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Carboxymethyl cellulose (CMC) salt stability is related to its degree of substitution (DS), with solutions having higher DS being more stable. However, the viscosity of sodium carboxymethyl cellulose salt solution decreases during storage, and the rate of decrease varies between products, so the solution cannot be stored for long periods of time.
DS is an important chemical index of carboxymethyl cellulose (CMC) salt. Sodium carboxymethyl cellulose salt is a cellulose derivative that maintains the high molecular structure of cellulose, consisting of numerous anhydroglucose units joined together. Additionally, each anhydroglucose unit has three hydroxyl groups that can be substituted by carboxymethyl. It is important to note that the degree of substitution is an average. As the DS increases, the transparency and stability of the solution will also increase, and the solubility will change with the degree of substitution.
Purity refers to the percentage of carboxymethyl cellulose (CMC) salt in a dried product. During production, impurities such as sodium chloride and sodium carbonate may be present due to incomplete or side reactions. This has produced different sodium CMC grades. Whether purification is necessary depends on customer demand, with food-grade CMC purity typically being 99.5% and industrial-grade produced according to customer requirements. For use in detergent synthesis, purification is not necessary, as impurities do not affect its quality, and the purity is generally 55-75%. If used in toothpaste, the purity needs to be above 96% due to the strict requirements for sodium chloride content.
Viscosity in water solution is the most important physicochemical index of carboxymethyl cellulose (CMC) salt, as it is mostly used to make colloidal solutions. It is worth noting that a sodium carboxymethyl cellulose salt water solution provided by CMC supplier belongs to a non-Newtonian fluid, exhibiting both pseudoplasticity and thixotropy.
Due to carboxymethylation not being evenly distributed into the cellulose molecular chain, even for the same solution, the viscosity with higher shear stress resulting in a lower viscosity at faster flow rates compared to lower shear stress, causing pseudoplasticity. Thixotropy occurs when the carboxymethyl cellulose (CMC) solution is left standing for a period of time, with low thixotropic solutions experiencing a slight increase in viscosity while high thixotropic solutions may even solidify into a gel state. Vigorous stirring can break down the gel's structure, and proper stirring can restore the original viscosity.
There are many factors that affect viscosity, such as pH value, temperature, and storage time, with storage time being the dominant factor. Therefore, using a unified viscosity measurement method can produce consistent results.
