Water soluble cellulose ether

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. 

A very frequently described family of polymers subjected to simple coacervation are cellulose derivatives, particularly ethyl cellulose (EC). ° While most cellulose ethers are soluble in water, EC and the cellulose esters are insoluble or only partly soluble in water, e.g., as a function of pH. For coacervation of EC, toluene is a preferred good solvent and cyclohexane a poor solvent. Gradual addition of cyclohexane to a solution of EC desolvates the polymer. Alternatively, EC can be dissolved in hot cyclohexane cooling to room temperature induces polymer phase separation. In both these cases, the coacervate film or droplets can be hardened by exposing the coacervate to a large volume of cyclohexane, whereby physical cross-links are formed. 

This nonionic cellulose ether is soluble in cold water, ethanol, and mixtures of ethanol and water. 

Cellulose ethers, such hydroxyethyl cellulose or hydrox5rpropyl cellulose, are water soluble cellulose derivatives which may be produced by etherification of alkali cellulose with epoxides, e.g., ethylene oxide or propylene oxide (36). Cellulose is made alkaline in sodium hydroxide solution and subsequently reacted with the corresponding alkylene oxides. 

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. 

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). 

CP can also be prepared by the reaction of cellulose with phosphoms oxychloride in pyridine (37) or ether in the presence of sodium hydroxide (38). For the most part these methods yield insoluble, cross-linked, CP with a low DS. A newer method based on reaction of cellulose with molten urea—H PO is claimed to give water soluble CP (39). The action of H PO and P2 5 cellulose in an alcohol diluent gives a stable, water-soluble CP with a high DS (>5% P) (40). These esters are dame resistant and have viscosities up to 6000 mPa-s(=cP) in 5 wt % solution. Cellulose dissolved in mixtures of DMF—N2O4 can be treated with PCl to give cellulose phosphite [37264-91-8] (41) containing 11.5% P and only 0.8% Cl. Cellulose phosphinate [67357-37-5] and cellulose phosphonate [37264-91 -8] h.a.ve been prepared (42). 

Properties. Ethyl cellulose [9004-57-3] (EC) is a nonionic, organo-soluble, thermoplastic cellulose ether, having an ethyl DS in the range of 2.2-2.7. Actually, EC is water-soluble at DS 1.2, but only those products that are thermoplastic and soluble in organic solvents are of commercial importance, because of thek abiUty to form tough, stable films. Above a DS of about 2.5, EC is soluble in many nonpolar solvents. 

Properties. Hydroxypropylcellulose [9004-64-2] (HPC) is a thermoplastic, nonionic cellulose ether that is soluble in water and in many organic solvents. HPC combines organic solvent solubiUty, thermoplasticity, and surface activity with the aqueous thickening and stabilising properties characteristic of other water-soluble ceUulosic polymers described herein. Like the methylceUuloses, HPC exhibits a low critical solution temperature in water. 

An example of the first type is the emulsion stabiliser as exemplified by sodium oleyl sulphate, cetyl pyridinium chloride and poly(ethylene oxide) derivatives. For a number of applications it is desirable that the latex be thickened before use, in which case thickening agents such as water-soluble cellulose ethers or certain alginates or methacrylates may be employed. Antifoams such as silicone oils are occasionally required. 

By use of a modification of the well-known Williamson synthesis it is possible to prepare a number of cellulose ethers. Of these materials ethyl cellulose has found a small limited applieation as a moulding material and somewhat greater use for surfaee eoatings. The now obsolete benzyl cellulose was used prior to World War II as a moulding material whilst methyl eellulose, hyroxyethyl eellulose and sodium earboxymethyl eellulose are useful water-soluble polymers. 

A number of water-soluble cellulose ethers are marketed." Methyl cellulose is prepared by a method similar to that used for ethyl cellulose. A degree of substitution of 1.6-1.8 is usual since the resultant ether is soluble in cold water but not in hot. It is used as a thickening agent and emulsifier in cosmetics, as a paper size, in pharmaceuticals, in ceramics and in leather tanning operations. 

Occasionally, water-soluble plastics are required. Poly(vinyl alcohol) is commonly the first to be considered but some cellulose ethers, polyethylene oxides, poly(vinyl pyrrolidone) and A-substituted polyamides are among many possible alternatives. 

Cellulose is also commercially modified by acetylation to produce a material suitable for X-ray and cine film. Commercially cellulose ethers are also prepared, such as methylcellulose. This material is water-soluble and gives a highly viscous solution at very low concentrations. Hence it is widely used as a thickener in latex paints and adhesives, in cosmetics and for coating pharmaceutical tablets. 

Semisynthetic gels are also very useful for the creation of drug delivery systems. Cellulose ethers are particularly important in drug delivery. These compounds are made by derivatizing the cellulose hydroxyls with various groups such as hydroxypropyl, methyl, or carboxymethyl. This substitution breaks up the crystallinity of native cellulose and makes it water-soluble [23], The degree... 

IX. Cellulose Ethers Soluble in Dilute Alkali but not in Water. 293... 

Cellulose ethers of a high degree of substitution are stable, relatively nonflammable, resistant to ultra-violet light and compatible with a wide range of solvents and plasticizers. Certain ethers of a low degree of substitution are soluble in water or alkali. It would appear from these properties that cellulose ethers should be ideally adapted for use in the plastics field and for many other uses. 

Treatment of alkali cellulose with sodium chloroacetate results in an ether with a free carboxyl group. This ether, in the form of its sodium salt, is water-soluble even when the degree of substitution is relatively low. Since the alkali-soluble modification of this substance is of much greater industrial importance it will be discussed in detail under that heading. 

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