Carboxymethyl Cellulose (CMC) is a water-soluble cellulose derivative. It is an anionic polymer compound formed by the reaction of cellulose with sodium chloroacetate under alkaline conditions, where part of the hydroxyl groups are replaced by carboxymethyl groups. CMC is widely used in many fields such as food, medicine, papermaking, textiles, oil drilling, building materials, and cosmetics for its excellent thickening, suspension, film-forming, stabilizing, and colloid protection properties.
The carboxylmethyl groups on the CMC molecular chain give it excellent hydrophilicity and adjustable water solubility, giving it good thickening and film-forming abilities. In addition, CMC also has good biocompatibility and non-toxicity, meets environmental protection and safety requirements, and has become an important functional additive in many industrial and consumer product formulations.
Chemical structure and properties
Chemical structure
The basic structure of CMC is a cellulose chain formed by β-D-glucose units connected by β-1,4-glycosidic bonds. Some hydroxyl groups (-OH) on cellulose are replaced by carboxymethyl groups (-CH2-COOH) to form carboxymethyl cellulose. Its general formula can be expressed as:
[-C6H7O2(OH)x(OCH2COONa)y-]n
Where x and y represent the substitution ratio of hydroxyl and carboxymethyl groups on the cellulose chain, respectively, which determines the degree of substitution (DS) of the product.
01
Molecular weight
CMC has a wide range of molecular weights, usually from tens of thousands to hundreds of thousands of Da. The size of the molecular weight directly affects its solubility, viscosity and mechanical properties.
02
Physical properties
Appearance: white to off-white powder or granules
Solubility: easily soluble in cold water, forming a transparent or milky viscous solution, insoluble in organic solvents
Viscosity: depending on the molecular weight and degree of substitution, the viscosity range can be widely adjusted, ranging from hundreds to tens of thousands of mPa·s
pH adaptability range is wide, generally stable in pH 6-10 environment
03
Chemical properties
CMC is an anionic polymer that easily combines with multivalent cations to form gel or precipitation
Stable under alkaline conditions, good heat resistance
Has good film-forming properties and colloidal stability
04
Production process
Raw material preparation
High-purity natural cellulose (such as wood pulp, cotton pulp or cotton linters) is used as raw material.
01
Alkalization: Mix cellulose with sodium hydroxide solution and alkalize the cellulose fibers at a certain temperature to activate the hydroxyl groups.
02
Etherification: Sodium chloroacetate is added to the alkalized cellulose to cause an etherification reaction, where the hydroxyl groups are replaced by carboxymethyl groups to form CMC.
03
Neutralization and washing Adjust pH by neutralization, remove unreacted alkali and by-products, and wash to purity.
04
Drying and crushing
After the drying process, a stable white powder is obtained, and then crushed and sieved to obtain a product with uniform particle size.
05
Application Areas
Food Industry
CMC is widely used as a food additive, and its main functions include:
Thickener: used in beverages, jams, ice cream, dairy products, etc. to improve product viscosity and taste.
Stabilizer: prevents food from stratification or precipitation and keeps the mixture uniform.
Film-forming agent and suspending agent: used in seasonings, candies, jellies, to improve the appearance and texture of the product.
Fat replacement agent: replaces part of the fat in low-fat foods to improve taste and structure.
Pharmaceutical industry
CMC is mainly used in the pharmaceutical field as:
Pharmaceutical excipients: as adhesives and thickeners for tablets and capsules.
Controlled release materials: preparation of sustained-release tablets to control the release rate of drugs.
Eye drops and hemostatic agents: have good biocompatibility and lubricity.
Topical dressings: excellent film-forming and moisturizing properties, which help wound healing.
Papermaking Industry
CMC is an important functional additive in the papermaking process:
Reinforcement agent: improves the dry and wet strength of paper.
Coating dispersant: improves the uniformity and stability of the coating.
Adhesive: enhances the bonding force between fibers and improves paper quality.
Textile Industry
Used as a yarn sizing agent to improve yarn strength and smoothness.
As a dye dispersant and stabilizer to improve dyeing results.
Provides fabric softness and wrinkle resistance.
Oil Drilling
In drilling fluid, CMC is mainly used as:
Viscosity regulator, to improve the sand carrying capacity of drilling fluid.
Suspending agent, to prevent the deposition of drill cuttings.
Filtration control agent, to reduce the filtration loss of drilling fluid and improve drilling efficiency.
Building materials
Used in cement mortar and putty powder to improve construction performance and film-forming properties.
Improve the water retention and bonding strength of materials.
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