Revestimentos híbridos sílica-poliuretano para a proteção contra a corrosão: efeitos dos parâmetros de processamento e de composição na estrutura e propriedades
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Data
2021-10-19
Autores
Braz, Álvaro Guimarães [UNESP]
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Universidade Estadual Paulista (Unesp)
Resumo
O uso do poliuretano (PU) como base para revestimentos protetores não é novidade, ou mesmo o seu uso em aplicações diversas, porém, o que torna essa classe de polímeros interessante é a potencialidade de aprimoramento estrutural com vistas à obtenção de propriedades especificas, devido às inúmeras possibilidades de combinações de tipos e quantidades de monômeros. Nesta tese foram preparados dois tipos de híbridos orgânicos-inorgânicos, uns com PU formado com glicerol na razão NCO:OH de 1:1, chamados de SPU e outros com razão NCO:OH de 1,32:1, chamados de NF. Nos dois casos a hibridização inorgânica foi realizada por meio da funcionalização com (3-Aminopropil)trietoxisilano (APTES) combinado com Tetraortosilicato de etila (TEOS), através do uso do processo sol-gel (PSG) para produzir os revestimentos híbridos orgânicos-inorgânicos (HOI) de classe II. Na caracterização dos híbridos e seus revestimentos foram utilizadas as técnicas de espectroscopia de impedância eletroquímica (EIS), microscopia de forças atômicas (AFM), ângulo de contato, medida de espessura, espectroscopia vibracional no infravermelho por transformada de Fourier (FTIR), ressonância magnética nuclear (RMN), espalhamento de raios X a baixo ângulo (SAXS) e termogravimetria (TG). Nos híbridos SPU foram avaliados os efeitos da variação da temperatura de síntese, da temperatura de cura e da velocidade de emersão. A temperatura de cura afetou tanto a estrutura da parte orgânica, convertendo grupos uretano em amina, quanto a nanoestrutura da parte inorgânica, permitindo obter revestimentos com módulo de impedância acima de 1010 Ω.cm2, com espessuras de 1,5 µm. Com os resultados obtidos foi definido que os melhores parâmetros para a produção dos híbridos SPU são: temperatura de síntese de 55 °C, temperatura de cura de 166 °C e velocidade de emersão de 21 cm/min. O aumento da quantidade de sílica nos revestimentos SPU preparados nessas condições permitiu aprimorar a impedância e estabilidade do material, melhorou a sua estabilidade térmica e produziu um revestimento mais fino sem alterar a estrutura da parte orgânica. Essas melhorias foram associadas às alterações na quantidade dos núcleos Q3 de Si presentes no material. Os NF foram utilizados para acomodar o aumento da quantidade de Si e a incorporação do agente promotor da autocicatrização (self-healing, ASH) do sistema. Os híbridos NF apresentam interações entre as carbonilas do uretano e ureia que não estavam presentes nos espectros de FTIR para os SPU, e também as análises de SAXS mostraram que esses HOI apresentaram um crescimento hierárquico da nano estrutura. Os melhores resultados para esse grupo foram obtidos para o revestimento NF1,50, o qual apresentou valores inicias de impedância de 109 Ω.cm2, com espessura de 1,5 µm e estabilidade térmica de 270 °C. A incorporação do ASH no sistema foi alcançada com sucesso, produzindo, no entanto, revestimentos com impedância não satisfatória, com exceção para o NF1,50_10%ASH. Para algumas amostras contendo o ASH foi observada maior estabilidade da impedância ao longo do tempo, indicando o possível efeito de regeneração do híbrido. Os revestimentos SPU apresentaram excelente desempenho como barreiras protetoras contra a corrosão e os NF tiveram um bom desempenho.
The polyurethane (PU) use as a core for protective coatings is not recent, or even its use in different applications, but what makes this class of polymers interesting is the potential for structural improvement in order to obtain specific properties, due to the numerous possible combinations of monomers in types and quantities. In this thesis two types of organic-inorganic hybrids were prepared, ones with PU formed from glycerol in 1:1 NCO:OH ratio, called SPU and others with an NCO:OH ratio of 1.32:1, called NF. In both cases, the inorganic hybridization was performed by functionalization with (3-Aminopropyl)triethoxysilane (APTES) combined with Tetraethyl orthosilicate (TEOS), through sol-gel process (PSG) to produce a class II organic-inorganic hybrid (HOI) coating. In the characterization of the hybrids and their coatings, the techniques of electrochemical impedance spectroscopy (EIS), atomic force microscopy (AFM), contact angle, thickness measurement, Fourier transform infrared vibrational spectroscopy (FTIR), nuclear magnetic resonance (NMR), small angle X-ray scattering (SAXS) and thermogravimetry (TG) were used. In SPU hybrids, the effects of variation in synthesis temperature, curing temperature and withdraw rate were evaluated. The curing temperature affected both the structure of the organic part, converting urethane groups into amines, and the nanostructure of the inorganic part, allowing the production of coatings with an impedance modulus above 1010 Ω.cm2, with thicknesses of 1.5 µm. With the results, it was defined that the best parameters for production of SPU hybrids are: synthesis temperature of 55 °C, curing temperature of 166 °C and withdraw speed of 21 cm/min. The increase in the amount of silica in the SPU coating prepared under these conditions allowed to improve the material’s impedance, thermal stability, and to produce a thinner coating without changing the structure of the organic part. These improvements were associated with changes in the amount of Si Q3 nuclei present in the material. The NFs were used to accommodate the increase of Si and the incorporation of the self-healing agent (ASH) in the system. The NF hybrids show interactions between the urethane and urea carbonyls that were not present in the FRIT spectra for the SPUs, and the SAXS analysis shows that these HOIs showed a hierarchical growth of the nanostructure. The best results for this group were obtained for the NF1,50 coating, which presented initial impedance values of 109 Ω.cm2 with a thickness of 1.5 µm and thermal stability of 270 °C. The incorporation of ASH in the system was successfully achieved, producing, however, coatings with unsatisfactory impedance, with the exception of NF1,50_10%ASH. For some samples containing ASH, higher impedance stability was observed over time, indicating the possible effect of coating regeneration. SPU coatings performed with excellence as corrosion protective barriers, and the NF coatings presented a good performance.
The polyurethane (PU) use as a core for protective coatings is not recent, or even its use in different applications, but what makes this class of polymers interesting is the potential for structural improvement in order to obtain specific properties, due to the numerous possible combinations of monomers in types and quantities. In this thesis two types of organic-inorganic hybrids were prepared, ones with PU formed from glycerol in 1:1 NCO:OH ratio, called SPU and others with an NCO:OH ratio of 1.32:1, called NF. In both cases, the inorganic hybridization was performed by functionalization with (3-Aminopropyl)triethoxysilane (APTES) combined with Tetraethyl orthosilicate (TEOS), through sol-gel process (PSG) to produce a class II organic-inorganic hybrid (HOI) coating. In the characterization of the hybrids and their coatings, the techniques of electrochemical impedance spectroscopy (EIS), atomic force microscopy (AFM), contact angle, thickness measurement, Fourier transform infrared vibrational spectroscopy (FTIR), nuclear magnetic resonance (NMR), small angle X-ray scattering (SAXS) and thermogravimetry (TG) were used. In SPU hybrids, the effects of variation in synthesis temperature, curing temperature and withdraw rate were evaluated. The curing temperature affected both the structure of the organic part, converting urethane groups into amines, and the nanostructure of the inorganic part, allowing the production of coatings with an impedance modulus above 1010 Ω.cm2, with thicknesses of 1.5 µm. With the results, it was defined that the best parameters for production of SPU hybrids are: synthesis temperature of 55 °C, curing temperature of 166 °C and withdraw speed of 21 cm/min. The increase in the amount of silica in the SPU coating prepared under these conditions allowed to improve the material’s impedance, thermal stability, and to produce a thinner coating without changing the structure of the organic part. These improvements were associated with changes in the amount of Si Q3 nuclei present in the material. The NFs were used to accommodate the increase of Si and the incorporation of the self-healing agent (ASH) in the system. The NF hybrids show interactions between the urethane and urea carbonyls that were not present in the FRIT spectra for the SPUs, and the SAXS analysis shows that these HOIs showed a hierarchical growth of the nanostructure. The best results for this group were obtained for the NF1,50 coating, which presented initial impedance values of 109 Ω.cm2 with a thickness of 1.5 µm and thermal stability of 270 °C. The incorporation of ASH in the system was successfully achieved, producing, however, coatings with unsatisfactory impedance, with the exception of NF1,50_10%ASH. For some samples containing ASH, higher impedance stability was observed over time, indicating the possible effect of coating regeneration. SPU coatings performed with excellence as corrosion protective barriers, and the NF coatings presented a good performance.
Descrição
Palavras-chave
PU, Glicerol, Híbrido orgânico-inorgânico, Revestimento protetor