Bruno Ribeiro

Evaluation of decomposition kinetics of poly (ether-ether-ketone) by thermogravimetric analysis

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.

Nonoxidative thermal degradation kinetic of polyamide 6,6 reinforced with carbon nanotubes

The thermal degradation of the polyamide 6,6 (abbreviated henceforth as PA 6,6) reinforced with different concentrations of carbon nanotubes (CNTs) was investigated by means of thermal analysis. In this study, the nanostructured composites were produced using 0.1, 0.5 and 1.0 wt% of CNT. X-ray diffraction analyses were performed in order to evaluate the crystallographic properties of nanostructured composite. The degradation kinetics of PA 6,6/CNT nanostructured composites were measured by thermogravimetric analysis at different heating rates under nitrogen flow. TGA experiments were performed to elucidate the thermal behavior and supply the data that characterize the degradation kinetic. The degradation parameter kinetics was determined using the Ozawa–Wall–Flynn (O-W-F) methods, which do not require knowledge of the reaction mechanism. In this work, the results show that the addition of CNT up to the amount of 0.5 wt% increases the thermal stability of PA 6,6.

Carbon nanotubes/polyamide 6.6 nanostructured composites crystallization kinetic study

Compared with the traditional composites, the incorporation of carbon nanotubes into polymeric matrices can generate materials with superior properties, especially thermal, electrical and tribological properties. The aim of this study was to study the polyamide 6.6/carbon nanotubes (PA 6.6/CNT) nanostructured composites crystallization kinetics. The solution mixing technique was used to obtain the nanostructured composites studied in this work. PA 6.6 films were produced with amounts of 0.1, 0.5, and 1.0 wt% (weight/weight) CNT. X-ray diffraction analyses were performed in order to determine the crystallographic properties of nanostructured composite. The nanostructured composites crystallization kinetic study was performed using the differential scanning calorimetry under isothermal and nonisothermal (dynamic) conditions. The results have shown addition of CNTs in the PA 6.6 reduces the Avrami exponent, affecting the crystallization process of the composite.

Estudo das propriedades elétricas e térmicas de compósitos nanoestruturados de poli(sulfeto de fenileno) reforçados com nanotubos de carbono

Neste trabalho o comportamento de cristalizacao e a condutividade eletrica de compositos nanoestruturados de poli(sulfeto de fenileno) reforcado com nanotubos de carbono de paredes multiplas obtidos atraves da tecnica de mistura em fusao foram estudados. A incorporacao do nanoreforco na matriz polimerica foi responsavel por um aumento da cristalinidade devido ao fenomeno de nucleacao heterogenea. A condutividade eletrica do PPS apresentou um aumento de 11 ordens de magnitude quando 2,0 m/m% de MWCNT foram adicionados a matriz polimerica. Alem disso, o limite de percolacao eletrica encontrado para este sistema foi de 1,4 m/m% de MWCNT, revelando a formacao de uma rede condutiva tridimensional no interior da matriz polimerica.

Estudo da Cinética de Decomposição de Compósitos Nanoestruturados de Poli (Sulfeto de Fenileno) Reforçados com Nanotubos de Carbono

O objetivo deste trabalho consiste na obtencao de compositos nanoestruturados de poli (sulfeto de fenileno) (PPS) reforcados com nanotubos de carbono de paredes multiplas (MWCNT) por meio da tecnica de mistura em fusao, e posterior caracterizacao de suas propriedades morfologicas e termicas. A analise por microscopia eletronica de transmissao foi utilizada com o intuito de avaliar a qualidade da dispersao dos MWCNTs na matriz polimerica. A partir das curvas de termogravimetria obtidas, foi observado um aumento na temperatura maxima de degradacao pela adicao do nanoreforco na matriz polimerica. Alem disso, o modelo matematico de Ozawa-Wall-Flynn foi utilizado com o intuito de determinar os parâmetros cineticos de degradacao. Os resultados mostraram um aumento de aproximadamente 25 oC na temperatura maxima de degradacao (Tmax) quando uma pequena quantidade de MWCNT (0,5 wt %) foi considerada. Este fato contribuiu para o aumento da estabilidade termica do PPS.

Carbon nanotube buckypaper reinforced polymer composites: a review

This review provides valuable information about the general characteristics, processing conditions and physical properties of carbon nanotube buckypaper (BP) and its polymer composites. Vacuum filtration is the most common technique used for manufacturing BP, since the carbon nanotubes are dispersed in aqueous solution with the aid of surfactant. Previous works have reported that mechanical properties of BP prepared by vacuum filtration technique are relatively weak. On the other hand, the incorporation of polymer materials in those nanostructures revealed a significant improvement in their mechanical behavior, since the impregnation between matrix and BP is optimized. Electrical conductivity of BP/polymer composites can reach values as high as 2000 S/m, which are several orders of magnitude greater than traditional CNT/polymer composites. Also, BP can improve remarkably the thermal stability of polymer matrices, opening new perspectives to use this material in fire retardant applications.

Electrical and rheological percolation behavior of multiwalled carbon nanotube-reinforced poly(phenylene sulfide) composites

Polyphenylene sulfide-based nanocomposites filled with unmodified multiwalled carbon nanotubes from 0.5 wt% to 8.0 wt% have been prepared by melt mixing technique with a single-screw extruder and hot press. Transmission electronic microscopy and scanning electron microscopy analysis were carried out in order to assess the multiwalled carbon nanotubes dispersion throughout the polyphenylene sulfide matrix. Electrical conductivity of the polymer was dramatically enhanced by about 11 decades between 2.0 wt% and 3.0 wt% of nanotubes, suggesting the formation of three-dimensional conductive network within the polymeric matrix. The storage modulus (G′) of neat polyphenylene sulfide presented an increase by two orders of magnitude when 2.0 wt% of pristine multiwalled carbon nanotubes was considered, with the formation of an interconnected nanotube structure, indicative of “pseudo-solid-like” behavior. In addition, percolation networks were formed when the loading levels achieve up to 1.5 wt% for multiwalled carbon nanotubes/polyphenylene sulfide composites.

Estudo da influência do condicionamento higrotérmico nas propriedades viscoelásticas de compósitos termoplásticos

Continued growth in the use of thermoplastic composites for structural components in the aerospace industry due, primarily, to the design flexibility, excellent mechanical properties and low density, combined with the high values of strength and stiffness and low incidence of corrosion meeting the stringent performance requirements of these structures while in service. However, components that requires structural requirements when exposed to harsh environments such as high temperature and moisture, can have their mechanical properties reduced by these environmental factors, and should be carefully evaluated before being placed in service. Although there are several studies in the literature reporting this problem for structural composites, few studies relate in a systematic way, assessing the moisture absorption with the viscoelastic behavior of PPS matrix reinforced with carbon fibers, when the composite is used in aeronautical applications. Thus, the aim of this study is to evaluate the influence of hygrothermal conditioning on the viscoelastic properties of PPS/carbon fiber composites. The results show that the laminates conditioned in a hygrothermal chamber had moisture absorption according to Fick laws, but it was not observed a significant glass transition temperature variation when compared conditioned and not conditioned specimens.