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Swelling and dissolution mechanisms of native cellulose fibres

Cuissinat, Céline (2006) Swelling and dissolution mechanisms of native cellulose fibres. PhD thesis Sciences et Génie des Matériaux, ENSMP - CEMEF Centre de Mise en Forme des Matériaux, ENSMP p.160.

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Abstract

Cellulose is a natural polymer, which belongs to polysaccharide family. Cellulose offers numerous product development opportunities but cellulose is difficult to process: it can not be melted. Thus cellulose must be either solubilised or derivetised. This is the main reason that pushed us to study and understand the swelling and dissolution mechanisms of native cellulose fibres (cotton, wood, sisal, abaca, hemp, flax and ramie). Data obtained with cotton and wood samples without outer layers, and cellulose derivatives allow us further information. The chemical agents, investigated as solvent or swollen agents, are aqueous (N-methylmorpholine N-oxide – water with various water content, or sodium hydroxide – water – additives) or ionic liquids. We identified five modes describing the behaviour of cellulose native fibres dipped in chemical agents:

Mode 1: fast dissolution by disintegration into fragments

Mode 2: large swelling by ballooning, and dissolution

Mode 3: large swelling by ballooning, and no dissolution

Mode 4: homogeneous swelling, and no dissolution

Mode 5: no swelling, and no dissolution

Despite the morphological differences between the different types of vegetal fibres or cellulose derivatives, they all follow the same modes of swelling and dissolving. We can distinguish different zones with one fibre during the ballooning. The three main components are the followings: the balloons, the membrane (surrounded the balloons with helicoidal feature) and the unswollen section. Each of these parts undergoes a typical swelling and dissolution behaviour. The components of the balloon membrane are the primary wall, plus part of the secondary wall. The membrane is the most difficult part to dissolve. Cellulose inside the balloons is not only swollen, but dissolved. The swelling and dissolution mechanisms of native cellulose fibres are not determined by the chemical nature of chemicals tested as solvent systems. Even if the quality of solvent plays a major role concerning the induced mechanisms, the key parameter is the morphological architecture of native cellulose fibres.

Item Type:PhD Thesis (PhD)
Thesis Supervisor:Navard, Patrick
Date:24 November 2006
Board of examiners:Puls, Juergen and Sixta, Herbert and Heinze, Thomas and Hofte, Herman and Navard, Patrick
Ecole Doctorale:ED 364 SCIENCES FONDAMENTALES ET APPLIQUEES
Discipline:Sciences et Génie des Matériaux
Collection (Fonds):ENSMP
Institution:ENSMP
Department:ENSMP - CEMEF Centre de Mise en Forme des Matériaux
Subjects:4. Materials Science, Mechanics and Mechanical Engineering
Uncontrolled Keywords:Cellulose, Polysaccharide, Gonflement, Dissolution, Hydroxyde de sodium, Cellulose, Polysaccharide, Swelling, Dissolution, Sodium hydroxide

References

Références Chapitre 1 :

[BAIL54] I.W. Bailey, Contributions to Plant Anatomy, Waltham, Mass., Chronica Botanica Company, 1954.

[BIGA02] O. Biganska, Doctorat Science et Génie des Matériaux de l’Ecole des Mines de Paris, Sophia Antipolis, 2002.

[BRED89] K. Brederick, Textilveredlung 1989, 24, 146.

[BROG39] A. Brogniart, A.B. Pelonze, R. Dumas, Rapport interne de l’Académie Française 1839, 8, 51.

[DAVI37] G.F. Davidson, J. Text. Ind. 1937, 28, 27.

[ESSA65] K. Esau, Plant anatomy, Willey & Sons, New York, 2nd Edition, 1965.

[FAIT45] W.L. Faith, Ind. Eng. Chem. 1945, 37, 9.

[FAN 87] L.T. Fan, M.M. Gharpuray, Y.H. Lee, Cellulose Hydrolysis, Biotechnologies Monographs, Springer - Verlag, New York, 1987.

[FENG92] D. Fengel, Holzforschung 1992, 46, 283.

[FINK92] H.P. Fink, B. Philipp, C. Zschunke, M. Hayn, Acta Polym. 1992, 43, 270.

[GARD74] K.H. Gardner, J. Blackwell, Biopolymers 1974, 13, 1975.

[HARR53] E.E. Harris, Tappi 1953, 36 , 402.

[HAIG86] C.H. Haigler, R.M. Brown R, Protoplasma 1986, 134, 111.

[HEAR62] J.W.S. Hearle, J. Text. Inst. Proc. 1962, 53, 143.

[HERM49]1 E.H. Herman, J. Polym. Sci. 1949, 4, 135.

[HERM49]2 E.H. Herman, Physics and Chemistry of cellulose fibres, Elsevier Publishing Company, Inc, New York, 1949.

[HON 00] N.S.D. Hon, N. Shiraishi, Wood and Cellulosic Chemistry, 2nd Edition, Marcel Dekker Inc, New York, 2000.

[HOWS63] J.A. Howsmon, W.A. Sisson, Structure and properties of cellulose fibers, Bsubmicroscopic Structure, in Cellulose and Cellulose Derivatives 1963, Part I, 231.

[JOCA84] B. Jocabasch, Oberflächen Faserbildender Polymere, Berlin: Akademieverlag, 1984.

[KATZ33] J.R. Katz, Trans. Faraday Soc. 1933, 29, 279.

[KLEM05] D. Klemm, B. Heublein, H.P. Fink, A. Bohn, Angew. Chem, Int. Edit 2005, 44, 3358.

[KLEM98] D. Klemm, B. Philipp, T. Heinze, Fundamentals and Analytical Methods, Comprehensive Cellulose Chemistry, vol 1, Wiley-VCH, Weinheim, Germany, 1998.

[KOLP76] F.J. Kolpak, J. Blackwell, Macromolecules 1976, 9, 273.

[KRAS93] H.A. Krässig, Cellulose: Structure, Accessibility and Reactivity, Polymer Monographs, Gordon and Breach Science publisher, New York, vol 11, 1993.

[KROO86] L.M.J. Kroon – Batenburg, J. Kroon, M.G. Nordholt, Polym. Commun. 1986, 27, 290.

[MARS41] J.Y. Marsh, Mercerising, Chapman & Hall Ltd, London, 1941.

[MILL03] B.A. Miller – Chou, J.L. Koenig, Prog. Polym. Sci. 2003, 28, 1223.

[MORR69] J.L. Morrison, M.A. Dzieciuch, Can. J. Chem. 1969, 37, 1379.

[MULD04] B. Mulder, J. Schel, A.M. Emons, Cellulose 2004, 11, 395.

[ORR 57] R.S. Orr, L.B. De Luca, A.W. Burgis, J.N. Grant, Text. Res. J. 1957, 29, 114.

[ORR 61] R.S. Orr, A.W. Burgis, L.B. De Luca, J.N. Grant, Text. Res. J. 1961, 31, 302.

[OTT 54] E. Ott, H.M. Spurlin, M.W. Grafflin, Cellulose and Cellulose Derivatives, Part 1, Intersciences Publisher, New York, 1954.

[PAYE42] A. Payen, Troisième mémoire sur le développement des végétaux - Extrait des Mémoires de l’Académie Royale des Sciences: Tome III des Savants étrangers, Imprimerie Royale, Paris, 1842.

[ROEL59] P.A. Roelofsen, The plant cell-wall, Encyclopedia of Plant Anatomy, Berlin – Nikolasse, 1959.

[RUAN04] D. Ruan, L. Zhang., Y. Mao, M. Zeng, X. Li, J. Membrane Sci. 2004, 241, 265.

[SAKA04] S. Saka, Wood as natural raw materials - Cellulose Acetates: properties and applications, Macromolecular Symposia, Rustemeyer Ed, Freiburg, 2004.

[SOBU39] H. Sobue, H. Kiesslig, K. Hess, Z. Physik. Chem. B 1939, 43, 309.

[STAU32] H. Staudinger, Die hochmolekularen organischen Verbindungen – Kautschuk und Cellulose, Springer Verlag, Berlin, 1932.

[SUGI91] J. Sugijama, R. Voong, H. Chanzy, Macromolecules 1991, 24, 4168.

[TIME67] T.E. Timell, Wood Sci. Technol. 1967, 1, 45.

[UEBE68] K. Ueberreiter, The solution process, in Diffusion in polymers, Academic Press publisher, New York, 1968.

[WARW66] J.O. Warwicker, R. Jeffries, R.L. Colbran, R.N. Robinson, A review of the literature on the effect of caustic soda and other swelling agents on the fine structure of cotton, Shirley Institute Pamphlet number 93, England, 1966.

[YOUN86] R.A. Young, R.M. Rowell, Cellulose: structure, modification and hydrolysis, John Wiley & Sons, 1986.

[ZUGE01] P. Zugenmaier, Prog. Polym. Sci. 2001, 26, 1341.

http://en.wikipedia.org (Advanced Research)

http://www.biologydaily.com (The Science of life, Advanced Research)

http://www.cermav.cnrs.fr (S. Pérez, W. Mackie, Structure and morphology of cellulose)

http://www.faculty.sfasu.edu

(http://www.faculty.sfasu.edu/mcbroommatth/Lectures/Wood_Science/Lecture_3_Wood_Cell

s.pdf)

Références Chapitre 2 :

[1] J. F. Kennedy, G.O. Philipp, P.A. Williams, “Cellulose and exploitation, industrial utilisation, biotechnology and physical – chemical properties”, Horwood limited publisher, London, 1990.

[2] K. M. Mannan, Z. Robbany, Polym. J. 1996, 37, 4639.

[3] H. Leipner, S. Fischer, E. Brendler, W. Voigt, Macromol. Chem. Physic. 2000, 201, 2041.

[4] H. Chanzy, P. Noe, M. Paillet, P. Smith, Appl. Polym.Symp. 1983, 37, 239.

[5] B. A. Miller – Chou, J. L. Koenig, Prog. Polym. Sci. 2003, 28, 1223.

[6] K. Ueberreiter, in: “The solution process, Diffusion in polymers”, Academic Press publisher, New York 1968, p.219.

[7] D. Klemm, B. Philipp, T. Heinze, U. Heinze, W. Wagenknecht, in: “Fundamentals and analytical methods. Comprehensive Cellulose Chemistry (vol 1)”, Wiley – VCH, Weinheim, 1998.

[8] H. A. Krässig, “Cellulose : structure, accessibility and reactivity. Polymer Monographs (vol 11)”, Gordon and Breach, New York, 1993.

[9] J. T. Marsh, “The growth and structure of cotton, Mercerising” Chapman & Hall Ltd, London 1941.

[10] E. Ott, H. M. Spurlin, M. W. Grafflin, “Cellulose and cellulose derivatives (Part 1)”, Interscience Publisher, New York 1954.

[11] M. M. Roy, M. K. Sen, J. Text. Inst. 1952, 43, 396

[12] T. Baldinger, J. Moosbauer, H. Sixta, “Supermolecular structure of cellulosic materials by fourier transform infrared spectroscopy (FT-IR) calibrated by WAXS and 13C NMR”, Internal report from LENZING AG, A- 4860 Lenzing, Austria, 2005.

[13] H. P. Fink, P. Weigel, H. J. Purz, J. Ganster, Prog. Polym. Sci., 2001, 26, 1473

[14] P. Navard, J. M. Haudin, J. Therm. Anal. 1981, 22, 107

[15] R. M. Armstrong, C. C. Corsley, J. K. Varga, Proceedings of the fifth international Tappi dissolving pulp conference, Vienna, 1980, 100.

[16] P. S. Drzaic, “Liquid crystals dispersion, series on liquid crystals (vol 1)”, World Scientific publisher, London 1995.

[17] J. F. Blachot, N. Brunet, P. Navard, J. H. Cavaille, Rheol. Acta 1998, 37, 107.

Références Chapitre 3 :

[1] D. Klemm, B. Heublein, H.P. Fink, A. Bohn, Angew. Chem. Int. Ed. 2005, 44, 3358.

[2] C. Cuissinat, P. Navard, Swelling and dissolution of cellulose, Part I: free floating cotton and wood fibres in N-methylmorpholoine N-oxide water mixtures. Macromol. Symp. accepted.

[3] J. Mercer, J. Franklin Instit. 1851, 52, 202.

[4] H. Sobue, H. Kiessig, K. Hess, Z. Physik Chem B. 1939, 43, 309.

[5] K. Kamide, K. Okajama, T. Matsui, K. Kowsaka, Polym. J. 1984, 12, 857.

[6] K. Kamide, K. Okajima, K. Kowsaka, Polym. J. 1992, 24, 71.

[7] C. Yamane, M. Saito, K. Okajima, Sen’i gakkaishi 1996, 52, 310. functionnalisation developments in cellulosics and wood, Cellusion 88, Kyoto, Japan, 1988.

[9] K. Kowsaka, K. Kamide, K. Okajima, International symposium on new functionnalisation developments in cellulosics and wood, Cellusion 88, Kyoto, Japan, 1988.

[10] T. Yamashiki, K. Kamide, K. Okajima, K. Kowsaka, T. Matsui, H. Fugase, Polym. J. 1988, 20, 447.

[11] K. Kamide, K. Yasuda, T. Matsui, K. Okajima, T. Yamashiki, Cellulose Chem. Technol. 1990, 24, 23.

[12] L: Zhang, J. Zhou, D. Ruan, Casting of cellulose film, China Patent ZL 00 114485.5 2003.

[13] L. Zhang, D. Ruan, J. Zhou, Ind. Eng. Chem. Res. 2001, 40, 5923

[14] L. Zhang, D. Ruan, S. Gao, J. Polym. Sci. Part B: Polym. Phys. 2002, 40, 1521

[15] D. Ruan, L. Zhang, Y. Mao, M. Zeng, X. Li, J. Membr. Sci. 2004, 241, 265

[16] J. Kunze, H.P. Fink, Macromol. Symp. 2005, 223, 175

[17] C. Roy, T. Budtova, P. Navard, O. Bedue, Biomacromol. 2001, 2, 687.

[18] M. Egal, T. Budtova, P. Navard, Biomacromol. Submitted

[19] C. Roy, These Science et Genie des matériaux de l’Ecole des Mines de Paris, France, 2002.

[20] G.F. Davidson, J. Text. Ind. 1937, 28, 27.

[21] T.P. Dirske, C. Postmus, J.R. and R. Vandenbosch, J. Am. Chem. Soc. 1954, 76, 6022.

[22] D. Klemm, B. Philipp, T. Heinze, Fundamentals and analatycal methods, comprehensive cellulose chemistry, vol 1, Wiley – VCH, Weinheim,1998.

[23] T. Baldinger, J. Moosbauer, H. Sixta, “Supermolecular structure of cellulosic materials by fourier transform infrared spectroscopy (FT-IR) calibrated by WAXS and 13C NMR”, Internal report from LENZING AG, A- 4860 Lenzing, Austria, 2005.

[24] V.A. Krakhmalev, A.A. Paiziev, Cellulose 2006, 13, 45

[25] N. LeMoigne, P. Navard, advanced report on the swelling and dissolution mechanisms of cotton fibres, Internal Report from CEMEF - Ecole des Mines de Paris, 2006.

Références Chapitre 4 :

[1] C. Cuissinat, P. Navard, Swelling and dissolution of cellulose, Part I: free floating cotton and wood fibres in N-methylmorpholine N-oxide water mixtures. Macromol. Symp. accepted.

[2] C. Cuissinat, P. Navard, Swelling and dissolution of cellulose, Part II: free floating cotton and wood fibres in NaOH – water – additives systems, Macromol. Symp. accepted.

[3] O. Lerouxel, D. M. Cavalier, A. H. Liepman, K. Keegstra, Plant Biol. 2006, 9, 1.

[4] C. Bret, K. Waldron, “Physiology and biochemistry of plant cell walls, 2nd edition”, Chapman and Hall, London, 1996.

[5] G. Refrégier, S. Pelletier, D. Jaillard, H. Höfte, Plant Physiol. 2004, 135, 959.

[6] J. F. Kennedy, G. O. Philipp, P.A. Williams, “Cellulose and exploitation, industrial utilisation, biotechnology, and physical – chemical properties”, Horwood limited publisher, London, 1990.

[7] E. Ott, H. M. Spurlin, M. W. Grafflin, “Cellulose and cellulose derivatives (Part 1)”, Interscience Publisher, New York, 1954.

[8] H. A. Krässig, “Cellulose : structure, accessibility and reactivity. Polymer Monographs (vol 11)”, Gordon and Breach, New York, 1993.

[9] K. Selby, C. C. Maitland, K. V. A. Thomson, Biochem. J. 1963, 88, 288.

[10] B. Focher, A. Marzetti, C. Santoro, V. Sarto, L. D. Angiuro, Macromol. Chem. Phys.

1982, 102; 187.

[11] M. Streamer, K. Eriksson, B. Petterson, Eur. J. Biochem. 1975, 59; 607.

[12] P. Kassenbeck, Text. Res. J. 1970, 40, 330.

[13] T. Baldinger, J. Moosbauer, H. Sixta, “Supermolecular structure of cellulosic materials by fourier transform infrared spectroscopy (FT-IR) calibrated by WAXS and 13C NMR”, Internal report from LENZING AG, A- 4860 Lenzing, Austria, 2005.

[15] C. R. Noder, J. Textile Inst. 1922, 13, 161.

[16] Kh. M. Mannan, Z. Robbany, Polymer 1996, 37, 4639.

[17] J. H. Carra, V. W. Tripp, R. S. Orr, Text. Res. J. 1962, 32, 1041.

[18] M. Horio, T. Kondo, Text. Res. J. 1953, 23, 373

[19] F. Hensen, Intern. Polym. Processing 1989, 4, 67.

[20] T. Matsuo, S. Kase, J. Polym. Sci. 1965, A3, 2541.

[21] V. A. Krakhmalev, A. A. Paiziev, Cellulose 2006, 31, 45.

[22] R.S. Orr, A. W. Burgis, L. B. De Luca, J. N. Grant, Text. Res. J. 1961, 31, 302.

[23] J. O. Warwicker, R. Jefries, R. L. Colbran, R. N. Robinson, “A Review of the Literature on the Effect of Caustic Coda and Other Swelling Agents on the Fine Structure of Cotton”, Shirley Institute, Manchester, 1996.

Références Chapitre 5 :

[1] D. J. Adams, P. J. Dyson, S. J. Taverner, Chemistry in Alternative Reaction Media, Chap 4: ionic liquids.J.Wiley & Sons, New York 2004.

[2] C. Graenacher, Cellulose solution, U.S. patent 1 1934, 943, 176

[3] R. P. Swatloski, S. K. Spear, J. D. Holbrey, R.D. Rogers, R, J. Am Chem. Soc. 2002, 124, 4974.

[4] T. Heinze, K. Schwikal, S. Barthel,.Macromol. Biosci. 2005, 5, 520.

[5] S. Barthel, T. Heinze, Green Chem. 2006, 8, 301.

[6] K. Schlufter, H .P. Schmauder, S. Dorn, T. Heinze, Macromol. Rapid Commun. 2006, 27, 1670.

[7] C. Cuissinat, P. Navard, Swelling and dissolution of cellulose, Part I: free floating cotton and wood fibres in N-methylmorpholine N-oxide water mixtures. Macromol. Symp. accepted.

[8] C. Cuissinat, P. Navard, Swelling and dissolution of cellulose, Part II: free floating cotton and wood fibres in NaOH-water-additives systems. Macromol. Symp. accepted.

[9] T. Baldinger, J. Moosbauer, H. Sixta, Supermolecular structure of cellulosic materials by fourier transform infrared spectroscopy (FT-IR) calibrated by WAXS and 13C NMR, Internal report from LENZING AG, A- 4860 Lenzing, Austria 2005.

[10] Cuissinat, C., Navard, P. Swelling and dissolution of cellulose, Part III: enzymatically – treated cotton and wood fibres in aqueous solvents. Carbohydr. Polym. in preparation.

Références Chapitre 6 :

[1] L. Y. Mwaikambo, P. A. Martin, J. Appl. Polym. Sci. 2002, 84, 2222.

[2] A. M. Donald, O. M. Astley, J. Mater. Sci. 2003, 38, 165.

[3] C. Baley, Techniques de l’ingénieur 2004, ref AM5130.

[4] C. Cuissinat, P. Navard, Swelling and dissolution of cellulose, Part I: free floating cotton and wood fibres in N-methylmorpholine N-oxide water mixtures. Macromol. Symp. accepted.

[5] C. Cuissinat, P. Navard, Swelling and dissolution of cellulose, Part II: free floating cotton and wood fibres in NaOH – water – additives systems, Macromol. Symp. accepted.

[6] C. Cuissinat, P. Navard, Swelling and dissolution of cellulose, Part III: enzymatically – treated cotton and wood fibres in aqueous systems, in preparation.

[7] C. Cuissinat, P. Navard, T. Heinze, Swelling and dissolution of cellulose, Part IV: free floating cotton and wood fibres in ionic liquids, in preparation.

[8] C. Chanzy, P. Noe, M. Paillet, P. Smith, Appl. Polym. Symp. 1983, 37, 239.

Références Chapitre 7 :

[1] D. Klemm, B. Philipp, T. Heinze, U. Heinze, W. Wagenknecht, in: “Fundamentals and analytical methods. Comprehensive Cellulose Chemistry (vol 1)”, Wiley – VCH, Weinheim, 1998.

[2] C. Cuissinat, P. Navard, Swelling and dissolution of cellulose, Part I: free floating cotton and wood fibres in N-methylmorpholine N-oxide water mixtures. Macromol. Symp. accepted.

[3] C. Cuissinat, P. Navard, Swelling and dissolution of cellulose, Part II: free floating cotton and wood fibres in NaOH – water – additives systems, Macromol. Symp. accepted.

[4] C. Cuissinat, P. Navard, Swelling and dissolution of cellulose, Part III: enzymatically – treated cotton and wood fibres in aqueous systems, in preparation.

[5] C. Cuissinat, P. Navard, T. Heinze, Swelling and dissolution of cellulose, Part IV: free floating cotton and wood fibres in ionic liquids, in preparation.

[6] C. Cuissinat, P. Navard, Swelling and dissolution mechanisms of native cellulose fibres, part V: free floating plant fibres in aqueous systems, in preparation.

[7] B. Bergen, W. Kraus, in “Textile fibre atlas, a collection of photomicrographs of common textile fibres”, American Wool Handbook Company, NewYork, 1942.

[8] K. Jardeby, U. Germgard, B. Kreutz, T. Heinze, U. Heinze, H. Lennholm, Cellulose 2005, 12, 167.

Table of content

Table of contents

Résumé francophone.

Introduction

Chapter 1: Bibliography.

Résumé francophone.

Introduction

Table of contents

I. The fibre structure

I.1 Cellulose molecule

I.2.Supermolecular structure

I.3. Ultrastructure

I.4.Conclusion on the fibre structure

II. Structure of plant cell walls

II.1. Biosynthesis of cellulose

II.2. The cell wall constituents

II.3. The cell wall structure

II.4. Conclusion on the structure of plant cell walls

III. Swelling and dissolution of cellulose fibres

III.1. Dissolution mechanisms of dissolution

III.2. Important classes of cellulose solvents systems

III.3. Accessibility of cellulose fibres

III.4. Conclusion on cellulose dissolution

Chapter 2: Swelling and dissolution mechanisms of native cellulose fibres, part I: free floating cotton and wood fibres in N-methylmorpholine-N-oxide – water mixtures

Chapter 3: Swelling and dissolution mechanisms of native cellulose fibres, part II: free floating cotton and wood fibres in NaOH – water – additives systems

Chapter 4: Swelling and dissolution mechanisms of native cellulose fibres, part III: enzymatically – treated cotton and wood fibres in aqueous systems

Chapter 5: Swelling and dissolution mechanisms of native cellulose fibres, part IV: free floating cotton and wood fibres in ionic liquids

Chapter 6: Swelling and dissolution mechanisms of native cellulose fibres, part V: free floating plant fibres in aqueous systems

Chapter 7: Swelling and dissolution mechanisms of native cellulose fibres, part VI: free floating cellulose derivatives in aqueous systems and ionic liquids

ID Code:2729
Deposited By:Brigitte HANOT
Deposited On:13 July 2007

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