Methylcellulose, Viscosity

Paint strippers are also formulated to have high viscosity, otherwise they run off vertical surfaces and thereby fail to penetrate or solubilise the paint to which they have been applied. Hydroxypropyl methylcellulose is the main thickener for paint strippers, which use methylene chloride (dicldoromethane) as the principal component. Hydroxypropyl methylcellulose is useful for this purpose because it is soluble in the orgaiuc component but is not sensitive to the presence of any water that may also be present in the paint stripper. 

Although untreated starches do not swell sufficiently, certain modified forms, such as sodium starch glycolate, do swell in cold water and are better as disintegrants. Various cellulose derivatives, including methylcellulose and carboxymethylcellulose, have been used in this role, but with limited success due to the marked increase in viscosity they produce around the dispersing tablet mass. 

Methylcellulose MC Cold water, GI fluids, organic solvents Useful polymer for aqueous films low-viscosity grade best... 

The major commercial viscous vehicles are hydroxypropyl methylcellulose (Isopto ) and polyvinyl alcohol (Liquifilm ). Isopto products most often use 0.5% of the cellulosic and range from 10 to 30 cP in viscosity. Liquifilm products have viscosities of about 4-6 cP and use 1.4% polymer. 

The main function of the foam stabilising agent is to reinforce the intercellular film wall by contributing rheological characteristics of viscoelasticity. The increased viscosity may also assist handling. The aim, as so often with auxiliaries, is to achieve an optimum balance. If the bubbles are too thin and wet too quickly they will collapse prematurely, whilst too stable a film could hinder uniform application. Examples of products used as foam stabilisers include thickening agents such as the polysaccharides, hydroxyethylcellulose, methylcellulose,... 

Because the viscosity of neoprene latex at a given solids content is less than that of natural rubber latex, thickeners are generally needed with the former. Methylcellulose and the water-soluble salts of poly(acrylic acid) are the two most commonly used thickeners. Natural and synthetic gums are also used. 

Obara S, Muto H, Shigeno H, et al. A three-month repeated oral administration study of a low viscosity grade of hydroxypropyl methylcellulose in rats. J Toxicol Sci 1999 24(1) 33—43. 

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... 

Other thickeners used include derivatives of cellulose such as methylcellulose, hydroxypropylmethylcellulose, and cellulose gum natural gums such as tragacanth and xanthan (see Cellulose ethers Gums) the carboxyvinyl polymers and the poly(vinyl alcohol)s. The magnesium aluminum silicates, glycol stearates, and fatty alcohols in shampoos also can affect viscosity. 

Korshak and his colleagues reported210 that polymerization of tri-O-methyllevoglucosan with boron trifluoride etherate in dichloromethane gives products having the highest reduced viscosity. The yield of polymer increased with temperature, and the reduced viscosity reached a maximum at -20°. In contrast to tri-O-methylcellulose, poly(tri-0-methyl-D-glu-coses) prepared in this way are insoluble in water, acetone, or ether, but are soluble in chloroform and a cresol. These workers concluded that the products are crystalline and unbranched. 

Their membrane consisted of sodium carboxy methylcellulose incorporated in viscose. 

Viscosity agents have been added to suspensions to retard crystallization in much the same manner that they are used to prevent crystallization to a more stable polymorph. Mullins and Macek (1960) found that suspensions of amorphous novobiocin lasted 22 day aA3c76 months at 2 before converting to the crystalline compound. By adding 1% methylcellulose to the suspension, they were able to extend this to more than 1 year aCJThaking a viable drug product when stored at room temperature. 

Carr, T.P., Gallagher, D.D., Yang, C.-H., and Hassel, C.A. 1996. Increased intestinal contents viscosity reduces cholesterol absorption efficiency in hamsters fed hydroxypropyl methylcellulose. J. Nutr. 126, 1463-1469. 

Gallaher, D.D., Hassel, C.A., and Lee, K.J. 1993. Relationships between viscosity of hydroxypropyl methylcellulose and plasma cholesterol in hamsters. J. Nutr. 123, 1732-1738. 

There are several ways to reduce or suppress the electroosmotic flow in capillaries. These methods involve either eliminating the zeta potential across the solution-solid interface or increasing the viscosity at this interface. One approach is to coat the capillary wall, physically, with a polymer such as methylcellulose or linear polyacrylamide. Because of the difficulty in deactivating the capillary surface reproducibly, however, alternative methods employing dynamic reduction of solute-capillary interactions have been developed. Dynamic reduction of these interactions include the addition of chemical reagents such as methylhydroxyethylcellulose, S-benzylthiouro-nium chloride, and Triton X-100. 

Figure 3 Profile of a complex viscosity (n ) and the storage (G ) and loss (G ) moduli of a 1 % konjac-xanthan—methylcellulose mixture in a 1 1 1 ratio, illustrating t e onset o gelation at Tge) approximating 60°C.

Blends of starch and konjac gum (Tye, 1991) and of some modified celluloses (Hercules, Inc., 1980) are synergistic. A ternary dispersion of 1% methylcellulose and 2.9% starch had almost 2.5 times the viscosity of a blend of 0.5% methylcellulose and 2.9% starch, and approximately 20 times the viscosity of 3.9% starch (Hegenbart, 1989). Methylcellulose-starch viscosity synergism was suggested as a formula to decrease caloric content (Henderson, 1989). Guar gum can increase starch paste viscosity tenfold (Christianson et al., 1981). 

Figure 6 Viscosity profile of gellan in water (1), gellan in 0.04-M tartaric acid (2), locust bean (3) and methylcellulose (4) in water, and CMC in 0.04-M tartaric acid (5).

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