Design and development of trivalent Fe ion-induced novel urushi organogels

Abstract

An organogel based on natural urushiol with a high mechanical strength was prepared in the presence of Fe3+ ions at 40 °C. Urushiol obtained from lacquer sap of the lacquer tree, which is a mixture of catechol derivatives having long alkyl side chains, was used as a monomer. The urushi organogels were formed through the polymerization of urushiol and coordination bonds in the presence of Fe3+ ions in the urushiol solution. The Fe3+ ions acted as catalysts for the polymerization of urushiol, which solves the problem of the bio-enzyme's activity (laccase) being uncontrollable in lacquer sap. The fabrication and properties of urushi organogels with different concentrations of Fe3+ ions were investigated. Coordination bonds between Fe3+ ion and urushiol acted as additional crosslinking sites to form a multi-network structure, which was confirmed by Raman spectroscopy. The formation of the coordination bonds improved the mechanical strength of the chemically crosslinked urushi organogel, in addition to the entanglement of the long alkyl side chains of the urushiol. A highly stretchable and durable urushi film was obtained owing to the multi-network system of the urushi organogel, which expands the applicability of environmentally friendly natural urushi.