Hidrogéis de celulose microcristalina oxidada via mediação por TEMPO modificados com β-ciclodextrina e κ-carragena para aplicação como adsorvente

Abstract

The oxidation method via N-oxyl-2,2,6,6-tetramethylpiperhydrin (TEMPO) mediation has been widely used as a pre-treatment to obtain nanocellulose from cellulose and, in addition, the oxidation allows a better dispersion in water and facilitates gel formation. Since cellulose is a widely available biopolymer, biodegradable, renewable and low-cost biopolymer, its use in the preparation of hydrogels has been gaining ground and the use of oxidized cellulose has not been different. Hydrogels prepared with the oxidized cellulose and chemically cross-linked by interaction with the hydroxyl groups of the cellulose allow the carboxylic groups to become available, allowing the application to remove cationic dyes, for example, due to negative charges. Therefore, the objective of the present work was to prepare hydrogels of oxidized microcrystalline cellulose via chemically cross-linked TEMPO mediation and to evaluate the introduction of β-cyclodextrin and κ-carrageenan modifiers on the adsorption efficiency of methylene blue. For this purpose, two chemical crosslinkers (epichlorihydrin and glutaraldehyde) were used and the one that best provided a more structured hydrogel (epichlorihydrin) was applied in the crosslinking of the hydrogel with the addition of β-cyclodextrin and κ-carrageenan. The effects of the two modifiers on the oxidized microcrystalline cellulose hydrogel were characterized by Fourier Transform Infrared Spectroscopy (FTIR), thermogravimetry, scanning electron microscopy (SEM), nitrogen adsorption/desorption and swelling degree. The hydrogels were applied in the adsorption of methylene blue to evaluate its removal efficiency and in the adsorption of gentamicin sulfate, and the hydrogels loaded with the drug were tested for bacteriostatic activity by disk diffusion. All hydrogels showed dye adsorption capacity and increases in cellulose concentration and the addition of β-cyclodextrin and κ-carrageenan improved the methylene blue adsorption process. In addition to electrostatic interactions, the optimal fit of kinetics in the adsorption for the pseudosecond order model suggests the contribution of chemical interactions in the adsorption process. In the adsorption of gentamicin sulfate, the hydrogel with κ-carrageenan showed better removal efficiency, but all charged hydrogels formed inhibition halos. Thus, the developed hydrogels proved to be materials with great potential for application as adsorbents.