Fluorescent Multifunctional Polysaccharides for Sustainable Supramolecular Functionalization of Fibers in Water

The paper describes the synthesis of multifunctional cellulose derivatives (MCDs) containing a fluorescent and a cationic moiety and their application in the functionalization of pulp fibers. The cellulose derivatives, namely N-(3-propanoic acid)- and N-(4-butanoic acid)-1,8-naphthalimide esters of cellulose, differed in the degree of substitution (DS) and by the aliphatic chain connecting naphthalimide photoactive groups to the polymer backbone. The derivatives were decorated with a cationic moiety, namely (3-carboxypropyl)trimethylammonium chloride. The fluorescent pulp fibers were prepared by direct self-assembly of the water-soluble fluorescent MCDs on the fibers in water at room temperature. The results indicated that the adsorption was mainly driven by an ion exchange mechanism. UV vis and fluorescence spectroscopic studies showed that the adsorption yield of the fluorescent MCDs depended on the length of the aliphatic chain of the photoactive groups. Because of the adsorption, the modified pulp fibers gained fluorescence in the visible part of the spectrum. Under black light illumination, the modified fibers fluoresced, which made them visually distinguishable from the reference fibers. Thus, the fluorescent pulp fibers prepared in a simple way can be potentially used as an authenticity indicator in packaging materials.