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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Simultaneous tracking of hardness, reactant conversion, solids concentration, and glass transition temperature in thermoset polyurethane coatings / Ting Wang in JOURNAL OF COATINGS TECHNOLOGY AND RESEARCH, Vol. 18, N° 2 (03/2021)  

[article]  inJOURNAL OF COATINGS TECHNOLOGY AND RESEARCH > Vol. 18, N° 2 (03/2021) . - p. 349-359 Titre : Simultaneous tracking of hardness, reactant conversion, solids concentration, and glass transition temperature in thermoset polyurethane coatings Type de document : texte imprimé Auteurs : Ting Wang, Auteur ; Juan José Segura, Auteur ; Erik Graversen, Auteur ; Claus Erik Weinell, Auteur ; Kim Dam-Johansen, Auteur ; Søren Kiil, Auteur Année de publication : 2021 Article en page(s) : p. 349-359 Note générale : Bibliogr. Langues : Américain (ame) Catégories : Analyse mécanique dynamique Catalyseurs Dureté (matériaux) Fourier, Spectroscopie infrarouge à transformée de Mesure Organostanniques Un organoétain ou organostannique est un composé organique comportant au moins une liaison covalente entre un atome de carbone et un atome d'étain. Il fait partie de la grande famille chimique des composés organométalliques. L'atome de carbone lié à l'étain appartient souvent à un groupe de type éthyle, propyle ou butyle. Les organoétains sont généralement peu solubles dans l'eau, mais très lipophiles. Comme la plupart des composés organométalliques, les organoétains présents dans l'environnement sont souvent toxiques et écotoxiques. Les chimistes ont identifié plus de 260 composés organostanniques et 36 d'entre eux sont toxiques et écotoxiques. Tous, hormis les méthylétains ont une origine anthropique. Ils ont une longue durée de vie dans l'environnement. Certains d'entre eux, les TBT (tributylétains, hautement toxiques pour de nombreux organismes marins, même à très faible dose, pour les algues et divers organismes marins dont les mollusques) ont été très utilisés dans les antifoulings, et sont particulièrement surveillés car hautement toxiques, rémanents dans les sédiments et sources d'imposex (changement de sexe) chez certaines espèces qui y sont exposées, dont chez des espèces commercialement importantes (bigorneau, buccin commun). (Wikipédia) Réticulation (polymérisation) Revêtements organiques solvants Thermodurcissables Index. décimale : 667.9 Revêtements et enduits Résumé : In this work, the curing and hardness evolution of a two-component polyurethane (PU) coating in four different environments, three of which were solvent evaporation-suppressed conditions, were studied. In contrast to previous studies, the simultaneous use of Fourier-transform infrared spectroscopy, gravimetric analysis, and pendulum hardness allowed a transient mapping of the degree of isocyanate conversion, solids concentration, and coating hardness. Furthermore, to explore in more detail the coupling of the underlying mechanisms, the evolution in the average coating glass transition temperature was estimated by dynamic mechanical analysis, and the data was simulated using the so-called Kelley–Bueche equation. For the curing conditions investigated, the final coating hardness differed by a factor of two, with the lowest values obtained for the evaporation-suppressed conditions. Due to the isocyanate groups reaching full conversion for all four series, the reason for the lower hardness was attributed entirely to the plasticizing effect of residual solvent. Using a Kα value of 0.687 in the Kelley–Bueche equation, the coating glass transition temperature as a function of the PU volume fraction could be successfully simulated and was found to increase from about 282 K at a volume fraction of 0.79 to 319 K at one of 0.93. In addition, when the experimental temperature was lower than the coating glass transition temperature, a proportional increase in the pendulum hardness with the reciprocal loss factor was seen. The effects of catalyst concentration in the coating were also investigated, and this parameter was found to have a strong influence on both the surface conversion, the solids concentration, and the coating hardness. A too fast curing rate shortens the time to vitrification, after which the solvent evaporation rate becomes diffusion-controlled and very low, leading to higher residual solvent contents and significantly lower hardness values. The results obtained provide guidelines for how to optimize ventilation conditions during the curing of solvent-based, thermoset PU coatings. Note de contenu : - OVERVIEW OF THE MECHANISMS UNDERLYING SIMULTANEOUS SOLVENT EVAPORATION AND CHEMICAL CURING OF A THERMOSET PU COATING - EXPERIMENTAL : Sample preparation - Curing conditions - Experimental procedures - FTIR spectroscopy of the coating samples - Pendulum hardness measurements - Dynamic mechanical analysis - RESULTS AND DISCUSSION : FTIR analysis - Effect of curing conditions on hardness - Effect of residual solvent concentration on the mechanical properties - Effect of catalyst concentration on hardness of coatings - Table 1 : The four different curing conditions used in the experiments - Scheme 1 : Crosslinking reaction of an isocyanate and a polyol to form a urethane linkage. R and R' symbolize alkyl or aryl groups DOI : https://doi.org/10.1007/s11998-020-00407-3 En ligne : https://link.springer.com/content/pdf/10.1007/s11998-020-00407-3.pdf Format de la ressource électronique : Pdf Permalink : https://e-campus.itech.fr/pmb/opac_css/index.php?lvl=notice_display&id=35599 [article]

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