Viscosity of Methylcellulose

Procedure Transfer 5.0 g of sample, previously dried at 105° for 2 h and accurately weighed, into a bottle containing 95 0.5 g of the appropriate solvent system. Shake or tumble the bottle until the sample is completely dissolved, and then adjust the temperature of the solution to 25° 0.1°. Determine the viscosity as directed under Viscosity of Methylcellulose, Appendix IIB, but make all determinations at 25° instead of at 20°. 

Viscosity Accurately weigh a sample, equivalent to 2 g of solids on the dried basis, transfer it to a wide-mouth, 250-mL centrifuge bottle, and add 98 g of water previously heated to between 80° and 90°. Stir with a mechanical stirrer for 10 min, then place the bottle in an ice bath until solution is complete, adjust the weight of the solution to 100 g, if necessary, and centrifuge it to expel any entrapped air. Adjust the temperature of the solution to 20° 0.1°, and determine as directed under Viscosity of Methylcellulose, Appendix IIB. 

Apparatus Viscometers used to determine the viscosity of methylcellulose and some related compounds are illustrated in Fig. 6 and consist of three parts a large filling tube, A an orifice tube, S and an air vent to the reservoir, C. 

Determination of the Viscosity of Methylcellulose Prepare a 2% solution of methylcellulose or other cellulose derivative, by weight, as directed in the monograph. Place the solution in the proper viscometer and determine the time, f, required for the solution to flow from the upper mark to the lower mark in orifice tube B. Separately determine the specific gravity, d, at 20720°. Viscosity, V = Kdt. 

Oils of known viscosities may be obtained from the Cannon Instrument Co., P.O. Box 812, State College, PA 16801. For determining the viscosity of methylcellulose, choose an oil that has a viscosity as close as possible to that of the type of sample to be tested. 

Solutions of methylcellulose are stable to alkalis and dilute acids at pH 3-11, at room temperature. At pH less than 3, acid-catalyzed hydrolysis of the glucose-glucose linkages occurs and the viscosity of methylcellulose solutions is reduced.On heating, solution viscosity is reduced until gel formation occurs at approximately 50°C see Section 10. 

The thermal gelation temperature for methylcellulose decreases as a function of concentration. The presence of additives can increase or decrease the thermal gelation temperature. The presence of drugs can influence the properties of methylcellulose gels. In addition, the viscosity of methylcellulose solutions can be modified by the presence of drugs or other additives. Aqueous solutions of methylcellulose can be frozen and do not undergo phase separation upon freezing. 

Huikari A. Effect of heat sterilization on the viscosity of methylcellulose solutions. Acta Pharm Penn 1986 95(1) 9—17. 

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. 

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. 

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... 

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. 

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). 

Increasing the viscosity of solutions administered to the nasal cavity with, for example, methylcellulose, hyaluronan etc., has been shown to increase the time the formulation is retained in the nasal cavity and to enhance the absorption of certain drugs. It is thought that, up to an optimum viscosity, higher viscosity solutions give a more localized deposition in the anterior portion of the nose (i.e. low clearance site). As viscosity can affect droplet size by altering the surface tension of the solution, the more localized deposition in the anterior of the nose may be due to viscosity-related changes in the particle size of the delivered droplets. 

There are two basic types of methylcellulose viscometers— one for cellulose derivatives of a range between 1500 and 4000 centipoises, and the other for less viscous ones. Each type of viscometer is modified slightly for the different viscosities. 

In tablet formulations, low- or medium-viscosity grades of methylcellulose are used as binding agents, the methylcellulose being added either as a dry powder or in solution.High-viscosity grades of methylcellulose may also be incorporated in tablet formulations as a disintegrant. " Methylcellulose may be added to a tablet formulation to produce sustained-release preparations. ... 

Tablet cores may also be spray-coated with either aqueous or organic solutions of highly substituted low-viscosity grades of methylcellulose to mask an unpleasant taste or to modify the release of a drug by controlling the physical nature of the granules. Methylcellulose coats are also used for sealing tablet cores prior to sugar coating.

High-viscosity grades of methylcellulose are used to thicken topically applied products such as creams and gels. 

---