Desenvolvimento de resina epóxi a partir de resíduo agroindustrial para aplicação em revestimentos anticorrosivos

Abstract

Epoxy resins are a class of very versatile prepolymers that combined with crosslinking agents produce thermosetting polymers with outstanding properties that allow their use in several segments, such as adhesives, composites, building materials, insulation components and especially in coatings. The search for new ways to obtain these resins has been increasing, mainly by using bio-based sources in order to minimize the use of toxic components, such as bisphenol A (BPA) and epichlorohydrin. The aim of this work was to use the Cashew Nut Shell Liquid (CNSL) as a precursor in the epoxy resin synthesis, completely replacing the commercial diglycidyl ether of bisphenol A-based resin (DGEBA) in the production of polymers with potential application in coatings for corrosion protection. The epoxidation of CNSL was performed using formic acid and hydrogen peroxide, which proved to be efficient in the synthesis of CNSL-based epoxy resin (E-CNSL). The chemical structure of E-CNSL was confirmed by Fourier Transform infrared spectroscopic (FT-IR) and 1H and 13C Nuclear Magnetic Resonance spectroscopy with elevated yield (90%). CNSL-E was mixed with diethylenetriamine (DETA), isophoronadiamine (IPDA) and p-phenylenediamine (PFDA) and the curing reaction was analyzed by Differential Scanning Calorimetry (DSC), in which the post cure temperatures of 130, 150 and 170 ° C were chosen. Gel content tests were carried out where it was observed that polymers cured at 150 ° C exhibited a higher crosslink density, thus, the other analyzes were performed for these polymers. The thermal properties of the polymers were evaluated by DSC and Thermogravimetric (TGA) analysis, showing glass transition values (Tg) between 10-18 ºC, thermal stabilities in N2 atmosphere in the range of 280-300 ºC and in atmosphere of synthetic air of 276-280 ° C. 1010 carbon steel panels were coated with the polymers produced to evaluate the adhesive and anticorrosive properties. The coatings had good adhesive properties with values of 10 MPa. The corrosion properties were analyzed by electrochemical impedance spectroscopy (EIS), exhibiting high impedance modulus values at low frequencies, evidencing that the coatings acted as a barrier, promoting an effective protection of the metal. According to the results, the obtained polymers have the potential to act as anticorrosive coatings.