Estrutura e propriedades térmicas de nanocompósitos PMMA-argilas contendo ferro
Carregando...
Data
2021-10-11
Autores
Ferreira, Camila Raiane [UNESP]
Título da Revista
ISSN da Revista
Título de Volume
Editor
Universidade Estadual Paulista (Unesp)
Resumo
Os nanocompósitos polímero-argila apresentam melhores propriedades térmicas e de retardamento de chama em comparação com a matriz polimérica. A barreira física induzida pela argila e o aprisionamento de radicais livres auxiliado pela presença de átomos 3d na fase inorgânica são responsáveis por essas propriedades. Este último efeito é a base desse trabalho, que se concentra na compreensão da influência da presença do íon Fe(III), inerente à estrutura da argila, durante o processo de decomposição térmica da matéria orgânica (polímero e acoplador orgânico). A partir de monitoramento in situ buscou-se compreender o efeito do ferro na decomposição da matriz de poli(metacrilato de metila) (PMMA) e as transformações químicas ocorridas sobre a totalidade da fase inorgânica com a finalidade de elucidar como os íons ferro retardam a decomposição de polímeros. Na primeira parte do estudo, a argila Laponita (Lap, da família das esmectitas) naturalmente isenta de ferro foi submetida a uma reação de troca iônica para inserção desse íon na estrutura, nas concentrações de 4%, 9% e 14% em massa de ferro (Fe-Lap). Por essa mesma reação, a argila ripidolita (Rip, da família das cloritas), que apresenta uma quantidade mínima de ferro, foi enriquecida com este íon. Amostras de nanocompósitos a base da argila nontronita (Non, da família das esmectitas) contendo 5,6% em massa de ferro também foram sintetizados. A segunda parte do estudo consistiu em compatibilizar a fase inorgânica mediante o método grafting, através da reação de superfície dos grupos silanóis/Si-OH com o agente acoplador TMSM (trimetoxisililpropilmetacrilato). Em seguida preparou-se nanocompósitos: PMMA-Lap, PMMA-Fe-Lap, PMMA-Rip, PMMA-Fe-Rip, PMMA-Non contendo diferentes proporções de argila. Para efeito de comparação nanocompósitos PMMA-óxido de ferro (óxido: α-FeOOH e γ- Fe2O3) e PMMA-óxido-Laponita também foram sintetizados. A análise do conjunto de nanocompósitos permitiu verificar a evolução das propriedades térmicas de acordo com a carga inorgânica empregada, de forma a compreender o efeito de diferentes variáveis na estabilidade térmica do PMMA: quantidade de argila em escala nanométrica, atmosfera empregada, composição química das argilas, forma como o ferro está localizado no interior da argila e o grau de dispersão da argila na matriz polimérica. A evolução das propriedades térmicas foi analisada por termogravimetria (TG), espectroscopia de absorção de raios X (XAS) e Microcalorimetria de combustão (MCC). As argilas modificadas com ferro e os respectivos nanocompósitos foram caracterizados por DRX, FTIR, Raman, MEV/MET. Os resultados mostram que a estabilização térmica aumenta em função da quantidade de argila dispersa no polímero através do mecanismo de barreira de difusão. Os dados de caracterização mostram que a inserção de ferro e a funcionalização ocorreram de maneira eficiente. O mecanismo de estabilização por formação de uma barreira física à permeabilidade de gases é reforçado pela formação de carvão. O monitoramento do ambiente químico dos íons Fe(III), por XAS, mostrou que os estágios de decomposição dos nanocompósitos são influenciados por diferentes espécies de ferro formadas durante a reação termo-oxidativa. Quando a carga inorgânica está dispersa no PMMA os íons Fe(III) são reduzidos a Fe(II), sendo que nas amostras PMMA-Fe-Rip, PMMA-Fe-Lap e PMMA-Non houve uma maior redutibilidade chegando a ferro metálico. Os mecanismos de estabilização revelados por este estudo indicam que a argila também estabiliza o PMMA através do sequestro de radicais por parte dos íons Fe(III). Um efeito sinérgico foi encontrado pela combinação de óxido de ferro e argila laponita (PMMA-α-FeOOH-Laponita), resultando em melhores propriedades térmicas devido ao reforço do efeito de barreira. Esse trabalho fornece uma visão minuciosa do efeito do ferro inerentemente presente em argilas sobre a termo-oxidação de nanocompósitos polímero-argila. Portanto, a estabilização térmica dos polímeros combinados com argilas ferruginosas se dá através de uma combinação de mecanismos, dentre eles a barreira de difusão, formação de carvão e sequestro de radicais. De forma geral, esse estudo poderá contribuir com o desenvolvimento de retardantes de chama ecologicamente corretos com melhor desempenho, pois considerando o processo de combustão em materiais poliméricos, as argilas poderão atuar como aditivos inertes e através de ação física agir como barreira ao transporte de gases, ou/e ainda, como um aditivo reativo, que por reações químicas retardem o processo de combustão.
Polymer-clay nanocomposites have better thermal and flame retardant properties compared to polymer matrix. The physical barrier induced by clay layers and radical trapping by the presence of 3d atoms in the inorganic phase are responsible for these properties. This last effect is the basis of this work, which focuses on understanding the influence of the presence of the Fe(III) ion, inherent to the clay structure, during the thermal decomposition process of organic matter (polymer and organic coupler). From in situ monitoring, it was sought to understand the effect of iron on the decomposition of the poly(methyl methacrylate) (PMMA) matrix and the chemical transformations that occurred over the entire inorganic phase in order to elucidate how iron ions retard the decomposition of polymers. In the first part of the study, the Laponite clay (Lap, from the smectite family) naturally free of iron was subjected to an ion exchange reaction to insert this ion into the structure at concentrations 4%, 9% and 14% by mass of iron (Fe-Lap). By this same reaction, ripidolite clay (Rip, from the chlorite family), which previously had a minimal amount of iron, was enriched with this ion to amplify its concentration in the structure. Samples of nanocomposites based on nontronite clay (Non, from the smectite family) containing 5.6% by mass of iron were also synthesized. The second part of the study consisted of making the inorganic phase compatible using the grafting method, through the surface reaction of the silanols/Si-OH groups with the coupling agent TMSM (trimethoxysilylpropylmethacrylate). Then, nanocomposites were prepared: PMMA-Lap, PMMA-Fe-Lap, PMMA-Rip, PMMA-Fe-Rip, PMMA-Non containing different clay proportions. For comparison purposes, PMMA-iron oxide (oxide: α-FeOOH and γ-Fe2O3) and PMMA-oxide-Laponite nanocomposites were also synthesized. The analysis of the nanocomposites allowed us to verify the evolution of thermal properties according to the inorganic load used, in order to understand the effect of different variables on the thermal stability of PMMA: amount of clay on a nanometric scale, atmosphere used, chemical composition of the clays, how the iron is located inside the clay and the degree of dispersion of the clay in the polymer matrix. The evolution of thermal properties was analyzed by thermogravimetry (TGA), X-ray absorption spectroscopy (XAS) and combustion microcalorimetry (MCC). The iron-modified clays and their nanocomposites were characterized by XRD FTIR, Raman, SEM and TEM. The results show that thermal stabilization increases as a function of the amount of clay dispersed in the polymer through the diffusion barrier mechanism. Characterization data show that iron insertion and functionalization occurred efficiently. The stabilization mechanism by forming a physical barrier to gas permeability is reinforced by char formation. The monitoring of the chemical environment of Fe(III) ions by XAS showed that the decomposition stages of the nanocomposites are influenced by different iron species formed during the thermo-oxidative reaction. When the inorganic charge is dispersed in the PMMA, the Fe(III) ions are reduced to Fe(II), and in the PMMA-Fe-Rip, PMMA-Fe-Lap and PMMA-Non samples there was a greater reducibility reaching metallic iron. The stabilization mechanisms revealed by this study indicate that clay also stabilizes PMMA through the scavenging of radicals by Fe(III) ions. A synergistic effect was found by the combination of iron oxide and Laponite clay (PMMA-α-FeOOH-Laponite), resulting in better thermal properties due to the reinforcement of the barrier effect. This PhD work provides a detailed view of the effect of iron inherently present in clays on the thermo-oxidation of polymer-clay nanocomposites. Therefore, the thermal stabilization of polymers combined with ferruginous clays occurs through a combination of mechanisms, including the diffusion barrier, char formation and radical trapping effect. In general, this study may contribute to the development of ecologically correct flame retardants with better performance, as considering the combustion process in polymeric materials, clays may act as inert additives and through physical action act as a barrier to the transport of gases, or/and still, as a reactive additive, which by chemical reactions delay the combustion process.
Polymer-clay nanocomposites have better thermal and flame retardant properties compared to polymer matrix. The physical barrier induced by clay layers and radical trapping by the presence of 3d atoms in the inorganic phase are responsible for these properties. This last effect is the basis of this work, which focuses on understanding the influence of the presence of the Fe(III) ion, inherent to the clay structure, during the thermal decomposition process of organic matter (polymer and organic coupler). From in situ monitoring, it was sought to understand the effect of iron on the decomposition of the poly(methyl methacrylate) (PMMA) matrix and the chemical transformations that occurred over the entire inorganic phase in order to elucidate how iron ions retard the decomposition of polymers. In the first part of the study, the Laponite clay (Lap, from the smectite family) naturally free of iron was subjected to an ion exchange reaction to insert this ion into the structure at concentrations 4%, 9% and 14% by mass of iron (Fe-Lap). By this same reaction, ripidolite clay (Rip, from the chlorite family), which previously had a minimal amount of iron, was enriched with this ion to amplify its concentration in the structure. Samples of nanocomposites based on nontronite clay (Non, from the smectite family) containing 5.6% by mass of iron were also synthesized. The second part of the study consisted of making the inorganic phase compatible using the grafting method, through the surface reaction of the silanols/Si-OH groups with the coupling agent TMSM (trimethoxysilylpropylmethacrylate). Then, nanocomposites were prepared: PMMA-Lap, PMMA-Fe-Lap, PMMA-Rip, PMMA-Fe-Rip, PMMA-Non containing different clay proportions. For comparison purposes, PMMA-iron oxide (oxide: α-FeOOH and γ-Fe2O3) and PMMA-oxide-Laponite nanocomposites were also synthesized. The analysis of the nanocomposites allowed us to verify the evolution of thermal properties according to the inorganic load used, in order to understand the effect of different variables on the thermal stability of PMMA: amount of clay on a nanometric scale, atmosphere used, chemical composition of the clays, how the iron is located inside the clay and the degree of dispersion of the clay in the polymer matrix. The evolution of thermal properties was analyzed by thermogravimetry (TGA), X-ray absorption spectroscopy (XAS) and combustion microcalorimetry (MCC). The iron-modified clays and their nanocomposites were characterized by XRD FTIR, Raman, SEM and TEM. The results show that thermal stabilization increases as a function of the amount of clay dispersed in the polymer through the diffusion barrier mechanism. Characterization data show that iron insertion and functionalization occurred efficiently. The stabilization mechanism by forming a physical barrier to gas permeability is reinforced by char formation. The monitoring of the chemical environment of Fe(III) ions by XAS showed that the decomposition stages of the nanocomposites are influenced by different iron species formed during the thermo-oxidative reaction. When the inorganic charge is dispersed in the PMMA, the Fe(III) ions are reduced to Fe(II), and in the PMMA-Fe-Rip, PMMA-Fe-Lap and PMMA-Non samples there was a greater reducibility reaching metallic iron. The stabilization mechanisms revealed by this study indicate that clay also stabilizes PMMA through the scavenging of radicals by Fe(III) ions. A synergistic effect was found by the combination of iron oxide and Laponite clay (PMMA-α-FeOOH-Laponite), resulting in better thermal properties due to the reinforcement of the barrier effect. This PhD work provides a detailed view of the effect of iron inherently present in clays on the thermo-oxidation of polymer-clay nanocomposites. Therefore, the thermal stabilization of polymers combined with ferruginous clays occurs through a combination of mechanisms, including the diffusion barrier, char formation and radical trapping effect. In general, this study may contribute to the development of ecologically correct flame retardants with better performance, as considering the combustion process in polymeric materials, clays may act as inert additives and through physical action act as a barrier to the transport of gases, or/and still, as a reactive additive, which by chemical reactions delay the combustion process.
Descrição
Palavras-chave
Nanocompósitos, PMMA, XAS, TG, MCC, Polímero, Argila, Óxido de ferro