Ultra-lightweight poly (sodium acrylate) modified TEMPO-oxidized cellulose nanofibril aerogel spheres and their superabsorbent properties

Abstract

In this article, we reported a facile method for synthesizing poly (sodium acrylate) (PAANa)-modified TEMPO-oxidized cellulose nanofibril (TOCN) aerogel spheres. The water absorbent capacity of the spheres could be as high as 1030 g/g, which has never been reported before. Practically, the 1 wt% TOCN suspension was simply dropped into an HCl solution to prepare physically crosslinked TOCN hydrogel spheres. Afterwards, PAANa, an anionic monomer, was added into TOCN gel spheres by solution replacement, and the monomer was polymerized and grafted to the TOCN spheres in the presence of N,N-methylenebisacrylamide as a crosslinker through in situ free radical polymerization. The physical crosslinking (through hydrogen bonding) of the spheres was replaced by chemical crosslinking after washing the gel spheres to neutral, which resulted in high volume expansion (about 27 times v/v) of the washed sphere. The expansion rate and morphologies of the obtained hybrid gel spheres were strongly dependent on the dosage of the crosslinker and monomer. The structure and morphologies of the hybrid spheres were characterized by FTIR, TGA and SEM. The water-absorbing behaviors of the hybrid spheres were dependent on the pH, concentration of the salt solution and crosslinker content. The freeze-dried aerogel spheres were highly porous (approximately 99.88 %) with density as low as 1.5 mg/cm3. All results indicated that TOCN–PAANa hybrid aerogel spheres could serve as a new type of superabsorbent.