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Chemically modified cellulose nanocrystals as polyanion for preparation of polyelectrolyte complex

Vasconcelos, Niédja Fittipaldi, Feitosa, Judith Pessoa Andrade, Andrade, Fábia Karine, Miranda, Marcus Aurélio Ribeiro, Sasaki, José Marcos, Morais, João Paulo Saraiva, e Silva, Lorena Mara Alexandre, Canuto, Kirley Marques, Rosa, Morsyleide de Freitas
Cellulose 2019 v.26 no.3 pp. 1725-1746
anions, cellulose, chitosan, crystal structure, ethanol, hydrolysis, hydrophilicity, isopropyl alcohol, moieties, nanocrystals, nuclear magnetic resonance spectroscopy, particle size, solubility, solvents, sulfuric acid, thermal properties, titration, zeta potential
Bacterial cellulose nanocrystals (BCNCs) have hydrophilic surfaces due to hydroxyl groups but are water-insoluble. The carboxymethylation improves the solubility of cellulose in polar media through the insertion of carboxymethyl groups. This study aims to evaluate the use of two different alcoholic solvents in the carboxymethylation reaction of BCNCs: ethanol and isopropanol. BCNCs were obtained under two hydrolysis conditions: sulfuric acid (BCNC-S) and combination of sulfuric and hydrochloric acids (BCNC-S/Cl). Two techniques (NMR and titration) were used to determine the degree of substitution (DS) values. Carboxymethylation of BCNC-S/Cl led to high DS compared to BCNC-S and the use of isopropanol promoted an even greater DS. The thermal properties were not affected after the chemical modification. However, functionalization provided an increase in the negative charge density at the surface of nanostructures and a change in the crystal structure (cellulose type Iα for amorphous), making this material a potential polyanion for the synthesis of polyelectrolyte complexes (PECs). The micrographs showed that the nanocrystals became soluble after carboxymethylation. Carboxymethylated bacterial cellulose nanocrystals hydrolyzed through the mixture of inorganic acids and modified using isopropanol (CBCNC-S/Cl-IPA) was a suitable polyanion to produce PECs with chitosan. The PECs produced had particle size ranging from 276 to 588 nm and zeta potential ranging from − 24.3 to + 39.0 mV.