Methanol degradation mechanisms and permeability phenomena in novolac epoxy and polyurethane coatings / Ting Wang in JOURNAL OF COATINGS TECHNOLOGY AND RESEARCH, Vol. 18, N° 3 (05/2021)  

[article]  inJOURNAL OF COATINGS TECHNOLOGY AND RESEARCH > Vol. 18, N° 3 (05/2021) . - p. 831-842 Titre : Methanol degradation mechanisms and permeability phenomena in novolac epoxy and polyurethane coatings Type de document : texte imprimé Auteurs : Ting Wang, Auteur ; Shicong Luo, Auteur ; Chenyu Wang, Auteur ; Jing Wang, Auteur ; Claus Erik Weinell, Auteur ; Kim Dam-Johansen, Auteur ; Juan José Segura, Auteur ; Erik Graversen, Auteur ; Søren Kiil, Auteur Année de publication : 2021 Article en page(s) : p. 831-842 Note générale : Bibliogr. Langues : Américain (ame) Catégories : Absorption Adsorption Epoxy novolac Liaisons hydrogène Méthanol Perméabilité Polyuréthanes Revêtements organiques Index. décimale : 667.9 Revêtements et enduits Résumé : On a global scale, methanol is one of the most important feedstocks and is used widely as solvent and co-solvent. However, due to the polar nature and associated ability to conduct current, the small molecule can take part in galvanic corrosion of metal storage tanks and degrade the barrier properties of protective coatings. In the present work, we investigated the degradation of two novolac epoxy coatings and a polyurethane (PU) coating exposed to methanol with the aim of quantifying the various degradation paths. Absorption and desorption rates were measured and the thermomechanical properties followed by dynamic mechanical analysis. For evaluation of the coating barrier properties (i.e., breakthrough time and steady state permeation rates of methanol), permeation cells were applied. During methanol absorption, simultaneous leaching of certain coating ingredients and bonding of methanol to the binder matrix via hydrogen bonds was evidenced. In terms of classification, the bonding of methanol took place by two types of mechanisms. In Type I, the methanol molecule forms a single hydrogen bond to the coating network, thereby acting as a plasticizer, which decreases the coating storage modulus and glass transition temperature. For Type II bonding of methanol, on the other hand, two hydrogen bonds to the coating network form per molecule, resulting in so-called physical crosslinking. The Type I mechanism boosted segmental mobility and contributed to the leaching of the plasticizer benzyl alcohol from the novolac epoxy coatings and residual solvents (i.e., naphtha and xylene) from the PU coating. Following the methanol desorption, and attributed to an increased effective crosslinking density from Type II bound methanol, the novolac epoxy and PU coatings exhibited significant increases in the glass transition temperatures. In addition, for the three coatings, a gradual decline in the permeability rate of methanol was observed over time. These enhanced (and unexpected) barrier properties result from a combination of effects ascribed to Type II bound methanol and the leaching process. Note de contenu : - Experimental methods for coating degradation studies and aims of the work - EXPERIMENTAL : Materials - Absorption and desorption experiments - Permeation rate experiments - Dynamic mechanical analysis - Gas chromatography-mass spectrometry - RESULTS AND DISCUSSION : Methanol absorption and desorption - Methanol permeation rate - Permeability measurement across thermoplastic films - Permeability measurement across methanol-exposed coating - Water and ethanol absorption and desorption - Table 1 : Main components of the experimental coatings. Additional details can be found in an earlier work on acid degradation of organic coatings. NE-CA = Novolac Epoxy-Cycloaliphatic Amine. NE-PA = Novolac Epoxy-Polyamide - Table 2 : Coating properties and weight changes after immersion for 168 h (Mi) and unrestricted evaporation for 168 h (Ml) of the NE-CA, NE-PA, and PU films - Table 3 : Weight loss (relative to the original nonexposed film), Ml, and the glass transition temperature of the NE-CA, NE-PA, and PU coatings (168 h methanol immersion) - Table 4 : Breakthrough velocity (Rb) and permeation rate (Rperm) of methanol across NE-CA, NE-PA, and PU films - Table 5 : Weight changes of NE-CA films after immersion for 168 h (Mi) followed by unrestricted evaporation for 168 h (Ml) - Scheme : Chemical structures of epoxy phenol novolac resin, copolymer of benzenamine and formaldehyde (one constituent of polyamide), 4,4′-methylenebis(cyclohexylamine) and 1,6-hexamethylene diisocyanate DOI : https://doi.org/10.1007/s11998-020-00446-w En ligne : https://link.springer.com/content/pdf/10.1007/s11998-020-00446-w.pdf Format de la ressource électronique : Pdf Permalink : https://e-campus.itech.fr/pmb/opac_css/index.php?lvl=notice_display&id=35933 [article]

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