AQUALON. Sodium Carboxymethylcellulose. Physical and Chemical Properties
1 CM AQUALON Sodium Carboxymethylcellulose Physical and Chemical Properties2 AQUALON An Anionic Water-Soluble Polymer CO...
C C M C C M C C M C C M C C M C C M C C M C C M C C M C C M C C M C C M C C M C C M C C M C C M C C M C C M C
Physical and Chemical Properties
AQUALON® CMC An Anionic Water-Soluble Polymer
PAGE Effect of Temperature . . . . . . . . . . . . . . . Effect of pH . . . . . . . . . . . . . . . . . . . . . . . Effect of Mixed Solvents . . . . . . . . . . . . . Stability . . . . . . . . . . . . . . . . . . . . . . . . . . . Microbiological Attack . . . . . . . . . . . . . . . Chemical Degradation . . . . . . . . . . . . . . . Compatibility . . . . . . . . . . . . . . . . . . . . . . . . Effect With Salts . . . . . . . . . . . . . . . . . . . Monovalent Cations . . . . . . . . . . . . . . . Polyvalent Cations . . . . . . . . . . . . . . . . Gelation of Solutions . . . . . . . . . . . . . . . . . . Effect With Water-Soluble Nonionic Gums . . PROPERTIES OF CMC FILMS . . . . . . . . . . . . PACKAGING AND SHIPPING . . . . . . . . . . . . . MICROBIOLOGICAL INFORMATION AND REGULATORY STATUS FOR USE IN FOODS, DRUGS, COSMETICS, AND TOILETRIES . . . Microbiological Information . . . . . . . . . . . . . Food Status . . . . . . . . . . . . . . . . . . . . . . . . Food Labeling . . . . . . . . . . . . . . . . . . . . . . . Pharmaceutical Use . . . . . . . . . . . . . . . . . . Cosmetics and Toiletries . . . . . . . . . . . . . . . APPENDIX—METHODS OF ANALYSIS . . . . . Viscosity of Solution . . . . . . . . . . . . . . . . . . Moisture Determination . . . . . . . . . . . . . . Solution Preparation . . . . . . . . . . . . . . . . Viscosity Measurement . . . . . . . . . . . . . .
AQUALON CMC — AN ANIONIC WATER-SOLUBLE POLYMER . . . . . . . . . . . . . . 2 APPLICATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . 3 CHEMISTRY . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 GRADES AND TYPES . . . . . . . . . . . . . . . . . . . . 6 Grades . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 Degree of Substitution . . . . . . . . . . . . . . . . . . . 6 Viscosity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 Particle Size . . . . . . . . . . . . . . . . . . . . . . . . . . 7 Product Coding . . . . . . . . . . . . . . . . . . . . . . . . 7 PROPERTIES . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 Moisture Absorption . . . . . . . . . . . . . . . . . . . . . 8 Physiological Properties . . . . . . . . . . . . . . . . . . 8 DISPERSION AND DISSOLUTION OF CMC . . . . 9 Solvent . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 Type of CMC . . . . . . . . . . . . . . . . . . . . . . . . . . 9 Shear Rate . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 Dispersion Methods . . . . . . . . . . . . . . . . . . . . . 9 Theory of Polymer Dissolution . . . . . . . . . . . . . 11 PROPERTIES OF CMC SOLUTIONS . . . . . . . . . 13 Viscosity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 Effect of Concentration . . . . . . . . . . . . . . . . 13 Effect of Blending . . . . . . . . . . . . . . . . . . . . 13 Blending Chart . . . . . . . . . . . . . . . . . . . . . . 13 Effect of Shear . . . . . . . . . . . . . . . . . . . . . . 16 Pseudoplasticity . . . . . . . . . . . . . . . . . . . 16 Thixotropy . . . . . . . . . . . . . . . . . . . . . . . . 17
© Hercules Incorporated, 1999.
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AQUALON® CMC AN ANIONIC WATER-SOLUBLE POLYMER
Aqualon® sodium carboxymethylcellulose (CMC) has a minimum purity of 99.5%. An anionic water-soluble polymer derived from cellulose, it has the following functions and properties: • It acts as a thickener, binder, stabilizer, protective colloid, suspending agent, and rheology, or flow control agent. • It forms films that are resistant to oils, greases, and organic solvents. • It dissolves rapidly in cold or hot water. • It is suitable for use in food systems. • It is physiologically inert. • It is an anionic polyelectrolyte. These properties and functions make it suitable for use in a broad range of applications in the food, pharmaceutical, cosmetic, paper, and other industries. To serve these diverse industries, the polymer is available in three grades: food, pharmaceutical, and standard, and in many types based on carboxymethyl substitution, viscosity, particle size, and other parameters. This booklet describes basic chemical and physical properties of Aqualon CMC in all its forms. The wide variety of types produced and the typical uses for this versatile polymer are also discussed. The contents page will guide the reader to subjects of special interest. Technical or semi-refined grades of sodium carboxymethylcellulose are also available and are described in Booklet 250-3, available from Aqualon by request.
Since its commercial introduction in the United States by Hercules Incorporated in 1946, sodium carboxymethylcellulose has found use in an ever-increasing number of applications. The many important functions provided by this polymer make it a preferred thickener, suspending aid, stabilizer, binder, and film-former in a wide variety of uses.
A representative listing of the many applications for sodium carboxymethylcellulose is given below and on the following page. Many of these applications do not require the use of the highly purified grade, and a technical grade of CMC is available for certain applications. Aqualon’s chemists and engineers continue to tailor-make various grades and types to meet the needs of specific customers and industries requiring water-soluble polymers.
The wide range of viscosity and substitution types available from Aqualon for the highly purified grades and the less highly purified technical grades of CMC continues to expand the uses for this product line.
APPLICATIONS FOR PURIFIED CMC(1) Types of Uses
Thickener; flavor stabilizer; suspending aid; binder
Shampoos; foamed products
Suspending aid; thickener; foam stabilizer; high water-binding capacity
Emulsion stabilizer; film-former; thickener
Thickener; gelling agent; film-former
Wet tack; long-lasting adhesion
Frozen desserts; soft-serve
Controls ice crystal growth; improves mouthfeel, body, and texture
Water binder; gravy thickener; extrusion aid; binder of fines
Retains water; improves mouthfeel
Batter viscosifier; improves moisture retention and texture
Suspending aid; rapid viscosifier; improves mouthfeel and body; protein stabilizer in acidified drinks
Desserts; icings; toppings
Odorless and tasteless; thickens; controls sugar crystal size; improves texture; inhibits syneresis
No caloric value(2); thickens; imparts body and mouthfeel
Clear; thickens; imparts favorable mouthfeel and body
Thickener and suspending aid; imparts mouthfeel
Animal feed; extrusion products
Lubricant; binder; film-former
Ointments; creams; lotions
Stabilizer; thickener; film-former
Thickener; gelling agent; protective colloid, film-former
Tablet binder; granulation aid
Physiologically inert; high water-binding capacity
Thickener; suspending aid
these applications, food grades (designated “F”) or pharmaceutical grades (designated “PH”) are used. These types may be referred to as “cellulose gum.” (2)Depends on test method.
APPLICATIONS FOR STANDARD GRADE OF CMC Types of Uses
Water-binding aid; adhesion; good open time; nonstaining
Thickener; water-binding and -suspending aid
Thickener; water-binding aid
Thickener; binder; suspending aid
Glazes Porcelain slips Vitreous enamels Refractory mortars
Binder for green strength; thickener; suspending aid
Welding rod coatings
Binder; thickener; lubricant
Foundry core wash
Binder; thickener; suspending aid
Latex paints; paper coatings
Rheology control; suspending aid; protective colloid
Whiteness retention through soil suspension
Fountain and gumming solutions
Hydrophilic protective film
Binder; rheology control; suspending aid
High-strength binder; improves dry strength of paper
High-strength binder; oil-resistant film-former; provides control of curl and porosity and resistance to oils and greases
Thickener; rheology control; water-retention aid
Laundry and fabric sizes
Latex adhesives; backing compounds Printing pastes and dyes
Rheology control; thickener; water binding and holdout
High film strength; good adhesion to fiber; low BOD value
Cigar and cigarette adhesive
Good wet tack; high film strength
High-strength binder and suspending aid
Paper and paper products
CMC is a cellulose ether, produced by reacting alkali cellulose with sodium monochloroacetate under rigidly controlled conditions.
Figure 1 Structure of Cellulose
Figure 1 shows the structure of the cellulose molecule; it is visualized as a polymer chain composed of repeating cellobiose units (in brackets). These, in turn, are composed of two anhydroglucose units (β-glucopyranose residues). In this structure, n is the number of anhydroglucose units (which are joined through 1,4 glucosidic linkages), or the degree of polymerization, of cellulose.
O HO H
Figure 2 Idealized Unit Structure of CMC, With a DS of 1.0
Each anhydroglucose unit contains three hydroxyl groups, shown in white. By substituting carboxymethyl groups for some of the hydrogens of these hydroxyls, as shown in Figure 2, sodium carboxymethylcellulose is obtained. The average number of hydroxyl groups substituted per anhydroglucose unit is known as the “degree of substitution,” or DS. If all three hydroxyls are replaced, the maximum theoretical DS of 3.0 (impossible in practice) results.
CASRN: 9004-32-4 CAS Name: Cellulose, carboxymethyl ether, sodium salt
Optimum water solubility and other desirable physical properties of CMC are obtained at a much lower degree of substitution than 3. The most widely used types of Aqualon® CMC have a DS of 0.7, or an average of 7 carboxymethyl groups per 10 anhydroglucose units. Higher degrees of substitution result in CMC products having improved compatibility with other soluble components.
Table I — Typical Molecular Weights for Representative Viscosity Types of Aqualon CMC (DS = 0.7 in All Cases)
Cellulose ethers, such as CMC, are long-chain polymers. Their solution characteristics depend on the average chain length or degree of polymerization (DP) as well as the degree of substitution. Average chain length and degree of substitution determine molecular weight of the polymer. As molecular weight increases, the viscosity of CMC solutions increases rapidly. Approximate values (weight averages) for the degree of polymerization and molecular weight of several viscosity types of Aqualon CMC are given in Table I. The degree of neutralization of carboxymethyl groups also impacts viscosity. In solution, the degree of neutralization is controlled by the pH. At the end of the carboxymethylation, the reaction mixture contains a slight excess of sodium hydroxide, which is usually neutralized. Although the neutral point of CMC is pH 8.25, the pH is generally adjusted to about 7-7.5. If the pH to which the CMC is neutralized is 6.0 or less, the dried product does not have good solubility in water; solutions are hazy and contain insoluble gel particles. If the pH is 4 or below, the dried product is insoluble in water.
Degree of Polymerization
High Medium Low
3,200 1,100 400
700,000 250,000 90,000
GRADES AND TYPES
DEGREE OF SUBSTITUTION
To serve its diverse markets, Aqualon produces CMC in several grades and in a wide variety of types, based on the degree of substitution, viscosity, particle size, and other parameters.
Aqualon CMC is produced with the following degrees of substitution:
Aqualon® CMC is available in the three grades outlined below.
7 9 12
Food, cosmetic, pharmaceutical
Sodium Content, %
0.65-0.90(b) 0.80-0.95 1.15-1.45
7.0-8.9 8.1-9.2 10.5-12.0
shown in this table are not necessarily current specifications. (b)ln 7S types, the upper limit of substitution is 0.95.
Higher degrees of substitution give improved compatibility with other soluble components such as salts and nonsolvents. Generally, the number given in the product designation is approximately 10 times the DS.
*P (1.2 D.S. types and CMC 7L2P) **PH (0.7 and 0.9 D.S. types)
Table II — Some Types of Aqualon CMC Designations for Indicated Substitution Types 7 9 12
Viscosity Range at 25°C,(c) cps (mPas) High—at 1% Concentration 2,500-6,000 1,000-2,800 1,500-3,000
7H4 7H3S, 7HOF 7H
Medium—at 2% Concentration 800-3,100 1,500-3,100 400-800 200-800 100-200
12M31 7M 7M8S 7M2
Low(d)—at 2% Concentration 25-50
—at 4% Concentration 50-200
shown in this table are not necessarily current specifications. even lower viscosity types are available. Contact your technical representative for additional information.
CMC is manufactured in a wide range of viscosities. Highviscosity types are prepared from high viscosity cotton linters. Medium-viscosity types are prepared from wood pulp of specified viscosity. Low-viscosity types are prepared by aging the shredded alkali cellulose and by using chemical oxidants. The foregoing methods of regulating the viscosity are based on controlling the DP. It is also possible to attain high viscosity by decreasing the solubility so that the product is highly swollen but not completely dispersed. This can be accomplished by decreasing the uniformity of the reaction and lowering the DS. For example, products at DS 1.2 do not have solution viscosities as high as products of DS 0.7 prepared in substantially the same way. However, the solutions of the higher-substituted products are much smoother.
Aqualon® CMC is available in several different particle sizes to facilitate handling and use in processing operations such as solution preparation and dry-blending. Screen analysis is given here for three of the types. Other types are available.
The viscosity ranges of some types are listed in Table II. Others are available to meet specific needs. Regular viscosity types with a DS of 0.7 meet most needs and are designated by the number 7, followed by the letter H (high), M (medium), or L (low). All other types are designated by an additional number following the letter which, when multiplied by a factor, gives the approximate upper viscosity limit. The factor and applicable concentration appear below.
High Medium Low
1,000 100 10
1 2 2
On U.S. 30, %, max On U.S. 40, %, max
On U.S. 20, %, max Through U.S. 40, %, max Through U.S. 80, %, max
On U.S. 60, %, max Through U.S. 200, %, min
55 5 0.5 80
screens are U.S. Bureau of Standards sieve series.
PRODUCT CODING An example of the coding used for ordering Aqualon CMC follows: For cellulose gum Type 7H3SCF: 7 means that the typical degree of substitution is approximately 0.7. H means high viscosity. 3 means that the viscosity of a 1% solution is in the range of 3,000 cps. S means smooth solution characteristics. C means coarse particle size. F means food grade.
Solutions of all CMC types display pseudoplastic behavior. (See page 16.) Some types, particularly those of higher molecular weight and lower substitution, also show thixotropic behavior in solution. (See page 17.) These thixotropic solutions will possess varying amounts of gel strength and are used where suspension of solids is required. The “S,” 9, and 12 types produce solutions with little or no thixotropy, and are utilized where smooth solutions without structure are required.
Aqualon can tailor the chemical and physical properties of CMC to meet special requirements. Users are encouraged to discuss their needs with their technical representative, or to call the 800 number shown on the back cover for product information.
Specific properties are available in certain other types. For example, the “O” type, 7HOF, provides the best solubility and storage stability in acid media.
Typical properties of Aqualon® CMC polymer and in solution and film form are shown in Table III. These are not necessarily specifications.
Figure 3 Effect of Relative Humidity on Equilibrium Moisture Content of Aqualon CMC at 25°C
Table III—Typical Properties of Aqualon CMC Equilibrium Moisture Content, %
Polymer Sodium carboxymethylcellulose— dry basis, %, min . . . . . . . . . . . . . . . . . . . . 99.5 Moisture content (as packed), %, max . . . . . . . 8.0 Browning temperature, °C . . . . . . . . . . . . . . . . 227 Charring temperature, °C . . . . . . . . . . . . . . . . . 252 Bulk density, g/ml . . . . . . . . . . . . . . . . . . . . . .0.75 Biological oxygen demand (BOD)(f), ppm 7H type . . . . . . . . . . . . . . . . . . . . . . . . . 11,000 7L type . . . . . . . . . . . . . . . . . . . . . . . . . . 17,300 Solutions pH, 2% solution . . . . . . . . . . . . . . . . . . . . . . . . 7.5 Surface tension, 1% solution, dynes/cm at 25°C. . . . . . . . . . . . . . . . . . . . . . 71 Specific gravity, 2% solution . . . . . . . . . . . . 1.0068 Refractive index, 2% solution . . . . . . . . . . . . 1.336
40 12M31P 7HF
Typical Films (Air-Dried) Density, g/ml . . . . . . . . . . . . . . . . . . . . . . . . . 1.59 Refractive index . . . . . . . . . . . . . . . . . . . . . . 1.515 Thermal conductivity, W/mK. . . . . . . . . . . . . . 0.238
40 60 Relative Humidity, %
PHYSIOLOGICAL PROPERTIES Dermatological and toxicological studies by independent laboratories demonstrate conclusively that sodium carboxymethylcellulose shows no evidence of being toxic to white rats, dogs, guinea pigs, or human beings. Feeding, metabolism, and topical use studies also show that CMC is physiologically inert. Patch tests on human skin demonstrated that sodium carboxymethylcellulose was neither a primary irritant nor a sensitizing agent. Additional information is available from Hercules Incorporated.
5 days’ incubation. Under these conditions, cornstarch has a BOD of over 800,000 ppm.
MOISTURE ABSORPTION CMC absorbs moisture from the air. The amount absorbed and the rate of absorption depend on the initial moisture content and on the relative humidity and temperature of the surrounding air. Figure 3 shows the effect of relative humidity on equilibrium moisture content of three types of Aqualon CMC. As Aqualon CMC is packed, its moisture content does not exceed 8% by weight. Because of varying storage and shipping conditions, there is a possibility of some moisture pickup from the “as-packed” value.
DISPERSION AND DISSOLUTION OF CMC
A number of factors such as solvent, choice of polymer, and shear rate affect dispersion and dissolution of CMC.
CMC particles have a tendency to agglomerate, or lump, when first added to water. To obtain good solutions easily, the dissolving process should be considered a two-step operation:
Aqualon CMC is soluble in either hot or cold water. The gum is insoluble in organic solvents, but dissolves in suitable mixtures of water and water-miscible solvents, such as ethanol or acetone. Solutions of low concentration can be made with up to 50% ethanol or 40% acetone. Aqueous solutions of CMC tolerate addition of even higher proportions of acetone or ethanol, the low-viscosity types being considerably more tolerant than the high-viscosity types, as shown below. ®
1. Dispersing the dry powder in water. Individual particles should be wet and the dispersion should not contain lumps. 2. Dissolving the wetted particles. When the proper technique is used, good dispersion is obtained, and CMC goes into solution rapidly. To prepare lumpfree, clear solutions, a variety of methods can be used:
Tolerance of Aqualon CMC Solutions for Ethanol
Method 1 Add CMC to the vortex of vigorously agitated water. The rate of addition must be slow enough to permit the particles to separate and their surfaces to become individually wetted, but it should be fast enough to minimize viscosity buildup of the aqueous phase while the gum is being added.
Volume Ratio of Ethanol to CMC Solution, 1% CMC Type
First Evident Haze
First Distinct Precipitate
7L 7M 7H
2.4 to 1 2.1 to 1 1.6 to 1
3.6 to 1 2.7 to 1 1.6 to 1
Method 2 Prior to addition to water, wet the powder with a watermiscible liquid such as alcohol, glycol, or glycerol that will not cause CMC to swell. Two to three parts of liquid per part of CMC should be sufficient.
Note: In these tests, ethanol (95%) was added slowly at room temperature to the vigorously stirred 1% CMC solution.
Method 3 Dry-blend the CMC with any dry, nonpolymeric material used in the formulation. Preferably, the CMC should be less than 20% of the total blend.
TYPE OF CMC The higher the degree of substitution, the more rapidly CMC dissolves. The lower the molecular weight, the faster the rate of solution.
Method 4 Use a water eductor (Figure 4) to wet out the polymer particles rapidly. The polymer is fed into a water-jet eductor, where a high-velocity waterflow instantly wets out each particle, thus preventing lumping. This procedure speeds solution preparation and is particularly useful where large volumes of solutions are required. For users wishing the convenience of an automatic system, a polymer solution preparation system (PSP), which is used in conjunction with a water eductor, is shown in Figure 5.
Particle size has a pronounced effect on the ease of dispersing and dissolving CMC. “C,” or coarse, types were developed to improve dispersibility of the granules when agitation is inadequate to produce a vortex on the liquid surface. Solution time, on the other hand, is extended considerably with a coarse material. For applications requiring a rapid solution time, CMC of fine particle size (X grind) is best. However, special dissolving techniques, such as prewetting the powder with a nonswelling liquid, mixing it with other dry materials, or using an eductor-type mixing device, are necessary to obtain dispersion.
Special, fast-dissolving fluidized polymer suspensions of CMC are available to give very rapid dissolution where it is required or where agitation is substandard. Users are encouraged to contact their technical representative for information on PSP units or fluidized suspensions of CMC.
SHEAR RATE Preparing solutions by extremely low shear agitation, such as shaking by hand, is generally not recommended. Properties of the resulting solution are quite different from those prepared by higher shear methods. The effect of shear on solution properties is discussed in more detail on pages 11 and 16.
Figure 4 Typical Installation of Eductor-Type Mixing Device
Makeup Water Workman Platform
Discharge Special Mixing Device This inexpensive equipment is most effective for quickly preparing uniform solutions of CMC.
Figure 5 Automated Polymer Solution Preparation (PSP) System
Dust Collector Polymer Hopper Polymer Eductor
Screw Drive Motor
Helical Screw Feeder
Air Eductor PSP Unit
THEORY OF POLYMER DISSOLUTION
time-dependent phenomenon, if CMC/salt solutions are allowed to stand, it is very possible that the final stage of disaggregation will be Stage 2 and the equilibrated viscosity will be higher than that of CMC in distilled water. Hence, one cannot assume that addition of salt will lower equilibrated solution viscosity, only that it will inhibit polymer disaggregation. With Types 9 and 12, the slight viscosity increase in saturated salt is caused by the “viscosity bonus effect” discussed on page 20.
When a polymer is dispersed in a solvent, the degree of disaggregation—i.e., separation of polymer molecules— is affected by the:
• • •
Chemical composition of the polymer. Solvating power of the solvent. Shear history of the resulting solution.
Figure 6 shows how these states of disaggregation may affect viscosity of the liquid. If CMC is added to a liquid and its degree of disaggregation reaches equilibrium, the polymer may:
• • • •
Figure 6 Idealized Curve Showing Effect of Degree of Disaggregation on Viscosity of Polymer Solution
Remain as a suspended powder, neither swelling nor dissolving (1). Swell to a point of maximum viscosity without completely dissolving (2). Reach maximum disaggregation (3). Exist in an intermediate state (1a, 1b, 2a).
Depending on choice of polymer, solvent, and mechanical means of preparing the solution, the user of CMC can alter its state of disaggregation to suit his needs. Table IV shows the effect of these factors on the disaggregation of CMC as measured by solution viscosity.
Increasing DS makes CMC more hydrophilic, or “waterloving”; hence, types having high DS are more readily disaggregated in water. Plotting solution viscosity at constant shear against increasing DS (Types 7 through 12) produces a curve similar in shape to that shown in Figure 6.
Increasing electrolyte concentration reduces disaggregation, as evidenced by the lower viscosity in saltwater of Type 7. The viscosities listed in Table IV were measured under quality control conditions—that is, two hours after solution was complete. At this point, CMC dissolved in an electrolyte solution is probably in the Stage 1 section of the disaggregation curve. CMC dissolved in distilled water under quality control conditions is at Stage 3 of the curve. Viscosities of CMC/salt solutions measured at this point will be lower than the viscosities of corresponding CMC solutions prepared in distilled water. Since disaggregation is a
Degree of Disaggregation
Table IV — Factors Affecting Disaggregation of Aqualon® CMC (This table shows the effect of polymer composition, solvent strength, and mechanical shear on disaggregation, as measured by solution viscosity. All data are at 25°C. Cellulose gum was added dry to the solvents listed.) Viscosity, cps (mPas) Anchor Stirrer
Cellulose Gum Type
In many cases, the high shear imparted by the Waring blendor can enhance viscosity development or disaggregation.
Figure 7 Effect of Solvent Strength on Disaggregation of Aqualon® CMC (1.75% CMC in Glycerin-Water)
The effect of solvent strength (polarity in binary solvent mixtures) on the disaggregation of CMC is shown in Figure 7. Note the similarity of these curves to the curve in Figure 6. The data in Figure 7 and in Table IV show that an increase in solvating power or an increase in mechanical shear breaks internal associations of gel centers and promotes disaggregation.
The effect of solutes such as salts or polar nonsolvents on the viscosity of CMC solutions also depends on the order of addition of the gum and solute. This is shown in Figure 8. If CMC is thoroughly dissolved in water and the solute is then added, it has only a small effect on viscosity. However, if the solute is dissolved before the CMC is added (as is the case with Table IV data), it inhibits breaking up of crystalline areas, and lower viscosities are obtained. This effect of solutes is less apparent with more uniformly substituted material containing fewer crystalline areas.
1,000 300 0
20 40 60 80 100 Water in Solvent, weight %
Figure 8 Effect of Solutes on Viscosity of CMC Solutions
Solute Added After CMC
Apparent Viscosity, cps
Solute Added Before CMC 100 80 60
40 30 20
Solutes Used: NaCl NaCl + NaOH (pH 10.1) Na2So4 Na4P2O7 • 10H2O (pH 9.5-9.8) KCl or LiCl
0.04 0.08 0.1 0.2 0.4 Molal Concentration of Cation, moles/1,000 g solvent 12
PROPERTIES OF CMC SOLUTIONS
Viscosity is the single most important property of CMC solutions. Aqualon has acquired considerable information on factors affecting viscosity, and these data are given here. Stability of CMC solutions to microbiological attack and chemical deterioration is also discussed in this section.
Equation: Because the viscosity-concentration relationship is an exponential function, the viscosity resulting from blending is not an arithmetic mean. The viscosity of a blend can, however, be approximated by use of the equation below, which is derived from the Arrhenius equation that relates viscosity with polymer concentration.
n log V1 + (100-n) log V2 Log Vs = 100 where Vs = Viscosity sought n = Percent (by weight) of the first component of the blend having a viscosity of V1 V2 = Viscosity of the second component of the blend
Solutions of CMC can be prepared in a wide range of viscosities. Such solutions are non-Newtonian because they change in viscosity with change in shear rate. Consequently, it is essential to standardize viscosity determination methods. This standardization must include the type and extent of agitation used to dissolve the CMC, as well as precise control of temperature, conditions of shear, and method of viscosity measurement. The procedure used in the Aqualon control laboratory is described in detail in the Appendix, page 27.
Note: All viscosities must be expressed at the same polymer concentration and in the same units. Use of the chart itself is simple. For example, suppose one wishes to obtain a solution with a viscosity of 900 cps at 3% concentration. The water-soluble polymer is available as Material A with a viscosity of 1,800 cps at 3% concentration, and Material B with a viscosity of 700 cps at 3% concentration. A line is drawn connecting these two viscosities on the chart. The point at which this line intersects the desired viscosity line is then determined, and the percentage it represents is read from the bottom of the chart. Thus, in this example, 28% of Material A and 72% of Material B are needed to yield the desired viscosity of 900 cps at a total polymer concentration of 3%.
Effect of Concentration The viscosity of aqueous CMC solutions increases rapidly with concentration. This is shown in Figure 10. The bands show the range of viscosity obtainable with standard viscosity types.
Effect of Blending Two viscosity types of CMC can be blended to obtain an intermediate viscosity. Because viscosity is an exponential function, the viscosity resulting from blending is not an arithmetic mean.
Limitations of Blending: The relationship between viscosity and concentration can vary significantly, depending on the chemical composition as well as the molecular weight (viscosity type) of the polymers involved. The greatest accuracy is obtained from use of the equation or the blending chart of Figure 9 if the following conditions are met. Departure from these conditions can result in deviation from the predicted value of viscosity.
A blending chart (VC-440), available from Aqualon, can be used to determine the result of blending various amounts of two viscosity types of CMC. It can also be used to determine the amount of CMC required to achieve a desired viscosity when blending two types of known viscosity.
Blending Chart The blending technique outlined in this bulletin can be used eqully well for Aqualon® cellulose gum (sodium carboxymethylcellulose), Natrosol® hydroxyethylcellulose, Culminal® methylcellulose and methyl hydroxypropylcellulose and Klucel® hydroxypropylcellulose. This technique is useful when it is desirable to blend two viscosity types of the same water-soluble polymer in order to obtain a solution having a predetermined viscosity and solids concentration. Blends can be calculated directly from the equation that follows; or, more conveniently, the blending chart in Figure 9 can be used. From this chart, one can determine, without calculations, the percentage of any two viscosities that must be blended to secure a desired intermediate viscosity. Likewise, it is possible to determine the viscosity that will result from utilizing any blend.
The chemical composition of the polymers must be similar— i.e., the type and level of chemical substitution must be the same.
The solution viscosities of the polymers should be as close together as possible.
Figure 9 Chart for Blending Aqualon Water-Soluble Polymers
5,000 4,000 3,000 Viscosity of Available Material A
Solution Viscosity at 25˚C, cps
Viscosity of Available Material B 1,000 900 800 700 600
Desired Viscosity in Example
500 400 300
100 90 80 70 60 50
Blend Needed for Desired Viscosity
Material A, % Material B, %
20 100 0
Figure 10 Effect of Concentration on Viscosity of Aqueous Solutions of Aqualon® CMC (Bands approximate the viscosity range for the types shown.)
7H4, 9H4 7H
7H3S, 7HOF 10,000 9M31, 12M31 7L
7M, 9M8, 12M8
Solution Viscosity at 25˚C, cps
7M2 7L2 1,000
10 5 0
CMC, weight %
Effect of Shear
Figure 11 Shear Stress vs. Shear Rate for Newtonian and Pseudoplastic Liquids
CMC is often used to thicken, suspend, stabilize, gel, or otherwise modify the flow characteristics of aqueous solutions or suspensions. Preparation and use of its solutions involve a wide range of shearing conditions. It is therefore important that the user understand how rheological behavior can affect the system.
Pseudoplasticity—Small amounts of CMC dissolved in water greatly modify its properties. The most obvious immediate change is an increase in viscosity. Interestingly, a single CMC solution will appear to have a different viscosity when different physical forces are imposed on it.
These physical forces may be conveniently referred to as high, intermediate, or low shear stress. For example, rolling or spreading a liquid as if it were an ointment or lotion would be high shear stress. After the liquid has been applied, gravity and surface tension control flow. These forces are conditions of low stress. Intermediate stress is typified by pouring a liquid out of a bottle.
Figure 12 Viscosity vs. Shear Rate
If a solution of high-viscosity CMC appears to be a viscous syrup as it is poured from a bottle, it will behave as a thin liquid when applied as a lotion, and yet when high shear stress is removed it will instantly revert to its original highly viscous state. This type of flow behavior is referred to as pseudoplasticity or time-independent shear-thinning—a form of non-Newtonian flow. It differs from the time-dependent viscosity change called thixotropy.
When viscosity (shear stress divided by shear rate) is plotted against shear rate, a Newtonian system gives a horizontal line. If viscosity decreases as shear rate is increased, the flow is pseudoplastic.
If shear stress is plotted vs. shear rate, as in Figure 11, a Newtonian fluid will produce a straight line passing through the origin. A pseudoplastic liquid, such as a CMC solution, will give a curved line. Plotting apparent viscosity against shear rate, as in Figure 12, produces a horizontal straight line for a Newtonian fluid and a curved line for a pseudoplastic liquid. Solutions of some medium- and high-viscosity types of CMC exhibit pseudoplastic behavior because their longchain molecules tend to orient themselves in the direction of flow; as the applied force (shear stress) is increased, the resistance to flow (viscosity) is decreased. When a lower stress is imposed on the same solution, the apparent viscosity is higher because random orientation of molecules presents increased resistance to flow.
Rheograms are helpful to illustrate the effect of thixotropy. A thixotropic solution will form a hysteresis loop when shear stress is plotted against shear rate, as shown in Figure 14A. The increased shear stress required to break the thixotropic structure has reduced the resistance to flow, or viscosity. If a solution has gel strength, a spur forms in the hysteresis loop; this is shown in Figure 14B. It is an indication of the stress necessary to break the gel structure and cause the solution to revert to its normal apparent viscosity.
Generally, solutions of the medium- and high-viscosity types with a high DS (i.e., 0.9 and 1.2) and “S” types are pseudoplastic rather than thixotropic. In contrast to this, regular high- and medium-viscosity gums of DS 0.7 (slightly less uniformly substituted) show thixotropic behavior in solution. (See Thixotropy, below.) Solutions of low-molecular-weight CMC – i.e., low-viscosity types—are less pseudoplastic than those of high-molecularweight gum. However, at very low shear rate, all CMC solutions approach Newtonian flow. Figure 13 shows these relationships.
Figure 14A Thixotropic Flow
Shear Rate 1% 7H3S
Figure 14B Extremely Thixotropic Flow With Gel Strength
Tumbling or Pouring
0.1 1 10 100 1,000 10,000 Shear Rate (Reciprocal sec) Brookfield Viscometer
Film Sag Under Gravity
Apparent Viscosity, cps
Figure 13 Effect of Shear Rate on Apparent Viscosity of Aqualon® CMC Solutions
Thixotropy—If long-chain polymers have a considerable amount of interaction, they will tend to develop a threedimensional structure and exhibit a phenomenon known as thixotropy. Thixotropy is a time-dependent viscosity change. It is characterized by an increase in apparent viscosity when a solution remains at rest for a period of time after shearing. In certain cases, the solution may develop some gel strength, or even set to an almost solid gel. If sufficient force (shear stress) is exerted on a thixotropic solution, the structure can be broken and the apparent viscosity reduced.
Figure 15 illustrates thixotropy in another manner. At a constant shear rate (D = K), viscosity decreases with time. When shear is removed (D = zero), viscosity increases significantly with time.
Figure 15 Thixotropic Flow Is a Time-Dependent Change in Viscosity
Thixotropic solutions are desirable, or even essential, for certain uses of CMC, such as suspension of solids. Highand medium-viscosity types of regular Aqualon® CMC (0.7 DS) generally exhibit thixotropic behavior. “S” types and high-DS types in medium and high viscosity have been developed for uses requiring clear, smooth solutions of little or no thixotropy. Figure 16 illustrates the difference in appearance between solutions of regular and “S”-type Aqualon CMC. “S” and high-DS types show the typical pseudoplasticity of long-chain molecules.
D = Zero
Figure 16 Thixotropic and Nonthixotropic Solutions of CMC The solution of regular Aqualon CMC, left, is thixotropic; “S”-type Aqualon CMC, right, is essentially nonthixotropic.
Figure 17 Effect of Temperature on Viscosity of Aqualon® CMC Solutions
1% 9M31 1% 12M31
20 30 40 Temperature, ˚C
Effect of Temperature
Figure 19 Stability of Aqualon Cellulose Gum in Organic Acids—1% Solution of Type 7HOF
Viscosity of CMC solutions depends on temperature, as shown in Figure 17. Under normal conditions, the effect of temperature is reversible, so temperature variation has no permanent effect on viscosity. However, long periods of heating at high temperatures will degrade CMC and permanently reduce viscosity. For example, a 7L type held for 48 hours at 180°F lost 64% of its original viscosity.
Viscosity at 25˚C, cps
Effect of pH CMC solutions maintain their normal viscosity over a wide pH range. In general, solutions exhibit their maximum viscosity and best stability at pH 7 to 9. Above pH 10, a slight decrease in viscosity is observed. Below pH 4.0, the less soluble free acid carboxymethylcellulose predominates and viscosity may increase significantly. Figure 18 shows the effect of pH on the viscosity of typical Aqualon® CMC grades.
1.0% Lactic Acid 1,000
1.0% Citric Acid
0.3% Fumaric Acid
Figure 18 Effect of pH on Viscosity of Aqualon CMC Solutions
1 2 3 4 5 Storage Time at 25˚C, months Effect of Mixed Solvents
5,000 Brookfield Viscosity, cps
5.0% Acetic Acid
The behavior of highly substituted CMC in mixed-solvent systems, such as glycerin-water, is similar to its effect in water alone. In mixed systems, however, viscosity of the solvent affects viscosity of the solution. For example, if a 60:40 mixture of glycerin and water (which is 10 times as viscous as water alone) is used as the solvent, the resulting solution of well-dispersed CMC will be 10 times as viscous as the comparable solution in water alone. This behavior is shown in Figure 19 and is commonly referred to as the “viscosity bonus effect.”
2.0% 9M31 1.0% 7H
Figure 20 Effect of Mixed Solvents on Viscosity of Aqualon CMC Solutions—1% Type 12M31
10,000 Tests with Aqualon CMC Type 7M have shown that very little polymer degradation takes place if solutions are allowed to stand overnight at room temperature at a pH as low as 2. However, at pH values of 4-5 and temperatures of 150°F, most of the viscosity is lost in 24 hrs.
1% CMC in Glycerin-Water 1,000 Apparent Viscosity, cps
In acidic systems, the order in which CMC is added to the solvent is also important. If a CMC solution is prepared prior to the addition of acid, a higher viscosity is obtained than when dry CMC is dissolved in an acidic solution. Aqualon cellulose gum Type 7HOF is a particularly efficient thickener for acidic systems. Clear, viscous solutions are obtained when it is dissolved in water and then acidified. Its stability in several organic acids, typical of those used in low-pH foods, is shown in Figure 19.
100 1% CMC in Water 10 Glycerin in Water 1 Water 10 -1 10
Chemical Degradation Under certain conditions, solutions of CMC are susceptible to chemical degradation. Permanent loss of viscosity can occur resulting from scission of the long-chain molecules. Such viscosity loss is accelerated by increasing the temperature and/or lowering the pH. Aqualon cellulose gum Type 7HOF provides improved resistance to viscosity degradation and precipitation in low-pH systems.
CMC is subject to microbiological attack and chemical degradation. However, corrective measures can be taken to prevent both from occurring.
Microbiological Attack Although CMC is more resistant to microbiological attack than many other water-soluble gums, its solutions are not immune. Heat treatment can be used to destroy many microorganisms while having little effect on CMC properties. Heating for 30 min at 80°C, or for 1 min at 100°C, is generally sufficient.
An oxidative type of degradation occurs under alkaline conditions in the presence of oxygen. The rate of viscosity loss is also increased by heat and/or ultraviolet light. Inclusion of an antioxidant, exclusion of oxygen, and avoidance of highly alkaline conditions are obvious preventive measures.
When solutions are stored, a preservative should be added to prevent viscosity degradation. If cellulases (hydrolytic, viscosity-destroying enzymes) have been introduced by microbial action, even in trace amounts, addition of most preservatives will not prevent degradation; therefore, it is important to preserve solutions as soon as possible after preparation.
To obtain the best stability during prolonged storage of CMC solutions, users should:
The preservatives shown below have proved effective for solutions of Aqualon® CMC. The preservative manufacturer should be consulted regarding the kind and amount to be added.
Protect against microbiological attack. Maintain solution pH as nearly neutral as possible (7.0 to 9.0). Avoid prolonged exposure to elevated temperatures. Exclude oxygen and sunlight.
Preservatives for Aqualon CMC
Busan 11M1, 85(g) Dowicide A(h) Dowicil 75, 200(h) Formaldehyde Methyl- and propylparabens(i)
Phenol Proxel GXL(j) Sodium benzoate(i) Sodium propionate(i) Sorbates (Na and K salts)(i)
Laboratories International, Inc. Chemical Co. (i)Preservatives cleared by the Food and Drug Administration for food, cosmetic, and pharmaceutical products. Pertinent regulations indicate maximum use levels (tolerances) in some cases. (j)Zeneca Biocides (h)Dow
Table V — Compatibility of Aqualon CMC With Inorganic Salt Solutions
Aqualon CMC is compatible in solution with most watersoluble nonionic and anionic polymers and gums. Its compatibility with salts depends on factors discussed in this section. ®
Effect With Salts Compatibility of CMC with inorganic salt solutions depends largely on the ability of the added cation to form a soluble salt of carboxymethylcellulose. For example, the potassium salt of carboxymethylcellulose is as soluble in water as the sodium salt; consequently, if potassium ion is added in moderate amounts to a CMC solution, it has little effect on solution viscosity, clarity, or other properties. On the other hand, the zirconium salt of carboxymethylcellulose is insoluble in water; therefore, if zirconium ion is added to a CMC solution, precipitation results.
Aluminum nitrate Aluminum sulfate Ammonium chloride Ammonium nitrate Ammonium sulfate Calcium chloride Calcium nitrate Chromic nitrate Disodium phosphate Ferric chloride Ferric sulfate Ferrous chloride Magnesium chloride Magnesium nitrate Magnesium sulfate Potassium ferricyanide Potassium ferrocyanide Silver nitrate Sodium carbonate Sodium chloride Sodium dichromate Sodium metaborate Sodium nitrate Sodium perborate Sodium sulfate Sodium sulfite Sodium thiosulfate Stannic chloride Zinc chloride Zinc nitrate Zinc sulfate
As a general rule, monovalent cations from soluble salts of carboxymethylcellulose, divalent cations are borderline, and trivalent cations form insoluble salts. Some exceptions to this rule are given in the following pages. The effect of salts varies with the particular salt, its concentration, pH of the solution, degree of substitution of the CMC, and manner in which the salt and CMC come in contact. Highly substituted CMC (i.e., DS 0.9 and 1.2) has a greater tolerance for most salts. Increased salt tolerance can also be obtained by dissolving the CMC before adding the salt. Adding dry CMC to a salt solution or dissolving the salt and gum simultaneously will reduce compatibility. Compatibility of Aqualon CMC with some inorganic salt solutions is shown in Table V. Solutions of 1% CMC Type 7H were prepared in distilled water. Aqueous solutions of salts were prepared at concentrations of 10% and either 50% or saturated. Then, 1 g of gum solution was added to 15 g of each salt solution, and the effect was observed. Monovalent Cations—As previously stated, monovalent cations usually interact with carboxymethylcellulose to form soluble salts. In aqueous systems containing these cations, viscosity depends primarily on the order of addition of gum and salt. If CMC is thoroughly dissolved in water prior to addition of such a salt, the latter has little effect on solution viscosity. However, the viscosity imparted by CMC will be depressed if the gum is added dry to a salt solution. (See Figure 8, page 12.) The effect of polymer composition, salt concentration, and shear history is shown in Table IV, page 11. Viscosity developed by “S” types of Aqualon CMC is less affected by salts of monovalent cations than that developed by other types, regardless of the order of addition.
50% or Saturated Solution
P P C C C C C P C P P P C C C C C P C C C C C C C C C P P P P
P P C C P P P P C P P P C C C C C P C C C C C C P C C P P P P
C = Compatible P = Precipitate Note: 1 g of a 1% solution of CMC Type 7H was added to 15 g of salt solution.
EFFECT WITH WATER-SOLUBLE NONIONIC GUMS
Polyvalent Cations—Generally, divalent cations will not form crosslinked gels with CMC. Viscosity reduction occurs, however, when divalent cations are added to a CMC solution, and it may be accompanied by the formation of a haze. Calcium, barium, cobalt, magnesium, ferrous, and manganous cations will perform this way. “S” types of Aqualon® CMC are only slightly affected by moderate concentrations of divalent cations if the cation is added to the CMC solution.
CMC is compatible with most water-soluble nonionic gums over a wide range of concentrations. In many instances, the low-viscosity types are compatible over a broader range than the high-viscosity types. When a solution of anionic CMC is blended with a solution of nonionic polymer such as NATROSOL® hydroxyethylcellulose or KLUCEL® hydroxypropylcellulose, a synergistic effect on viscosity is observed. Such a polymer mixture produces solution viscosities considerably higher than would ordinarily be expected, as shown in Table Vl. The polymers can be blended dry, then dissolved; or solutions can be prepared first, then blended. If other electrolytes are present in the system, the effect is reduced.
Trivalent salts form insoluble precipitates with CMC. Trace amounts of heavy metal cations of lesser valence also form precipitates. Precipitation occurs by crosslinking, ionic bonding, or complex formation. Included in this classification are cuprous, cupric, silver, ferrous, uranium, chromous, stannous, plumbous, and zirconium cations.
GELATION OF SOLUTIONS
Table Vl – Synergistic Effect on Viscosity When a Nonionic Polymer Is Blended With Aqualon CMC
The effect of trivalent cations on CMC solutions can be controlled and used to advantage where gelation is desired. Gels of varying texture can be produced by careful addition of certain salts of trivalent metals, such as aluminum. Gradual release of aluminum ions to a CMC solution will result in uniform crosslinking of the polymer molecules between carboxymethyl groups. Gradual release of aluminum ions can be accomplished by using a slowly soluble aluminum salt such as monobasic aluminum acetate, AIOH (C2H3O2)2; soluble salts such as aluminum sulfate, Al2 (SO4)3, in combination with appropriate chelating agents; or insoluble salts such as dihydroxyaluminum sodium carbonate (DASC), Al(OH)2OCOONa, followed by in situ formation of the soluble acid form of DASC.
Properties of CMC gels depend on many factors. In general, the stiffness of a CMC gel increases with:
• • • •
An increase in CMC concentration. An increase in CMC molecular weight. An increase in the concentration of trivalent metal ion. A decrease in solution pH.
Cellulose gum, Type 7H3SF Natrosol 250 HR
Cellulose gum, Type 7H3SF Klucel H
Techniques for producing CMC gels by crosslinking with trivalent metals are discussed in more detail in Aqualon Bulletin VC-521 and Bulletin VC-522.
Viscosity Viscosity of a Blend of a 1% of Equal Parts Solution at at 25°C, cps (mPas) 25°C, cps (mPas) Expected(k) Actual
blending chart, VC-440.
PROPERTIES OF CMC FILMS
CMC is seldom used to prepare free or unsupported films. However, its ability to form strong, oil-resistant films is of great importance in many applications. Clear films can be obtained by evaporating the water from CMC solutions. These fairly flexible films are unaffected by oils, greases, or organic solvents. Their typical properties are given in Table Vll. The films were 2 mils thick and contained about 18% moisture. Where improved flexibility and elongation are desired, plasticizer is added to the casting solution. By including 10 to 30% glycerol in a formulation, elongation can be improved by 40 to 50%, and folding endurance can be increased to 10,000 MIT double folds. Plasticizers that have proved effective with CMC are:
• • • • •
Ethanolamines Ethylene glycol Glycerol 1,2,6-hexanetriol Mono-, di-, and triacetin
• • • •
1,5-pentanediol Polyethylene glycol (mol wt 600 or less) Propylene glycol Trimethylolpropane
Table Vll—Typical Properties of Films Prepared From Aqualon® CMC CMC Property
Elongation at break, %
Flexibility, MIT double folds
Tensile strength, psi (kg/cm2)
PACKAGING AND SHIPPING
Aqualon® CMC is packed at a moisture content no higher than 8%. Because of varying storage and shipping conditions, there is a possibility of some moisture pickup from the “as-packed” value. The standard package is a 50-lb-net, 3-ply, polyethylene-lined multiwall kraft paper bag. The type, lot number, and bag number are stenciled on the bottom of each bag.
Truckload shipments originate from Hopewell, Virginia. Less-than-truckload quantities are also available from Hopewell or from warehouse stocks conveniently located near industrial centers. Read and understand the Material Safety Data Sheet (MSDS) before using this product.
MICROBIOLOGICAL INFORMATION AND REGULATORY STATUS FOR USE IN FOODS, DRUGS, COSMETICS, AND TOILETRIES lulose gum) meet standards set by the U.S. Code of Federal Regulations, Title 21, Section 182.1745—Substances that are generally recognized as safe (GRAS). The FDA defines this GRAS substance as the sodium salt of carboxymethylcellulose, not less than 99.5% on a dry-weight basis, with maximum substitution of 0.95 carboxymethyl groups per anhydroglucose unit, and with a minimum viscosity of 25 cps for 2% (by weight) aqueous solution at 25°C. Aqualon foodgrade (F) cellulose gum meets these requirements. Aqualon cellulose gum is also certified to be kosher.
MICROBIOLOGICAL INFORMATION Aqualon production facilities for carboxymethylcellulose (CMC) are operated in compliance with Current Good Manufacturing Practice Regulations (CGMPRs) as promulgated in the U.S. Code of Federal Regulations. While extreme care is exercised at every process step and the product is of excellent microbiological quality, CMC is not marketed as a sterile material. Aqualon CMC is routinely sampled and subjected to microbiological testing by an independent laboratory and data are tabulated to provide an ongoing indicator of control in production. The data generated are not intended to be used to provide product specifications, but typical results using our standard protocol, are shown below.
Both the Food Chemicals Codex and the Food and Agriculture Organization of the United Nations World Health Organization (FAO/WHO) have established specifications for identity and purity of sodium carboxymethylcellulose, which are also met by Aqualon food-grade cellulose gum.
Aerobic plate count, cfu/g . . . . . . . . . . . . . . . . . . . . . .