A novel pressure sensing material composed of poly (butylene adipate-co-terephthalate) (PBAT) and montmorillonite-polypyrrole (Mt-PPy) was prepared using melt mixing and injection molding. The structure and properties of the PBAT/Mt-PPy composites were evaluated and compared with those of the PBAT/PPy blends. The PBAT/Mt-PPy displays a very sharp insulator-conductor transition and its percolation threshold was reached at 6.5 wt% of Mt-PPy, which was lower than that for PBAT/PPy (11.0 wt% of PPy). The transmission electron microscopy analysis shows that Mt-PPy displays a high aspect ratio and was better distributed and dispersed into PBAT compared to PPy. PBAT/Mt-PPy exhibits a decrease in the electrical resistivity with an applied compressive stress due to the formation of new conducting pathways. The electromechanical response was dependent on Mt-PPy and the maximum sensitivity was observed for the composite containing 10 wt% of Mt-PPy. In this system, the electrical resistivity drops from 9 x 106 to 2 x 106 Ω cm when a compressive stress of 0.25 MPa was applied. The electrical resistivity changes with applied compressive stress, the reproducibility and the reversibility makes PBAT/Mt-PPy a suitable material for the development of pressure sensors.
In this study, composites based on polyurethane (PU) derived from castor oil and montmorillonite/polypyrrole doped with dodecylbenzenesulfonic acid (MMt-PPy.DBSA) were developed. In order to investigate the potential use of these materials for electromagnetic shielding applications, the electrical and mechanical properties of PU/MMt-PPy.DBSA composites were determined and compared with composites containing neat PPy.DBSA. The electrical conductivity of PU/MMt-PPy.DBSA composites was found to be higher than those for PU/PPy.DBSA with a similar filler content. Additionally, with a higher conductive additive content, significant increases in the tensile stress (σ) and elastic modulus (E) were observed, suggesting that MMt-PPy.DBSA acts as reinforcing agent for the PU matrix. The electromagnetic interference shielding effectiveness (EMI SE) of composites is mainly dependent on the morphology and filler content. The PU/MMt-PPy.DBSA composite containing 25 wt % of MMt-PPy.DBSA showed a maximum EMI SE of -21 dB, which is similar to the value required for commercial applications (-20 dB). The results revealed that PU/MMt-PPy.DBSA composites are promising materials for electromagnetic shielding applications.
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.
Montmorillonite/polypyrrole (MMT/PPy) nanocomposites were prepared by the in situ polymerization of pyrrole in the presence of clay, natural sodium bentonite, (MMT-Na+) in aqueous solutions with or without an anionic surfactant, sodium dodecyl sulfate (SDS), using Iron (III) chloride hexahydrate (FeCl3.6H2O) as oxidant. The structure and properties of the nanocomposites obtained by the in situ polymerization of pyrrole in the presence of SDS (MMT/PPy.SDS) and without surfactant (MMT/PPy) were compared and evaluated by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), thermogravimetric analysis and the four-point probe method. The XRD patterns of the MMT/PPy composites shows that the d001 spacing in MMT (1.42 nm) was changed to higher values, indicating the intercalation of PPy on MMT for both nanocomposites. The XRD pattern, SEM and TEM images of the MMT/PPy.SDS nanocomposites confirmed that the presence of SDS in the reaction medium promoted, beyond intercalation, the partial exfoliation of the clay. The MMT/PPy.SDS nanocomposites showed electrical conductivity (9.50 S/cm) higher than the MMT/PPy nanocomposites (4.44 S/cm). The presence of the clay significantly improved the thermal stability of PPy.
Nanocompósitos de montmorilonita/polipirrol (MMT/PPy) foram preparados a partir da polimerização in situ do pirrol na presença de argila, bentonita sódica natural, (MMT-Na+) em solução aquosa com ou sem surfactante aniônico, dodecil sulfato de sódio (SDS), utilizando-se o cloreto de ferro (III) hexahidratado (FeCl3.6H2O), como oxidante. A estrutura e propriedades dos nanocompósitos obtidos pela polimerização in situ do pirrol na presença de SDS (MMT/PPy.SDS) e sem surfactante (MMT/PPy) foram avaliadas e comparadas a partir da espectroscopia de infravermelho com transformada de Fourier (FTIR), difração de raios X (DRX), microscopia eletrônica de varredura (MEV), microscopia eletrônica de transmissão (MET), análise termogravimétrica (TG) e método padrão quatro pontas. Os difratogramas dos nanocompósitos revelaram que o espaçamento basal d001 da MMT (1,42 nm) foi alterado para valores maiores, indicando a intercalação do PPy na MMT para ambos os nanocompósitos obtidos. Os difratogramas e as imagens de MET e MEV dos nanocompósitos de MMT/PPy.SDS confirmaram que a presença do SDS na reação promoveu, além da intercalação, esfoliação parcial da argila. Os nanocompósitos MMT/PPy.SDS apresentaram condutividade elétrica (9,50 S/cm) maior do que o nanocompósito de MMT/PPy (4,44 S/cm). A presença da argila melhorou de forma significativa a estabilidade térmica do PPy.
The aim of this study was to obtain and evaluate the electrical, thermal and mechanical properties of iron oxide-filled castor oil polyurethane (PU/Fe2O3). The iron oxide used in this study was a residue derived from the steel pickling process of a Brazilian steel rolling industry. Polymeric composites with different iron oxide volume fractions (2.5, 5.0, 7.5, 10.0 and 12.5%) were prepared through the casting process followed by compression molding at room temperature. The composites were analyzed by FTIR, XRD and densities, tensile strength, Young's modulus, electrical and thermal conductivities measurements. By increasing the iron oxide content, the apparent density, tensile strength, Young's modulus and electrical conductivity values of the composites were also increased. The iron oxide additions did not change significantly the value of thermal conductivity (from 0.191 W.mK-1 for PU up to 0.340 W.mK-1 for PU enriched with 12.5% v/v of iron oxide). Thus, even at the higher iron oxide concentration, the compounds as well as the pure polyurethane can be classified as thermal insulators.