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Preparation of porous spherical cellulose
Reactive Polymers, 1 (1983) 145-147
145
Elsevier Science Publishers B.V., Amsterdam - Printed in The Netherlands
S H O R T COMMUNICATION
PREPARATION OF POROUS SPHERICAL CELLULOSE J. STAMBERG and J. PESKA
Institute of Macromolecular Chemistry, Czechoslovak Academy of Sciences, 162 06 Prague 6 (Czechoslovakia) (Received June 3, 1982; accepted November 3, 1982)
also to some modern intensively studied solvents [3-5].
INTRODUCTION Cellulose is widely used in the synthesis of functional polymers (especiallS, absorbents), ion exchangers, chelating sorbents, packing for chromatographic columns, carriers of biological functions, and so on. In most cases, optimal results cannot be obtained by using native or other available physical forms of cellulose. Synthetic functional polymers are available in a regular bead form which has proved suitable both because of easy handling and use in columns and due to its effectiveness in application, easier reproducibility and interpretation of results. Functional polymers based on cellulose can now also be prepared in bead form [1,2]. In order to prepare spherical particles, cellulose or its derivative is transformed into the liquid state; the latter is divided into drops through ejection or dispersion in a solvent immiscible with water, subjected to liquidsolid transition and then to final treatment. The procedure used in the preparation of bead cellulose resembles suspension polymerization; similarly, solidification is the sensitive point of the process. Bead shaping of cellulose has been described for various solutions of cellulose and its derivatives and for molten cellulose acetate [2]. Even though most attention has been devoted to the usual solvent systems, the results obtained may be applied 0167-6989/83/$03.00
R E S U L T S AND D I S C U S S I O N A simple and reliable procedure for the preparation of bead porous cellulose has been developed, based on the thermal sol-gel transition (TSGT process). In this procedure, maximum attention is paid to requirements analogous with those of suspension polymerization [6]. An aqueous solution of cellulose xanthogenate (technical viscose) is dispersed in a solvent immiscible with water, and the sol-gel transition is brought about by raising the temperature above 90°C [7]. The rise in temperature accelerates the splitting of ionic xanthate groups until a sudden change in solubility, corresponding to phase transition, takes place. At the same time, physical crosslinks are formed in unsubstituted sections of polymer chains due to cellulose being organized into microcrystalline domains linked with hydrogen bonds. The sol-gel transition occurs simultaneously throughout the droplet, so that skinformation on the external particle surface is reduced. Skin formation occurs more readily in such procedures in which the sol-gel transition is brought about by adding a precipitant to the dispersing medium. Particle size is controlled by adding
© 1983 Elsevier Science Publishers B.V.
146
Fig. 1. Micrograph of bead cellulose (mean size 300 /tm).
surfactants to the stirred mixture, constituting an easier route than a change in the stirring conditions. This is the difference between the preparation of bead cellulose and suspension polymerization; the reasons should be sought in the viscosity of the dispersed phase. The regeneration of cellulose in solidified bead particles may be completed by using acid or alkaline solutions. The latter are more advantageous owing to reduced skin formation, low sulphur content in the product and lower exhalation. The spherical product obtained by the TSGT process is called bead cellulose. The external physical shape is shown in Fig. 1; the particle size can be varied between 50 and 1500 #m, and the width of particle size distribution is the same as that of products prepared by suspension polymerization. Undried particles possess high porosity ( P = 90%), which simple after-treatments [8] allow to be reduced to the required level (up to P = 55%); alternatively products of high porosity can be prepared in the dry state (> 300 m2/g) [2]. In the Experimental section, a simple pro-
cedure is described for the preparation of bead cellulose which can readily be effected in the laboratory. The TSGT process can be accomplished by employing simple equipment and cheap raw materials, under economic conditions, and may be integrated into the traditional production of viscose rayon and cellophane.
EXPERIMENTAL Materials
Viscose is a technical intermediate from the production of rayon cord. It was prepared from a mixture of spruce sulphite cellulose (65%) and beech sulphate cellulose (35%) with the respective degrees of polymerization 750 and 600. It contained 8.3% cellulose, 6.2% NaOH and 2.4% S. The solution showed operational maturity. The chlorobenzene was of technical grade, and the potassium oleate of medical grade.
147
Procedure
REFERENCES
A sulfonation flask (250 ml) equipped with a paddle agitator was filled with chlorobenzene (120 ml). Potassium oleate was dissolved in viscose up to 0.3%. At 750 r.p.m., the viscose solution (30 ml) was dispersed in chlorobenzene. The reaction flask was heated (15 min) up to 90°C, kept at this temperature (30 min) and then cooled to room temperature. The yellow spherical product was separated by suction and washed with boiling water until its colour changed to a snow white appearance. Bead cellulose (yield 28 ml) was stored in aqueous suspension and conserved with 0.01% sodium azide. Porosity was 89.5%, and particle size 0.1-0.5 mm.
1 J. Stamberg, J. Pegka, D. Paul and B. Philipp, Acta Polymerica, 30 (1979) 734. 2 J. Stamberg, J. Pegka, H. Dautzenberg and B. Philipp, in: T.C.J. Gribnau, J. Visser and R.J.F. Nivard (Eds.), Analytical Chemistry Symposia Series, Vol. 9, Affinity Chromatography and Related Techniques, Elsevier, Amsterdam, 1982, p. 131. 3 A.F. Turbak, R.B. Hammer, R.E. Davies and H.L. Hergert, Chemtech., 10 (1980) 51. 4 B. Philipp, H. Schleicher, W. Wagenknecht and K.J. Linow, Das Papier, 33 (1979) 552. 5 H.L. Hergert, Das Papier, 33 (1979) 562. 6 J. Pe~ka, J. Stamberg and Z. Bla~e, US Patent 4,055,510 (1977). 7 0 . Quadrat, P. Pavlik, J. Pegka and J. Stamberg, Acta Polymerica, 32 (1981) 461. 8 J. Pegka, J. Stamberg and Z. Pelzbauer, Cellul. Chem. Technol., 21 (1978) 419.
145
Elsevier Science Publishers B.V., Amsterdam - Printed in The Netherlands
S H O R T COMMUNICATION
PREPARATION OF POROUS SPHERICAL CELLULOSE J. STAMBERG and J. PESKA
Institute of Macromolecular Chemistry, Czechoslovak Academy of Sciences, 162 06 Prague 6 (Czechoslovakia) (Received June 3, 1982; accepted November 3, 1982)
also to some modern intensively studied solvents [3-5].
INTRODUCTION Cellulose is widely used in the synthesis of functional polymers (especiallS, absorbents), ion exchangers, chelating sorbents, packing for chromatographic columns, carriers of biological functions, and so on. In most cases, optimal results cannot be obtained by using native or other available physical forms of cellulose. Synthetic functional polymers are available in a regular bead form which has proved suitable both because of easy handling and use in columns and due to its effectiveness in application, easier reproducibility and interpretation of results. Functional polymers based on cellulose can now also be prepared in bead form [1,2]. In order to prepare spherical particles, cellulose or its derivative is transformed into the liquid state; the latter is divided into drops through ejection or dispersion in a solvent immiscible with water, subjected to liquidsolid transition and then to final treatment. The procedure used in the preparation of bead cellulose resembles suspension polymerization; similarly, solidification is the sensitive point of the process. Bead shaping of cellulose has been described for various solutions of cellulose and its derivatives and for molten cellulose acetate [2]. Even though most attention has been devoted to the usual solvent systems, the results obtained may be applied 0167-6989/83/$03.00
R E S U L T S AND D I S C U S S I O N A simple and reliable procedure for the preparation of bead porous cellulose has been developed, based on the thermal sol-gel transition (TSGT process). In this procedure, maximum attention is paid to requirements analogous with those of suspension polymerization [6]. An aqueous solution of cellulose xanthogenate (technical viscose) is dispersed in a solvent immiscible with water, and the sol-gel transition is brought about by raising the temperature above 90°C [7]. The rise in temperature accelerates the splitting of ionic xanthate groups until a sudden change in solubility, corresponding to phase transition, takes place. At the same time, physical crosslinks are formed in unsubstituted sections of polymer chains due to cellulose being organized into microcrystalline domains linked with hydrogen bonds. The sol-gel transition occurs simultaneously throughout the droplet, so that skinformation on the external particle surface is reduced. Skin formation occurs more readily in such procedures in which the sol-gel transition is brought about by adding a precipitant to the dispersing medium. Particle size is controlled by adding
© 1983 Elsevier Science Publishers B.V.
146
Fig. 1. Micrograph of bead cellulose (mean size 300 /tm).
surfactants to the stirred mixture, constituting an easier route than a change in the stirring conditions. This is the difference between the preparation of bead cellulose and suspension polymerization; the reasons should be sought in the viscosity of the dispersed phase. The regeneration of cellulose in solidified bead particles may be completed by using acid or alkaline solutions. The latter are more advantageous owing to reduced skin formation, low sulphur content in the product and lower exhalation. The spherical product obtained by the TSGT process is called bead cellulose. The external physical shape is shown in Fig. 1; the particle size can be varied between 50 and 1500 #m, and the width of particle size distribution is the same as that of products prepared by suspension polymerization. Undried particles possess high porosity ( P = 90%), which simple after-treatments [8] allow to be reduced to the required level (up to P = 55%); alternatively products of high porosity can be prepared in the dry state (> 300 m2/g) [2]. In the Experimental section, a simple pro-
cedure is described for the preparation of bead cellulose which can readily be effected in the laboratory. The TSGT process can be accomplished by employing simple equipment and cheap raw materials, under economic conditions, and may be integrated into the traditional production of viscose rayon and cellophane.
EXPERIMENTAL Materials
Viscose is a technical intermediate from the production of rayon cord. It was prepared from a mixture of spruce sulphite cellulose (65%) and beech sulphate cellulose (35%) with the respective degrees of polymerization 750 and 600. It contained 8.3% cellulose, 6.2% NaOH and 2.4% S. The solution showed operational maturity. The chlorobenzene was of technical grade, and the potassium oleate of medical grade.
147
Procedure
REFERENCES
A sulfonation flask (250 ml) equipped with a paddle agitator was filled with chlorobenzene (120 ml). Potassium oleate was dissolved in viscose up to 0.3%. At 750 r.p.m., the viscose solution (30 ml) was dispersed in chlorobenzene. The reaction flask was heated (15 min) up to 90°C, kept at this temperature (30 min) and then cooled to room temperature. The yellow spherical product was separated by suction and washed with boiling water until its colour changed to a snow white appearance. Bead cellulose (yield 28 ml) was stored in aqueous suspension and conserved with 0.01% sodium azide. Porosity was 89.5%, and particle size 0.1-0.5 mm.
1 J. Stamberg, J. Pegka, D. Paul and B. Philipp, Acta Polymerica, 30 (1979) 734. 2 J. Stamberg, J. Pegka, H. Dautzenberg and B. Philipp, in: T.C.J. Gribnau, J. Visser and R.J.F. Nivard (Eds.), Analytical Chemistry Symposia Series, Vol. 9, Affinity Chromatography and Related Techniques, Elsevier, Amsterdam, 1982, p. 131. 3 A.F. Turbak, R.B. Hammer, R.E. Davies and H.L. Hergert, Chemtech., 10 (1980) 51. 4 B. Philipp, H. Schleicher, W. Wagenknecht and K.J. Linow, Das Papier, 33 (1979) 552. 5 H.L. Hergert, Das Papier, 33 (1979) 562. 6 J. Pe~ka, J. Stamberg and Z. Bla~e, US Patent 4,055,510 (1977). 7 0 . Quadrat, P. Pavlik, J. Pegka and J. Stamberg, Acta Polymerica, 32 (1981) 461. 8 J. Pegka, J. Stamberg and Z. Pelzbauer, Cellul. Chem. Technol., 21 (1978) 419.