Sodium carboxymethyl cellulose is widely used in industry, pharmaceuticals and food production. This compound is made on the basis of wood and is a biologically inert material, that is, it does not participate in physiological processes. Due to the special properties of solutions with this component, it is possible to adjust the viscosity of substances and other technical parameters.
Description
Sodium carboxymethyl cellulose (CMC) is a sodium salt of cellulose glycolic acid. The chemical name of the compound according to the IUPAC nomenclature is poly-1,4-β-O-carboxymethyl-D-pyranosyl-D-glycopyranose.
The empirical formula for technical sodium carboxymethyl cellulose is: [67 O 2 (OH) 3- x (OCH 2 COONa) x ] n . In this expression, x is the degree of substitution in the CH 2 —COOH groups, and n is the degree of polymerization.
The structural formula is shown in the figure below.
The properties
In appearance, technical sodium carboxymethyl cellulose is an odorless powdery, fine-grained or fibrous material with a bulk density of 400–800 kg / m 3 .
Na-CMC has the following characteristics:
the molecular weight of the compound is [236] n ;
quickly soluble in both hot and cold water, insoluble in mineral oils and organic liquids;
forms films resistant to oils, greases and organic solvents;
increases the viscosity of solutions and gives them thixotropy - with an increase in mechanical stress, a decrease in resistance to flow occurs;
well absorbs water vapor from the air, so the substance must be stored in dry rooms (under normal conditions contains 9-11% moisture);
the compound is non-toxic, not explosive, but in a dust-like state it can ignite (self-ignition temperature +212 ° C);
in solutions it exhibits the properties of an anionic polyelectrolyte.
With a change in temperature, the laboratory viscosity of sodium carboxymethyl cellulose in solutions varies greatly. This is one of the most important characteristics of this compound, which determines the scope of its application. A high degree of polymerization provides higher viscosity and vice versa. At pH <6 or greater than 9, the decrease in flow resistance drops significantly. Therefore, this salt is advisable to apply in neutral and slightly alkaline environments. Changes in viscosity under normal conditions are reversible.
Sodium carboxymethyl cellulose also has chemical compatibility with many other substances (starch, gelatin, glycerin, water-soluble resins, latexes). When heated to temperatures above 200 ° C, salt decomposes to sodium carbonate.
The main factor affecting the characteristics of this compound is the degree of polymerization. Solubility, stability, mechanical properties and hygroscopicity depend on molecular weight. The substance is produced in seven grades according to the degree of polymerization and two grades according to the content of the main substance.
Getting
On an industrial scale, sodium carboxymethyl cellulose has been manufactured since 1946. CMC production currently makes up at least 47% of the total volume of cellulose ethers.
The main raw material for the synthesis of this compound is wood pulp - the most common organic polymer. Its advantages are low price, biodegradability, lack of toxicity and simplicity of the processing process.
Sodium carboxymethyl cellulose is obtained by the reaction of alkaline cellulose with C₂H₃ClO₂ (monochloracetic acid) or its sodium salt. In recent years, work has been carried out to find new sources for the extraction of raw materials (flax, straw, cereals, jute, sisal and others), since the demand for this material is constantly growing. To improve the quality of the substance, the finished salt is washed from impurities, cellulose is activated or microwaved.
Sodium carboxymethyl cellulose: industrial applications
Due to its special properties, CMC is used for the following purposes:
thickening of various compositions, gelation;
binding of finely dispersed particles in paint films (film formation);
use as a water retention agent;
stabilization of physical and chemical properties;
increasing the viscosity of solutions for uniform distribution of their ingredients;
modification of rheological characteristics;
protection against coagulation (sticking of suspended particles).
One of the largest consumers of sodium carboxymethyl cellulose is the oil and gas industry, in which this compound is used to improve the performance of drilling fluids.
The substance is also used in the manufacture of the following technical products:
detergents;
printing products;
mortars for construction finishing work;
adhesive compositions, sizing materials;
dry building mixes, cement (to prevent the formation of cracks);
paints and varnishes;
cutting fluids;
environment for hardening rails;
coating of welding electrodes and others.
To stabilize the foam, sodium carboxymethyl cellulose is used in fire fighting, the food industry, and in the manufacture of perfumes and ceramic products. According to technical experts, this compound is used in more than 200 areas of technology and medicine.
Protective coatings
One of the promising areas is the introduction of nanoparticles synthesized from CMC suspensions as stabilizing additives in corrosion-resistant coatings. This allows you to change the structure of the polymers, increase adhesion to the base material, improve the physical and mechanical properties of the coating without significantly increasing the cost of the composition. Nanoparticles form microclusters, making it possible to obtain composites with valuable technical properties.
The advantage of such an additive is also that it is environmentally friendly and biodegradable. For its production, the use of organic solvents is not required, therefore, the risk of pollution of wastewater and the atmosphere is reduced, specialized equipment and a high temperature range are not necessary.
Food supplement
Sodium carboxymethyl cellulose is used as a food additive (E-466) in a concentration of not more than 8 g / kg. The substance performs several functions in the products:
thickening;
stabilization of properties;
moisture retention;
extension of the shelf life;
preservation of dietary fiber after thawing.
Most often, this compound is added to fast food, ice cream, confectionery, marmalade, jelly, processed cheeses, margarine, yogurt, canned fish.
Medicine and cosmetology
In the pharmaceutical industry, the sodium salt of carboxymethyl cellulose is used in such groups of drugs as:
eye drops, solutions for injection - to prolong the therapeutic effect;
tablet shells - to control the release of the active substance;
emulsions, gels and ointments - to stabilize the forming substances;
antacid preparations - as ion-exchange and complexing components.
In the production of hygiene and cosmetics, this compound is used as part of toothpastes, shampoos, shaving gels and showers, creams. The main function is to stabilize properties and improve texture.
Impact on humans and animals
Sodium carboxymethyl cellulose is hypoallergenic, biologically inactive, does not have a carcinogenic effect and does not impair the reproductive function of living organisms. The use of food additives in a safe concentration does not lead to negative consequences. Dust of the compound can cause irritation if it enters the eyes and upper respiratory tract (aerosol maximum concentration limit is 10 mg / m 3 ).
Films containing sodium salt release the active component in the alkaline environment of the intestine. The compound is excreted from the human and animal body unchanged. In water bodies for economic purposes, the substance belongs to the third hazard class (moderately hazardous). MPC in this case is 2 mg / L.