plant trial with screened enzyme Plant scale trial was conducted at one of the units of Ballarpur Industries Limited a wood based paper mill situated in western part of India. The mill was producing writing printing papers using hardwood, softwood and bleached chemi-thermo mechanical pulp in its pulp furnish. The trial was conducted using two screened enzymes based on the lab study. Control data were collected for 10 days plant running in normal conditions. Trial with enzyme-3 Plant scale trial was taken with the use of Enzyme- 3 for a period of 12 days. The trial was taken with enzyme dose level of 50-100 g/t of pulp. During the trial improvement of 2 degree Schopper riegler (SR) in freeness of the pulp was observed. During the trial, double disc refiner (DDR) at paper machine was bypassed. In the wet- end area first pass ash retention (FPAR) and first pass retention (FPR) were improved with the use of Enzyme-3 during plant trial. Slight improvement in freeness of the Head box and Machine chest pulp was also observed. Breaking length of the paper was improved in both the directions i.e. machine direction (MD) and cross direction (CD) from 2961 m to 3720 m, and 1567 to 1813 m, respectively. Tear factor of the paper was reduced marginally during the trial run. Detailed results of plant scale trial taken with Enzyme-3 are given in Table 3. Fig. 1 SEM micrograph of unrefined mixed hardwood pulp fibers Fig. 2 SEM micrograph of refined mixed hardwood pulp fibers Fig. 3 SEM micrograph of refined mixed hardwood pulp fibers after enzymatic treatment
TRIPATHI et al.: REDN IN REFINING ENERGY AND IMPROVEMENT IN PULP FREENESS 53 Table 3 Results of the plant scale trial taken with enzyme-3 and Enzyme-4 Particulars Blank data Trial with enzyme-3 Trial with Enzyme-4 Min Max Avg. Min Max Avg. Min Max Avg. Enzyme dose (g/tp) -- --- -- 50 100 75 60 100 80 Refining properties SR (Head Box) 22 27 24 24 29 26 27 33 29 Stock DDR (kwh) 98 108 103 97 106 103 62 96 83 M/C DDR (AMP) 31 71 61 -- -- -- -- -- -- Wet end properties B/w consistency (%) 0.1 0.15 0.12 0.09 0.14 0.11 0.09 0.13 0.11 FPR (%) 72.1 80.8 77.1 75.7 82.8 79.4 77.2 83.2 79.4 FPAR (%) 41.4 50.1 46.9 44.9 53 49.5 47.1 53.1 48.6 Paper properties Bulk (cc/g) 1.38 1.49 1.44 1.4 1.47 1.43 1.4 1.46 1.44 Gurley porosity (s/100ml) 6 10 8 6 10 8 6 9 7 Tear factor MD 49 65 57 50 58 54 47 53 50 CD 54 70 62 56 64 59 52 61 56 Breaking length (m) MD 2481 3386 2961 3277 4416 3720 3190 3953 3475 CD 1387 1768 1567 1539 2175 1813 1712 1921 1798 Burst Factor 9.7 13.6 11.3 10 14.6 11.8 9.11 12.29 10.85 Trial with enzyme-4 Plant scale trial was taken with the use of Enzyme- 4 for the period of 5 days. The trial was taken with enzyme dose level of 60-100 g/t of pulp. During the trial, improvement of 5 units of o SR in freeness of the pulp was observed. During the trial with enzyme-4, a reduction of ~20% in refining energy was observed. In addition the machine DDR was also bypassed during the trial run. In the wet- end area FPAR and FPR were improved with the use of Enzyme-4 during plant trial. Significant improvement in freeness (5 units of o SR) in the Head box and Machine chest pulp was observed. 2.0% increase in the ash percentage of the paper was obtained during trial run with Enzyme- 4. Breaking length of the paper was improved in both the directions i.e. MD and CD from 2961 to 3475 m, and 1567 to 1798 m, respectively. Tear factor of the paper was reduced marginally during the trial run with Enzyme-4. Detailed results of plant scale trial taken with Enzyme-4 are given in Table 3. Advantages and disadvantages of mill scale trials Advantages: Improvement in freeness of pulp, reduction in refining energy, reduction in wastage of input materials due to improved FPAR and FPR, improvement in ash content thereby reduction in input cost of paper, improvement in breaking length of paper. Disadvantages: Marginal reduction in tear factor of paper. Conclusions Enzymatic pre-treatment of mixed hardwood pulp reduced the refining energy requirement by 17.9-29.3% in the lab scale experiments. Post refining enzymatic treatment of mixed hardwood pulp improved drainage rate by 11.1%. In plant scale trials enzymatic pretreatment of pulp reduced the electrical energy requirement during refining of pulp by 20% with improvement in FPAR by 3.6% and FPR by 3.0%. During plant scale trial breaking length of the paper was improved in both the directions i.e. MD and CD by 17.4 and 14.7%, respectively. Tear factor of the paper was reduced marginally with enzymatic treatment of pulp. References 1 Bhardwaj N K, Bajpai P & Bajpai P K, Use of enzymes to improve drainability of secondary fibers, Appita J, 48 (1995) 378-380. 2 Tripathi S, Sharma N, Mishra O P, Bajpai P & Bajpai P K, Enzymatic refining of chemical pulp, Ippta J, 20 (2008) 129-132. 3 Bajpai P, Mishra S P, Mishra O P, Kumar S & Bajpai P K, Use of enzymes for reduction in refining energy Laboratory studies, Tappi J, 5 (2006) 25-32. 4 Singh R, Bhardwaj N K & Choudhury B, An experimental study of the effect of enzyme assisted refining on energy consumption and paper properties for mixed hardwood pulp, Appita J, 67 (2014) 226-231. 5 Verma P K, Bhardwaj N K & Singh S P, Upgradation of recycled pulp using endoglucanase enzyme produced by
54 J SCI IND RES VOL 78 JANUARY 2019 Pycnoporus sanguineus NFCCI-3628, Iran J Chem Chem Eng, 36 (2017) 191-201. 6 Kuhad R C, Gupta R & Singh A, Microbial cellulases and their industrial applications, Enz Res, 2011 (2011) 1-10. 7 Bajpai P K, Solving the problems of recycled fiber processing with enzymes, BioResources, 5 (2010) 1311-1325. 8 Singh R, Bhardwaj N K & Choudhury B, Cellulase-assisted refining optimization for saving electrical energy demand and pulp quality evaluation. JSIR, 74 (2015) 471-475. 9 Buzala K P, Przybysz P, Kalinowska H & Derkowska M, Effect of cellulases and xylanases on refining process and kraft pulp properties, PlosOne J, 11 (2016) 1-14. 10 Ghose T K, Measurement of cellulase activities, Pure & Appl Chem, 59 (1987) 257-268. 11 Bailey M J, Biely P & Poutanen K, Interlaboratory testing of methods for assay of xylanase activity, J of Biotech, 23 (1992) 257-270. 12 Litchfield E, Dewatering aids for paper applications, Appita J, 47 (1994) 62-65. 13 Jackson L S, Heitmann J A & Joyce T W, Enzymatic modifications of secondary fiber, Tappi J, 76 (1993) 147-154. 14 Efrati Z, Talaeipour M, Khakifirouz A & Bazyar B, Impact of cellulase enzyme treatment on strength morphology and crystallinity of deinked pulp, Cell Chem Technol, 47 (2013) 547-551. 15 Suchy M, Hakala T, Kangas H, Kontturi E, Tammelin T, Pursula T & Vuorinen T, Effects of commercial cellobiohydrolase treatment on fiber strength and morphology of bleached hardwood pulp, Holzforschung 63 (2009) 731-736.