Fabrication and characterization of a starch-based superabsorbent hydrogel composite reinforced with cellulose nanocrystals from potato peel waste

A semi-interpenetrating polymer network (semi-IPN) superabsorbent hydrogel composite based on starch (St)graft-poly(acrylic acid (AA)-co-acrylamide (AM))/polyvinyl alcohol (PVA) and cellulose nanocrystals (CNC) was synthesized using free radical aqueous polymerization method. Cellulose nanocrystals were extracted from potato peel waste using alkali treatment followed by acid hydrolysis. FTIR analysis affirmed the grafting reaction of acrylate-based monomers onto starch backbone as well as composite formation. The structural and morphological features of the hydrogels were examined by XRD, SEM, and TEM techniques. The hydrogel composite exhibited higher equilibrium swelling ratio (921.8 g/g) compared with the neat hydrogel (772.4 g/g). The swelling kinetics of the prepared hydrogels had high compliance with the first order swelling kinetic model. The diffusion coefficient value of the hydrogel composite was higher than that of the neat hydrogel, revealing that the incorporation of cellulose nanocrystals into the hydrogel matrix had resulted in faster penetration of water molecules into the polymeric network. The examination of the viscoelastic behavior of hydrogel samples by rheological tests revealed that the elastic behavior of the samples prevails over their viscous behavior. Moreover, the storage modulus of hydrogel composite was higher than that of the neat hydrogel over the entire frequency range which shows the stiffer network of the hydrogel composite. The hydrogel composite exhibited high saline absorbency under load, good deswelling kinetics in different saline solutions, desirable swelling/drying capability, and acceptable pH-dependent swelling reversibility which make it a potential candidate for agricultural and horticultural applications.