Cellulose ether esters

Cellulose ether esters can be s mthesizedby the reaction of alkylene oxides with alkaline-activated cellulose and further by grafting of the cellulose ether with lactones (36). 

By the combination of the ether and the ester functionality and a proper selection of the degree of substitution, an increased range of property profiles can be achieved. 

The dependence of the softening point of the cellulose ether esters versus composition is shown in Table 5.12. 

Hydroxyalkyl celluloses with degrees of substitution of less than 1 may be reacted in conventional organic solvents, such as dioxan, di-methylacetamide, N-methylpyrrolidone or terf-butyl alcohol, with 

Suitable 2-hydroxy carboxylic acid derivatives are the cyclic dimers glycolide, L-lactide, D-lactide and meso-lactide, as well as lactic acid esters and lactic acid oligomers (37). 

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Uses. Solvent for cellulose ethers, esters, resins, and dyes liquid propellant binder in foundry cores manufacture of resins including furfuryl alcohol resin (furan resin) and furfuryl alcohol-formaldehyde resins... 

Cellulose derivatives are widely used in biomedical and pharmaceutical applications. Most significant from a commercial and technical point of view are cellulose ether and cellulose ether esters. 

For the synthesis of cellulose ether esters at industrial scale, purified cellulose ether is reacted with carboxylic anhydrides in acetic acid as solvent system and sodium acetate as catalyst. The dissolved cellulose ether ester is being obtained then by precipitation after addition of water. Purification is performed by washing with water. 

Hydroxypropyl methylcellulose acetate succinate (HPMCAS), a cellulose ether ester derived from HPMC esterifled with acetate and succinate groups, is an enteric polymer soluble only in water of high pH or in polar organic solvents like acetone or tetrahydrofuran (THE). The enteric performance is due to the presence of carboxylic groups. At low pH, HPMCAS exists in its protonated... 

J. Kalbe, H.P. Muller, R. Koch, J. Engelhardt, W. Koch, K. Szablikowski, and G. Weber, Thermoplastic cellulose ether ester graft copolymers and process for their production, US Patent 5 466 794, assigned to Wolff Walsrode Aktiengesellschaft (Walsrode, DE), November 14,1995. 

Hydroxyethylcellulose (HEC) and hydroxypropylcellulose (HPC) are prepared by nucleophilic ring opening of ethylene oxide and propylene oxide, respectively, by the hydroxyl anions on the anhydroglucose ring of cellulose. Reactions are conducted commercially in caustic aqueous slurry processes (72). Laboratory methods recently have been reported for preparation of cellulose ethers, esters, and carbamates imder homogeneous reaction conditions in organic solvents (88-91). Such solvents may lead to development of new commercial processes for cellulose derivatives with more imiform substitution. 

Two important classes are cellulose esters (qv) and cellulose ethers (qv). Cellulose esters are not water soluble and are not discussed here cellulose ethers are an important segment of water-soluble polymers. 

Cellulosics. CeUulosic adhesives are obtained by modification of cellulose [9004-34-6] (qv) which comes from cotton linters and wood pulp. Cellulose can be nitrated to provide cellulose nitrate [9004-70-0] which is soluble in organic solvents. When cellulose nitrate is dissolved in amyl acetate [628-63-7] for example, a general purpose solvent-based adhesive which is both waterproof and flexible is formed. Cellulose esterification leads to materials such as cellulose acetate [9004-35-7], which has been used as a pressure-sensitive adhesive tape backing. Cellulose can also be ethoxylated, providing hydroxyethylceUulose which is useful as a thickening agent for poly(vinyl acetate) emulsion adhesives. Etherification leads to materials such as methylceUulose [9004-67-5] which are soluble in water and can be modified with glyceral [56-81-5] to produce adhesives used as wallpaper paste (see Cellulose esters Cellulose ethers). 

Cellulose acids, cellulose esters, cellulose nitrates, cellulose ethers, cellulose xanthogenates... 

Cellulose Deriva.tives, Cellulose can be derivatized to make both water-soluble gums and hydrophobic polymers. The preparation of the hydrophobic cellulose esters (qv), cellulose acetates and cellulose nitrates, has already been mentioned. The water-soluble cellulose derivatives are cellulose ethers (qv). 

Both the sulfite and alkaline (kraft) methods can be modified to produce high purity chemical ceUulose. These pulps, usuaUy in the form of "dissolving pulps," are not only mosdy free of lignin and hemiceUulose, but the molecular weight of the ceUulose is degraded. This increases solubUity in alkah and provides desired viscosity levels in solution. These dissolving pulps are used to make derivatives such as sodium ceUulose xanthate [9051 -13-2] via alkah ceUulose, and various esters and ethers (see Cellulose esters Cellulose ethers). 

Over the past years considerable attention has been paid to the dispersing system since this controls the porosity of the particle. This is important both to ensure quick removal of vinyl chloride monomer after polymerisation and also to achieve easy processing and dry blendable polymers. Amongst materials quoted as protective colloids are vinyl acetate-maleic anhydride copolymers, fatty acid esters of glycerol, ethylene glycol and pentaerythritol, and, more recently, mixed cellulose ethers and partially hydrolysed polyfvinyl acetate). Much recent emphasis has been on mixed systems. 

Of somewhat greater technical interest are the addition compounds and the cellulose esters and ethers. Of the apparent addition compounds the most important is alkali cellulose produced by steeping cellulose in caustic soda and considered to be of general form (CgHioOs), (NaOH) ) rather than a sodium alcoholate compound. Alkali cellulose is a particularly important starting point in the manufacture of cellulose ethers. The ability of aqueous cuprammonium hydroxide solutions to dissolve cellulose appears to be dependent on addition compound formation. 

Cellulose in the form of cotton linters, wood pulp or regenerated cellulose is used as the raw material for the commercial production of cellulose ethers. The advantage which linters possess over wood pulp in the manufacture of cellulose esters is not so apparent in the case of the ethers. 

See also Inorganic cellulose esters Organic cellulose esters dyeing, 9 197-198 U.S. production, 5 429t Cellulose ethers, 4 712, 716 5 445-466 20 560-561... 

Cellulose acetate phthalate (CAP) dissolves at pH higher than 6 and is soluble in ketones, ethers, esters, and alcohols. Permeation of water vapor and gastric fluids is a concern but can be overcome by adding other materials such as shellac. Plasticizers that are used with CAP include diethyl phthalate, triacetin, tributyl citrate, and acetylated monoglyceride. 

Like all carbohydrates, cellulose possesses the clearly marked prominent properties of an alcohol owing to the presence of hydroxyl (alcoholic) groups. The presence of those groups explains the ability of cellulose to form esters with nitric acid and with acetic acid which have attained great practical importance, and also with sulphuric, phosphoric and different organic adds, as well as the formation of cellulose ethers. 

Formation of cellulose ethers and esters has shown that for every six carbon atoms contained in one C6H,0O5 group there are three free hydroxyl groups capable of undergoing esterification or forming ethers. It has also been established that the copper salts of Fehling s solution are reduced by cellulose only to a small extent. Those facts, supported by a series of studies devoted to the products of uncomplete hydrolysis of cellulose, for instance the isolation of cellotriose (Haworth, Hirst and H. A. Thomas [16]), provide suffident evidence that a molecule of cellulose... 

Solutions of cellulose, its esters and ethers are colloidal solutions. They are reversible lyophilic colloids. The most important characteristics of such solutions are as follows. 

On the other hand, numerous observations favour the opinion that the solvent enters into a chemical combination with nitrocellulose to form solvates. Some of those solvates are stable only at low temperatures. For instance, cellulose dinitrate does not dissolve in methyl alcohol at room temperature, though on cooling it does so. The cellulose nitric ester precipitates again when the solution is heated. Similar behaviour is observed with ethyl alcohol a lower temperature causes nitrocellulose to swell or even to dissolve more readily. The solvent seems likely to be bound to free hydroxyl radicals (Highfield [36]). The hypothesis explains why nitrocellulose is soluble in a mixture of ether and alcohol, though neither of these solvents, when used separately, is capable of dissolving it. It is assumed that first an alcohol solvate of nitrocellulose is formed which then dissolves in the ether. 

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