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Epoxy matrix toughness improvement via reactive bio-resin alloying

A facile solvent-less approach to toughen epoxy thermosets by means of a bio-based resin, that is, poly(furfuryl alcohol) (PFA; furan resin) is reported. The bio-resin PFA was firstly synthesized through polycondensation reaction of furfuryl alcohol as a bio-monomer and maleic anhydride as a catalyst. Different amounts of PFA were blended with diglycidyl ether of bisphenol A epoxy resin and cured by diethylenetriamine as a hardener, which simultaneously cross-linked both of the epoxy and PFA resins. The curing process was studied by Furrier transform infrared spectroscopy and differential scanning calorimetry. Scanning electron microscopy of the chemically cured blends revealed no phase separation. It was found remarkable increase in flexural modulus and strength of the neat and modified epoxies with increasing PFA content up to around 15%. Moreover, in comparison with neat epoxy, the epoxy-PFA thermosets showed 60% increase in critical stress intensity factor and 123% increase in critical strain energy release rate. In fact, chemical reaction of PFA-incorporated epoxy could toughen the epoxy matrix without sacrificing the flexural strength and modulus. Toughening was obtained through cross-link density reduction. As exhibited by dynamic mechanical thermal analysis, Tan δ and magnitude of β-relaxation were also increased for the epoxy-PFA alloys. Overall, this green, simple, concise and cost-effective approach was suggested for being considered to produce toughened epoxy thermosets in industrial scale.