The role of electrostatic interactions of anionic and cationic cellulose derivatives for industrial applications: A critical review

Some of the most popular cellulose derivatives exhibit charged functional groups, either cationic (generally, quaternary ammonium moieties) or anionic (most typically, carboxylate groups). Noticeably, the second most successful cellulosic derivative in the world, in terms of market share, is the salt of a negatively charged polymer: sodium carboxymethyl cellulose. However, many of the applications that have long been proposed by researchers have never proven feasible on a large scale. In light of this, the present review critically discusses the current and potential applications of anionic and cationic cellulose derivatives: (i) coagulation-flocculation or direct flocculation processes, for which the limited molecular weight of cellulose derivatives is a key limitation; (ii) thickening and rheology modification in general, where polymer-water interactions play a major role; (iii) stabilization of colloids or emulsions, in such way that the repulsive electrostatic forces prevent aggregation unlike coagulation-flocculation; (iv) adsorption of cations by anionic cellulose, of anions by cationic cellulose, and adsorption mediated by other mechanisms; (v) encapsulation of bioactive compounds for drug delivery or other purposes; (vi) filtration by means of cellulose-based membranes, and (vii) production of antimicrobial materials by exploiting the interactions between cationic cellulose and the phospholipid bilayer of microorganisms. We highlight the recent trends and, closely related to them, the knowledge gaps in the literature on anionic and cationic derivatives. For instance, the survey remarks on the increasing popularity of anionic or cationic nanocellulose (generally, as nanofibers or nanocrystals), progressively outweighing both conventional fibers and soluble derivatives.