Bio-based epoxy/chitin nanofiber composites cured with amine-type hardeners containing chitosan

Sorbitol polyglycidyl ether (SPE) which is a bio-based water-soluble epoxy resin was cured with chitosan (CS) and/or a commercial water-soluble polyamidoamine- or polyetheramine-type epoxy hardener (PAA or PEA). Furthermore, biocomposites of the CS-cured SPE (CS-SPE) and CS/PAA- or CS/PEA-cured SPE (SPE-CA or SPE-CE) biocomposites with chitin nanofiber (CNF) were prepared by casting and compression molding methods, respectively. The curing reaction of epoxy and amino groups of the reactants was confirmed by the FT-IR spectral analysis. SPE-CS and SPE-CA were almost transparent films, while SPE-CE was opaque. Transparency of SPE-CS/CNF and SPE-CA/CNF became a little worse with increasing CNF content. The tan δ peak temperature of SPE-CS was higher than those of SPE-PAA and SPE-PEA. SPE-CA or SPE-CE exhibited two tan δ peak temperatures related to glass transitions of the CS-rich and PAA-rich or PEA-rich moieties. The tan δ peak temperatures related to the CS-rich and PAA-rich moieties increased with increasing CNF content. A higher order of tensile strengths and moduli of the cured resins was SPE-CS ≫ SPE-CA > SPE-CE. The tensile strength and modulus of each sample were much improved by the addition of 3 wt% CNF, while further addition of CNF caused a lowering of the strength and modulus.