The structure and characteristic of CMC
CMC is a kind of main raw materials are made of high polymerization cellulose ether with cellulose, caustic soda and chloroacetic acid, compound with a molecular weight ranging from thousands to millions of. CMC is white or yellowish powder, granular or fibrous solid, odorless, tasteless, non-toxic. CMC is a kind of high molecular chemical substances to water swelling, swelling in water to form transparent sticky glue, waterSuspension of the P H value of 6.5 ~ 8.5.
The substance does not dissolve in alcohol, ether, acetone and chloroform and other organic solvents. Solid CMC on the light and the room temperature were relatively stable in dry ringEnvironment, can be preserved for a long time. The main indicators to measure the quality of CMC is the degree of substitution (DS) and degree of polymerization (DP). The substitution degree of carboxymethyl sodium base refers to the connection in each unit of cellulose The average number of groups. Glucose anhydride cellulose molecules of 3 alcohol group: 1 primary and 2 secondary alcohol alcohol. 3 alcohol radicals can react with chloride sodium acetate. Job activity groups react with the alcohol Large, so the substituent first will replace the groups make the reactant molecules of variable length. Replace the maximum degree is 3, but uses in industry is the largest degree of substitution is 0.5 ~ 1.2 CMC. Generally speaking, D S is different, the nature of CMC is also different: D S bigger, better transparency and stability of the solution; when D S>0.3 is soluble in an aqueous alkaline solution; DS = 0.7, is soluble in hot glycerine; when D S>0.8, then the acid resistance and salt resistance are good, and do not precipitate.
The degree of polymerization refers to the cellulose chain length, determines the size of its viscosity. The cellulose chain longer solution viscosity is bigger, so is the CMC solution. The CMC molecule exhibits a linear structure.
The size of CMC viscosity and pH, the length of heating time, the presence or absence of salt and other factors. The solution is pseudoplastic fluid, with increasing shear rate, the apparent viscosity drop low, has nothing to do with the shear time, when the shear is stopped immediately restored to the original viscosity; dry CMC can withstand 140 ~ 150 temperature a few minutes; and most of the same solution,
When reducing the viscosity temperature increases CMC solution, cooling after the recovery, but a long time at high temperature may cause the degradation of CMC and lead to reduce the viscosity; with decreasing solution P H value, viscosity fall, this is due to the acidic pH conditions, carboxyl suppressed ionization resulting viscosity decreases; some metal salts and CMC reaction, cellulose glycollic acid metal salt precipitation corresponding. Aluminum salt, tin salt and lead salt, Gao Tieyan, silver, copper salt and zirconium Yandu would react to salt precipitation and CMC, the solution viscosity CMC will not be lost; calcium salt and magnesium salt reaction precipitation, so it can be used for water; weak concentration of alkali metal salt presence often reduce the viscosity of solution of alkali metal salt, but the existence of strong concentration will increase the viscosity of solution, in some even cause gelation condition; CMC is not soluble in organic solvents, although may produce some swelling reaction, but CMC can't be dissolved; CMC is a hygroscopic material, placed in the air, dry CMC can absorb 12% ~ 25% of water, dry CMC less susceptible to microbial action, and its aqueous solution by bacteria can cause the effect of biological degradation, viscosity decreased. CMC as absorbent properties of colloid, with all of the colloid. In addition, CMC solution can also be used in adhesives, gelling agent, stabilizing agent and dispersing agent and film forming agent.