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CMC knowlege

1、Product Overview
     Product Name: CMC-Na (Sodium Carboxymethyl Cellulose), customarily shorten form CMC, the abbreviation is CMC. CMC is a representative cellulose ethers, its sodium salt used widely in industry, CMC belongs to anionic polymer electrolyte, besides CMC-Na, it has other salt, such as ammonium and aluminum salt. CMC sometimes can change to CMC acid. D.S, that is the average of the hydroxyl which reacts with substitute on each anhydrous glucose unit, when D.S is 1:00, its molecular formula is [C6H7O2(OH)2OCH2COONa]n,
    Structure general wrote as follows:
2、Main Properties of Products
2.1 Appearance
CMC is odorless, tasteless, non-toxic white powder or micro-yellow fibrous in pure state. 
2.2 Solubility
    CMC is easy to absorb moisture, it dissolves easily in cold or hot water as colloidal solution, it can not dissolve in many organic solvents such as methanol, ethanol, acetone, chloroform, benzene and so on. The degree of substitution (D.S) is an important factor affects its water-soluble, the viscosity also affects its water-soluble greatly. CMC is usually alkali when viscosity between 25mPa.s-50000mPa.s, D.S is about 0.3. CMC is water-soluble when its D.S is more than 0.4. With the increase of D.S, the transparency of the CMC water substitution becomes much better. Like other macromolecule dielectric, when CMC dissolving, the first phenomenon is expansion, and then dissolved gradually. So in preparation solution, the particles should be uniform wetting, then the CMC can be dissolved quickly. Otherwise, the CMC are expansion in water solution, the particles form a strong involucres or plastic coating, so that the particles scattered difficulty resulting dissolution difficulty. 
 2.3 Hygroscopic Nature
The balance moisture of CMC with the increase of air humidity increased, with the rise in temperature decreases. At room temperature and the average humidity 80-85%, the balance of moisture more than 26 percent, however the moisture of products less than 10%, lower than the balance moisture. Even if the moisture content at about 15 percent, there have no difference in appearance. But when moisture content at more than 20 percent, some particles adhere to one another will be able to see, the higher the viscosity, the more obvious of the phenomenon.
    The CMC is a polarity macromolecule compound, its degree of absorbing moisture dominated by the relative humidity, but also the number of polarity group. The higher the D.S, that is, if the number of polarity group is larger, the degree of absorbing moisture is bigger. 
 2.4 Solution Viscosity
2.4.1 The viscosity of CMC water solution is the specific performance of Polymerization Degree of the cellulose, it depends on the average degree of materials cellulose, and the degradation of polymerization degree in the course of basification and etherification reaction, including the reaction uniformity. The viscosity of the CMC solution with the increase of its concentration, and the increase trend was similar to a straight line. Solution viscosity have relative with the polymerization degree of the cellulose and its distribution, but also have relative with the solution concentration, pH value, temperature, velocity gradient, D.S and so on.
2.4.2 The Effect Factors of Viscosity
A, Concentration: Regardless of high, medium and low viscosity of the CMC, the viscosity increased with its concentration increase, the logarithm value about concentration and viscosity is approximating beeline.   
B, pH Value: The viscosity of the 1% CMC solution is in the largest and most stable state when pH value at 6.5-9.0. Generally, the changes of the viscosity is not very large when the pH at 9.0-11.0. However, PH <6, the viscosity will decline rapidly, and began to form CMC acid, and decline entirely when PH ≌ 2.5; if PH> 9, the viscosity will decline also, at first decline slowly, but when the PH> 11.5, it began a sharp decline. This is because the un-substitution hydroxyls combined with the base molecules, and promote cellulose scattered.
    C, Temperature: The viscosity of the CMC solution with increase of temperature. When cooling, the viscosity will rebound, but when the temperature rose to a certain extent, it will be in permanent lower viscosity state. The decline of the viscosity has a closely related to its degree of substitution, the higher the D.S, the viscosity less affected by temperature.
    D, Impact of Salt: The existence of all kinds of inorganic salt ions would reduce the viscosity of CMC solution, the effect almost depends on the value of the cation. Generally, it is water-soluble salt when met one value cation, it is water-insoluble salt when met trivalent cation, the water-soluble is between one and trivalent when met bivalent cation.
    E, Impact Velocity Gradient: Because the CMC solution is non-Newtonian fluid, but belongs to the pseudoplastic fluid. Their mobile properties can not be depicted by a simple Newton's formula, but the apparent viscosity of the solution is still the function of velocity gradient at determining.
    For Newtonian fluid, the relationship of its velocity gradient and tangential force is direct proportional. For pseudoplastic fluid, the increase of the velocity gradient with the increase of tangential force is faster than a straight line, that is to see, the viscosity will reduce with the increase of the tangential force.
    For the CMC solution, its viscosity changes with the velocity gradient can be explained: Because the dispersed phase of CMC is hydrophilic, after sopping water, at first it will expansion, and then dissolved as macromolecules. Because the volume of the molecules is large, the viscosity is great. If the tangential force is increasing, the macromolecules begin directional function, the long axis will be gradually transformed into the flow direction, and the tangential force bigger, the more complete the turning, so the viscosity resistance becoming smaller when the CMC solution flowing. At the same time, the solvent layer around the CMC can also be deformed due to tangential force changing, which is the reason for the resistance reducing. In low concentrations CMC solution, velocity gradient affect on the viscosity is very small, when the solution concentration increases, the velocity gradient affect on viscosity also increases.
    F, The viscosity of the CMC solution will increase with the D.P increasing, but the increase rate of the viscosity is different because of the degree of substitution.  
 2.5 CMC will deposit when met with heavy metal salts, such as PbSO4, FeCl3, FeSO4, CuSO4, K2Cr2O7, AgNO3, SnCl2, and so on.

 
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