The Effects of Magazine and Filler on the Flotation Deinking of Newsprint

Transcription

1 i The Effects of Magazine and Filler on the Flotation Deinking of Newsprint M.K. LETSCHER and F.J. SUTMAN The exact roles which magazine inclusion and filler usage play in the flotation deinking of newsprint have been poorly understood. The objective of this study was to define what increases in brightness could be expected when magazine or filler is added to the newsprint furnish. Another objective was to determine whether the brightness increases were due to filler retention or to improved ink removal across the flotation cell. t was concluded that the fillers in the study did not significantly improve the flotation deinking efficiency of old newsprint. Retention of synthetic silica did improve brightness, but retention of kaolin clays did not. Addition of magazine as an ash source signijkantly reducedjlotation feed brightness and increased brightness across the flotation cell. Flotation accepts brightness with magazine was not significantly different from that of newsprint alone. Brightness increase across the flotation cell had a strong inverse correlation with process yield. Flotation did not selectively fractionate ash into the rejects. NTRODUCTON Ash Loading A common belief throughout the paper industry is that efficient flotation deinking of newsprint (ONP) requires a significant ash loading into the flotation cell. Old magazines (OMG) are currently an inexpensive source for this filler. M.K. Letscher and F.J. Sutman Betz Paperchem nc Baymeadows Way Jacksonville, FL, USA Currently, the plans for most new newsprint flotation deinking plants include incorporation of substantial quantities of old magazines into their furnish. However it is likely that the demand for magazines as furnish will outstrip the available supply in the future. A study by Andover nternational concluded that the availability of OMG could be a problem as early as 1995 [l]. norganic fillers may be used to supplement or replace old magazines as an ash source. The papermakers designing new flotation deinking facilities for ONP are regularly told that they will need to maintain an ash loading of 8-10% on an 0.d. fibre basis into the flotation cell [2,3]. f they cannot maintain this level with magazine addition, they are told that additional filler must be purchased and used. Temanex Consulting nc. reports a 70:30 ratio of 0NP:magazine (pigmented) grades is recommended, since (flotation) deinking efficiency is maximized by the presence of about 8-10qo mineral pigment which acts as a catalyst [4]. The 8-10% filler level is probably based upon an OMG content of 30-40% of total furnish, rather than vice-versa. n turn, an OMG content of 30-40% is exactly what is collected with postconsumer ONP in many western European countries (where flotation deinking gained its initial popularity). Deinking Efficiency The effect of filler content on deinking efficiency is not widely understood, although some studies have been performed. n 1967, Raimondo observed that the percentage of ink removed was higher when using 100% magazine stock than when using 100% newspaper. Flotation was more efficient when paper with a substantial filler content was used; in particular, coated illustrated papers worked well. Raimondo suggested that the attachment of ink to the coating layer, as opposed to the fibres, made the ink more easily removable from these types of papers. He theorized that the coating, rather than the fillers themselves, leads to the improved deinking of illustrated paper P. More recently, Zabala and McCool studied the deinking efficiency of a 100% newsprint furnish using moderate dispersion in the pulper and adding a collector to the flotation cell. They reported that deinking efficiency (as measured by the number and area of ink particles removed) improved with the addition of clay to the pulper. Their work showed that 2% clay was sufficient to achieve the enhanced deinking effect [6]. Schriver et al. studied the effect of filler addition on newsprint deinking with fatty acid and displector deinking chemistry. They concluded that, when using fatty acid chemistry, the addition of a calcined clay filler provided the best brightness increase - followed by talc and zeolite. Using displector chemistry, they again found that calcined filler clays provided the best brightness increase - followed by zeolites. Schriver et al. assumed that filler retention did not significantly affect brightness, but did not investigate this effect [7]. Study Objectives This paper assesses the utility of fillers in ONP-flotation deinking plants. JOURNAL OF PULP AND PAPER SCENCE: VOL. 18 NO. 6 NOVEMBER

2 This laboratory study had three objectives: - Determine whether the increases in deinking efficiency that occur with magazine usage are due to the filler content of the magazine or due to undefined factors. - Determine if inorganic fillers by themselves can enhance ink removal as much as magazine usage at equal pulp ash content. - Determine what portion of the improvement in deinked pulp brightness with filler usage is due to improved deinking efficiency and what portion is due to filler retention. EXPERMENTAL Experimental Design This experiment was designed to investigate the effect of filler type and content on the increase in brightness across the flotation cell. Ash addition levels of 1.8 (background ash level in the newsprint), 5, and 10% were chosen. The sources of ash used were magazine; calcined, water-washed filler clay and No. 1 coating kaolin clays; and a synthetic amorphous precipitated silica. The physical properties of the fillers are listed in Table. The amounts of newsprint and magazine or filler used were adjusted to keep a constant 0.d. solids level in the flotation cell regardless of ash level or furnish mix. Each treatment was replicated three times and the order of the runs was randomized. n the experiment, brightness increases due to ash retention were isolated. A baseline brightness curve was generated for each ash source. This curve illustrated the effect which ash retention had on the brightness of repulped stock if flotation did not occur. Additional baseline ash versus brightness data were generated at the 3 and 7% filler addition levels to improve the precision of the curve. Furnish Six-month old overissue newsprint (process 4-colour offset) and postconsumer magazines (heat-set offset) were obtained. Generous amounts of each furnish were cut into 2.5 x 2.5 cm (1 X l in.) squares. The furnish was stored under controlled temperature and humidity conditions until used. The equilibrium moisture content of the newsprint and magazine was measured by oven drying per TAPP Method T412. Samples of the furnish were ashed per TAPP Method T211 at 575 C. Repulping and Flotation Repulping of the newsprint and magazine blends was performed using a Laboratory Repulping Apparatus. This apparatus consisted of a Waring Blender Jar and Blade Assembly that is powered by a Servodyne motor. This motor TABLE THE PHYSCAL PROPERTES OF FLLERS USED Filler Type Particle Size Brightness (%) Calcined Clay [O] 80 84% <2 pm Water-washed Filler Clay [O] 55-65% <2 &m 84 No. 1 Coating Clay % <2 pm Synthetic Amorphous Precipitated Silica [ 111 mean = 6pm 96.0 minimum provided a controlled rotor revolution rate. The orientation of the rotor was reversed to prevent cutting of the fibres. Flexible heating tape was wrapped around the blender jar. A constant temperature was provided via a thermocouple immersed in the pulp slurry and a temperature controller. Pulping time was controlled with an automatic timer. Pulping conditions were: 5% consistency, 49 C (120"F), 45 min, and 750 rpm. The initial ph in the pulper was adjusted to 9 with sodium hydroxide. Six pounds per ton of 0.d. solids (0.3% by wt.) of a formulated multicomponent surfactant-based flotation aid was added to the pulper prior to furnish addition. For each run, the stock from two pulper batches was combined and diluted to 1% consistency to provide enough stock to run the flotation cell. When filler was used to provide additional ash, the newsprint was repulped as described previously. After pulping, the stock from two pulper batches was combined. A 30% by wt. aqueous slurry of the filler was added to the stock and mixed for 5 min using an American LR41D mixer and a Lightnin 316 SS high shear, dispersing impeller (R-500). The mixture was then diluted to 1 Yo consistency. Flotation of the stock was done using a Wemco Laboratory Flotation Machine. A 300 ml sample of the feed stock was saved for flotation feed retained ash and brightness measurements. The remaining stock was added to the cell and warmed to 49 C (120 F) using an immersion heater. Then the stock was floated for 5 min using full air (inlet valve 100% open) and an agitation rate of 1200 rpm. Froth rejects were skimmed using a rotating paddle and collected. Reject Consistency and Yield Calculations Reject volume was measured using a graduated cylinder. The reject consistency was determined by filtering a measured volume of the rejected liquid through a pre-weighed qualitative filter paper and then weighing the dried pad. Total solids loss was calculated by multiplying the reject consistency by the total reject volume. Percent yield was calculated as follows: solids added to the flotation cell - reject solids solids added to the flotation cell Pulping Brightness and Ash Content Determination Pulp brightness was chosen as the response variable to quantify deinking performance. Brightness is most strongly influenced by the smallest ink particles in the sheet when these particles are present in sufficient numbers. Previous experience with image analysis had shown that the vast majority of ink particles in laboratory repulped newsprint were not visible with the naked eye ( < 50 pm) when this type of chemistry was employed. The small number of ink particles that were >50 pm were the major contributor to visible dirt in the sheet. Visible dirt or speck reduction is an important function of flotation deinking. Yet, the small number of larger particles present do not characterize the majority of the population. n previous work by the present authors, a technique which integrates the light reflectance curve over the entire visible wavelength range was developed. This technique can provide more information on the aesthetic qualities of the sheet than a measurement at a single monochromatic wavelength. This measurement system is not an industry-wide method; the decision was made to present these data in a system which would be familiar to everyone. Pulps pads were formed from 300 ml samples of the flotation feed and accepts using 15 cm qualitative, medium filtration speed filter paper in a Buchner funnel. The pads were pressed and dried according to TAPP Method T218. TAPP brightness of the pads was measured at 457 nm using a Technidyne Brightimeter according to TAPP Method T452. Four replicate brightness measurements were made on the top of each pad. The amount of retained ash in each pulp pad was determined by ashing one half of the pad in a muffle furnace at 575 C per TAPP Method T211. Analysis Technique For each filler and magazine, the replicate baseline brightness measurements were plotted against the retained ash at the 1.8, 3, 5, 7, and 10% added ash levels. Linear regression analysis was used to fit a line to the data. The 95% confidence limits on the regression line were calculated using published procedures [8,9]. The mean flotation feed and accept brightness and retained ash were calcu JOURNAL OF PULP AND PAPER SCENCE: VOL. 18 NO. 6 NOVEMBER 1992

3 lated for newsprint blended with each filler and magazine at the 1.8,5, and 10% added ash levels. The 95% confidence limits on each brightness mean were calculated. For each filler or magazine blended with newsprint, the feed and accept brightness means and their confidence limits were plotted on the baseline graphs at the mean retained ash level. The flotation accepts brightness of each filler type and level was compared to the flotation accepts brightness of the control (no magazine or filler) via a oneway analysis of variance [9]. Differences between means were compared at a 0.05 level for significance. RESULTS Data Summary The experimental results are summarized in Figs Each graph summarizes the data for one ash source. The regression line and 95% confidence limits represent the relationship between filler retention and brightness without flotation deinking. This baseline brightness versus retained ash curve is important because it separates the effects of ash retention on brightness from the effects of flotation on brightness for each ash source. The mean value of each flotation feed and accepts brightness at the background, 5, and 10% ash addition levels is plotted. These values are bracketed by their confidence intervals. The background data are common to all five graphs. Data are summarized (including the statistical significance of the results) in Table 11. Ash Reduction Across Flotation Cell Figures 1-5 show that the reduction in pulp ash content during the flotation process is consistently very small. This is indicated by the minimal decrease in retained ash between the flotation feed and accepts for the different runs. All 11 combinations of filler type and level showed mean ash losses across the flotation cell of < 1% on an 0.d. stock basis. Generally, the filler split evenly with the fibre. Since the flotation cell did not act as a filler fractionator, the role which filler plays in flotation deinking was questioned. Ash Retention on Filter Pads The flotation feed filter pads had lower ash levels than the dosage of filler applied. The retained ash level in the filter pad correlated with the particle size distribution of the filler in most cases. The coating clay had the smallest particle size (90-94% <2 pm) and the poorest ash retention (an average of 42% retention for all runs). Of the kaolin clays, the filler clay had the largest particle size (55-65% < 2 pm) and the highest ash retention (an average of 62% retention for all runs). The magazine had the highest ash retention of all, averaging 78%. This may be because the magazine filler was present as microscopic coating flakes rather than discrete filler particles. Ash retention on a mediumporosity filter paper averaged 56% for the entire experiment. Ash retention on a commercial dewatering or washing device would likely be lower. Clearly, dewatering or washing would be the fillerfractionating stage in a commercial operation. Effects of OMG Addition on Deinking Efficiency OMG addition to the furnish without flotation clearly lowered the baseline brightness (see Fig. 1). This was an unexpected result. OMG s high margin brightness (brightness of unprinted stock) would lead one to expect increased feed brightness with increased substitution level. One plausible explanation is that higher concentrations of different inks exist in the OMG furnish. Addition of OMG significantly increased the brightness difference across the flotation cell. This is indicated by the wide separation of the confidence intervals for the mean flotation feed and accept brightnesses at the 5 and 10% added ash levels. However, due to the lowering of the baseline brightness, there was no significant difference between the final brightness (flotation accepts) of the background and when magazine was the filler source. OMG did not improve flotation deinking efficiency of newsprint based on flotation accepts brightness. Effects of Silica Filler Addition on Deinking Efficiency The addition of silica filler increased the baseline brightness (see Fig. 2). Filler addition at the 10% level significantly improved the final brightness over the background level. The overlap of the confidence intervals for the mean flotation feed and accept brightnesses clearly indicates that the improved brightness is due to filler retention - not improved deinking efficiency. Effects of Kaolin Clay Addition on Deinking Efficiency The kaolin clays tested (calcined, filler, and coating clay) did not significantly affect baseline brightness. The JOURNAL OF PULP AND PAPER SCENCE: VOL. 18 NO. 6 NOVEMBER 1992 J227

4 -Background ~ -0, 10% Added Ash 52 - Flotation Accepts 5% Added Ash 51 - Background Flotation Accepts Flotation 50 i/ Accepts 49 - io% Added Ash ~ ~ Background 45 Flotation 44 Feed 5% Added Ash --.- ~. 43 1' Baseline Ash Content' i Fig. 1. Effect of ash from magazine on flotation deinking efficiency , Fig. 2. Effect of ash from silica on flotation deinking efficiency ~ Background i T i o n Accepts 10% Added Ash - 5% Added Ash 1, Flotation Accepts,Flotation Accepts u) 43.: lo ~. u) u) ~.. --~~..~~.~...~~...~~~.~~~.~~~---.~~... a 48 a, % Added Ash C c *-.- m!l --.. L m ~ "\5% Added Ash -. U- - Baseline Ash Content ' Baseline Ash Content 40-, 1, Fig. 3. Effect of ash from calcined clay on flotation deinking efficiency. Fig. 4. Effect of ash from filler clay on flotation deinking efficiency \ ~ a''.\ C r 47 U L 46.. _- Flotation Accepts Fig. 5. Effect of ash from coating clay on flotation deinking efficiency Yield (%) Fig. 6. Effect of flotation cell yield on brightness gain of all filler sources JOURNAL OF PULP AND PAPER SCENCE: VOL. 18 NO. 6 NOVEMBER 1992

5 2 B, D slope of the ash versus brightness regression line (with no flotation) remained flat in all three cases (see Figs. 3-5). Normally, one Would expect clay addition and retention to improve newsprint stock brightness. Before flotation, stock has a relatively high concentration of ink particles which should be removed before papermaking. One plausible explanation for the unchanging brightness levels is that the darkening effect of the ink parany brightening effect significantly improved baseline brightness whereas the kaolin clays did not. This may be due to silica s very high brightness (96 minimum) as compared to the brightness of the various clay grades (80-88). Calcined clay (see Fig. 3) significantly increased brightness across the flo- 10% addition level. on accepts brightness y different than that of the background data. Filler clay (see Fig. 4) significantly increased brightness across the flotation cell at the 5% addition level. The flotation accepts brightness at the 5% addition level was significantly higher than that of the background. The same effects were not observed at the 10% addition level. The behaviour at the 5% addition level may be an experimental anomaly, since it was not repeated at the higher addition rate. Coating clay (see Fig. 5) significantly dropped the flotation accepts brightness at the 5% addition level. This again could be an experimental anomaly. The behaviour was not repeated at the loolo addition level. Addition at the 10% level significantly increased brightness across the flotation cell. The flotation accepts brightness at 10% was not signficantly different than the background level. Correlation between Yield and Brightness A strong inverse correlation between yield and brightness increase across the cell was observed. Figure 6 illustrates that the brightness gain increased as the process yield decreased. DSCUSSON Effect of Particle Size on Flotation Efficiency The above results indicate that fillers do not play a significant role in improving the flotation deinking of newsprint (as measured by brightness). The results also show that flotation did not selectively fractionate filler away from the fibre. The kaolin clays used in the study all had median particle sizes of <2 pm [lo]. The silica filler used in the study had a mean particle size of 6 pm [ll]. Work by Mattingley states that a particle that is <5 pm is undesirable for flotation deinking [12]. A paper by Zabala and McCool also showed that flotation deinking is increasingly ineffective in remov- ing particles that are <5 pm. Small particle fractions are much more efficiently removed by washing [6]. A study by Marchildon et al. on the flotation deinking of newsprint defined all particles <SO pm as a small fraction. They indicated that, while flotation could remove about 50% of these particles, it was effective in removing 95% of particles > 140 pm [13]. Based upon these results, and the particle size of the fillers tested in this experiment, flotation probably should not selectively remove a large fraction of the filler from the process. f filler and ink particles formed larger agglomerates during the collection process, a significant removal of filler with the rejects might occur. The experimental results in this study do not indicate this to be the case. f filler was not selectively fractionated into the froth rejects during flotation, it is difficult to understand how it could be responsible for increased ink removal. A study by Liphard et al. showed that filler removal and ink removal during flotation were not easily optimized during the same flotation step. However, filler removal could be enhanced through the use of anionic surfactants [14]. Foam Stability The use of OMG in the furnish consistently contributed to foam stability. The use of fillers by themselves did not. The physical form of the filler in the repulped OMG may be different than in a filler that is simply added to a slurry. The microscopic coating flakes in OMG could possibly contribute to stability whereas discrete pigment particles would not. f filler content does not encourage foam stability, a component in the OMG other than the fillers may cause the beneficial effect. There are many other components of coating colour other than filler. Table 111 lists some of the more common ingredients in coating formulations [15]. The nature and quantity of latex and starch binders in coatings make them likely candidates to be foam builders and stabilizers. However, identification of the possible foam stabilizing component(s) and how they function was beyond the scope of this study. Other Benefits of Magazine Magazine usage in an ONP-tonewsprint deinking operation has other substantial benefits which must not be overlooked. Virgin newsprint typically has a low percentage of long fibre in the sheet network (due to the very high mechanical pulp content). Recycling degrades the few long fibres present, damaging tensile strength. Old magazines (No. 5 grade LWC) typically will have at least 50% bleached kraft fibre as basestock furnish. The inclusion of OMG in the furnish can give a valuable boost to web tensile strength where required. Flotation Chemistry There are many different systems of deinking chemistry and equipment available. We have not attempted to extrapolate these findings to all systems. The flotation aid used in this study is a multi-component formulation of synthetic surfactants. t is designed to aid in the separation of ink particles from fibres in the pulper and enhance their subsequent attachment to air bubbles in the flotation cell. The chemistry employed is similar to displector chemistry but provides stronger collecting than dispersing properties. Traditionally, displectors are alkoxylated fatty acid derivatives. They are designed to add dispersing properties to the collecting properties of fatty acid. Our experience is that to expect one chemical formulation to both disperse and collect is a compromise situation. The flotation aid used in this experiment differs from fatty acids in that an ONP/OMG pulper may be run at a ph of 9 with excellent results. A ph of 9 provides adequate fibre swelling for ink Effect of Filler Source on Frothing The runs containing OMG consistently exhibited moderately stable froth in the rejects. All of the runs using filler slurries and the background control runs had very unstable froth but did produce rejects. The magazine rejects were generally higher in volume, lower in consistency, and higher in solids loss than the rejects of the filler or background runs. 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6 removal and defiberizing. The ph levels of commonly employed with other chemistries are not required. At these ph levels, peroxide bleach liquor (peroxide, silicate, and chelant) must be added to minimize mechanical fibre yellowing. Repulping at ph 9 avoids fibre yellowing and the addition of bleach liquor is not necessary. Bleaching chemicals are saved until after ink removal, where they effectively increase brightness. The use of synthetic surfactants also eliminates the requirement for calcium chloride (as a soap insolubilizer). CONCLUSONS Retention of kaolin clay fillers did not significantly improve the brightness of the ONP stock. None of the kaolin clay fillers consistently improved flotation accepts brightness. Retention of the synthetic silica filer did significantly improve the brightness of the ONP stock. A significant increase in flotation accepts brightness with silica filler at the 10% addition level was due to filler retention, not improved deinking efficiency. Addition of OMG to the ONP stock significantly reduced flotation feed brightness. The brightness increase across the cell significantly improved with increasing OMG use. Flotation accepts brightnesses with OMGONP were not significantly higher than those obtained with ONP alone. Based on flotation accepts brightness, OMG addition did not improve deinking efficiency. OMG usage does have other significant benefits such as stabilizing foam and improving strength. None of the individual fillers stabilized foam. ndependent of filler source, brightness increase across the flotation cell had a strong inverse correlation with process yield. The flotation cell did not selectively fractionate ash into the rejects. The ash level from the flotation feed to accepts dropped only slightly. The major ftfer loss from the pulp was caused by drainage of the water from the fibres through filter paper. ACKNOWLEDGEMENTS The authors wish to thank Betz Paper Chem, nc. for its support of this work. We also thank J.M. Huber Corp. and Englehard Corp. for contributing REFERENCES 1. Paper ndustry Demand For Old Magazines will Quadruple By 2000, Paper Recycler 2(2):10 (1991). 2. SCHRVER, K.E., Mill Chemistry Must Be Considered Before Making Deink Line Decision, Pulp and Paper 64(3):76 (1990). 3. McCOOL, M.A. Personal Communication. Beloit Corporation ONDES, G.N., Trip Report From European Deinked Newsprint Mill Visits, Temanex Consulting Report. 5. RAMONDO, F.E., Deinking of Printed Wastepapers by Flotation, Tappi J. 50(9):69A (1967). 6. ZABALA, J.M. and McCOOL, M.A., Deinking at Papelera Peninsular and the Philosophy of Deinking System Design, Tappi J. 71(8):62 (1988). 7. SCHRVER, K.E. et al., The Function of Clay in Flotation Deinking, Proc. 9. FREESE F., in Elementary Statistical Methods for Foresters, Ag. Handbook 317, Corvallis, 0R:OSU Bookstores nc., Corvallis, OR, pp , (1980). 10. Englehard Corp., Edison, NJ, Product Specification Brochure (1991). 1. J.M. Huber Corp., Havre DeGrace, MD, Product Specification Brochure (1991). 12. MATTNGLEY, J.T., Residual Chemical Effects in Secondary Fibre Operations, Tappi J. 67(6):74 (1984). 13. MARCHLDON, L. et al., The nfluence of Particulate Size in the Flotation Deinking of Newsprint, Preprints 74th Ann. Mtg., Tech. Sect., CPPA, pp. B61-B66 (1988). 14. LPHARD M. et al., nterfacial Studies and Application Tests on the Flotation of Printing nks and Fillers, Proc. TAPP Pulping Conf., Bk 2:965 (1990) MacDONALD, R.G., Ed., Pulp and Paper Manufacture, 2nd ed., New York, McGraw-Hill, 2:497 (1969) JOURNAL OF PULP AND PAPER SCENCE VOL. 18 NO. 6 NOVEMBER 1992