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Cationic Starches of High Degree of Functionalization: 12. Modification of Cellulose Fibers toward High Filler Technology in Papermaking Svetlana Bratskaya,*,† Simona Schwarz,‡ Gudrun Petzold,‡ Tim Liebert,§ and Thomas Heinze§ Institute of Chemistry, Far East Department of Russian Academy of Sciences, 159, AVe. 100-letiya VladiVostoka, VladiVostok 690022, Russia, Leibniz Institute of Polymer Research Dresden, Hohe Strasse 6, D-01069 Dresden, Germany, and Center of Excellence for Polysaccharide Research, Friedrich Schiller UniVersity of Jena, Humboldtstrasse 10, D-07743 Jena, Germany
Modification of cellulose fibers via adsorption of highly functionalized 2-hydroxy-3-trimethylammonium propyl chloride starch (HPMA starch) with a degree of substitution (DS) in the range from 0.25 to 1.54 was investigated by electrokinetic measurements and filler retention tests. It was found that the amount of cationic HPMA starch adsorbed at the isotherm plateaus depends on two parameters: the DS of the starch derivative and, more remarkably, the amylose/amylopectin ratio. All studied HPMA starches allow significant improvement of kaolin particle retention in comparison to untreated fibers and fibers modified with low-substituted commercial starch. We suggest that, because of the local overcharging of the cellulose surface through the adsorption of starch macromolecules, the filler retention capacity is enhanced even at low and moderate degrees of coverage when the surface has a net-negative charge. Taking into account the efficiency and cost of starch cationization, the optimum DS of the HPMA starch for cellulose modification in papermaking was found to be in the range 0.6-0.7, where a degree of filler loading of 500 mg/g can be reached at a level of HPMA starch addition of 0.5-0.6%. Introduction Fillers, primarily, calcium carbonate and kaolin, are widely used in papermaking to improve the smoothness, light-scattering ability, print gloss, and ink receptivity of paper. Over the past few decades, the degree of filler loading has shown a sustained tendency to increase, primarily for economic reasons. Fillers are substantially cheaper than cellulose fibers, and their price is relatively stable, in contrast to the continuously fluctuating price of wood pulp.1 However, the increase in the degree of filler loading, which now reaches a level of 30-35% for some types of paper, has a negative effect on paper strength by weakening the fiber-to-fiber binding. The application of cationic starches to enhance paper strength2-4 and filler retention5 is a common practice in papermaking, which, nevertheless, has its limitations and disadvantages. Most of the commercially available cationic starches used as binding and wet-strength agents have a degree of substitution (DS) less than 0.2.6 This level of cationization can be insufficient to provide a high affinity between starch and the substrate or even to overcompensate the natural netnegative charge of potato starch resulting from the presence of phosphate groups.7 The retention of commonly used lowsubstituted cationic starches on cellulose fibers is usually not higher than 80%, which results in a loss of starch-based agents with wastewater in the coating process. This not only increases the production costs but also complicates water recycling, which has become a universal procedure in papermaking. Moreover, low-substituted starches are not very efficient for binding anionic trash,8 which has a detrimental effect on paper quality. Although the addition of significant amounts of low-substituted cationic starches to pulp allows moderate levels of filler loadings to be * To whom correspondence should be addressed. E-mail: sbratska@ ich.dvo.ru. Tel./Fax: +7(4232)313-583. † Russian Academy of Sciences. ‡ Leibniz Institute of Polymer Research Dresden. § Friedrich Schiller University of Jena.
attained, other chemicals and technologies, such as polyelectrolyte-microparticle retention systems9 or dual-polyelectrolyte systems,10 should also be applied to attain filler loading values of 300-350 mg per 1 g of pulp desirable for the modern papermaking industry. We have previously shown11 that highly cationic starches with a DS in the range from 0.25 to 1.54 are efficient flocculants for kaolin dispersions and can potentially be used in coating processes in the papermaking industry. In this article, we report data on the adsorption behavior of these highly substituted starches on softwood cellulose fibers and the effect of surface modification on filler retention. We show that the application of these starch products allows a marked increase in the degree of filler loading at addition levels significantly lower than those used for conventional cationic starches. Experimental Section Materials. (i) Cellulose. Never dried, bleached long cellulose fibers from Chili pinewood were provided by the paper institute PTS Heidenau (Heidenau, Germany). The beating degree of the fibers was 22 SR. (ii) Kaolin. Kaolin (USP-type, Sigma) was used in all experiments as supplied. Kaolin dispersions with a solid content of 10 g‚L-1 in Tris [tris(hydroxymethyl)aminomethane] HCl buffer solution (pH ) 8 ( 0.1) were prepared by ultrasonic treatment for 15 min followed by vigorous stirring for 1 h. The average size of the kaolin particles in the dispersions (Tris buffer, pH ) 8) was 610 nm as determined by means of a flowtype histogram analyzer (FPIA-2100, Sysmex, Japan) based on the microscopy principle. (iii) Cationic Starches. Cationic potato starch derivatives (2hydroxy-3-trimethylammonium propyl chloride starch, HPMA starch, Figure 1a) with degrees of substitution (DS) ranging from 0.25 to 1.54, corresponding to between 25 and 154 quaternary ammonium groups per 100 glucose units, were synthesized according to the procedures described elsewhere,12 using potato
10.1021/ie060135z CCC: $33.50 © 2006 American Chemical Society Published on Web 09/30/2006
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Figure 1. Chemical structures of (a) 2-hydroxy-3-trimethylammonium propyl chloride starch (HPMA starch) and (b) Praestol 644BC.
starch with an amylose content of 28% and a molecular weight of 40 × 106 g‚mol-1 (Emsland Sta¨rke GmbH, Emlichheim, Germany) as the starting material. Cationic wheat starch (amylose content 25%, molecular weight 35 × 106 g‚mol-1) and amylose-rich Hylon VII starch (amylose content 70%, molecular weight 25 × 106 g‚mol-1), both with DS ) 0.6, were synthesized according to the same procedure from wheat starch (Fluka) and Hylon VII starch (National Starch and Chemical Ltd., Manchester, U.K.), respectively. DS values of the derivatives were determined by nitrogen and chlorine elemental analysis, as described elsewhere.7 Commercial cationic potato starch with a DS of about 0.05 was a gift from Su¨dsta¨rke GmbH, Schrobenhausen, Germany. Stock starch solutions with a concentration of 5 g‚L-1 were prepared by dissolving appropriate amounts of starch with stirring for 1 h at 60 °C and then for 24 h at room temperature. (iv) Other Chemicals. Cationic polyacrylamide copolymer Praestol 644BC (Figure 1b) with 60 cationic groups per 100 repeat units and a molecular weight of about 6 × 106 g‚mol-1 was supplied by Degussa, Krefeld, Germany. Other chemicals purchased from Sigma-Aldrich were of analytical grade. Deionized water with a conductivity of 0.6 is required only if the desired degree of filler loading is above 50%. At the highest level of filler content used by today’s papermaking industry (35%), all of the studied cationic starches with DS ) 0.25-1.54 are applicable. However, moderately substituted derivatives (DS ) 0.6-0.7) appear to be more beneficial, because the linear correlation between DS and efficiency holds up to this limit and the extra costs for cationic starch production can still be balanced by the substantially reduced amounts of starch required for good filler retention. Acknowledgment The authors thank the Paper Institute PTS Heidenau for providing cellulose fibers. Literature Cited (1) Baker, C. Latest techniques for papermaking fillers. Pub. Pira Int. 2005 (cited at http://pira.atalink.co.uk/articles/pulp/150).
(2) Brown, G. H. Cationic starch improves strength of groundwood papers. Paper Trade J. 1969, 35. (3) Howard, R. C.; Jowsay, C. J. Effect of Cationic Starch on the Tensile Strength of Paper. J. Pulp Paper Sci. 1989, 15 (6), J225. (4) Roberts, J. C.; Au, C. O.; Clay, G. A.; Lough, C. A study of the effect of cationic starch on dry strength and formation using C14 labeling. J. Pulp Paper Sci. 1987, 13 (1), 1. (5) Marton, J. The role of surface chemistry in fines-cationic starch interactions. Tappi J. 1986, 63 (4), 87. (6) Kweon, M. R.; Sosulski, F. W.; Bhirud, P. R. Cationization of waxy and normal corn and barley starches by an aqueous alcohol process. Starch/ Stark. 1997, 49, 59. (7) van de Steeg, H. G. M.; de Keizer, A.; Cohen Stuart, M. A.; Bijsterbosch, B. H. Adsorption of cationic potato starch on microcrystalline cellulose. Colloids Surf. A 1993, 70, 91. (8) Bobacka, V.; Eklund, D. The influence of charge density of cationic starch on dissolved and colloidal material from peroxide bleached thermomechanical pulp. Colloids Surf. A 1999, 152, 285. (9) Wagberg, L.; Bjo¨rklund, M.; Asell, I.; Swerin, A. On the mechanism of flocculation by microparticle retention-aid systems. Tappi J. 1996, 79, 157. (10) Petzold, G. Dual-Addition Schemes. In Colloid-Polymer Interactions: From Fundamentals to Practice; Farinato, R. S., Dubin, P. L., Eds.; Wiley-Interscience: New York, 1999. (11) Bratskaya, S.; Schwarz, S.; Liebert, T.; Heinze, T. Starch derivatives of high degree of functionalization: 10. Flocculation of kaolin dispersions. Colloids Surf. A 2005, 254, 75. (12) Haack, V.; Heinze, T.; Oelmeyer, G.; Kulicke, W.-M. Starch derivatives of high degree of functionalization: 8. Synthesis and flocculation behavior of cationic starch polyelectrolytes. Macromol. Mater. Eng. 2002, 287, 495. (13) van de Steeg, H. G. M.; de Keizer, A.; Cohen Stuart, M. A., Bijsterbosch, B. H. Adsorption of cationic amylopectin on microcrystalline cellulose. Colloids Surf. A 1993, 70, 77. (14) Hedborg, F.; Lindstro¨m, T. Adsorption of cationic starch on bleached softwood cellulosic fibers. Nord. Pulp Paper Res. J. 1993, 2, 258. (15) Shirazi, M.; van de Ven, T. G. M.; Garnier, G. Adsorption of Modified Starches on Pulp Fibers. Langmuir 2003, 19, 10835. (16) Nedelcheva, M. P., Stoilkov G. V. Cationic starch adsorption by cellulose I. J. Colloid Interface Sci. 1978, 66 (3), 475. (17) Merta, J.; Garamus, V. M.; Kuklin, A. I.; Willumeit, R.; Stenius, P. Determination of the Structure of Complexes Formed by a Cationic Polymer and Mixed Anionic Surfactants by Small-Angle Neutron Scattering. Langmuir 2000, 16, 10061. (18) Winter, L.; Wågberg, L.; O ¨ dberg, L.; Lindstro¨m, T. Polyelectrolyte Adsorbed on the Surface of Cellulosic Materials. J. Colloid Interface Sci. 1986, 111, 537. (19) Eklund, D.; Lindstrom, T. Paper Chemistry. An Introduction; DT Paper Science Publications: Grankulla, Finland, 1991. (20) Wågberg, L.; Bjo¨rklund, M. Adsorption of cationic potato starch on cellulose fibers. Nord. Pulp Paper Res. J. 1993, 4, 399. (21) Callaghan, P. T.; Lelievre, J. The size and shape of amylopectin: A study using pulsed-field gradient nuclear magnetic resonance. Biopolymers 1985, 24, 441.
ReceiVed for reView February 1, 2006 ReVised manuscript receiVed June 20, 2006 Accepted August 26, 2006 IE060135Z
