Effect of Different Curing Agents on Cure Reaction and Exposure Resistance of Phenolic-Epoxy Resins in Hot Acid Solutions

Linear phenolic-epoxy polymers were cured with diaminodiphenyl sulfone (DDS), metaphenylene diamine (m-DPA), and phenolic aldehyde amine (PAA), respectively, to prepare several anti-corrosion materials that are coating components. The effect of different curing agents on energy of activation (E_a) and glass transition temperature (T_g) of polymers was investigated using differential scanning calorimetry (DSC). E_a of phenolic-epoxy/DDS is higher than that of phenolic-epoxy/PAA, and lower than that of phenolic-epoxy/m-DPA. The three anti-corrosion materials were immersed in 10% sulfuric acid (H₂SO₄) solution at 80°C for 800 h. T_g of phenolic-epoxy/DDS material varies very little before and after acid immersion testing, while T_g of phenolic-epoxy/PAA material drastically decreases after the acid immersion test. A gravimetric liquid sorption experiment indicates that weight loss of phenolic-epoxy/DDS material is the smallest among three anti-corrosion materials. X-ray photoelectron spectroscopy (XPS) analysis demonstrates that the carbon-to-oxygen (C/O) ratio of phenolic-epoxy/DDS material after exposure testing is higher than that of phenolic-epoxy/m-DPA material and phenolic-epoxy/PAA material. The high T_g, high C/O ratio, and low weight loss of phenolic-epoxy/DDS material as a coating component during exposure are connected directly with the strong corrosion resistance of the coating.