Bio-based epoxy-anhydride thermosets from six-armed linoleic acid-derived epoxy resin

Abstract

Six-armed linoleic acid-derived epoxy resin with a rigid triazine core (EHL) was prepared through the esterification reaction between linoleic acid and hexamethylol melamine, followed by epoxidation of unsaturated fatty acid chains by using hydrogen peroxide. Bio-based epoxy-anhydrides thermosets were then produced from this resin by using 4-methyl hexahydrophthalic anhydride as the hardener and 1,8-diazabicyclo[5.4.0]undec-7-ene as the catalyst; the properties of these thermosets were then systematically investigated. The epoxy oligomer was fully characterized and confirmed through Fourier-transform infrared spectroscopy, nuclear magnetic resonance, and matrix-assisted laser desorption and ionization time-of-flight mass spectrometry. The physical properties of this oligomer were also studied according to its bulk viscosity, epoxy equivalent weight, and density. The curing extent of the bio-based epoxy-anhydride thermosets were measured through differential scanning calorimetry and gel content testing. The properties of these thermosets were characterized through tensile testing, dynamic mechanical thermal analysis, and thermogravimetric analysis. Compared with thermosets based on benchmark bio-based epoxy resins, such as epoxidized soybean oil and epoxidized sucrose soyate, EHL-based thermosets showed higher glass transition temperatures, and enhanced tensile strength and modulus for a given cross-link density. These enhancements can be rationalized according to the rigidity of the triazine core, and the cohesive energy stemmed from the inter-molecular interaction of highly polarized heterocycle.