The non-isothermal thermogravimetric methods have been used extensively for the determination of kinetic parameters in polymers. The poly (ether ketones) are used as matrix in advanced high performance composites due its high thermal stability, excellent environmental performance and superior mechanical properties. In this work, the non-isothermal decomposition kinetics of the polymer poly (ether ether ketone) (PEEK) was evaluated in nitrogen and synthetic air atmospheres, using the Flynn-Wall-Ozawa and Coats Redfern models. The results showed that the necessary time for the material decomposes in 5% is approximately 216 years if it is submitted to temperatures of 350 °C in nitrogen atmosphere. On the other hand, if the material is submitted to air atmosphere, this decomposition time drops to about 1,05 years in the same temperature and for the same conversion rate. The decomposition kinetics study by Coats Redfern showed that the D3 mechanism (three-dimensional diffusion (Jander equation)) had better adjustment to the decomposition kinetics of the material in nitrogen atmosphere, while in synthetic air the R1 mechanism (phase boundary controlled reaction (one-dimensional movement)) has better adjustment to the decomposition kinetics of the material.

qualidade, reprodutibilidade e previsibilidade do comportamento sobre a vida da estrutura, têm impulsionado a produção de materiais de elevadas resistência mecânica e rigidez, baixa massa específica e custo competitivo [1] .Atualmente, alguns polímeros termoplásticos de alto desempenho, tais como: PEEK (poli (éter-éter-cetona)), PEI (poliéterimida) e PPS (poli (sulfeto de fenileno)) vêm apresentando uma grande participação no mercado aeronáutico. Embora estes polímeros apresentem excelentes proprie- IntroduçãoOs compósitos poliméricos avançados utilizados em aplicações aeronáuticas e espaciais vêm conquistando cada vez mais uma maior participação no mercado internacional. O rápido desenvolvimento na ciência e tecnologia dos materiais, a necessidade de materiais de elevado desempenho e o desenvolvimento de sofisticados métodos numéricos para análise estrutural, aliados à necessidade de garantia da Resumo: A matriz termoplástica semicristalina PEKK (poli (éter-cetona-cetona)) tem recebido nos últimos anos uma atenção crescente pelas indústrias aeronáutica e espacial, no processamento de compósitos poliméricos avançados. As características de elevados valores de temperatura de transição vítrea, de resistência mecânica e de módulo de elasticidade, baixa absorção de umidade, excelente resistência a variações de condições climáticas, combinadas a uma relativa baixa massa específica faz do PEKK uma atrativa opção para uma variedade de aplicações, principalmente na área aeronáutica. O objetivo deste trabalho é correlacionar parâmetros térmicos e reológicos do PEKK, por meio das técnicas de calorimetria explorató-ria diferencial (DSC), termogravimetria (TG) e reológica, no estabelecimento de um ciclo térmico de processamento, a ser utilizado na obtenção de laminados de PEKK com fibras de carbono, pela técnica de moldagem por compressão a quente de compósitos termoplásticos. Os resultados obtidos mostram que o PEKK apresenta um excelente balanço de propriedades, tais como elevada temperatura de transição vítrea (153-156 °C) e moderadas temperaturas de processamento, localizadas entre suas temperaturas de fusão (310-325 °C) e de degradação (352-366 °C), principalmente quando comparado com as matrizes atualmente mais utilizadas no setor aeronáutico: o PEEK (poli (éter-éter-cetona)); o PEI (poli (éter-imida)) e o PPS(poli(sulfona). A partir dos resultados térmicos e reológicos obtidos estabeleceu-se um ciclo térmico a ser utilizado no processamento de laminados PEKK/fibras de carbono pelo uso da moldagem por compressão a quente. Palavras-chave: PEKK, compósitos termoplásticos avançados, análises térmicas, análises reológicas, processamento. Thermal and Rheological Evaluation of PEKK Thermoplastic Matrix for Aeronautical ApplicationAbstract: Semi-crystalline PEKK thermoplastic matrix used in advanced polymeric composites have received a lot of interest for aerospace application in the last years. The higher glass transition temperature, high strength and stiffness, low moisture absorption, excellent environmental resistance c...

The accelerated aging effects on mechanical properties of carbon fiber-reinforced polyetherketoneketone (PEKK) thermoplastic composites are reported. Ultraviolet (UV) radiation and moisture absorption may induce property changes that weaken the polymeric matrix and/or deteriorate the matrix fiber interface by debonding or microcracking. The aim of the present work is to correlate the influence of the accelerated aging effects on compression and shear properties of carbon fiber-reinforced PEKK thermoplastic composite manufacturing by hot compression molding. The hot compression molding process was shown to be a good alternative for producing the thermoplastic composite, with an appropriate impregnation. The UV radiation/condensation conditioning effect did not show significant influence on shear strength properties. However, the most significant change was observed in the compression and shear strength after the specimens were submitted to the hygrothermal conditioning, which presented a marked increase. This behavior suggests an antiplasticization effect.

In the last years, thermoplastic composites have been introduced as structural materials for high performance aerospace applications. However, these materials can present problems when exposed to moisture, temperature, and UV radiation, and besides it may occur as the synergy among the main degradation mechanisms. Among the thermoplastic composite materials, carbon fiber reinforced poly(ether-ketone-ketone) (PEKK) laminates have shown excellent balance of properties, including high glass transition temperature, high strength, stiffness and fracture toughness values, low moisture absorption, and good environmental resistance. The aim of the present work was to evaluate the influence of the environmental effect on the viscoelastic behavior and glass transition temperature of carbon fiber reinforced PEKK thermoplastic composites. In this work, the effects of environmental degradation on the viscoelastic properties of this composite material were studied by dynamic mechanical analyses. The most significant change was observed for the UV radiation accelerated weathering conditioning effects. A decrease of the storage modulus from 40 to 10 GPa and the Tg from 147 to 105℃ is observed, which decreases consequently the composite stiffness and the service temperature after exposed environmental effects. A synergetic degradation mechanism between UV radiation accelerated weathering test and hygrothermal conditioning is clearly verified.

The poly (aryl ether ketones) are used as matrices in advanced composites with high performance due to its high thermal stability, excellent environmental performance and superior mechanical properties. Most of the physical, mechanical and thermodynamic properties of semi-crystalline polymers depend on the degree of crystallinity and morphology of the crystalline regions. Thus, a study on the crystallization process promotes a good prediction of how the manufacturing parameters affect the developed structure, and the properties of the final product. The objective of this work was to evaluate the thermoplastics polymers PEKK e PEEK by DSC, aiming to obtain the relationship between kinetics, content, nucleation and geometry of the crystalline phases, according to the parameters of the Avrami and Kissinger models. The analysis of the Avrami exponents obtained for the studied polymers indicates that both showed the formation of crystalline phases with heterogeneous nucleation and growth geometry of the type sticks or discs, depending on the cooling conditions. It was also found that the PEEK has a higher crystallinity than PEKK.