Carboxymethyl cellulose (CMC) is a polymer with important industrial value. It is a water-soluble anionic cellulose ether derived from natural cellulose. Cellulose is one of the most abundant organic polymers in nature and is the main component of plant cell walls. Cellulose itself has poor solubility in water, but through chemical modification, cellulose can be transformed into derivatives with good water solubility, and CMC is one of them.
The molecular structure of CMC is obtained by etherifying the hydroxyl (—OH) part of the cellulose molecule with chloroacetic acid (ClCH2COOH) to generate a carboxymethyl substituent (—CH2COOH). The structure of CMC retains the β-1,4-glucose chain structure of cellulose, but some of the hydroxyl groups in it are replaced by carboxymethyl groups. Therefore, CMC retains the polymer chain characteristics of cellulose and has the functionality of the carboxymethyl group.
Chemical properties of CMC
CMC is an anionic polymer. Since the carboxyl (—CH2COOH) group in its structure can ionize to generate negative charges in aqueous solution, CMC can form a stable colloidal solution after dissolving in water. The water solubility and solubility of CMC are affected by its degree of substitution (DS) and degree of polymerization (DP). The degree of substitution refers to the number of hydroxyl groups replaced by carboxyl groups in each glucose unit. Generally, the higher the degree of substitution, the better the water solubility. In addition, the solubility and viscosity of CMC at different pH values are also different. Generally, it shows better solubility and stability under neutral or alkaline conditions, while under acidic conditions, the solubility of CMC will decrease and may even precipitate.
Physical properties of CMC
The viscosity of CMC solution is one of its most important physical properties. Its viscosity is related to many factors, including solution concentration, degree of substitution, degree of polymerization, temperature and pH value. This viscosity characteristic of CMC enables it to show thickening, gelling and stabilizing effects in many applications. The viscosity of CMC also has the characteristics of shear thinning, that is, the viscosity will decrease under high shear force, which makes it advantageous in certain applications that require high fluidity.
Application areas of CMC
Due to its unique physical and chemical properties, CMC is widely used in many fields. Here are some of the main application areas:
Food industry: CMC is used as a thickener, stabilizer and emulsifier in the food industry. It can improve the texture and stability of food, such as common applications in ice cream, yogurt, jelly and sauce.
Pharmaceutical industry: CMC is used as an excipient for drugs and an adhesive for tablets in the pharmaceutical field. It is also used as a moisturizer and film-forming agent in wound dressings.
Daily chemicals: In daily products such as toothpaste, shampoo, detergent, etc., CMC is used as a thickener, suspending agent and stabilizer to help the product maintain a good appearance and performance.
Oil drilling: CMC is used as a viscosity enhancer and filtration agent in oil drilling fluids, which can improve the rheological properties of drilling fluids and prevent excessive penetration of drilling fluids.
Textile and papermaking industries: In the textile industry, CMC is used for textile pulp and finishing agents, while in the papermaking industry, it is used as a reinforcing agent and sizing agent for paper to improve the strength and smoothness of paper.
Environmental protection and safety
CMC is an environmentally friendly material that can be degraded by microorganisms in nature, so it will not cause long-term pollution to the environment. In addition, CMC has low toxicity and high safety, and has a good safety record in food and pharmaceutical applications. Nevertheless, due to its large-scale production and application, attention should still be paid to the treatment of chemical wastes that may be generated during its production process.
Carboxymethyl cellulose (CMC) is a functionally diverse water-soluble anionic polymer. CMC obtained by chemical modification retains the excellent properties of natural cellulose while having good water solubility and unique physical and chemical properties. With its thickening, gelling, stabilization and other functions, CMC has been widely used in many industries such as food, medicine, daily chemicals, oil drilling, textiles and papermaking. Its environmental protection and safety also make it the preferred additive in many products.