In this study, the relationship between structure and mechanical properties of aged PBT composite was investigated. Short glass fiber reinforced PBT composites were subjected to aging tests in environments typically found in hermetic compressors. Diffusion kinetics were addressed by a periodic control of samples weight, and samples aged in oil presented mass variation of 1.2-1.6%, depending on test temperature. Most diffusion curves followed Fickian behavior, and the diffusion coefficient for each condition was obtained. Aging effect was investigated by 3-point bending tests, where samples aged at 180°C presented a significant reduction in all evaluated properties. Control environment induced minor variations, supposedly related to physical aging and increase in crystallinity. Imaging analyses through scanning electronic microscopy (SEM) technique allowed observation of the predominant fracture mechanism. Aged samples presented few or no localized plastic deformation at all, which is in accordance with the lower strain observed in mechanical tests. Differential scanning calorimetry (DSC) analyses proved degree of crystallinity increase for all aged samples, depending mainly on temperature of exposure. Infrared (FTIR) analysis proved the presence of oil absorbed in PBT chemical structure, and it was proposed a method for comparing degree of crystallinity, based on the absorbance bands ratio A0(1458 cm-1)/A0(956 cm-1).
This work aims to investigate the viability of natural amorphous silicate short fibers (FNSA) as reinforcing agent of thermoplastic engineering polymers, and their possible use as an alternative to short glass fibers in industrial applications. Different surface modifications were performed in order to improve interface adhesion between the matrix and FNSA, and consequently improve mechanical properties. The surface treatments of FNSA were applied with silane coupling agents provided with different organofunctional groups. PBT was chosen as matrix due to its easy manufacturing process even after incorporation of large quantities of additives. The surface chemistry after modification was evaluated through thermogravimetric analyses coupled to a Fourier transformed infrared spectroscopy equipment. Mechanical resistance and composite fracture were investigated through tensile tests and image analyses by scanning electron microscopy. Finally, the tensile strength of modified fibers reinforced PBT was 40% higher than neat PBT.
O presente trabalho visa investigar a viabilidade de utilização de fibras naturais de sílica amorfa (FNSA) como agente de reforço em polímeros de engenharia, assim como avaliar o seu potencial como alternativa às fibras de vidro curtas em aplicações industriais. Diferentes modificações na química de superfície dessas fibras foram avaliadas buscando melhorar a adesão na interface entre fibras e matriz, e consequentemente, melhorar as propriedades mecânicas do compósito. As modificações superficiais das FNSA foram realizadas através de agentes de acoplamento do tipo silano, providos com funções orgânicas distintas. O PBT foi selecionado como matriz devido a sua conhecida facilidade de processamento, mesmo após a incorporação de grandes quantidades de aditivos. A modificação das FNSA foi avaliada a partir da análise termogravimétrica acoplada à espectroscopia no infravermelho com transformada de Fourier. A resistência mecânica e fratura dos compósitos foi investigada por ensaios de tração e microscopia eletrônica de varredura. Finalmente, obtiveram-se compósitos com fibras modificadas com resistência à tração 40% superior ao material base puro.