CMC sodium carboxymethyl cellulose, referred to as CMC, is a typical cellulose ether, which belongs to the polymer anion electrolyte. CMC sodium carboxymethyl cellulose is an odorless, tasteless, non-toxic white or slightly yellow powder.
The viscosity of carboxymethyl cellulose aqueous solution is a specific manifestation of cellulose DP (degree of polymerization). It depends on the average DP of the cellulose feedstock, the degree of degradation of the cellulose DP during alkalization and etherification, and the uniformity of the reaction. The viscosity of CMC sodium carboxymethyl cellulose aqueous solution increases almost linearly with the increase of concentration. In addition to the DP and distribution of cellulose, solution viscosity is also affected by solution concentration, pH, temperature, velocity gradient, and degree of substitution.
(1) Effect of solution concentration: For CMC sodium carboxymethyl cellulose in food with high, medium and low viscosity, the viscosity will increase with the increase of the solution concentration, and there is an almost linear relationship with the solution concentration.
(2)Influence of pH value: 1% sodium carboxymethyl cellulose solution has the highest viscosity and is most stable at pH value of 6.5 to 9.0. In general, the pH value is in the range of 9.0 to 11.0 and there will be no major change in viscosity. But when the pH is below 6, the viscosity decreases rapidly, and then begins to form CMC sodium carboxymethyl cellulose, which is commonly used in food, and the latter is completed at pH ≌ 2.5. If the pH is above 9, the viscosity will also decrease, but initially slowly; if the pH is above 11.5, it will start to decrease rapidly. This is because the bonding between the unsubstituted hydroxyl groups and the basic molecules helps to facilitate the dispersion of cellulose.
(1) Influence of temperature: The viscosity of carboxymethyl cellulose solution will decrease with the increase of temperature. When it cools, the viscosity rises again immediately, but when the temperature rises to a certain point, there is a permanent drop in viscosity. It must be pointed out that the decrease in viscosity is closely related to the degree of substitution of carboxymethyl cellulose. The higher the degree of substitution, the smaller the effect of temperature on viscosity.
(4) Influence of salt: The presence of various inorganic salt plasmas will reduce the viscosity of solution of sodium carboxymethyl cellulose in food. The effect of salt on viscosity is almost dependent on the valence of the cation. When encountering salts of monovalent cations, the solution exhibits water solubility; when encountering salts of trivalent cations, it is insoluble in water; and when encountering salts of divalent cations, it is in between.