Nanostructured and Advanced Designs from Biomass and Mineral Residues: Multifunctional Biopolymer Hydrogels and Hybrid Films Reinforced with Exfoliated Mica Nanosheets.

Transforming potential waste materials into high-value-added sustainable materials with advanced properties is one of the key targets of the emerging green circular economy. Natural mica (muscovite) is abundant in the mining industry, which is commonly regarded as a byproduct and gangue mineral flowing to waste rock and mine tailings. Similarly, chitin is the second-most abundant biomass resource on Earth after cellulose, extracted as a byproduct from the exoskeleton of crustaceans, fungal mycelia, and mushroom wastes. In this study, exfoliated mica nanosheets were individualized using a mechanochemical process and incorporated into regenerated chitin matrix through an alkali dissolution system (KOH/urea) to result in a multifunctional, hybrid hydrogel, and film design. The hydrogels displayed a hierarchical and open nanoporous structure comprising an enhanced, load-bearing double-cross-linked polymeric chitin network strengthened by mica nanosheets possessing high stiffness after high-temperature curing, while the hybrid films (HFs) exhibited favorable UV-shielding properties, optical transparency, and dielectric properties. These hybrid designs derived from industrial residues pave the way toward sustainable applications for many future purposes, such as wearable devices and tissue engineering/drug delivery.

Hybrid films of cellulose nanofibrils, chitosan and nanosilica-Structural, thermal, optical, and mechanical properties.

Organic-inorganic hybrid films were fabricated from cellulose nanofibrils (CNF) and nanosilica (5-30% wt) embedded in a chitosan (Chi) biopolymer matrix using a slow evaporation method. The self-standing films exhibited high strength and modulus up to 120 ± 5 MPa and 7.5 ± 0.4 GPa, respectively, which are remarkably high values for biopolymer/chitosan hybrids. Scanning electron microscopy showed that the nanosilica is formed of larger aggregates within the lamellar CNF network structure. This observation was further confirmed using synchrotron-based scanning transmission x-ray microscopy (STXM) with the capability to determine the spatial and chemical distribution analysis of the constituents of films. It is interesting that the thermal stability of the hybrid films improved as the nanosilica content increased. Furthermore, the nanosilica effectively filled the pores in the CNF network, thus decreasing the UV transmission and the visible light transmittance of the films.