Results on enzymatic deinking of paper pulps are shown. The process includes paper pulping, with an enzymatic cocktail, followed by flotation and dewatering. Three different wastepaper samples were used and tested. The deinking of the pulp was monitored by image analysis. Physical, mechanical and optical properties of pulp and paper were also determined. The obtained data revealed the effectiveness of the assayed enzyme preparation. However, enzyme use needs further optimisation as paper strenght properties suffered important alteration

Gama, F. M.

Mota, M.

Pala, H.

Universidade do Minho: RepositoriUM

PRELIMINARY STUDIES ON ENZYMATIC DEINKING •' I ,, tPala, H.; Gama, F • ..,..; Mota, M. , Dept. Engenharia ·Biologica, lnstituto de Biotecnologia e fQufmica Fina, . Universidade do Minho, Campus de • Gualtar, 4709 Braga Codex, Portugal ABSTRACT Results on enzymatic deinking of paper pulps are shown. The ocess includes paper pulping, with an enzymatic cocktail, llowed by flotation and dewatering. Three different astepaper samples were used and tested. The deinking of the Ip was monitored by image analysis. Physical, mechanical d optical properties of pulp and paper were also determined. he obtained data revealed the effectiveness of the assayed yme preparation. However, enzyme use needs further as paper strength properties suffered important astepaper recycling is nowadays mandatory, because of the rid-wide lack of virgin fibre, and in order to reduce the llulosic residues produced in developed societies. The orporation of secondary fibres in paper production became accepted reality, and research on recycling technologies, mely for effectively removal of pulp contaminants (deinking) necessary. aditional processes use expensive, potentially environmental aging chemicals. An alternative to these methods are logical treatments, which use enzymes to peel away Iulose fibrils, thus removing attached ink particles which are n removed by flotation [l]. Enzymatic technology is also wn as specially advantageous to deink mixed office waste OW), the best quality wastepaper. The reuse of MOW is Hy limited by its high content of noncontact inks, which are y difficult to remove by application of current thodologies [2]. So far, a satisfactory theory describing the y the enzymes act removing the ink particles from the fibres face has not been presented. The main purpose of this work s to develop an efficient experimental methodology to study enzymatic deinking methods. Further work will follow, with aim of analysing the fundamentals of the process, both in s of the enzymes surface activity and reactivity. experimental sequence used in the enzymatic deinking is wn in Figure 1. Chemical deinking sequence was similar. In er to conveniently estimate the enzymatic action, a blank a control were made parallel to the enzymatic assays. The refers to the starting pulp (no treatment was performed). trol pulps were processed in a similar manner as those en the enzymatic treatment described above, except that no zyme was added. Pulp Slushing Enzymatic treatment --+ ( 3% consistency; t = JO min) ---+ (T = 50°C, pH= 5,0; 1 = 30 min) Enzyme deactivation (T = 100°C; I= 5 min) Flotation (0,6% consistency; 1,14 Lair/min; Swfacrant aid; I= 20 min) l Deinked pulp Figure 1: Experimental sequence Enzymatic Preparation ink --+ The enzymatic cocktail used was a commercial preparation kindly supplied by Buckman Laboratories. Its relevant activities are presented in Table I. Assay procedures used to determine enzymatic activities are the following: Carboxymethy/cellulase (CMCase) 0,5 mL of the diluted enzyme was incubated in 0,5 mL of carboxymetylcelullose solution 1 % (sodium citrate buffer, 0,05 M, pH = 5,0). The enzymatic reaction took place at SO"C, during 30 min. Released sugars were measured by DNS method, using glucose as the standard. Filter paper activity (FPase) 0,5 mL of diluted enzyme was added to 1 mL of sodium citrate buffer containing 50 mg of Whatman n°1 filter paper. After incubating for 60 min at T= SO"C, released sugars were measured by DNS method, using glucose as the standard. Xylanase activity 0,5 mL of diluted enzyme was incubated in 1,5 mL of oat spelt xylan solution l % (sodium citrate buffer, 0,05 M, pH = 5,0). After incubating for 30 min at T= 65°C, released sugars were measured by DNS method, using glucose as the standard. TABLE I: ENZYMATIC ACTIVITIES Activity CM Case FPase Xylanase Paper Furnish Activity (U/mL) 6 3 29 Dosage (U/g OD pulp) 1,2 0,6 5,8 The current work aims to study the potential of enzymes in the deinking of three different wastepaper samples: (i) photocopy printed paper; (ii) a chemical pulp; (iii) a mechanical pulp. The last two samples were kindly supplied by Renova and the first one was prepared at U.M. laboratory by soaking photocopy printed paper in warm water and disintegrating for about 30 minutes. Cl89 Enzymatic Pulping After a 10 minutes fiberization step with sodium citrate buffer 0,05 M, pH 5,0, the enzyme was added to the mixer and was allowed to react with the pulp during 30 minutes at 3% consistency. To finish up the trial, the enzyme was deactivate by heating the pulp at 100°C and boiling for approximately 5 minutes. After this, the pulp was floated. Chemical Pulping After a 10 minutes fiberization step with water, deinking chemicals were added and pulping continued for another 30 minutes (pH = 11,0), followed by immediate floating of the pulp. The chemicals used were 0,7% NaOH, 15% sodium silicate and 0,6% hydrogen peroxide based on OD weight of pulp. Pulp consistency was 6%. Flotation A laboratory flotation unit was developed and optimised at the U.M. laboratories in order to separate fibres from ink particles. It actually consists on an airlift reactor (Figure 2) which operates with 4,5L sludge (0,6% consistency) during 20 minutes at room temperature and an air flow of 1,14 L/min. During the flotation process a surfactant is added. .......... " ..... ..... ... . . .. - .. ·. t ~ J. ~· J. t This kind of reactor is characterised by liquid and solid phases cyclic flow. The circulation in the reactor is established by the difference between fluids densities in the downcomer (descending tube) and in the riser (ascending tube). This variation arises from the injection of air through the reactor's bottom. At the top of the reactor there is a degaseification zone, where the gas used in the impulsion is released and the formed foam and retained ink are collected. Figure 2: Airlift reactor Dewatering and Handsheet Preparation The floated samples were recovered and dewatered on a vacuum filter. Handsheets were made according to the usual standard T APPi procedures. Physical, Mechanical and Optical Properties Properties of pulp and paper were determined according to the standard T APPi procedures. Parameters as drainage rate, burst, tensile, tear and brightness were measured. Image Analysis The image analysis system is composed of a magnification lens, charge-coupled device (CCD) camera, image displayer and computer. All the images were acquired with the same magnification and lightning in order for comparable results to Cl90 2 be obtained [3]. A 4x objective was chosen, as a reasonable compromise between image enlargement and analysed area. Several authors have already demonstrate that the two sides of the same handsheet can lead to different results as contaminants tend to accumulate differently on either side [3,4]. Therefore, all the handsheets were analysed in the same side. Particle counts, shapes and sizes were examined using a commercial available software (Globalab Image). To ensure image analysis results reproducibility a suitable threshold value was selected to identify the contaminants and maintained in all performed analysis with the same kind of pulp [3). For each handsheet 40 images were retained and treated. Image Analysis Calibration A calibration of the image analysis system was done as follows: Six handsheets were made, using different proportions of deinked and non-deinked chemical pulps. The predicted ink concentration, calculated on the basis of the particles concentration in each of the two "pure" pulps, was compared with the obtained one. Brightness values were also determined. RESULTS AND DISCUSSION Image analysis calibration The smallest spot which could be distinguished, under operation conditions, had a surface area of 299 µm2. average analysed area was 355 mm2• Figure 3 shows correlation between real ink concentration and the predic one, demonstrating the applicability of the technique . effect of random sampling errors was calculated for coverage and particle areas using the correlations suggested Zayer et al [3). The greatest confidence interval (%CI) for confidence level of 95% is 9%. 8000 7000 6000 ~ 5000 c. ]j 4000 ~ 3000 2000 1000 0 0 y = 1.0002x + 104.8 R2 = 0.9988 2000 4000 Predicted ppm 6000 8000 Figure 3: Actual ink concentration versus predicted ink concentration A good correlation between brightness and ink p concentration was found, which cannot be attributed to particles concentration. The effect of ink particles on brig !j ' I values has been shown to be a compleJf i;me. Darker particles contribute more heavily to the decre brightness values than do lighter partl~les of the same si and smaller particles sizes cause brightness to decline rapidly [6). Evaluation of enzymatic deinking performance Figures 4 and 5 summ'.arise image analysis results. The analysed area was the same in each case. The obtained information demonstrate enzymatic, :µ.eatment efficiency on ink removal from secondary fibre. Mechanical pulp deinking seems to be less effective. 115000 ""' .5 10000 I I 5000 0 -------------! •Blank DControl CAssay PhotOCopy Chenical pulp Mechanical pulp Figure 4: Enzymatic deinking efficiency 1600 1200 c ,. 0 u .!! 800 i! ~ 400 0 Photocopy Chemical pulp Mechanical pulp Figura 5: Particle count and ink particle size median variation 800-.-~~~~~~~~~-.=~~~~~ 700 600 § 500 8 :§ 400 ~ 300 200 '-----------i! •Photocopy II Chemical pulp 1------------1CMechanicaJ pulp 100 o.i.m:u..i1ta.J..-u.,1UJ...mu...11iU..a:a+11ia:......,...,....,..a..t 500 1000 1500 2000 2500 3000 3500 4000 4500 5000 5500 Particle size distribution (µm2) ;-igura 6: Particle size distribution for the different non reated pulp samples 'he enzymatic improvement on deinking has been justified by ~e peeling effect that enzymes perform on fibre surface, which ;ould facilitate the ink detachment [7,8]. However, as the ctached ink is usually removed by flotation, the efficiency of 1e overall process depends not only on the detachment of the 3 ink particles but also on the size of the detached particles, because that is one of the critical factors of the flotation process. The smaller particles are the most difficult to remove, and every deinking process has to be optimised so that particle size is not excessively reduced (9]. This situation can probably justify the lower deinking efficiency in the case of the mechanical pulp: as shown in Figure 6, the mechanical pulp presents the lowest average ink particle size. Brightness was also measured. Only the chemical and mechanical pulps had higher values following deinking (Table II). In these cases, brightness increased when either flotation or enzymatic treatment plus flotation were applied. By comparing the obtained brightness values with residual ink concentration, it can be concluded that, when the average particle size is small, traditional brightness measuring techniques do not reflect the relative ink concentration in the paper [5,6,10]. As a matter of fact, the mechanical pulps present lower brightness values, even if chemical pulp is the one that presents the higher residual ink concentration. Assay Control Blank TABLE II: BRIGHTNESS(%) Chemical Pulp 91,3 85,9 84,5 Mechanical Pulp 78,8 74,6 72,9 The enzymatic treatment changed also significantly the ink size distribution profile. Figure 7 presents particle size distributions of treated and untreated chemical pulps. Photocopy paper and mechanical pulp exhibited profiles similar to this one. Median values of ink particle size for the several pulps are shown in Figure 5. As suggested by Prasad et al. [4], the larger particles have apparently either been removed from the pulp, or reduced in size after the enzymatic treatment and flotation. 300 250 § 200 0 c.> ~ 'E .. a.. 150 100 50 0 •Blank mcontrol CAssay 500 1000 1500 2000 2500 3000 3500 4000 4500 5000 5500 Particle size distribution (µm2) Figura 7: Particle size distribution for different samples of chemical pulp Finally, physical and mechanical properties of pulp and paper were determined. The obtained results are presented on Table III. Burst, tensile and tear indexes were reduced, and surprisingly, only the photocopy paper exhibited a slight improvement in drainability. C191 A high enzyme concentration in the pulping process may reduce the overall hydrogen bonding potential of the fibres, and therefore the paper mechanical resistance [ 11]. This is probably the reason why the mechanical indexes registered in this work were significantly lower after the enzymatic treatment. Work remains to be done regarding the optimisation of the process, conveniently optimising the enzyme concentration for efficient ink removal, and at the same time not affecting the paper mechanical properties [8,9]. TABLE III: ENZYMATIC ACTION ON PULP AND PAPER PROPERTIES Sample Drainability Burst Index Tensile Index Tear Index ( 0 SR) (I<Pa.m2ij!) (N.mlj!) (mN.m2/!l) Photocopy Assay 32,5 2,5 44,8 4,0 Control 41,8 3,6 54,3 10,l Blank 35.5 3,8 55,6 10,l Chemical Assay 49,5 1,4 30,8 3,1 Control 45,5 2,6 40,5 8,9 Blank 33,5 2,5 37,7 9,2 Mechanical Assay 67,3 1,5 32,3 3,1 Control 64,0 2,7 41,7 8,9 Blank 47,5 2,2 35,7 9,0 Evaluation of chemical versus deinking performance This study compares enzyme and chemical deinking of a chemical pulp. It was verified that the enzyme facilitated deinking to a greater extent than chemicals (Figure 8). The used chemical preparation did not affect significantly the paper mechanical properties, and it even allowed for a slight increase in resistance; on the other hand, the pulp drainage rate was lowered. This can be explained as the effect of alkaline pH, which causes fibre to swell, increasing its surface area and intensifying fibre bonding. Also the chemical deinking allowed for a brightness improvement of the paper sheets, but lower than the one resulting from the enzymatic treatment. e 12000 a. .e 10000 c ~ 8000 ~ 6000 2! c 0 4000 u 'iii "' 2000 "Cl ·;; &! 0 1253 Blank Control Enzyrmtic nvithod Chenical nvithod Figure 8: Deinking efficiency and particle count CONCLUSIONS The present work confirms the efficiency of cellulase/xylanase cocktails on paper pulps deinking, although considerable loss of the paper pllysical properties resulted under the used C192 4 experimental conditions. The main objective of this work, at this stage, was to establish all the necessary techniques for future enzyme testing and selection: a very effective flotation device, different from those described in the literature, has been used, and standard procedures for image analysis of paper sheets have been defined. The tested enzyme preparation proved to be more effective on ink removal than a conventional chemical methodology. Optimisation of the process will follow. Pulping time, consistency, pH, enzyme concentration and the presence of surfactants are factors that will be analysed in order to improve the enzymatic performance. The mechanism of the deinking process will also be analysed in future work. REFERENCES [l] JEFFRIES, T., KLUNGNESS, J.H., SYKES, M,, RUTLEDGE-CROPSEY, K., "Preliminary results of enzyme· enhanced versus conventional deinking of xerographic printed paper", TAPP! 1993 Recycling Symposium, 183 - 188 (1993). [2] PRASAD, D.Y., " Enzymatic deinking of laser and xerographic office wastes", Appita, 46 (4): 289 - 292 (1993). [3] ZEYER, C., VENDETTTI, R.A., PUANGCHINDA, K.W., and HEITMANN, J.A., "The distribution of impurities in pulp and paper: the effects of the random distribution of impurities on image analysis", Tappi Journal, 78 (2): 168 - 175 (1995). (4) PRASAD, D.Y., HEITMANN, J.A., and JOYCE, T.W "Enzyme deinking of black and white letterpress print newsprint waste", Progress in Paper Recycling, 1 (3): 21 - 3 ( 1992). [5] RIVIELLO, A.E., SCAMEHORN, J.F., CHRISTIAN, S.D and BORCHARDT, J.K., "The use of image analysis measure brightness of paper'', 1995 Pulping Conferenc Proceedings, TAPPI PRESS, Atlanta, 165 - 177 (1995). [6] MCKINNEY, R.W.J., Tappi Journal, 72 (1): 129 (1989). [7] DANIELS, M.J., Paper Technology, 33 (6): 14 (1992). [8] JEFFRIES, T., KLUNGNESS, J.H., SYKES, RUTLEDGE-CROPSEY, K., "Comparison of enzy enhanced with conventional deinking of xerographic and las printed paper", Tappi Journal, 77 (4): 173 - 179 (1994). [9] OW, S.K., PARK, J.M., and HAN, S.H, "Effects of enzy on ink size and distribution during the enzymatic dei process of old newsprint", Biotechnology in the pulp and pa Industry, 163 - 165 (1994). [10) JORDAN, B.D., and POPSON, S.J., Journal of Pulp Paper Science, 20 (6): 1161 (1994). [11) POMMIER, J.C., FUENTES, J.L., and GOMA, "Using enzymes to improve the process and the product qua in the recycled paper industry, Part I: The basic laborat work", Tappijournal, 72 (6): 187 - 191 (1989). ACKNOWLEDGEMENTS The authors gratefully acknowledge Portucel Viana providing laboratory facilities to carry out part of this work a all the Physical laboratory staff for t~j!ir help ;,ind support. I' ,4, 'I 

Preliminary studies on enzymatic deinking

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