With the World Cotton Day, we found it interesting and important to highlight the obtaining process of one of the most widely used products in both the ceramics and the chemical industry in general: carboxymethylcellulose.
Chemical structure of carboxymethylcellulose. Source: Wikimedia Commons.
Carbohydrates (CH2O)n are naturally occurring organic compounds and are nature’s most abundant chemicals. The biological and industrial importance is such that they are used in many chemical industries. Among the most used carbohydrates we find sugars, starch and cellulose.
Cellulose is the fundamental component of the plant cell wall in plants, wood and natural fibers. In cotton and linen, the cellulose fibers are of high purity (90-95%) and are usually used in the textile industry.
In the ceramic industry, most of the CMC that are commercialized come from wood.
However, CMC from cotton is gaining popularity among fans, since cotton linters can also be used to obtain carboxymethylcellulose for the ceramic industry.
CMC is obtained from the chemical modification of cellulose, through reactions that are easily applicable on an industrial scale. This method is known as the druvacell process.
Sodium carboxymethylcellulose is obtained by two consecutive reactions: the formation of alkali cellulose by reaction of cellulose with sodium hydroxide, called alkalization, swelling or mercerization, and the etherification of alkali cellulose by reaction with sodium chloroacetate or monochloroacetic acid.
If the product is not purified after etherification, the final product obtained is called technical CMC, where the purification level ranges from 55 to 73%. For purified grades, the product is refined by washing to a minimum purity of 98.0% (dry basis). The final product is dried, ground, packaged and subjected to strict quality control.
Among the multiple properties and benefits they have, in ceramics are the following:
– High rheology control in aqueous solutions.
– High viscosity stability over time.
– High binding capacity.
– High stability against bacterial degradation.
– Excellent glaze stabilizers.
– High compatibility with all kinds of colloidal materials.
– Presentation in the form of finely divided powder.
– High solubility.
– Colorless and odorless.
Regarding the chemical properties of the most important CMCs for the ceramic industry, we find:
- Purity: the CMC’s offered by Aditivos Cerámicos S.L. and marketed under the generic name of ADICEL, have a guaranteed minimum purity of 98.5%. Given their low salt content and their zero calcination residue, they are possibly the most suitable for the ceramic industry in general and sanitary ceramics in particular.
- Viscosity: depends to a large extent on the molecular weight of the initial cellulose. We find the CMC of high and low viscosity. Depending on the process and the needs of each client, we recommend one or the other CMC. The most important variables to consider are drying time and density.
- Degree of substitution: this index indicates the number of times that the hydroxy group (OH–) is substituted by the carboxymethyl group (-CH2COOH) in the cellulose polymer. In turn, a high degree of substitution in the final CMC guarantees its complete solubility in water. The CMC that we commercialize present DS greater than 0.65.