Water-soluble Ethers of Cellulose

The introduction of certain types of ether groups into the cellulose molecule enhances the hydrophilic properties of the latter. In particular, such groups as methoxyl, hydroxyethyl and carboxymethyl, when present in the proper amounts, render the cellulose derivative soluble in water. 

The solubility of methylcellulose in water is dependent upon (1) the degree of substitution (2) the degree of polymerization (3) the temperature of the water and (4) the uniformity of substitution. Consequently no definite limits can be stated. Certain generalizations can, however, be made. 

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Ethers and water-soluble derivatives of cellulose have been assayed spectro-photometrically following reaction of D-glucose or substituted o-glucose derivatives released on hydrolysis with 4-hydroxybenzoylhydrazine. Hydrolysis of the polysaccharides was achieved more readily with trifluoroacetic acid than with sulphuric acid. 

Semisynthetic derivatives of cellulose soluble in water are ethers of cellulose, both nonionic and ionic, with appropriate degrees of substitution. The following alkyl-, hydroxyalkyl- and hydroxyalkylalkyl celluloses will be examined in this chapter ... 

Carboxymethylcellulose Sodium. Carboxymethyl ether of cellulose sodium salt (Citmcel) (8) is a white granular substance soluble in water depending on the degree of substitution. It is equally soluble in cold and hot water and may be prepared by treating alkaU cellulose with sodium chloroacetate. 

The methyl ether of cellulose has a methoxyl content which varies between 6 and 33 %. Methylcellulose can be prepared by the action of methyl chloride or methyl sulfate on cellulose that has been previously treated with alkali. Purification is accomplished by washing the reaction product with hot water. The degree of methylation can be controlled to yield products with varying viscosities. Seven viscosity types of methylcellulose are currently produced with centipoise values ranging from 10 to 4000. Methylated cellulose of low methoxy content is soluble... 

The ethyl ether of cellulose contains no less than 45% and not more them 50% ethoxy groups. It is available as a free-flowing stable white powder, insoluble in water, glycerol, and other hydrophilic solvents, but soluble in organic solvents such as ethanol, ethylacetate, and chloroform. This cellulose derivative is mainly used as a tablet binder. 

Methylcellulose occurs as a white, fibrous powder or granules. It is the methyl ether of cellulose. It is soluble in water and in a limited number of organic solvent systems. Aqueous solutions of Methylcellulose are surface active, form films upon drying, and undergo a reversible transformation from sol to gel upon heating and cooling, respectively. 

Ethylcellulose is an ethyl ether of cellulose containing 44-51% of ethoxyl groups. It is insoluble in water but soluble in chloroform and in alcohol. It is possible to form water-soluble grades with a lower degree of substitution. 

Methylcellulose is thus a methyl ether of cellulose containing about 29% of methoxyl groups it is slowly soluble in water. A 2%... 

Water-Soluble Starches, Gums, Cellulose Derivatives, and Synthetic Polymers. Water-soluble plant starches and gums have historically been used as glues and should be reversible. Some of the modern water-soluble polymers (e.g., cellulose ethers and esters and soluble nylon) should also be reversible. 

Hydroxypropylcellulose is a non-ionic, water-soluble, polyhydroxypropy I cellulose ether that is commercially available in a wide range of molecular weights (50000-1,250,000 g mol ). It is widely used in the pharmaceutical industry as a binder for tablets, in film coatings and as a controlled release matrix (255). 

Of considerable interest are the co-(p-aminoacetophenone) ethers of cellulose containing about one ether group for each three glucose units 10a). These may be diazotized and coupled to provide cellulose-azo dyes, and the latter may be rendered water-soluble by carboxymethylation. 

Solutions of natural and synthetic high molecular mass substances in water, e.g., starch, dextrins, casein, cellulose ethers, water-soluble derivatives of poly(acrylic acid), poly(vinyl alcohol), poly(vinyl pyrrolidone) (adhesive sticks). Uses paper, fiberboard. Glutins (glues of animal origin). Uses wood, paper, fiberboard, moistenable adhesive tapes. 

Prolonged release from compressed hydrophilic matrices is dependent on the rate and extent the cellulose excipient hydrates in forming an external pseudo-gel layer. Earlier investigations performed in this laboratory [33] have shown for example that not all the water-soluble ethers are convenient for preparation of tablets by direct compression that will remain coherent for many hours when in contact with water (Table 8). 

MC, HPC and HPMC are water soluble ethers with good film-forming properties. In order to avoid the formation of agglomerates the dissolution of these nonionic cellulose ethers must be done in two steps dispersion and hydration. Wherever possible, they should be put into solution before other soluble ingredients are added or should be dispersed in water miscible nonsolvent such as glycerol, ethanol or propylene glycol and then add the slurry to water. The solutions of these cellulose ethers are stable at pH 2-11 and are compatible with surfactants, other water-soluble polysaccharides, and with salts. 

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). 

Water-Soluble Films. Water-soluble films can be produced from such polymers as poly(vinyl alcohol) (PVOH), methylceUulose, poly(ethylene oxide), or starch (qv) (see Cellulose ethers Polyethers Vinyl polymers). Water-soluble films are used for packaging and dispensing portions of detergents, bleaches, and dyes. A principal market is disposable laundry bags for hospital use. Disposal packaging for herbicides and insecticides is an emerging use. 

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