Composite protective coatings. Resistance to acid penetration of coatings based on epoxy resins

• V.A. Golovin and A.B. Il’in

A.N. Frumkin Institute of Physical Chemistry and Electrochemistry, Russian Academy of Sciences, Leninsky pr. 31, 119071 Moscow, Russian Federation

Abstract: A complex of diffusion–sorption methods is used to study the effect of the chemical nature of the curing agent and polymer epoxy matrix on the solubility and diffusion of corrosive acid media and also to test the possibility of decreasing the acid penetration into laminated composite coatings. A significant effect of the chemical nature of the curing agent and polymer matrix composition on the solubility of corrosive media is observed. This is manifested as a fundamental difference in the behavior of epoxy materials cured by amines and acid anhydrides: lower solubility (5–10-fold) and lower acid penetration rate constants (2–10-fold) are typical of anhydride-cured epoxy binders. It is shown that both amine (polyethylene polyamine (PEPA)) and anhydride (succinic anhydride (SA)) aliphatic curing agents form more permeable epoxy matrices with higher acid solubility as compared to aromatic curing agents, such as metaphenylene diamine (MPDA) and phthalic anhydride (PA). It is also important that a pronounced mechanism of sorption with binding is realized in the case of amine-cured resins with residual and reduced amino groups in the case of acid penetration. This principally allows ion-selective properties to be imparted to the cured resin. It is suggested that materials containing not only residual but also functional acid groups can be used for the development of laminated composite coatings. As shown for chlorosulfonated polyethylene (CSPE) as an example, the penetration depth of sulfuric acid is comparable to that in anhydride-cured epoxy resins. Moreover, data of luminescent analysis indicate that complexes are formed between CSPE functional groups and the penetrating acid. The results show that the penetration depth of mineral acids decreases considerably for laminated composite coatings with an upper layer of materials comprising functional acid groups. This effect is observed for phosphoric acid at temperatures up to 100°C and also for nonvolatile H₂SO₄ and volatile HCl in the temperature range of 20–70°C.

Keywords: protective polymer coatings, corrosive media, composite materials

Int. J. Corros. Scale Inhib., 2020, 9, no. 4, 1530-1549 PDF (869 K)
doi: 10.17675/2305-6894-2020-9-4-22

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