Sérgio Henrique Pezzin

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 properties of polypropylene reinforced with recycled-pet fibres

Abstract We present an experimental study of the incorporation of fibres of recycled poly(ethylene terephthalate) (PET) in polypropylene (PP). Composites of PP/PET with 3, 5 and 7% of PET fibres (w/w) were prepared by monoscrew extrusion followed by injection moulding and the mechanical behaviour was estimated by the measurement of the tensile strength, the Izod impact strength and the surface hardness (Shore D). The morphology was determined by scanning electron microscopy (SEM), showing good dispersion of the fibres but no interaction between the polymer phases. It was observed that the incorporation of recycled-PET fibres (rPETFs) in PP is an efficient way to recycle PET, increasing significantly the mechanical properties of PP.

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.

Blendas biodegradáveis de poli(3-hidroxibutirato)/poli(e-caprolactona): obtenção e estudo da miscibilidade

Due to its biodegradability, poly(3-hydroxybutyrate) P(3-HB) has attracted much attention in the environmental sector. However, some characteristics of this polymer, such as high crystallinity, poor processability and high brittleness, have lead several research groups to study polymeric blends in order to modify P(3-HB) properties. Poly(e-caprolactone) (PCL) is a synthetic polyester which is completely degraded after about one year when buried in soil. In general, it acts as a polymeric plasticizer lowering the elastic modulus and enhancing the processability of the blend. Blends of two biodegradable polymers, P(3-HB) and PCL have been prepared by casting in different compositions. Miscibility, thermal behavior and morphology of these blends were studied using modulated differential scanning calorimetry (MDSC), scanning electron microscopy (SEM) and polarizing light microscopy (PLM). The two glass transition temperatures, detected by MDSC, suggest the immiscibility of the system. Phase separation was confirmed by PLM.

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.

Reduction of trace quantities of chromium(VI) by strong acids

The chemical behavior of Cr(VI) at low concentrations (10-4 to 10-7 mol L-1) in several strong acids was studied using high specific activity 51Cr(VI) as a tracer. The speciation of the products from these systems was carried out by ion exchange chromatography with stepwise elution. The results show that trace quantities of Cr(VI), monitored by means of radiochromium (51Cr), are reduced in the presence of mineral acids such as perchloric, hydrochloric, hydrofluoric, sulfuric, nitric and trifluoromethanesulfonic acids, even in the absence of conventional reducing agents, producing different measureable Cr(III) species, depending on the acid anion. Detailed studies of the reduction of low concentrations of Cr(VI) with nitric acid have shown that the relative rate of reduction increases as the concentration of the acid increases or as the concentration of the Cr(VI) decreases.

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.

Efeito da incorporação de talco nas características térmicas, mecânicas e dinâmico-mecânicas de poliuretanos termoplásticos

The aim of this work was to investigate the effect of adding talc, a nucleating agent widely used in general purpose thermoplastic formulations, on the crystallization behavior and the mechanical properties of two thermoplastic polyurethanes (TPUs) of different molecular weight. In this study, differential scanning calorimetry (DSC), thermogravimetry (TGA), dynamic-mechanical analysis (DMTA) and mechanical tests were employed. It was observed that the addition of talc increased the crystallization and the decomposition temperature of the highest average molecular weight TPU, although no change was observed at concentrations above 0.5 wt%. DMA analyses showed an increase in storage modulus only for the TPU with the highest average molecular weight. Mechanical testing did not show significant changes in the evaluated properties. The study demonstrated the importance of knowing the particular effects of adding talc as a nucleating agent in TPU compounds, aimed at improving their performance.

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