Hydroxy Ethyl Cellulose

Water Soluble Thickener, Viscosity Booster, Rheology Modifier

Introduction

Hydrocel - Hydroxy Ethyl Cellulose (HEC) is a nonionic watersoluble polymer derived from cellulose. Like Pioma cellulose gum (sodium carboxymethylcellulose), it is a cellulose ether, but it differs in that it is nonionic and its solutions are unaffected by cations. Hydrocel-HEC dissolves readily in cold or hot water. Its solutions have somewhat different flow properties from those obtained with other water-soluble polymers. It is used to produce solutions having a wide range of viscosity. Such solutions are pseudoplastic—that is, they vary in viscosity depending on the amountof shear stress applied. It describes the properties of Hydrocel-HEC, Hydrocel-HEC solutions, and Hydrocel-HEC films.

It suggests the use of Hydrocel-HEC as a thickener, protective colloid, binder, stabilizer, and suspending agent in a variety of industrial applications, including pharmaceuticals, textiles, paper, adhesives, decorative and protective coatings, emulsion polymerization, ceramics, and many miscellaneous uses.

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Properties

Our Sodium Carboxymethyl Cellulose comes in highly purified form with purity of 99.5%. It is an anionic water-soluble polymer derived fromcellulose. It is white toalmost white, odorless, tasteless, hygroscopic granularpowder.

Solubility In Water

Hydrocel-HEC dissolves quickly in cold or hot water to form clear, smooth, uniform solutions. Solutions of Hydrocel-HEC do not gel or precipitate, even when heated to the boiling point of water.

Moisture Absorption

Hydrocel-HEC can absorb moisture from the atmosphere, as doother hygroscopic or finely divided materials. The amount of moisture absorbed depends on the initial moisture content of Hydrocel-HEC and on the relative humidity of the surrounding air. Opened bags not totally used may experience moisture uptake. The moisture content of Hydrocel-HEC, does not exceed 5% by weight. During prolonged storage, the moisture content of Hydrocel tends to reach an equilibrium level that varies with the humidity of the surrounding atmosphere, particularly after the bag is opened.

Equilibrium moisture content of Hydrocel-HEC at 73°F:

At50%relative humidity . . . . . . . . . . . . . . . . . . . 6%

At84%relative humidity . . . . . . . . . . . . . . . . . . . 29%

To maintain its original moisture content, Hydrocel should be stored in tightly closed containers in a dry atmosphere.

Dermatology and Toxicology

Animal toxicology and human dermatology studies have been conducted on Hydrocel-HEC in independent laboratories. Acute oral toxicity tests showed no adverse effects on rats at doses up to 7 g/kg body weight. Subchronic oral tests resulted in no gross signs of toxicity in rats fed up to 5% in the diet. In addition, gross and microscopic examinations of organs and tissues did not reveal any abnormalities that could be attributed to the feeding of Hydrocel-HEC. Moderate eye irritation, which cleared in 24 hours, was observed in albino rabbits after instilling 3 mg of dry Hydrocel-HEC into the eyes. Instillation of aqueous solutions (0.2 to 2.0%) caused very mild or mild transient irritation.

Hydrocel-HEC was found to produce no more skin irritation in the Schwartz prophetic patch test in humans than did commercial wheat starch, which caused mild erythema in some subjects, and showed no evidence of causing sensitization. Human repeat-insult patch tests indicated that Hydrocel-HEC is nonirritatingand nonsensitizing.

As a result of these tests, Hydrocel-HEC has found use in many pharmaceuticals and cosmetic preparations. It is available in both R-treated and nontreated grades. Pioma does not recommend the use of R-grade material in pharmaceutical products intended for oral use or in those that will contact mucous membranes. R-grade Hydrocel is suitable for use only in topical applications. Hydrocel is not recommendedfor use in preparations for parenteral injections. Additional data are reported in Pioma Bulletin T-101, Hydrocel-HEC,Summary of Toxicological Investigations.

FDA and EPA Status

Hydrocel Hydroxy Ethyl Cellulose is included in the list of materials that are in compliance with requirements of the U.S. Food and Drug Administration for use in adhesives and in resinous and polymeric coatings employed on the food contact surfaces of metal, paper, or paperboard articles, and other suitable substrates intended for use in food packaging as specified in the U.S. Code of Federal Regulations, Title 21, subject to the limitations and requirements of each regulation under the following Sections. Hydrocel Rgrades, are in compliance with the requirements specified in 21 CFR, Sections 175.105, 176.170, and 176.180.

Hydrocel - Hydroxy Ethyl Cellulose (HEC) is routinely sampled and subjected to microbiological testing by an independent laboratory to provide evidence of good manufacturing practice. This testing is not done on a lot-by-lot basis, and microbiological specifications have not been formalized.

Pioma utilizes officially approved methods to determine the above microbial parameters but recommends that users of HEC assure themselves of compliance with any microbiological specification by testing each lot.

Product Safety

As with most organic materials, Hydrocel-HEC is a flammable dust when finely divided and suspended in air. If the suspended dust is ignited, it can cause an explosion. Proper design and operation of facilities and good housekeeping practices can minimize this hazard. Surfaces subject to spills or dusting with Hydrocel will become extremely slippery, particularly when wetted with water. Follow good housekeeping practices and clean up spills promptly.

Read and understand the Material Safety Data Sheet (MSDS) for Hydrocel-HEC before using this product.

Effects on Viscosity of Solutions of Hydrocel-HEC

Effect of Concentration

When Hydrocel-HEC is dissolved in water, the viscosity of the aqueous solution increases rapidly with concentration. The viscosity concentration relationship is nearly linear when viscosity is plotted vs. concentrationon a semilog basis.


Effect of Blending

Two viscosity types of Hydrocel-HEC can be blended to obtain an intermediate viscosity. Because viscosity is an exponential function of concentration and degree of polymerization, the viscosity resulting from blending is not an arithmetic mean. A blending chart (VC-440), which is available from Pioma, can be used to determine the result of blending various amounts of two viscosity types of Hydrocel-HEC. Or, it can be used to determine the amount of Hydrocel-HEC required to achieve a desired viscosity when blending two types of known viscosity.


Effect of Shear Rate

A solution of Hydrocel-HEC in water will appear to have a wide range of viscosities when different conditions of physical force are imposed on the solution. These conditions of physical forcemay be referred to as high, intermediate, or low stress. For example, rolling or spreading a liquid as if itwere an ointment or lotion would be high stress. On the other hand, after the liquid has been applied, gravity and surface tension control flow. These forces are conditions of low stress. Intermediate stress can be typified by pouring a liquid out of a bottle. Thus, if a solution of high-viscosity Hydrocel-HEC appears to be a viscous syrup as it is poured froma bottle, itwill behave as a runny liquid when applied as a lotion, and yet when high stress is removed, it will instantly revert to its original high viscosity. This type of flow behavior is referred to as pseudo plastic, or non-Newtonian. This behavior differs from the time-dependent viscosity change that is usually called thixotropy. A different molecular weight or viscosity grade of Hydrocel-HEC will behave in a similar fashion, but to a different degree. The lower the molecular weight, the less change in viscosity will occur as stress conditions are varied.


Effect of Mixed Solvents

Hydrocel-HEC will also impart varied thickening properties to solvent systems other than plain water. Behavior of Hydrocel-HEC in these mixed solvent systems is similar to its behavior inwater. However, the viscosity of the solvent must be taken into account. For example, if sucrose-water is the solvent, and if this solvent is 50 times thicker than water, the resulting solution of Hydrocel- HEC in the mixed solvent will be 50 times thicker than it will be in water. This behavior, is predictable formany solvent-water mixtures.


Effect of Temperature

The viscosity of solutions of Hydrocel-HEC changes with temperature, increasing when cooled, decreasing when warmed. Figure 10 presents a convenient nomograph from which, knowing the viscosity of a solution of Hydrocel-HEC at one temperature, one can conveniently estimate its viscosity at a different temperature. The viscosity of the solution is 100 cps at 25°C. The unknown is the viscosity when the temperature is raised 20°C. By placing a straightedge at 20 in the right column and at 100 in the center column, one can read the answer in the left column, 52 cps.


Effect of pH

Solutions of Hydrocel-HEC undergo little viscosity change over the pH range of 2 to 12. However, solutions possess the greatest viscosity stability in the pH range of 6.5 to 8.0. Below pH 3, solutions may show some drop in viscosity resulting from acid hydrolysis. This is common to all water-soluble polysaccharide polymers, and is accelerated by high temperature and high acidity. Under highly alkaline conditions, some oxidative degradation may occur, accelerated byheatand light, that will lower the viscosity.

Compatibility with other materials

Hydrocel-HEC, being a nonionic polymer, is compatible with a broad range of water-soluble materials, including other water-soluble polymers and natural gums.

Latex Emulsions

Hydrocel-HEC is compatible with a broad range of latex emulsions, hence its general use as a thickener and protective colloid for these systems.

Cellulosic Water-soluble Polymers

Hydrocel-HEC is generally compatible with other cellulosic water soluble polymers to give clear, homogeneous solutions. However, when it is mixed with an anionic polymer such as carboxymethylcellulose, an unusually high viscosity can be obtained owing to a tendency for interaction between anionic and nonionic polymers.

Water-soluble Resins

The nonionic Hydrocel-HEC has a wide tolerance for water-soluble resins. As shown in the table, solutions with Elvanol may show synergistic viscosity increase, as evidenced with anionic polymers such asCMC.


Natural Gums

Hydrocel-HEC has excellentcompatibility with natural gums.

Preservative or Biocides

A variety of preservatives can be used with Hydrocel-HEC.

Surfactants and Detergents

Hydrocel-HEC has excellent tolerance for anionic, nonionic, amphoteric, and cationic surfactants. No unusual effects were observed.


Defoamers

Silicone-in-oil dispersions, silicone emulsions, and organic defoamers can all be used with Hydrocel-HEC with no unusual effects.

Plasticizers

Water-soluble plasticizers generally do not adversely affect the quality of solutions of Hydrocel-HEC.

Organic Solvents

Although Hydrocel is insoluble in most common organic solvents, it will tolerate relatively high concentrations of many water-miscible polar solvents.

Dissolving Hydrocel-HEC in Water

Hydrocel-HEC is readily soluble in either hot or cold water. However, as with mostwater-soluble thickeners, the particles have a tendency to agglomerate, or lump, when first wetted with water. Thus, the time required to achieve complete solution of Hydrocel-HEC is usually governed by the degree of lumping that is allowed to develop during the solution process. In general, the low-viscosity types are more easily dissolved than are the high viscosity types. Solutions of the H-type, for instance, should not be prepared at greater than2%solids concentration. Pioma has solved the problem of lumping and slow dissolving by producing a surface-treated grade of Hydrocel-HEC, known as the R-grade. This grade disperses without lumping when added to water. After an inhibition period, the dispersed particles begin to dissolve and smooth, lump-free solutions are readily achieved. All viscosity types are available in the R-grade. Additional information on the dissolution characteristics of the R-grade is given in the section entitled Hydrocel-HEC R-Grade. If the R-grade is not used, the following procedures are suggested for the easiestand mostefficient preparation of solutions of Hydrocel-HEC.

Method 1

Hydrocel-HEC should be sifted slowly into the vortex of vigorously agitated water. The rate of addition should be slow enough for the particles to separate in water without lump formation, but not so slow that the solution thickens appreciably before all the solid is added. Agitation should be continued until all of the swollen or gelatinized particles are dissolved to yield a smooth solution.

Method 2

Excellent solution rates can be obtained by prewetting Hydrocel-HEC with a water miscible organic liquid before the powder is added towater. Anhydrous ethyl alcohol, higher alcohols, and ketones are suitable for this use, as are other organic liquids such as diethylene glycol monoethyl ether, diethylene glycol monoethyl ether acetate, ethylene glycol monobutyl ether acetate, or hexylene glycol. Ethylene glycol, however, is not recommended, as it swells the particles slightly so that they tend to stick together instead of separating as the prewetting liquid is dissolved away.

Method 3

Improved solution rates can be obtained by dry-blending Hydrocel-HEC with other dry materials (preferably insoluble) that are to be added to the solution. This technique effectively separates particles of Hydrocel-HEC so thatno lumping is experiencedwhenthe dry mix is added towater.

Solubility in Organic Solvents

Hydrocel-HEC water-soluble polymer is essentially insoluble in organic solvents. It is, however, either swollen or partly soluble in some solvents. Usually those that are miscible with water, or that contain polar groups, show some effect, Table IV reports solubility behavior with typical organic solvents. Data were obtained by adding 1 g of Hydrocel-HEC to 100 g of the respective solvent at 25°C (cold) and 55 to 60°C (hot).

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