The viscosity of sodium carboxymethyl cellulose is also divided into many grades according to different uses. The viscosity of washing type is 10~70 (below 100), the upper limit of viscosity is from 200~1200 for building decoration and other industries, and the viscosity of food grade is even higher. They are all above 1000, and the viscosity of various industries is not the same.
Because of its wide range of uses.
The viscosity of sodium carboxymethyl cellulose is affected by its relative molecular mass, concentration, temperature and pH value, and it is mixed with ethyl or carboxypropyl cellulose, gelatin, xanthan gum, carrageenan, locust bean gum, guar gum , agar, sodium alginate, pectin, gum arabic and starch and its derivatives have good compatibility (ie synergistic effect).
When the pH value is 7, the viscosity of sodium carboxymethyl cellulose solution is the highest, and when the pH value is 4~11, it is relatively stable. Carboxymethylcellulose in the form of alkali metal and ammonium salts is soluble in water. Divalent metal ions Ca2+, Mg2+, Fe2+ can affect its viscosity. Heavy metals such as silver, barium, chromium or Fe3+ can make it precipitate out of solution. If the concentration of ions is controlled, such as the addition of the chelating agent citric acid, a more viscous solution can be formed, resulting in a soft or hard gum.
Sodium carboxymethyl cellulose is a kind of natural cellulose, which is generally made of cotton linter or wood pulp as raw materials and subjected to etherification reaction with monochloroacetic acid under alkaline conditions.
According to the specifications of the raw materials and the substitution of the hydroxyl hydrogen in the cellulose D-glucose unit by the carboxymethyl group, water-soluble polymer compounds with different degrees of substitution and different molecular weight distributions are obtained.
Because sodium carboxymethyl cellulose has many unique and excellent characteristics, it is widely used in daily chemical industry, food and medicine and other industrial production.
One of the most important indicators of sodium carboxymethyl cellulose is the viscosity of sodium carboxymethyl cellulose. The value of viscosity is related to various factors such as concentration, temperature and shear rate. However, factors such as concentration, temperature and shear rate are the external factors that affect the viscosity of sodium carboxymethyl cellulose.
Its molecular weight and molecular distribution are the internal factors that affect the viscosity of sodium carboxymethyl cellulose solution. For the production control and product performance development of sodium carboxymethyl cellulose, researching its molecular weight and molecular weight distribution has extremely important reference value, while viscosity The measurement can only play a certain reference role.
Newton’s laws in rheology, please read the relevant content of “rheology” in physical chemistry, it is difficult to explain in one or two sentences. If you have to say it: for a dilute solution of cmc close to a Newtonian fluid, the shear stress is proportional to the cutting edge rate, and the proportional coefficient between them is called the viscosity coefficient or kinematic viscosity.
Viscosity is derived from the forces between cellulose molecular chains, including dispersion forces and hydrogen bonds. In particular, the polymerization of cellulose derivatives is not a linear structure but a multi-branched structure. In the solution, many multi-branched cellulose are intertwined to form a spatial network structure. The tighter the structure, the greater the forces between the molecular chains in the resulting solution.
To generate flow in a dilute solution of cellulose derivatives, the force between the molecular chains must be overcome, so a solution with a high degree of polymerization requires greater force to generate flow. For viscosity measurement, the force on the CMC solution is gravity. Under the condition of constant gravity, the chain structure of the CMC solution with a large degree of polymerization has a large force, and the flow is slow. The slow flow reflects the viscosity.
The viscosity of sodium carboxymethyl cellulose is mainly related to the molecular weight, and has little to do with the degree of substitution. The greater the degree of substitution, the greater the molecular weight, because the molecular weight of the substituted carboxymethyl group is larger than the previous hydroxyl group.
The sodium salt of cellulose carboxymethyl ether, an anionic cellulose ether, is a white or milky white fibrous powder or granule, with a density of 0.5-0.7 g/cm3, almost odorless, tasteless, and hygroscopic. It is easy to disperse in water to form a transparent colloidal solution, and is insoluble in organic solvents such as ethanol. The pH of 1% aqueous solution is 6.5 to 8.5. When pH>10 or <5, the viscosity of sodium carboxymethylcellulose is significantly reduced, and the performance is the best when pH=7.
It is thermally stable. The viscosity rises rapidly below 20℃, and changes slowly at 45℃. Long-term heating above 80℃ can denature the colloid and reduce the viscosity and performance significantly. It is easily soluble in water, and the solution is transparent; it is very stable in alkaline solution, and it is easy to hydrolyze in the presence of acid. When the pH value is 2-3, it will precipitate.
Post time: Nov-07-2022