Evaluation of hybridized bio-based building blocks as coating materials

Commercial epoxy resins are often the oligomeric reaction products of bisphenol A (BPA) with epichlorohydrin. BPA is a toxic petrochemical and a well-known endocrine disruptor which can mimic the body’s own hormones and may lead to several negative health effects. The most common curing agents are also the derivatives of toxic amines such as aniline, ethylene di-amine, and ammonia etc. which are under strict regulations and restrictions by TSCA and (REACH) agencies. Therefore; there is a growing demand to develop epoxy and amine systems from non- or less- toxic and annually renewable precursors derived from bio-mass to replace depleting petrochemicals. Within this context, cardanol molecule is combined with vanillyl alcohol through electrophilic substitution reaction to synthesize a bis-phenol type resin (VAC). Di-glycidyl ether of the VAC (EVAC) is mixed with di-glycidyl ether of bisphenol A (DGEBA) at varying ratios and cured with di-furan di-amine (DFDA) which is previously a well-studied bio-based diamine derived from furfurylamine. Thermally cured blends demonstrated improved modulus and char yields relative to aliphatic and cyloaliphatic amines due the furanic nature of DFDA as demonstrated via thermo-physical and mechanical tests. Although, the replacement of EVAC with DGEBA resulted in a reduction in glass transition temperature (Tg) and the modulus of the network, desired flexibility and toughness for coatings applications were imparted due to the aliphatic nature of the cardanol molecule. In addition, rheological studies demonstrated improved gel time and lower viscosity with increasing EVAC content along with improved vapor barrier properties. These bio-derived epoxy-amine formulations demonstrated promising performance to completely or partially replace the BPA and other toxic amines in the thermoset networks for surface coating applications.