Elaboration of Novel Biocomposite Hydrogel Polymers made of Alginate and Sepiolite and endowed with Enhanced Properties

Nowadays growing attention is given to the design and development of novel interpenetrating polymer networks (IPN) from the combination of hydrogel polymers loaded with natural clay. In this work, we used the eco-friendly IPN strategy to develop novel hydrogel biocomposite beads, made of alginate (ALG), with improved clay dispersion, higher pH sensitivity, better stretchability and swellability, together with enhanced regenerability properties and biodegradability resistance. Fibrous clay, namely sodium sepiolite (NaS), was loaded into alginate simple biocomposite network (SBN) beads, via manual co-grinding mixture/encapsulation method, at different sepiolite loads. Alginate double biocomposite network (DBN) beads were also prepared at different sepiolite loads, via the diffusion of acrylamide monomer (AAM) inside alginate single biocomposite network (SBN) beads, followed by in situ free radical polymerization of AAM into poly-acrylamide (pAAM), using ammonium persulfate (APS) as polymerization initiator and N,N-methylenebisacrylamide (Bis) as covalent crosslinker agent. The as-elaborated SBN and DBN beads were then characterized by digital camera recording, XRD analysis, ATR-FTIR characterization and SEM observation. FTIR results showed that NaS and pAAM were successfully incorporated into DBN beads, whilst XRD analysis revealed the enhancement of fibrous clay dispersion, even at relatively high sepiolite loads. Besides, SEM microscopy confirmed the porous spongious nature of DBN beads. The properties of the as-elaborated SBN and DBN beads were also evaluated by test touching, swelling rate measurements, adsorption/desorption experiments and biodegradability evaluation. DBN beads properties were always found enhanced in comparison with those of SBN beads: very good stretchability, good swelling behavior and stability in water whatever the pH, either in acidic or alkaline solution, enhanced adsorption/desorption properties towards methylene blue (MB) dye, very good regenerability and delayed biodegradability. In summary, this work showed an interesting and safe IPN/biocomposite approach to develop high-performance alginate biocomposite polymers as a promising system towards their use in eco-friendly processes.