Citation: Bashir, M.A. Cure Kinetics of Commercial Epoxy-Amine Products with Iso-Conversional Methods. Coatings 2023, 13, 592. https://doi.org/10.3390/ coatings13030592 Academic Editor: Fengwei (David) Xie Received: 19 February 2023 Revised: 5 March 2023 Accepted: 7 March 2023 Published: 9 March 2023 Copyright: © 2023 by the author. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). coatings Article Cure Kinetics of Commercial Epoxy-Amine Products with Iso-Conversional Methods Muhammad Ahsan Bashir Jotun Performance Coatings, Jotun A/S, 3209 Sandefjord, Norway; muhammad.bashir@jotun.no Abstract: The dependence of the apparent activation energy for the epoxy-amine reaction on the degree of conversion can be obtained by applying iso-conversional methods to the non-isothermal cure data obtained by using differential scanning calorimetry (DSC). The application of three iso- conversional methods has been utilized for the analysis of non-isothermal DSC cure data for three commercial high solids epoxy-amine coatings. The average apparent activation energy for cure of the fully formulated commercial product(s) is very similar to that previously reported for the epoxy-amine clear coats, indicating that the presence of additives does not influence the epoxy-amine apparent activation energy. Among the methods tested, Friedman’s method performed the best in fitting the experimental DSC data. In addition, all three methods underpredict the experimental isothermal cure data for three commercial products at two different cure conditions (i.e., 23 ◦ C/50% RH and 40 ◦ C/70% RH), showing that the non-isothermal DSC experiments cannot capture the catalytic effect of water on the curing reaction of epoxy-amine coatings. Furthermore, for high-solids epoxy-amine products, at least 60% conversion is required to achieve the time when the applied coating will not show any tackiness (i.e., the T2 time measured using the Beck Koller method). Keywords: model-free kinetics; epoxy-amine coatings; drying time; isothermal cure 1. Introduction Two-component (2K) epoxy-amine organic coatings, used for anticorrosion applica- tions on structures such as automobiles, bridges, oil and gas pipelines, windmills, oil rigs, etc., cure by the reaction of epoxy groups with the amine groups following the step-growth polymerization process. This curing process is complicated and involves the ring-opening reaction of the epoxy ring, which produces secondary amines that further react with the epoxy groups to produce tertiary amines, causing branching or crosslinking (see Figure 1a). The hydroxyl group produced during the polymerization can form hydrogen bonds with the unreacted epoxy groups, thereby promoting the nucleophilic attack of the amino groups on the epoxy groups. Such a reaction is termed an autocatalytic reaction and is shown schematically in Figure 1b. The electrophilicity of the epoxy group and the nucleophilicity of the amino group determine the reaction kinetics for 2K epoxy-amine coatings [1]. In addition, temperature and catalysts also influence the curing kinetics for epoxy-amine coatings. Water and other compounds containing hydroxyl groups, in general, act as catalysts for epoxy-amine cure [2,3]. The curing process for epoxy-amine coatings involves different stages, such as gelation and vitrification, depending upon the type of epoxy resin, the curing agent, and the curing temperature used. Gelation happens when the three-dimensional polymeric network has formed throughout the network with significant chain branching. At this point, the average molecular weight can be considered to be infinity [4], and the coating seems to be a ‘gel’ with significant tackiness. Vitrification occurs if the cure temperature is sufficiently lower than the glass transition temperature (T g ) of the formed polymer network, causing the transition from a gel-like structure to a glass-like structure. Vitrified epoxy-amine coatings can appear to be fully cured. Cure kinetics for epoxy-amine polymerization are influenced Coatings 2023, 13, 592. https://doi.org/10.3390/coatings13030592 https://www.mdpi.com/journal/coatings