(Received March 4, 1992) CHANGES IN ZETA-POTENTIALS OF AMORPHOUS CELLULOSE PARTICLES WITH CHITOSAN SALTS

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1 (121) Vol. 48, No. 11(1992) 655 Transaction (Received March 4, 1992) CHANGES IN ZETA-POTENTIALS OF AMORPHOUS CELLULOSE PARTICLES WITH CHITOSAN SALTS Akira Isogai, Makoto Hasegawa, Fumihiko Onabe, and Makoto Usuda Faculty of Agriculture, The University of Tokyo, Bunkyo-ku, Tokyo, 113 Japan salts to suspensions were studied, where amorphous partcles were prepared from microcrystalline cellulose powder, linter cellulose, and softwood and hardwood bleached kraft pulps (SBKP and IMP, respectively). Chitosan salts with 75 and 85% degrees of deacetylation and with Cl- and AcO- as counter ions addition of chitosan salt lower than 0.1% on dry weight of amorphous samples to the suspensions, although HBKP reouired the addition of chitosan more than 0.2% in some cases. The effects of degrees of pies were stable within 1 day after the addition of chitosan salts. 1. INTRODUCTION Cationic polymers have been used in wet-end of papermaking primarily as retention aids of sizing chemicals, fillers, fines, and other paper components, which have negative charges in suspensions. As to the retention mechanisms of paper components with cationic polymers, the bridging model and / or the patch model have been reported, and these mechanisms are different from those for controls of surface charges of paper components by inorganic compounds such as aluminium sulfate Cl). In the practical papermaking process, the retention controls with cationic polymers have to be well-balanced with flocculation and formation of paper sheet under dynamic papermaking conditions [2). Measurements of ~- Potentials of paper components in the presence cationic polymers in suspensions, however, often indicate suitable conditions for the retention controls in the practical papermaking of process. It has been reported that the best running takes place at the isoelectric point of paper components. Here the repulsion forces between the components are nonexistent, so that there is unimpeded approach of particles and potential measurements often provide helpful suggestion for wet-end controls, as long as their limitations are noticed. Cationic polyacrylamide, polyaminepolyamide-epychlorohydrin, polyethylene imine, polydiallyl dimethylammonium chloride, trimethylglycol chitosan, cationic starch, and others have been reported as cationic components. Cationic polymers having the higher molecular weight with the higher cation densities seem to be more effective for the control of surface charges of paper components, although some exceptions were reported (3-11). In the practical papermaking process, cationic polyacrylamide, polyaminepolyamide-epychlorohydrin, and cationic starch have been widely used as cationic polyelectrolytes. Although synthetic polymers with cationic groups have indeed high productivity as commercial products and high runnability as retention aids in the practical papermaking process, the use of bio-degradable cationic polymers may be significant in future from the environmental aspects. Cationic starches are prepared from starch with either diethyl-

2 aminoethyl chloride or 3-ehloro-2-hydroxypropyltrimethylammonium chloride under alkaline conditions (12). Degrees of substitution (DS) of these cationic groups are generally lower than Chitosan is a bio-degradable cationic polysaccharide, and is generally prepared from chitin by deacetylation under alkaline conditions. Chitosan has primary amine at C2 of anhydroglucosamine residue, and thus compared with cationic starches, chitosan has higher cation density and has more rigid chain- Allan et al. reported that chitosan had the positive effects on the wet and dry strength of paper sheets, where chitosan was added to sheets as a wet-end additive or was sprayed on the surface of sheets (13). Laleg and Pikulik also showed that the addition of chitosan to wet-end at ph of 10 brought about the increase in mechanical properties of wet web, dry paper, and re-wetted paper [14). In these cases, amine groups in chitosan may play a significant role in the increase in physical properties of paper, although the mechanisms for these effects have not been clarified yet. On the other hand, the utilization of amine groups in chitosan seems to be one of the most effective directions for functionalization of chitosan, i. e. the use of chitosan as cationic polyelectrolytes for wetend of papermaking. amorphous cellulose or pulp particles in the presence of aluminium sulfate in suspensions were reported in terms of carboxyl content of cellulose or pulp samples, drying methods of amorphous particles, stability or pulp samples and the amounts of aluminium sulfate in suspensions were obtained, and the carboxyl con- titles. In this study, the interactions between amorphous regions of cellulose or pulp samples and chitosan-salt in suspensions were examined in terms of carboxyl content of samples, degrees of deacetylation of chitosan- counter ions of cationic chitosan, stability 2. EXPERIMENTAL 2.1 Samples Microcrystalline cellulose powder (Avicel, Asahi Chemicals Co. Ltd., DPv = 200), linter cellulose, and softwood and hardwood bleached kraft pulps (SBKP and HBKP, respectively) were commercially available, and were used as original cellulose samples. Carboxyl contents were 0.08, 1.48, 3.35, and 6.50 meq/ 100 g for microcrystalline cellulose powder, linter cellulose, SBKP, and HBKP, respectively [15). Amorphous samples were prepared from the above mentioned cellulose and pulp samples according to the previous paper, and were used as solvent-exchanged and dried particles (15). Two chitosan samples were commercially available (CLH and PSH, Yaizu Suisan Co. Ltd.), and were used after purification by dissolution in dilute acetic acid followed by regeneration with dilute NaOH solutions. Degrees of deacetylation of chitosan samples were measured by 'H-NMR method, and degrees of polymerization were determined by gel permeation chromatography of phenyl carbanirates of chitosans (Table 1) (16). Chitosan-acetic acid salt was prepared by dissolution of chitosan in dilute acetic acid, followed by regeneration with acetone. Chitosan-HCI salt was prepared by dissolution of chitosan in dilute hydrochloric acid with freezing and defrosting treatments, followed by regeneration with acetone. These chitosan salts were thoroughly washed with acetone, and were dried in vacuo. 2.2 Measurement of Zeta-potentials A sample (50 mg by dry weight) was suspended in 50 ml of distilled water, and was left standing for one day for sufficient swelling. Then a designed amount of chitosan-salt solutions was added to the Potentials of the particles were measured at 10 min and 1 day after the addition of the chitosan solution, using a micro-electrophoresis apparatus (Mark 11, Rank Brothers Co.) with a flat cell and a CD camera. Mobilities were obtained from average migration veloc. potentials were calculated from the mobilities, according to the Helmholtz-Smoluchowski's equation (17).

3 (123) Vol. 48. No. 11(1992) 657 Fig. 1. of amorphous particles with chitosan sample 1, in Table 1, in suspensions. Measured at were prepared from microcrystalline cellulose pow chitosan sample 2, in Table 1, in suspensions. Measured at were oreoared from microcrystalline cellulose pow- weight of amorphous samples. Amounts of the chito with an increase in carboxyl content of the original potentials was observed for all samples by the 1% addition of the chitosan salt. Standing of the suspensions for one day at room potentials between 10 min and 1 day after the addition were about 5-10 mv (Fig. 2). The ph values were for all systems, and were unchanged at least within 1 day after the addition of the chitosan salt. chitosan sample 1, in Table 1, in suspensions. Measurea at l day after the addition of chitosan. Amorphous particles with chitosan-acoh salt in the suspensions, where were prepared from microcrystalline cellulose powder 85% deacetylated chitosan was used. The amount of almost equal to those obtained in Fig. 1. In these those in Fig. 1, especially for % addition of and pulp samples with chitosan-acoh salt in suspensions. This chitosan had 75% deacetylation. All amor- changed for 1 day after the addition of this chitosan sample, as shown in Fig. 4. The ph range was also constant within the range of tion of chitosan-acoh salt lower than 0.1% on dry

4 chitosan sample 2, in Table 1, in suspensions. Measured at 1 day after the addition of chitosan. Amorphous particles were nrenared from microcrvstalline cellulose powder chitosan sample 3, in Table 1, in suspensions. Measured at 1 day after the addition of chitosan. Amorphous particles were prepared from microcrystalline cellulose powder ing of the suspensions for 1 day after the addition of the chitosan-hci salt were larger for the amorphous samples with the higher carboxyl content (Fig. 6). The ph values decreased from 6.0 to 5.3 with an increase in chitosan-hci salt added to suspension. 4. DISCUSSION The effects of degrees of deacetylation, cation con- of amorphous cellulose and pulp samples were studied. The amounts of chitosan salts, which were required lower than 0.1% on dry weight of sample 3, in Table 1, in suspensions. Measured at samples prepared from microcrystalline cellulose powder, linter cellulose, and SBKP, for all chitosan salt samples were prepared from microcrystalline cellulose pow- used. These amounts increased with an increase in carboxyl content of cellulose and pulp samples. The with chitosan-hci salt in suspensions. This chitosan tween 10 min and 1 day after the addition of the chitosan had 85% deacetylation. These amophous samples ex- salts were smaller than those in the case of the addition of aluminium sulfate, as reported previously almost equal to those in Figs. 1 and 3. The amor pies were nearly unchanged within I day after the of about 20 mv negative to those observed in Figs. 1 addition of chitosan salts to pulp suspension. and 3, for the % chitosan addition. The As shown in Table 1, the cation content of chito- salt was san-hci higher than those of chitosan-

5 (125) Vol. 48, No. 11(1992) 659 Table 1 Chitosan Salts Used in This Study components in wet-end of papermaking. a) Cation content was calculated from degrees of deacetylation. AcOH salts. Although the amounts of chitosan-hci re- phous sample prepared from HBKP were larger than those in the case of chitosan-acoh. Probably the affinity of the chitosan salts to amorphous cellulose or hemicellulose surface is different between chitosan- AcOH and chitosan-hci salts. Little difference between 75 and 85% deacetylated chitosan samples was observed for the amounts of chitosan-acoh salts re- Matin-Lof, TappiJ, 57(12), 94 (1974) 7. E. E. Moore, TappiJ, 59 (6), 120 (1976) 1% addition of 75% deacetylated chitosan-acoh salt were about twice as much as those for 85% deacetylated chitosan-acoh salt. Since molecular weight of these two chitosan samples were almost equal to each other, as shown in Table 1, either conformations of chitosan molecules or hydrophilic interactions between solid cellulose surface and chitosan salt molecules may be different between the 75 and 85% deacetylated chitosan samples. Compared with synthetic cationic polymers reported as retention aids, slightly large amounts of chito- Making", Ed. by Fundamental Research Commit- tee, British Paper & Board Industry Federation, of cellulose and pulp samples, although chitosan salts had higher cation content than synthetic polymers. Since chitosan has a primary amine, its cationic property appears only when the protonation occurs at the amine group. Thus, the cationic property can not be expected on chitosan under alkaline conditions, where most of chitosan is precipitated. Thus, conversion of the primary amine to some quaternary amine groups may extend the possibility of the use of chitosan as a bio-degradable retention aid of paper ACKNOWLEDGEMENT This research was supported by a Grant-in-Aid for Science Research (No and ) from the Ministry of Education, Japan. The authors thank Yaizu Suisan Co. Ltd. for providing chitosan samples. REFERENCES 1. J. E. Unbehend and K. W. Britt, "Pulp and Paper", J. P. Casey Ed., Vol. 3, p (1981) 2. K. W. Britt, Tappi J., 56 (3), 83 (1973) 3. E. Strazdins, TappiJ.. 57(12), 76 (1974). 4. K. W. Britt and J. E. Unbehend, TappiJ, 57(12), 81 (1974) 5. R. W. Davison, Tappi J. 57(12), 85 (1974) 6. T. Lindstrom, C. Soremark, C. Heinegard, and S. 8. F. Onabe, J. Appi. Polym. Sci.. 23, 2909 (1979) 9. A. M. Springer and T. E. Taggart, Tappi J., 69 (5), 116 (1986) 10. L. Wagberg and L. Odberg, Nordic Pulp & Paper, 4, 135 (1989) 11. P. H. Brouwer, Tappi J.. 74 (1), 170 (1.991) 12. S. Katsura, A. Isogai, F. Onabe, and M. Usuda, Carbohvdr. Polvrn., 18, 283 (1992) 13. G. G. Allan, J. R. Fox, G. D. Crosby, and K. V. Sarkanen, "Fiber-Ifater Interactions in Paper- London, p. 765 (1977) 14. M. Laleg and I. I. Pikulik, Nordic Pulp & Paper, 6,99(1991) 15. A. Isogai, F. Onabe, and M. Usuda, Sen'i Gakkaishi, 48, 649 (1992) 16. M. Hasegawa, unpublished methods 17. J. T. G. Overbeek, "Fiber-11 ater Interactions in Paper-Making'", Ed. by Fundamental Research Committee, British Paper & Board Industry Federation, London, p. 85 (1977)