Investigação da morfologia e de propriedades mecânicas, térmicas e reológicas de nanocompósitos de Poli(tereftalato de etileno)/óxido de grafeno
Tipo
Dissertação
Data de publicação
2020-07-10
Periódico
Citações (Scopus)
Autores
Pinto , Gabriel Matheus
Orientador
Fechine, Guilhermino José Macêdo
Título da Revista
ISSN da Revista
Título de Volume
Membros da banca
Souza, Adriana Martinelli Catelli de
Ribeiro, Helio
Ribeiro, Helio
Programa
Engenharia de Materiais e Nanotecnologia
Resumo
Este trabalho está no campo do desenvolvimento de nanocompósitos poliméricos, sendo estudado o sistema entre politereftalato de etileno (PET) e óxido de grafeno (GO). O principal objetivo deste trabalho foi a obtenção e caracterização de nanocompósitos de PET/GO para o setor de embalagens. Inicialmente foi obtido o óxido de grafite (GrO) usando a metodologia de oxidação do grafite desenvolvida por Hummers, seguido de caracterização por termogravimetria analítica (TGA), difratometria de raios-X (DRX) e espectroscopia Raman, observando-se um grau moderado de oxidação, o que permitiu manter uma alta integridade de folha. Em seguida, o GrO foi esfoliado em dois meios de esfoliação (água e etanol) e notou-se por microscopia de força atômica (AFM) que a esfoliação em água permite que o GO mantenha maior tamanho lateral de folha. Foram produzidos nanocompósitos PET/GO com três teores de carga (0,05, 0,1 e 0,3% em massa), utilizando uma extrusora dupla rosca como meio de mistura. Os resultados obtidos nos ensaios mecânicos de tração indicaram que o compósito com 0,1% em massa de GO esfoliado em água apresentou aumentos expressivos tanto em resistência à tração (19%), quanto em alongamento (238%) e tenacidade (590%) quando comparado ao polímero puro. Embora técnicas de espectroscopia no infravermelho (FTIR) e Raman não tenham sido sensíveis a interações carga/polímero, foi observado por análises dinâmico-mecânicas que há uma redução de tan em função da concentração. Isto indica uma redução da mobilidade molecular das cadeias poliméricas, i.e., a presença de GO aumenta o componente elástico do material, gerando um comportamento mais pseudo-sólido. Com relação à cristalização do polímero, foi observado por DSC que o GO atua como agente nucleante e aumenta a perfeição dos cristais, uma vez que a temperatura de cristalização e fusão aumentam com a inserção de GO. Também foi observado que o GO pode aumentar a cinética de nucleação, gerando cristais mais finos, conforme observado por espalhamento de raios-x de baixo ângulo (SAXS) e DRX. Com relação à morfologia e distribuição do GO na matriz, foi observado em imagens obtidas por microscopia óptica (MO), eletrônica de varredura (MEV) e microtomografia de raios-X (XR-MT) que o compósito que apresentou as melhores propriedades mecânicas também apresentou elevado molhamento da carga pela matriz, assim como a melhor distribuição de partículas e menor tamanho de aglomerados. Por fim, o comportamento reológico dos compósitos também foi avaliado sob diferentes tensões de cisalhamento. Quando submetido a tensões elevadas, e.g., em reometria capilar, a viscosidade dos compósitos é inferior à do polímero puro, o que sugere um efeito de lubrificação por parte da carga. Isto pode ser industrialmente interessante, pois pode atuar como um “auxiliar de processamento” durante a compostagem e moldagem dos compósitos, permitindo o uso de parâmetros menos severos. Porém quando submetido a tensões mais baixas, e.g., em reometria de placas paralelas, a viscosidade dos compósitos é superior à do PET puro. Esta característica, associada ao aumento do módulo de armazenamento e menor inclinação deste em baixas frequências (), indica que o efeito de lubrificação não é alcançado, permitindo que os compósitos apresentem um comportamento mais elástico devido à menor mobilidade molecular de longo alcance. Portanto, foi produzido neste trabalho um nanocompósito de PET/GO com baixíssima concentração (0,1% em massa), sendo apresentadas melhorias não convencionais em propriedades do polímero original pela inserção de derivados de grafeno. Este resultado é ainda mais significativo ao considerar a técnica utilizada para sua produção, mistura no estado fundido, a qual apresenta maiores desafios para dispersão e distribuição do nanomaterial do que técnicas como mistura de soluções ou polimerização in-situ.
This work is in the field of the development of polymeric nanocomposites, being studied the system of polyethylene terephthalate (PET) and graphene oxide (GO). The main goal of this work was to obtain and characterize PET/GO nanocomposites for the packaging sector. Initially, graphite oxide (GrO) was obtained using the graphite oxidation methodology developed by Hummers, followed by analytical thermogravimetry (TGA), X-ray diffractometry (XRD) and Raman spectroscopy characterizations, being observed a moderate degree of oxidation, which allowed to maintain high sheet integrity. Then, the GrO was exfoliated in two exfoliation media (water and ethanol) and it was noticed by atomic force microscopy (AFM) that exfoliation in water allows the GO to maintain a larger lateral sheet size. PET/GO nanocomposites were produced with three filler contents (0.05, 0.1 and 0.3wt%), using a twin-screw extruder for melt mixing. The results obtained in the mechanical tensile tests indicated that the composite with 0.1wt% of water-exfoliated GO showed significant increases in tensile strength (19%), elongation (238%) and toughness (590%) when compared to the neat polymer. Although infrared (FTIR) and Raman spectroscopies were not sensitive to filler/polymer interactions, it was observed by dynamic-mechanical analysis that there is a reduction in tan as a function of GO content. This indicates a reduction in the polymer chains molecular mobility, i.e., the presence of GO increases the material elastic component, generating a more pseudo-solid behavior. Regarding the polymer crystallization, it was observed by DSC that GO acts as a nucleating agent and increases the crystals perfection, since the crystallization and melting temperatures increase with the GO addition. It was also observed that GO can increase the nucleation kinetics, generating thinner crystals, as observed by small angle X-ray scattering (SAXS) and XRD. Regarding the morphology and GO distribution in the matrix, it was observed in images obtained by optical microscopy (OM), scanning electron microscopy (SEM) and X-ray microtomography (XR-MT) that the composite that had the best mechanical properties also showed high filler wetting by the matrix, as well as the better particle distribution and smaller size of agglomerates. Finally, the rheological behavior of the composites was also evaluated under different shear stresses. When subjected to high stresses, e.g., in capillary rheometry, the composites' viscosity is lower than that of neat PET, which suggests a lubricating effect by the filler. This can be industrially interesting, as it can act as a “processing aid” during the composites' compounding and molding, which would enable the use of less severe parameters. However, when subjected to lower stresses, e.g., in parallel plate rheometry, the composites' viscosity is higher than that of neat PET. This, associated with the increase of storage modulus and its lower slope at low frequencies (), indicates that the lubrication effect is not achieved, allowing the composites to have a more elastic behavior due to a lower long-range molecular mobility. Therefore, a PET/GO nanocomposite with a very low content (0.1wt%) was produced in this work, having presented unconventional improvements in the properties of the pristine polymer by the addition of graphene derivatives. This result is even more significant when considering the technique used for its production, melt mixing, which presents greater challenges for the nanomaterial dispersion and distribution than techniques such as solution blending or in-situ polymerization.
This work is in the field of the development of polymeric nanocomposites, being studied the system of polyethylene terephthalate (PET) and graphene oxide (GO). The main goal of this work was to obtain and characterize PET/GO nanocomposites for the packaging sector. Initially, graphite oxide (GrO) was obtained using the graphite oxidation methodology developed by Hummers, followed by analytical thermogravimetry (TGA), X-ray diffractometry (XRD) and Raman spectroscopy characterizations, being observed a moderate degree of oxidation, which allowed to maintain high sheet integrity. Then, the GrO was exfoliated in two exfoliation media (water and ethanol) and it was noticed by atomic force microscopy (AFM) that exfoliation in water allows the GO to maintain a larger lateral sheet size. PET/GO nanocomposites were produced with three filler contents (0.05, 0.1 and 0.3wt%), using a twin-screw extruder for melt mixing. The results obtained in the mechanical tensile tests indicated that the composite with 0.1wt% of water-exfoliated GO showed significant increases in tensile strength (19%), elongation (238%) and toughness (590%) when compared to the neat polymer. Although infrared (FTIR) and Raman spectroscopies were not sensitive to filler/polymer interactions, it was observed by dynamic-mechanical analysis that there is a reduction in tan as a function of GO content. This indicates a reduction in the polymer chains molecular mobility, i.e., the presence of GO increases the material elastic component, generating a more pseudo-solid behavior. Regarding the polymer crystallization, it was observed by DSC that GO acts as a nucleating agent and increases the crystals perfection, since the crystallization and melting temperatures increase with the GO addition. It was also observed that GO can increase the nucleation kinetics, generating thinner crystals, as observed by small angle X-ray scattering (SAXS) and XRD. Regarding the morphology and GO distribution in the matrix, it was observed in images obtained by optical microscopy (OM), scanning electron microscopy (SEM) and X-ray microtomography (XR-MT) that the composite that had the best mechanical properties also showed high filler wetting by the matrix, as well as the better particle distribution and smaller size of agglomerates. Finally, the rheological behavior of the composites was also evaluated under different shear stresses. When subjected to high stresses, e.g., in capillary rheometry, the composites' viscosity is lower than that of neat PET, which suggests a lubricating effect by the filler. This can be industrially interesting, as it can act as a “processing aid” during the composites' compounding and molding, which would enable the use of less severe parameters. However, when subjected to lower stresses, e.g., in parallel plate rheometry, the composites' viscosity is higher than that of neat PET. This, associated with the increase of storage modulus and its lower slope at low frequencies (), indicates that the lubrication effect is not achieved, allowing the composites to have a more elastic behavior due to a lower long-range molecular mobility. Therefore, a PET/GO nanocomposite with a very low content (0.1wt%) was produced in this work, having presented unconventional improvements in the properties of the pristine polymer by the addition of graphene derivatives. This result is even more significant when considering the technique used for its production, melt mixing, which presents greater challenges for the nanomaterial dispersion and distribution than techniques such as solution blending or in-situ polymerization.
Descrição
Palavras-chave
poli(tereftalato de etileno). , óxido de grafeno , nanocompósitos
Assuntos Scopus
Citação
PINTO , Gabriel Matheus. Investigação da morfologia e de propriedades mecânicas, térmicas e reológicas de nanocompósitos de Poli(tereftalato de etileno)/óxido de grafeno. 2020.94 f. Dissertação( Engenharia de Materiais e Nanotecnologia) - Universidade Presbiteriana Mackenzie, São Paulo.