Bio-based curing agent for epoxy resins: Simultaneously improved toughness, strength, and flame retardancy

Improving the toughness of epoxy resin (EP) while maintaining its strength is still considered a huge challenge. Herein, a novel bio-based curing agent, PA–DAD, has successfully been developed for EP that provides both mechanical reinforcement and flame retardancy. This agent was prepared via a straightforward neutralizing process between phytic acid (PA) and 1,10-diaminodecane (DAD). A series of bio-based curing agents labeled PA1–DAD6, PA1–DAD9, and PA1–DAD12 were produced by adjusting the PA and DAD stoichiometric ratio. During the curing process, PA–DAD dissociates into PA and DAD, PA functions as an ionic cross-linking site within the EP structure. This considerably enhances the mechanical properties of the EP compared with using DAD alone as a curing agent. As a consequence, the tensile, flexural, and the impact strength values of EP/5 % PA1–DAD6 enhanced by 103 %, 70 %, and 168 %, respectively, compared with EP/5 % DAD at a 5 wt% addition. Additionally, the tensile and flexural toughness values of EP/5 % PA1–DAD6 were 1250 % and 649 % higher compared to those of EP/5 % DAD, respectively, demonstrating the exceptional toughening effect of PA–DAD on EP. Furthermore, the flame retardancy of EP/PA–DAD improved because of the high P content in PA–DAD. Compared with EP/5 % DAD, EP/5 % PA1–DAD6 shown decreases of 10.7 % in peak heat release rate, 8.4 % in total heat release, and 13.6 % in total smoke production. The straightforward fabrication process, exceptional mechanical enhancement, and use of sustainable bio-based raw materials make PA–DAD highly suitable for large-scale production of advanced EP materials. [Display omitted] •A novel bio-based curing agent for epoxy resin is prepared by a facile neutralization reaction.•The curing agent endows epoxy resin with excellent mechanical properties.•The toughening mechanism for epoxy resin was proposed by constructing sacrificial bonds in the matrix.•The curing agent endows the epoxy resin with favourable fire resistance.