Resina epóxi monocomponente sustentável: novo revestimento anticorrosivo de alto desempenho a partir de subproduto agroindustrial

Abstract

In the present study, an epoxy resin produced from an agro-industrial byproduct, cashew nut shell liquid (CNSL), was utilized to develop a one-component epoxy coating with anticorrosive capabilities. The CNSL-based epoxy resin (CNSL-E) was synthesized using a solvent-free methodology, employing in situ generated performic acid. The chemical structure of the resin was confirmed via FTIR and 1H NMR. Curing reaction was facilitated by an epoxy-phenol system using 1-methylimidazole (1MIM) as an accelerator, which was preliminarily investigated through differential scanning calorimetry (DSC). The use of only 5% by mass of 1MIM proved efficient in catalyzing the reaction, yielding the lowest curing temperature (150 ºC). The coating exhibited high crosslinking of 95.4 ± 0.3% and favorable thermomechanical properties, with an initial decomposition temperature around 200 ºC and a glass transition temperature of 30 ºC. The anticorrosive performance of CNSL-E/MIM5 exposed to salt fog and a 3.5% mass NaCl solution was monitored using electrochemical impedance spectroscopy (EIS), adhesion tests, and visual evaluation during the exposure period. Additionally, a saturated humidity test with visual assessment was conducted. A commercial DGEBA coating was employed as a reference in the salt fog and saturated humidity exposure tests. As reported in literature, coatings with |Z|0.01Hz above 108 Ω.cm2 provide high protection properties, while those with |Z|0.01Hz below 106 Ω.cm2 offer low-performance protection for carbon steel substrates. The CNSL-E/MIM5 coating demonstrated a high impedance modulus at 108 Ω.cm2 and excellent adhesive properties of 16 ± 0.7 MPa, experiencing minimal delamination during testing, whereas the reference coating exhibited an impedance modulus at 106 Ω.cm2 . Thus, the developed one-component biobased coating shows promise for corrosion protection applications.