Unveiling the multifunctionality of deep eutectic solvents: Their role as solvents, extracting, and curing agents in β-chitin nanowhisker/DGEBA epoxy composites-A comparative study with α-chitin

Chitin, a highly valuable mucopolysaccharide, has revolutionized the biomedical industry due to its exceptional properties and versatile applications. With a focus on green chemistry and sustainable development, this study extracted α-chitin from Metapenaeus monoceros and β-chitin from Uroteuthis duvaucelli using an eco-friendly Deep Eutectic Solvent (DES) system, consisting of choline chloride (hydrogen bond acceptor) and malonic acid (hydrogen bond donor). Chitin nanowhiskers (CNWs) were synthesized via DES and uniformly incorporated into DGEBA epoxy resin using a modified slurry compounding technique. The epoxy was cured with a novel salicylic acid-triethylenetetramine DES system, enhancing the sustainability of the process. This is the first study to compare α- and β-CNWs as sustainable reinforcements in epoxy resin composites. The results revealed that α-CNW composites exhibited remarkable mechanical properties, including 33 % higher tensile strength, 206 % improved impact strength, and 197 % greater fracture toughness compared to β-CNW composites. On the other hand, β-CNW composites demonstrated superior tensile modulus (25.98 %), dynamic mechanical performance, and thermal stability, attributed to β-chitin's high purity and ease of synthesis despite its lower crystallinity. This work underscores the transformative potential of DES in advancing green material design and highlights β-CNWs as promising candidates for high-performance, bio-based composite applications.