Luiz Antonio Ferreira Coelho

Effect of carbon nanotubes addition on the mechanical and thermal properties of epoxy matrices

In this work, nanocomposites were prepared by adding a small amount of single walled carbon nanotubes (SWCNTs) to an epoxy resin aiming to study the resulting mechanical, viscoelastic and thermal properties of the nanocomposites. To optimize the processing of the nanocomposites and to favor a homogeneous dispersion of the SWCNTs on the matrix, acetone was used to reduce resin viscosity, increasing diffusion of the SWCNTs in the solution. The epoxy/SWCNTs/acetone systems were also sonicated in order to minimize entanglement of the SWCNTs. The systems were characterized by Fourier transform infrared spectroscopy, Raman spectroscopy, thermogravimetry, differential scanning calorimetry and dynamic mechanical analysis. The results indicated that the addition of small amounts of SWCNTs to epoxy leads to slight structural changes in the epoxy matrix which, together with the presence of SWCNTs, may reflect on its mechanical and viscoelastic properties

The Effect of Acetone Addition on the Properties of Epoxy

In this work, a varied amount of acetone was employed to dissolve an epoxy resin and then a route was followed to remove the acetone, simulating a frequently used method to disperse nanofillers in thermoset matrices. Analyses were then carried out to address the influence of residual acetone on the curing process and on the epoxy properties. The results showed a detrimental effect on the mechanical properties of the cured epoxy due to the presence of residual acetone and also a less brittle-like fracture of the specimen. Fourier transform infrared spectroscopy and thermogravimetric analyses were additionally used to characterize the cured resins and have also indicated the presence of a small amount of acetone. Nevertheless, rheological measurements indicated that 10.0 wt.% acetone addition on the resin causes a significant decrease in viscosity (around 50%) which may promote a better dispersion of nanofillers.

Mechanical and Dilatometric Properties of Carboxylated SWCNT/Epoxy Composites: Effects of the Dispersion in the Resin and in the Hardener

In this study the effects of the dispersion of carboxylated single-walled carbon nanotubes (SWCNT-c) in epoxy matrices using two different routes were investigated. In the first route, SWCNT-c were dispersed in the resin using solvent and tip sonication. In the second route, SWCNT-c were dispersed in the hardener in two different ways: with and without solvent, but both with tip sonication. For comparison purposes, neat epoxy was also prepared using the same curing conditions. The samples were characterized via mechanical and dilatometric testing, raman and FTIR analyses, SEM images, and dilatometric tests. An increase of 88% was found for Young’s modulus in the route with dispersion in the resin aided by solvent. Dispersing the SWCNT-c into the hardener showed a significant increase in some mechanical properties, indicating that this is a possible route for preparing nanocomposites. In addition it was observed that all nanocomposites presented smaller volumetric expansion than neat epoxy.

Study of epoxy/CNT nanocomposites prepared via dispersion in the hardener

In this study, carboxylated (SWCNT-c) and pristine (SWCNT) single-walled carbon nanotubes were randomly dispersed in a hardener prior to mixing it with an epoxy resin. The influence of several parameters on the dispersion process were investigated. The produced samples were characterized by infrared spectroscopy, differential scanning calorimetry, dilatometry, dynamic mechanical analysis, scanning electron microscopy and mechanical testing (tensile, flexural and microhardness). The results obtained with the nanocomposites with SWCNT-c suggested that the lowest time and amplitude of sonication improved the mechanical properties. The use of a solvent (acetone) was important to improve dispersion, ultimately increasing microhardness and Youngs Modulus up to 32%. Nanocomposites with 0.25 wt. (%) SWCNT-c presented superior mechanical properties compared to those with 0.50 wt. (%) SWCNT. Two simple mathematical models (rule of mixtures and Halpin-Tsai) were used to predict Youngs Modulus of the composites yielding results very close to the experimental ones.

Glass fiber hybrid composites molded by RTM using a dispersion of carbon nanotubes/clay in epoxy

Nanocomposites based on epoxy and a mixture of clays and multi-walled carbon nanotubes (MWCNT) were produced by casting, and also molded by RTM using glass fibers as reinforcement, yielding a hybrid multi-scale micro/nanocomposite material. Two types of montmorillonite clays were used, natural (MMT-Na) and organophilic (MMT-30B). Higher viscosity was obtained for the mixture with MMT-30B and it was observed that this clay did not perform as well as the MMT-Na in helping the dispersion of the carbon nanotubes (CNT). The glass transition temperature (T g ) of the nanocomposites increased in up to 6 °C with the addition of MWCNT and up to 10 °C with the addition of MMT-30B, differently from the MMT-Na which did not alter the T g of the material. By transmission electron microscopy, it was verified that more homogeneous dispersions and more intercalated structures were obtained with the MMT-30B than with the MMT-Na. Finally, the low clay content used and, especially, the very low MWCNT content, did not significantly alter the studied flexural properties.

Influence of intercalation methods in properties of Clay and carbon nanotube and high density polyethylene nanocomposites

In this work, nanocomposites with simultaneous dispersion of carbon nanotubes and clays in a high density polyethylene (HDPE) matrix were prepared. Two different processes of preparation were employed: solution or melt intercalation. Two different montmorillonite clays were used separately: a natural (MMT-Na) or an organoclay (MMT-30B) and it was used multiwalled carbon nanotubes (MWCNT). Thermal properties were evaluated by DSC and TGA, mechanical properties were evaluated by nanoindentetion and morphology was investigated by transmission electronic microscopy (TEM). Alterations of 20% in crystallinity were detected, increases in Young´s modulus up to 12% were observed and up to 20% of increase was observed in Oliver-Pharr hardness. It is possible to explain part of those results based on the state of dispersion observed in our TEM results.

Purification of Single-Wall carbon nanotubes by heat treatment and supercritical extraction

Arc discharge is the most practical method for the synthesis of single wall carbon nanotubes (SWCNT). However, the production of SWCNT by this technique has low selectivity and yield, requiring further purification steps. This work is a study of purification of SWCNT by heat treatment in an inert atmosphere followed by supercritical fluid extraction. The raw arc discharge material was first heat-treated at 1250 °C under argon. The nanotubes were further submitted to an extraction process using supercritical CO2 as solvent. A surfactant (tributylphosphate, TBP) and a chelating agent (hexafluoroacetylacetone, HFA) were used together to eliminate metallic impurities from the remaining arc discharge catalysts. Analysis of Inductively Coupled Plasma-Atomic Emission Spectrometry (ICP-AES) showed an efficient removal of iron and cobalt (>80%). The purified nanotubes were further analyzed by TGA and Raman spectroscopy.

Polymer Matrix Nanocomposites and Nanostructured Materials

1 Center for Technological Sciences, State University of Santa Catarina, 89223-100 Joinville, SC, Brazil 2 Department of Macromolecular Science and Engineering, Case Western Reserve University, Cleveland, OH 7202, USA 3 Institut für Kunststoffe und Verbundwerkstoffe, Technical University of Hamburg-Harburg, 21073 Hamburg, Germany 4 CINVESTAV-Querétaro (Materials Science & Technology), Libramiento Norponiente 2000, 76230 Santiago de Querétaro, QRO, Mexico

Nanoreinforcements for Nanocomposite Materials

The range of materials currently available as fillers for nanocomposites include nanoparticles, nanoplatelets, carbon nanotubes, nanofibers, and, more recently, graphenes or even a combination of these unique materials. Several companies already supply a variety of ceramic, metal and polymer nanocomposite products that reach into many industrial sectors, such as aerospace, energy and sporting goods. Polymer nanocomposites attract most of the research and development effort and, as a result, more traditional microreinforced materials are already being substituted. Indeed, the combination of nanomaterials with thermoplastic or thermoset polymers may lead to very interesting mechanical or physical properties. As shown in this chapter, these nanofillers are slowly finding their way into mainstream commercial use and their even wider application can be foreseen when difficulties regarding cost, homogeneous dispersion and poor adhesion to the host matrix are further minimized.

Hybrid Nanocomposites Based on Epoxy/silsesquioxanes Matrices Reinforced with Multi-walled Carbon Nanotubes

The aim of this work was the synthesis of hybrid organic-inorganic epoxy-copolysilsesquioxane nanocomposites reinforced with multi-walled carbon nanotubes (MWCNT). Copolysilsesquioxanes oligomers from 3-aminopropyltriethoxysilane (APTES) and phenyltriethoxysilane (PTES) precursors have been synthesized by a sol-gel process and chemically incorporated to an epoxy resin based on diglycidyl ether of bisphenol A (DGEBA). MWCNT (0.25 wt%) was added to the hybrid matrixes with different degrees of condensation. Fourier transform infrared analysis showed that a high degree of cure was achieved, suggesting that the MWCNT did not affect the curing reaction of the hybrid matrixes. Hybrid nanocomposites obtained by sonication technique presented improvement on thermal stability, exhibiting onset degradation temperatures higher than 340 °C under N2. Tensile tests presented Young’s modulus and maximum stress values up to 2.9 GPa and 47 MPa, respectively, indicating that the new hybrid epoxy/MWCNT nanocomposites show a moderate enhancement of the mechanical properties in comparison with the neat epoxy resin.