Cellulose
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| Material type: | Polymer | Material group: | Homo polysaccharide, linear beta-(1-4)-glycan |
Monomer(s): | D-glucose | Links: | beta-(1-4) | Origin of the polymer: | Natural | CAS-Number: | 9004-34-6 | EINECS-Number: | 232-674-9 |
Structure
(→4)-β-D-glucose(1→). There are two types of cellulose: Cellulose I, a microcrystalline cellulose, and cellulose II, mercerized cellulose [1,15]. Two additional types are known, but they are derived from heat or alkali tratment of type I and II [15].Highly ordered fibers that form a crystalline structure. The crystalline regions vary in size and represent areas of great mechanical strenght and high resistance to attack by chemical reagents and hydrolytic enzymes [3].
Chemical properties
Solubility parameterδ=14.5-16.5 [2].
Behavior in solution
Chrystalline cellulose is partailly soluble in water with some swelling [3].
Behavior in with other polymers
♦ Xyloglucans adhere strongly to cellulose microfibrils through hydrogen bonds between the xyloglucan backbone and cellulose. The binding is quantitatively to both types of cellulose [1]. The binding to cellulose I is almost the same at pH 5-12 and 1M NaCl as in destilled water [1]. At pH 13 the binding diminishes 14% [1].
♦ Scizophyllan binds quantitatively to cellulose I, but only sparingly to cellulose II [1]. The binding to cellulose I is almost the same at pH 5-11 and 1M NaCl as in destilled water [1]. At pH 12 and 13 the binding diminishes 15 and 35% respectively [1]. The binding mechanism is presumed to be different from binding of other polymers, depending on the ability to form triple-helices, which is only possible for (1→3)-β-D-glucans at high molecular weight [1].
♦ Locust bean gum and barley β-D-glucan can bind quantitatively to both cellulose I and II [1].
♦ Chitosan dissolved in acetate buffer adheres strongly to both cellulose I and II [1]. Tests on chitobiose and chitotriose which are water soluble, confirms that the binding of chitosan is a property of the chitosan itself [1].
♦ Specific adhesion to cellulose was not observed for pullulan, cyclosophoran, pustulan, yeast mannan, arabinogalactan, xanthan gum, succinoglycan and carboxymethyl cellulose [1].
Grafting
♦ Polystyrene can be grafted onto cellulose using an initiator of ceric ammonium nitrate with nitric acid. The cellulose/polystyrene is thermally more stabel than cellulose and polystyrene and is biodegradeable [9].
♦ Order of reactivity of the hydroxyl groups toward methylation and carboxymethylation: 2-OH>6-OH>3-OH. There are experimental results showing that 6-OH is more reactive than 2-OH [5].
♦ Many substitutions can be made by an alkali cellulose intermediate, followed by treatment with a halogenated substituent (Williamson ether synthesis) [16,17]
Crosslinking
Cellulose derivatives can be cross linked with oxalylchloride in p-dioxane solution containing a tertiary amine as the catalyst [8].
Oxidation
Oxidizing cellulose poses a series of problems in regards to producing material which is homogenous in chemical and physical properties. Several oxidation agents are not selective, and many methods are topochemical. Also physical degradation of the fibres are a problem, giving a friable material that powders easily [12].
♦ A non-specific oxidation of cellulose can be obtained by nitrogen dioxide, giving a fibrous material which is not friable [12]. The method is relative simple exposing the cellulose to NO2 until the desired DS and rinsing with destilled water until the water is no longer acidic [12]. Max DS by this method is 0.25 [13]. There are two versions of this method called 'cyclic method' and 'static method' refering to the way the cellulose fibres are exposed to NO2 [12]. The method has a preference for oxidation of primary alcohols i.e. C(6) [13]. Cellulose derivatives from nitrogen dioxide are yellow to brown in color, and are highly degraded [11].
♦ Selective oxidation of C(6) in the glucose unit (DS>90%) is done by oxidation with phosphoric acid and sodium bromate, sodium chorate and sodium chlorite as oxidant. Of these, sodium bromate was the best, giving a DS=96%, and a lesser ring opening degradation of the chains, while sodium chorate and sodium chlorite severly degraded and ring opened the cellulose and only had a DS of 90 and 95% respectively [10]:
♦ Selective oxidation of C(6) in the glucose unit is also possible (DS>95%) by oxidation with phosphoric acid and sodium nitrite or sodium nitrate. Cellulose is dissolved in phosphoric acid and treated with sodium nitrite or sodium nitrate. The oxidations at C(2) and C(3) are reduced by treatment with sodium borohydride. When using nitrate, only a small excess of nitrate is needed (4 nitrate per 3 glucose), while using nitrite an excess of 4 nitrite per glucose unit is needed. Both reactions will reduce the molecular weight of the polymer. The reaction time is decreased by increasing the temperature, but the degradation of the polymer increases significantly at elevated temperatures. The reaction has been done at 4 - 20°C. The oxidation and subsequent reduction of the glucose units gives some epimerization. Experiments on the same reaction on ß-cyclodextrin show that the reaction is autocatalytic [14]:
♦ Other oxidation methods are oxidation by periodate [11]. The periodat oxidation was an attempt to selectively oxidize C(6). The reaction however was not specific, giving an overoxidation, and DS at C(6) was only 0.63. The low oxidation of C(6) by periodate is suggested to be due to sterical hindrance, as analogue oxidation on alginate only gave a DS = 0.44 while xylan had a DS= 1.0 [11].
Misc.
Crystallographic data [7].
Biological properties
Used in food and pharmaceuticals as filler, binder, disintegrating agent and lubricant [3]. Retards gastric emptying when used as a dietary fiber. The fiber decrease postprandial insulin levels, indicating a slowing down of glucose absorption. The fiber decrease postprandial insulin levels, indicating a slowing down of glucose absorption [6].Used for treatment of severe burns, skin grafting, and chronic skin ulcers [4].
Physical properties
Appearance | ||
| Physical state @ 20°C: | Solid | |
| Color: | White | |
Bulk properties | ||
| Molecular weight (g/mol): | > 50,000 [2] | |
| Degree of polymerization: | > 3000 [3] | |
Occurence, isolation & synthesis
SourceUniversal in higher plants, occurs in a few algae and bacteria. Obtained from cotton or wood. Xanthan gum, a D-glucurono-D-manno-D-glucan from Xanthomonas species [3].
History
Oxidation of cellulose has been done since 1883, where Witz tested oxidizing agents on cellulose [12].References
1: Mishima,T., Hisamatsu,M., York,W.S., Teranishi,K., Yamada,T. Adhesion of ß-D-glucans to celluloseCarbohydr. Res. (1998) 308 (3-4) 389-396
2: Zikakis,J.P. Chitin, Chitosan, and Related Enzymes
(1984) Academic press
3: Glicksman,M. Gum Technology in the Food Industry
(1969) Academic Press
4: Cannon,R.E., Anderson,S.M. Biogenesis of Bacterial Cellulose
Crit. Rev. Microbiol. (1991) 17 435-447
5: Zeller,S.G., Griesgraber,G.W., Gray,G.R. Analysis of Positions of Substitution of O-Carboxymethyl Groups in Partially O-Carboxymethylated Cellulose by the Reductive-Cleavage Method
Carbohydr. Res. (1991) 211 41-45
6: Begin,F., Vachon,C., Jones,J.D., Wood,P.J., Savoie,L. Effect of Dietary Fibers on Glycemia and Insulinemia and on Gastrointestinal Function in Rats
Can. J. Physiol. Pharmacol. (1989) 67 1265-1271
7: Sundararajan,P.R., Marchessault,R.H. Bibliography of crystal structures of polysaccharides 1977-1979
Adv. Carbohydr. Chem. Biochem. (1982) 40 381-399
8: Rees,D.A. Structure, conformation, and mechanism in the formation of polysaccharide gels and networks
Adv. Carbohydr. Chem. Biochem. (1969) 24 267-332
9: Cruz, R.A., Mendoza,A.M., Vieira,M.C., Heinze,T. Studies on grafting of cellulosic materials isolated from Agave lechuguilla and fourcryodes
Die Angewandte Makromolekulare Chemie (1999) 273 86-90
10: Pagliaro,M. Autocatalytic oxidations of primary hydroxyl groups of cellulose in phosphoric acid with halogen oxides
Carbohydr. Res. (1998) 308 (3-4) 311-318
11: Painter,T.J. Preparation and periodate oxidation of C-6-oxycellulose: Conformational interpretation of hemiacetal stability
Carbohydr. Res. (1977) 55 95-103
12: Yackel,E.C., Kenyon,W.O. The oxidation of cellulose by nitrogen dioxide
J. Am. Chem. Soc. (1942) 64 121-127
13: Unruh,C.C., Kenyon,W.O. Investigation of the properties of cellulose oxidized by nitrogen dioxide
J. Am. Chem. Soc. (1942) 64 127-131
14: de Nooy,A.E.J., Pagliaro,M., van Bekkum,H., Besemer,A.C. Autocatalytic oxidation of primary hydroxyl functions in glucans with nitroven oxides
Carbohydr. Res. (1997) 304 117-123
15: Chandrasekaran,R. X-ray Diffraction of Food Polysaccharides
Adv. Food Nutr. Res. (1998) 42 131-210
16: Schwarzkopf,R. Method of Manufacture of Raw Alkali-cellulose for Working into Viscose
Patent GB 165743 (Issued/Filed Date: June 30, 1920)
17: Lilienfeld,L. Alkyl Ethers of Cellulose and Process of Making the Same
Patent US 1188376 (Issued/Filed Date: June 20, 1916)
© Michael Pilgaard
Created: March 4, 2008