The use of polysaccharide-based polyelectrolytes for cellulose fiber modification

Modification of biomaterials to tune their properties and increase their range of applications is of great interest, as this could give natural polymers some of the flexibility that synthetic materials have. Among the biomaterials with great potential to replace synthetic polymers, cellulose wood pulp, a commodity, and its derivatives, such as cellulose microfibers/nanofibers, could gain new uses if some of their properties could be modified. Layer-by-layer self-assembly of polyelectrolytes is a useful method to recover substrates with functional nanostructured layers. Among the biobased polyelectrolytes, several are based on polysaccharides, both anionic and cationic, such as carboxymethyl cellulose and chitosan. Cellulose pulp and nanocellulose produced from pulp are available in aqueous suspension, since the production of these materials is necessarily in this medium. Here we describe studies involving the use of two polysaccharides, carboxymethyl cellulose and chitosan, for the modification of cellulose wood pulp. Various substrates were used to study the deposition process of CMC and chitosan, including glass, polyethylene and regenerated cellulose films before studying their deposition on suspended wood pulp. To understand the process, cellulose nanocrystals were modified and the zeta potential was used to follow the deposition process. The effect of pH on film growth and its relationship with the conformation of the polyelectrolyte in solution was also described. The process was applied to bleached eucalyptus wood pulp fibers and up to 30 CNC/chitosan bilayers were deposited. The materials were characterized by scanning electron microscopy (SEM) and laser scanning confocal microscopy (LSCM). The surface of the wood pulp was imaged using the LSCM technique and the deposition of the polyelectrolyte complex was observed outside and inside the wood pulp fibers, since cellulose fibers are tube-like materials. The inclusion of other substances between the sublayers could be a useful technique to produce functional materials. After fiber modification, the fibers remain suspended in the same way they were at the beginning, showing the possibility of using the process on an industrial scale. Acknowledgements: The author thanks CNPq process 308709/2023-3 for the financial support.