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Carboxymethyl cellulose CMC is a water-soluble cellulose ether obtained by chemically modifying natural cellulose. Due to the poor water solubility of the carboxymethyl cellulose acid structure, in order to better apply it, its products are generally made into sodium salt carboxymethyl cellulose sodium, an important property of which is to form a colloid solution with a certain viscosity when dissolved in water. What factors affect the viscosity of carboxymethyl cellulose CMC ?
The influence of the concentration of CMC sodium carboxymethyl cellulose: for high, medium, and low viscosity sodium carboxymethyl cellulose, their viscosities increase almost linearly with the increase of the concentration of the solution, especially for high viscosity sodium carboxymethyl cellulose.
The influence of the pH of sodium carboxymethyl cellulose: for a 1% solution of CMC sodium carboxymethyl cellulose, the viscosity is the highest, and it is most stable at a pH of 6.5 to 9.0. Generally, the viscosity does not change much when the pH is between 9.0 to 11.0. However, when the pH is less than 6, the viscosity rapidly decreases, and carboxymethyl cellulose acid begins to form. The latter completely forms at a pH of about 2.5. If the pH is greater than 9, the viscosity also decreases, but it decreases slowly at first. If the pH exceeds 11.5, it will begin to decrease rapidly. This is because the un-substituted hydroxyl groups help to promote the dispersion of cellulose by combining with alkaline molecules.
The viscosity of a solution of sodium carboxymethyl cellulose decreases as the temperature rises. When it cools down, the viscosity immediately rises again, but when the temperature rises to a certain extent, permanent viscosity reduction appears. The generally accepted temperature limit is 50℃. It must be pointed out that the viscosity reduction is closely related to the DS (degree of substitution) of sodium carboxymethyl cellulose. The higher the degree of substitution, the less the temperature affects the viscosity. When the DS exceeds 1.2, it is very stable.
The influence of the heating time of CMC sodium carboxymethyl cellulose: After heating a 1% sodium carboxymethyl cellulose solution at various temperatures for 20 minutes, the viscosity gradually decreases, especially when the temperature is above 50℃.
The presence of various inorganic salt solutions reduces the viscosity of cellulose gel solution. The influence of salt on viscosity almost depends on the valence of the cation. In the presence of monovalent cation salts, the solution is water-soluble, while in the presence of trivalent cation salts, it is insoluble in water. When encountering salts of divalent cations, it is between the two.