Synthesis Route of CMC

The conventional method for CMC synthesis is the alkylation-etherification process. In every research work related to the synthesis of CMC, this idiosyncratic process has long been used from the very beginning of CMC synthesis from various cellulosic precursors. The only difference between these works is in the applied ratios of the affined chemicals to the cellulosic extents of the precursors and variation in the reaction parameters such as temperature, reaction time, pH, etc.

It is noteworthy that all of the natural and industrial cellulosic precursors (e.g., leaves, stems, pulps, paper wastes, microbial as well as various textile-based precursors such as cotton linters, knitted rags, etc.) may not possess similar compositional characteristics that can provide a fixed amount of cellulose extract every time. Most precursors contain a considerable amount of lignin, pectin, ash, and other minerals (e.g., phosphorous, potassium, calcium, etc.) besides the cellulosic percentiles.

Therefore, on occasion, some pre-carboxymethylation steps such as proteolysis (treatment with protease enzyme), inactivation of various enzymes of the plant-based precursors (e.g., deactivation of pectic enzymes present in orange peels) , delignification, dewaxing , bleaching, defatting , and acid washing, as well as treatment with some essential chemical compounds (e.g., methanol, ethanol, chloroform, etc.) and removal of hemicellulose are carried out for the extraction of pure ɑ-cellulose from natural sources.

Carboxymethylation of the pure ɑ-cellulose is performed basically in two significant steps. In the first step, the pre-purified cellulose extracts are mixed with alkali reagents (e.g., NaOH) in a reaction vessel for a specific time. During this time, the pure cellulose contents are mercerized. Subsequently, –OH functional groups from each AGU unit are substituted by –ONa groups targeted for the posterior substitution by carboxymethyl groups in the etherification step . Concentrations of the alkali, ratios between the alkali and cellulose, and reaction temperature should be maintained very carefully. A slight change in these parameters can significantly change the final product’s DS value and other physicochemical properties.

An inert solvent (such as ethanol , 2-propanol , isopropyl alcohol, or isobutyl alcohol, etc.) is added in this step as a diluent as well as a swelling agent that facilitates the penetration of the affined reagents into the cellulose structure.