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How to Prepare Aqueous Solutionsof METHOCEL Cellulose EthersJ - Tablet coating

0 2 4 6 8 10HYDRATION DELAY TIME OF SURFACE-TREATEDMETHOCELTM PRODUCTS AS A FUNCTION OF PHHydration time, minute // pH1001 000101METHOCEL cellulose ether products are carbohydratepolymers which dissolve in cold water (and in some instancesin certain organic solvents) by swelling and subsequenthydration. There is no sharp solubility limit such as occursin the dissolution of ionizing salts. The concentration ofMETHOCEL in solution is usually limited by the viscositythat a manufacturer is equipped to handle. It also dependson the viscosity and chemical type of METHOCEL productused. Solutions of low-viscosity products can be made at10% to 15% concentration while high-viscosity products havea normal limit at 2% to 3% concentration.The form of METHOCEL cellulose ether product chosen(powder, surface-treated powder or granules) influencesthe techniques used to make solutions. Surface-treated andgranular products can be added directly to aqueous systems.They disperse readily with mild agitation and dissolve(build viscosity) gradually under neutral conditions. Thedissolution rate of surface-treated products can be increasedby adjusting to an alkaline pH after dispersing the powderin water. Although untreated METHOCEL powders aresoluble in cold water, they must first be thoroughly dispersedin the water to prevent lumping.Working with Surface-treated DispersiblePowdersIn many applications, the combination of easy dispersion incold water and rapid hydration (viscosity build) is desirable.Surface-treated METHOCEL powders are chemicallytreated so that they become temporarily insoluble in coldwater. This allows the METHOCEL product to be added toa formulation and dispersed at relatively low shear withoutany significant initial increase in viscosity.This time delay of hydration or viscosity build is a functionof the level of surface treatment as well as temperature,pH of the system, and concentration of the METHOCEL

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product. Normally, the concentration of METHOCEL in thesystem does not become a factor until the concentrationexceeds 5% by weight (relative to water in the system).

At higher concentrations, the time of hydration (referredto as delay time) is reduced. The delay time is generally

reduced as temperature is raised. In many cases it isdesirable to trigger viscosity build immediately followingdispersion. Aqueous slurries can be held for 45 minutesand still remain usable in neutral systems. A trigger canbe conveniently initiated by adding a small amount of a03 METHOCELTM METHOCELTM 04base, such as ammonium hydroxide, sodium bicarbonate,etc. If METHOCEL is dispersed in neutral water (pH approximately 7), there is adequate time for thoroughdispersion. Addition of base to raise the pH to approximately9 causes the hydration to be completed in just a few minutes.

For best results and to achieve maximum hydration, surfacetreatedpowders should be added with good agitation to aneutral pH system. The system should be agitated thoroughlyfor a few minutes, followed by an adjustment of pH to 8.5to 9.0 with continued agitation, until full viscosity is reached(usually 10 to 30 minutes). Once the pH has been shiftedto the alkaline side (pH 8.5 to 9.0), allowing full and rapidsolubilization of the surface-treated product, solutions will bestable over the pH range of 3 to 11.The addition of a slurry to an alkaline pigment grind or fillerdispersion, or the addition of a slurry to a basic pigmentlatexformulation, provides rapid solubilization and uniformviscosity development. The addition of dry, alkaline pigmentsor fillers to a slurry on high-speed or low-speed mixingequipment also results in rapid solubilization and viscositydevelopment.CAUTION: Attempts to adjust the pH of high-concentrationslurries may lead to excessively high viscosity that willprevent pumping or pouring. The pH adjustment should bemade only after the slurry is diluted to the concentration atwhich it will be used.Working with Untreated Powders

Although METHOCEL powders are soluble in cold water,they must first be thoroughly dispersed in the water toprevent lumping. In some applications, dispersion can beaccomplished at ambient temperatures or in cold water byusing an eductor funnel or high-shear mixer. However, ifuntreated powders are added directly to cold water withoutsufficient agitation, a lumpy solution may result. Lumpingresults from incomplete wetting of the individual powder

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particles. Only part of the powder dissolves, and a gelatinousmembrane shields the remaining powder from completehydration. Several dispersion techniques are commonly usedand are described below. Each has advantages in certainapplications.

Dispersion in Hot WaterOften called the hot/cold technique, this method takesadvantage of the insolubility of METHOCEL celluloseethers in hot water. The powder is first dispersed by mixingthoroughly with 1/5 to 1/3 of the total required volume ofwater that has been heated to above 90C (194F). Mixingcontinues until all particles are thoroughly wetted.For complete solubilization, the remainder of the water isthen added as cold water or ice to lower the temperature ofthe dispersion. Once the dispersion reaches the temperatureat which that particular METHOCEL product becomes

water soluble, the powder begins to hydrate and viscosityincreases.In some applications, it may be desirable to heat the entirevolume of water, disperse the METHOCEL powder, andthen cool the mixture while agitating until hydration iscomplete. It is very important, however, to have adequatecooling after wetting with hot water to ensure completehydration and viscosity development.Dispersion in Concentrated Salt SolutionsBoth untreated and surface-treated METHOCEL celluloseethers can be dispersed in concentrated salt solutions.Dissolution occurs when the brine is diluted with cold water.Dispersion Techniques1. Add the METHOCELTM cellulose etherto the non-solvent. A ratio of 5-8 partsnon-solvent to 1 part METHOCELTM isrecommended to obtain a liquid slurry.2. Agitate the mixture and METHOCELTMpowder until the particles of METHOCELTMcellulose ether are evenly dispersed.3. The dispersion of METHOCELTM in a nonsolventmedium may be added to coldwater, or cold water may be added to thedispersion.4. Continue mixing until the METHOCELTMpowder is completely hydrated and thesolution is smooth. You can now add theremaining ingredients in your formulation.1. Add the surface-treated METHOCELpowder to the water. Begin agitation.

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2. Continue agitation and add sufficientammonium hydroxide, sodiumbicarbonate, or other alkaline material(e.g., pigment grind) to the dispersion toobtain a pH of 8.5 to 9.0. This will result in

rapid viscosity development.Continue agitation until sufficient hydrationhas been achieved..METHOCELMETHOCELMETHOCELMETHOCELMETHOCELMETHOCELDispersion by Dry-BlendingDry-blending involves mixing METHOCEL powder with

other dry ingredients before adding the water component.Dry-blending separates the particles of METHOCELcellulose ethers to allow thorough wet-out and completehydration when water is added. The minimum ratio of otherdry, powdered ingredients to METHOCEL powder varies