AQUALON. Sodium Carboxymethylcellulose. Physical and Chemical Properties

Transcription

1 CM AQUALON Sodium Carboxymethylcellulose Physical and Chemical Properties

2 AQUALON An Anionic Water-Soluble Polymer CONTENTS PAGE AQUALON AN ANIONIC WATER-SOLUBLE POLYMER APPLICATIONS CHEMISTRY GRADES AND TYPES Grades Degree of Substitution Viscosity Particle Size Product Coding PROPERTIES Moisture Absorption Physiological Properties DISPERSION AND DISSOLUTION OF Solvent Type of Shear Rate Dispersion Methods Theory of Polymer Dissolution PROPERTIES OF SOLUTIONS Viscosity Effect of Concentration Effect of Blending Blending Chart Effect of Shear Pseudoplasticity Thixotropy 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 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 Hercules Incorporated,

3 AQUALON AN ANIONIC WATER-SOLUBLE POLYMER Aqualon sodium carboxymethylcellulose () 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 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. 2

4 APPLICATIONS 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. The wide range of viscosity and substitution types available from Aqualon for the highly purified grades and the less highly purified technical grades of continues to expand the uses for this product line. 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 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. APPLICATIONS FOR PURIFIED (1) Types of Uses Specific Applications Properties Utilized Cosmetics Toothpaste Thickener; flavor stabilizer; suspending aid; binder Shampoos; foamed products Suspending aid; thickener; foam stabilizer; high water-binding capacity Creams; lotions Emulsion stabilizer; film-former; thickener Gelled products Thickener; gelling agent; film-former Denture adhesives Wet tack; long-lasting adhesion Foods Frozen desserts; soft-serve Controls ice crystal growth; improves mouthfeel, body, and texture Pet food Water binder; gravy thickener; extrusion aid; binder of fines Protein foods Retains water; improves mouthfeel Baked goods Batter viscosifier; improves moisture retention and texture Beverages 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 Low-calorie foods No caloric value (2) ; thickens; imparts body and mouthfeel Syrups Clear; thickens; imparts favorable mouthfeel and body Dressings; sauces Thickener and suspending aid; imparts mouthfeel Animal feed; Lubricant; binder; film-former extrusion products Pharmaceuticals Ointments; creams; lotions Stabilizer; thickener; film-former Jellies; salves Thickener; gelling agent; protective colloid, film-former Tablet binder; granulation aid High-strength binder Bulk laxatives Physiologically inert; high water-binding capacity Syrups Thickener Suspensions Thickener; suspending aid (1)For 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. 3

5 APPLICATIONS FOR STANDARD GRADE OF Types of Uses Specific Applications Properties Utilized Adhesives Wallpaper paste Water-binding aid; adhesion; good open time; nonstaining Starch-corrugating adhesive Thickener; water-binding and -suspending aid Latex adhesives Thickener; water-binding aid Aerial-drop fluids Insecticides Thickener; binder; suspending aid Drift-control agent Thickener Ceramics Glazes Binder for green strength; thickener; suspending aid Porcelain slips Vitreous enamels Refractory mortars Welding rod coatings Binder; thickener; lubricant Coatings Foundry core wash Binder; thickener; suspending aid Latex paints; paper coatings Rheology control; suspending aid; protective colloid Detergents Laundry Whiteness retention through soil suspension Lithography Fountain and gumming Hydrophilic protective film solutions Water-based inks Binder; rheology control; suspending aid Paper and paper Internal addition High-strength binder; improves dry strength of paper products Surface addition High-strength binder; oil-resistant film-former; provides control of curl and porosity and resistance to oils and greases Pigmented coatings Thickener; rheology control; water-retention aid Textiles Laundry and fabric sizes Film-former Latex adhesives; backing Rheology control; thickener; water binding and holdout compounds Printing pastes and dyes Warp sizing High film strength; good adhesion to fiber; low BOD value Tobacco Cigar and cigarette adhesive Good wet tack; high film strength Reconstituted sheet High-strength binder and suspending aid 4

6 CHEMISTRY is a cellulose ether, produced by reacting alkali cellulose with sodium monochloroacetate under rigidly controlled conditions. 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. 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: CAS Name: Cellulose, carboxymethyl ether, sodium salt Optimum water solubility and other desirable physical properties of are obtained at a much lower degree of substitution than 3. The most widely used types of Aqualon have a DS of 0.7, or an average of 7 carboxymethyl groups per 10 anhydroglucose units. Higher degrees of substitution result in products having improved compatibility with other soluble components. Cellulose ethers, such as, 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 solutions increases rapidly. Approximate values (weight averages) for the degree of polymerization and molecular weight of several viscosity types of Aqualon 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 is ph 8.25, the ph is generally adjusted to about If the ph to which the 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. Figure 1 Structure of Cellulose HO H H OH CH 2 OH H OH CH 2 OH O OH H H H H O OH H H H H H O OH H H H H O OH H H O O CH 2 OH H OH CH 2 OH n-2 H OH 2 Figure 2 Idealized Unit Structure of, With a DS of 1.0 H CH2OCH2COONa H O H O OH OH H H H H H OH OH H O CH2OCH2COONa Table I Typical Molecular Weights for Representative Viscosity Types of Aqualon (DS = 0.7 in All Cases) Viscosity Degree of Molecular Type Polymerization Weight High 3, ,000 Medium 1, ,000 Low ,000 O H O OH 5

7 GRADES AND TYPES To serve its diverse markets, Aqualon produces in several grades and in a wide variety of types, based on the degree of substitution, viscosity, particle size, and other parameters. GRADES Aqualon is available in the three grades outlined below. Grade Designation Intended Use Food F Food, cosmetic, P* pharmaceutical Pharmaceutical PH** Cosmetic, pharmaceutical Standard None Industrial *P (1.2 D.S. types and 7L2P) **PH (0.7 and 0.9 D.S. types) DEGREE OF SUBSTITUTION Aqualon is produced with the following degrees of substitution: Substitution Sodium Type Range (a) Content, % (b) (a)ranges shown in this table are not necessarily current specifications. (b)ln 7S types, the upper limit of substitution is 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. Table II Some Types of Aqualon Viscosity Range at 25 C, (c) cps (mpas) Designations for Indicated Substitution Types High at 1% Concentration 2,500-6,000 7H4 9H4 1,000-2,800 7H3S, 7HOF 1,500-3,000 7H Medium at 2% Concentration 800-3,100 12M31 1,500-3,100 9M M 9M8 12M M8S M2 Low (d) at 2% Concentration L at 4% Concentration L2 (c)ranges shown in this table are not necessarily current specifications. (d)some even lower viscosity types are available. Contact your technical representative for additional information. 6

8 VISCOSITY 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. 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. Viscosity Type Factor Concentration, % High 1,000 1 Medium Low 10 2 Solutions of all 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. Specific properties are available in certain other types. For example, the O type, 7HOF, provides the best solubility and storage stability in acid media. PARTICLE SIZE Aqualon 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. Designation Description Particle Size (e) None Regular On U.S. 30, %, max 1 On U.S. 40, %, max 5 C Coarse On U.S. 20, %, max 1 Through U.S. 40, %, max 55 Through U.S. 80, %, max 5 X Fine On U.S. 60, %, max 0.5 Through U.S. 200, %, min 80 (e)aii screens are U.S. Bureau of Standards sieve series. PRODUCT CODING An example of the coding used for ordering Aqualon 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. Aqualon can tailor the chemical and physical properties of 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. 7

9 PROPERTIES Typical properties of Aqualon polymer and in solution and film form are shown in Table III. These are not necessarily specifications. Table III Typical Properties of Aqualon Polymer Sodium carboxymethylcellulose dry basis, %, min Moisture content (as packed), %, max Browning temperature, C Charring temperature, C Bulk density, g/ml Biological oxygen demand (BOD) (f), ppm 7H type ,000 7L type ,300 Solutions ph, 2% solution Surface tension, 1% solution, dynes/cm at 25 C Specific gravity, 2% solution Refractive index, 2% solution Typical Films (Air-Dried) Density, g/ml Refractive index Thermal conductivity, W/mK (f)after 5 days incubation. Under these conditions, cornstarch has a BOD of over 800,000 ppm. MOISTURE ABSORPTION 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. As Aqualon 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. Figure 3 Effect of Relative Humidity on Equilibrium Moisture Content of Aqualon at 25 C Equilibrium Moisture Content, % Relative Humidity, % PHYSIOLOGICAL PROPERTIES 12M31P 7HF 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 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. 8

10 DISPERSION AND DISSOLUTION OF A number of factors such as solvent, choice of polymer, and shear rate affect dispersion and dissolution of. SOLVENT Aqualon 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 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. Tolerance of Aqualon Solutions for Ethanol Volume Ratio of Ethanol to Solution, 1% First Evident First Distinct Type Haze Precipitate 7L 2.4 to to 1 7M 2.1 to to 1 7H 1.6 to to 1 Note: In these tests, ethanol (95%) was added slowly at room temperature to the vigorously stirred 1% solution. TYPE OF The higher the degree of substitution, the more rapidly dissolves. The lower the molecular weight, the faster the rate of solution. Particle size has a pronounced effect on the ease of dispersing and dissolving. 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, 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. 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. DISPERSION METHODS 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: 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 goes into solution rapidly. To prepare lumpfree, clear solutions, a variety of methods can be used: Method 1 Add 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. Method 2 Prior to addition to water, wet the powder with a watermiscible liquid such as alcohol, glycol, or glycerol that will not cause to swell. Two to three parts of liquid per part of should be sufficient. Method 3 Dry-blend the with any dry, nonpolymeric material used in the formulation. Preferably, the should be less than 20% of the total blend. 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. Special, fast-dissolving fluidized polymer suspensions of 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. 9

11 Figure 4 Typical Installation of Eductor-Type Mixing Device Lightnin Mixer Polymer Feed Funnel Mix Tank Mixing Device Air Bleed- Holes Water Inlet Eductor Makeup Water Workman Platform Discharge Special Mixing Device This inexpensive equipment is most effective for quickly preparing uniform solutions of. Figure 5 Automated Polymer Solution Preparation (PSP) System Dust Collector Polymer Hopper Polymer Eductor Water Screw Drive Motor Helical Screw Feeder Air PSP Unit Eductor Preparation Tank 10

12 THEORY OF POLYMER DISSOLUTION 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 is added to a liquid and its degree of disaggregation reaches equilibrium, the polymer may: 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 can alter its state of disaggregation to suit his needs. Table IV shows the effect of these factors on the disaggregation of as measured by solution viscosity. Increasing DS makes 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, dissolved in an electrolyte solution is probably in the Stage 1 section of the disaggregation curve. dissolved in distilled water under quality control conditions is at Stage 3 of the curve. Viscosities of /salt solutions measured at this point will be lower than the viscosities of corresponding solutions prepared in distilled water. Since disaggregation is a time-dependent phenomenon, if /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 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. Figure 6 Idealized Curve Showing Effect of Degree of Disaggregation on Viscosity of Polymer Solution Viscosity 1 1a 1b Degree of Disaggregation 2 2a 3 Table IV Factors Affecting Disaggregation of Aqualon (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 Waring Blendor Cellulose Distilled Saturated Distilled Saturated Gum Type Water 4% NaCl NaCl Water 4% NaCl NaCl 7HF 1, ,040 2,440 7H3SF 1, ,720 9M31F M31P

13 In many cases, the high shear imparted by the Waring blendor can enhance viscosity development or disaggregation. The effect of solvent strength (polarity in binary solvent mixtures) on the disaggregation of 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 solutions also depends on the order of addition of the gum and solute. This is shown in Figure 8. If 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 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. Figure 7 Effect of Solvent Strength on Disaggregation of Aqualon (1.75% in Glycerin-Water) Viscosity, cps 100,000 10,000 9M8F 12M8P 7MF 1, Water in Solvent, weight % Figure 8 Effect of Solutes on Viscosity of Solutions 300 Solute Added After 200 Solute Added Before Apparent Viscosity, cps Solutes Used: NaCl NaCl + NaOH (ph 10.1) Na 2 So 4 Na 4 P 2 O 7 10H 2 O (ph ) KCl or LiCl Molal Concentration of Cation, moles/1,000 g solvent 12

14 PROPERTIES OF SOLUTIONS Viscosity is the single most important property of solutions. Aqualon has acquired considerable information on factors affecting viscosity, and these data are given here. Stability of solutions to microbiological attack and chemical deterioration is also discussed in this section. VISCOSITY Solutions of 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, 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. Effect of Concentration The viscosity of aqueous 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 can be blended to obtain an intermediate viscosity. Because viscosity is an exponential function, the viscosity resulting from blending is not an arithmetic mean. A blending chart (VC-440), available from Aqualon, can be used to determine the result of blending various amounts of two viscosity types of. It can also be used to determine the amount of 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. 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 V 1 + (100-n) log V 2 Log V s = 100 where V s = Viscosity sought n = Percent (by weight) of the first component of the blend having a viscosity of V 1 V 2 = Viscosity of the second component of the blend 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%. 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. 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. 13

15 Figure 9 Chart for Blending Aqualon Water-Soluble Polymers 5,000 4,000 3,000 2,000 Viscosity of Available Material A Solution Viscosity at 25 C, cps 1, Desired Viscosity in Example Viscosity of Available Material B Blend Needed for Desired Viscosity 30 Material A, % Material B, %

16 Figure 10 Effect of Concentration on Viscosity of Aqueous Solutions of Aqualon (Bands approximate the viscosity range for the types shown.) 30,000 20,000 7H4, 9H4 7H 7H3S, 7HOF 10,000 9M31, 12M31 7M, 9M8, 12M8 7L Solution Viscosity at 25 C, cps 1, M2 7L , weight % 15

17 Effect of Shear 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 dissolved in water greatly modify its properties. The most obvious immediate change is an increase in viscosity. Interestingly, a single 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. If a solution of high-viscosity 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. 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 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 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. Figure 11 Shear Stress vs. Shear Rate for Newtonian and Pseudoplastic Liquids Shear Stress Pseudoplastic Figure 12 Viscosity vs. Shear Rate Shear Rate Newtonian 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. Apparent Viscosity Newtonian Pseudoplastic Shear Rate 16

18 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 i.e., low-viscosity types are less pseudoplastic than those of high-molecularweight gum. However, at very low shear rate, all solutions approach Newtonian flow. Figure 13 shows these relationships. Figure 13 Effect of Shear Rate on Apparent Viscosity of Aqualon Solutions Apparent Viscosity, cps 10,000 1, % 7L 100 1% 7H3S ,000 10,000 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. Figure 14A Thixotropic Flow Shear Stress Shear Rate Film Sag Under Gravity Shear Rate (Reciprocal sec) Brookfield Viscometer Tumbling or Pouring Home Mixer Waring Blendor Figure 14B Extremely Thixotropic Flow With Gel Strength 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. Shear Stress Shear Rate 17

19 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. Thixotropic solutions are desirable, or even essential, for certain uses of, such as suspension of solids. Highand medium-viscosity types of regular Aqualon (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. S and high-ds types show the typical pseudoplasticity of long-chain molecules. Figure 15 Thixotropic Flow Is a Time-Dependent Change in Viscosity Apparent Viscosity D = K D = Zero t Figure 16 Thixotropic and Nonthixotropic Solutions of The solution of regular Aqualon, left, is thixotropic; S -type Aqualon, right, is essentially nonthixotropic. 18

20 Figure 17 Effect of Temperature on Viscosity of Aqualon Solutions 10,000 1% 7H 2% 9M8 1,000 2% 7M Viscosity, cps 1% 9M31 1% 12M % 7L Temperature, C 19

21 Effect of Temperature Viscosity of 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 and permanently reduce viscosity. For example, a 7L type held for 48 hours at 180 F lost 64% of its original viscosity. Effect of ph 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 grades. Figure 18 Effect of ph on Viscosity of Aqualon Solutions Brookfield Viscosity, cps 5,000 1, % 9M31 1.0% 7H 2.0% 7H ph Tests with Aqualon 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. In acidic systems, the order in which is added to the solvent is also important. If a solution is prepared prior to the addition of acid, a higher viscosity is obtained than when dry 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. Figure 19 Stability of Aqualon Cellulose Gum in Organic Acids 1% Solution of Type 7HOF Viscosity at 25 C, cps 10,000 1, % Fumaric Acid 5.0% Acetic Acid 1.0% Lactic Acid 1.0% Citric Acid Storage Time at 25 C, months Effect of Mixed Solvents The behavior of highly substituted 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 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. Figure 20 Effect of Mixed Solvents on Viscosity of Aqualon Solutions 1% Type 12M31 Apparent Viscosity, cps 10,000 1, % in Glycerin-Water 1% in Water Glycerin in Water Water ,000 10,000 Shear Rate, sec -1 20

22 STABILITY is subject to microbiological attack and chemical degradation. However, corrective measures can be taken to prevent both from occurring. Microbiological Attack Although 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 properties. Heating for 30 min at 80 C, or for 1 min at 100 C, is generally sufficient. 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. The preservatives shown below have proved effective for solutions of Aqualon. The preservative manufacturer should be consulted regarding the kind and amount to be added. Chemical Degradation Under certain conditions, solutions of 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. 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. To obtain the best stability during prolonged storage of solutions, users should: 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 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) (g)buckman Laboratories International, Inc. (h)dow 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 21

23 COMPATIBILITY Aqualon 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 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 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 solution, precipitation results. 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, and manner in which the salt and come in contact. Highly substituted (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 before adding the salt. Adding dry to a salt solution or dissolving the salt and gum simultaneously will reduce compatibility. Compatibility of Aqualon with some inorganic salt solutions is shown in Table V. Solutions of 1% 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 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 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 is less affected by salts of monovalent cations than that developed by other types, regardless of the order of addition. Table V Compatibility of Aqualon With Inorganic Salt Solutions 50% or 10% Saturated Salt Solution Solution Aluminum nitrate P P Aluminum sulfate P P Ammonium chloride C C Ammonium nitrate C C Ammonium sulfate C P Calcium chloride C P Calcium nitrate C P Chromic nitrate P P Disodium phosphate C C Ferric chloride P P Ferric sulfate P P Ferrous chloride P P Magnesium chloride C C Magnesium nitrate C C Magnesium sulfate C C Potassium ferricyanide C C Potassium ferrocyanide C C Silver nitrate P P Sodium carbonate C C Sodium chloride C C Sodium dichromate C C Sodium metaborate C C Sodium nitrate C C Sodium perborate C C Sodium sulfate C P Sodium sulfite C C Sodium thiosulfate C C Stannic chloride P P Zinc chloride P P Zinc nitrate P P Zinc sulfate P P C = Compatible P = Precipitate Note: 1 g of a 1% solution of Type 7H was added to 15 g of salt solution. 22

24 Polyvalent Cations Generally, divalent cations will not form crosslinked gels with. Viscosity reduction occurs, however, when divalent cations are added to a 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 are only slightly affected by moderate concentrations of divalent cations if the cation is added to the solution. Trivalent salts form insoluble precipitates with. 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 The effect of trivalent cations on 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 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 (C 2 H 3 O 2 ) 2 ; soluble salts such as aluminum sulfate, Al 2 (SO 4 ) 3, in combination with appropriate chelating agents; or insoluble salts such as dihydroxyaluminum sodium carbonate (DASC), Al(OH) 2 OCOONa, followed by in situ formation of the soluble acid form of DASC. Properties of gels depend on many factors. In general, the stiffness of a gel increases with: An increase in concentration. An increase in molecular weight. An increase in the concentration of trivalent metal ion. A decrease in solution ph. Techniques for producing gels by crosslinking with trivalent metals are discussed in more detail in Aqualon Bulletin VC-521 and Bulletin VC-522. EFFECT WITH WATER-SOLUBLE NONIONIC GUMS 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 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. Table Vl Synergistic Effect on Viscosity When a Nonionic Polymer Is Blended With Aqualon Viscosity Viscosity of a Blend of a 1% of Equal Parts Solution at at 25 C, cps (mpas) 25 C, cps Polymer (mpas) Expected (k) Actual Cellulose gum, Type 7H3SF 1,500 Natrosol 250 HR 1,800 Cellulose gum, Type 7H3SF 1,500 Klucel H 1,640 (k)from blending chart, VC ,650 3,200 1,570 3,280 23

25 PROPERTIES OF FILMS 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 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 are: Ethanolamines 1,5-pentanediol Ethylene glycol Polyethylene glycol Glycerol (mol wt 600 or less) 1,2,6-hexanetriol Propylene glycol Mono-, di-, and triacetin Trimethylolpropane Table Vll Typical Properties of Films Prepared From Aqualon Property Type 7L Type 7M Type 7H Tensile strength, psi (kg/cm 2 ) 8,000 (563) 13,000 (915) 15,000 (1,056) Elongation at break, % Flexibility, MIT double folds Electrostatic charge Negative Negative Negative Refractive index Specific gravity