16th International Conference on Composite StructuresICCS 16

A. J. M. Ferreira (Editor) FEUP, Porto, 2011

DISPERSION EVALUATION OF CARBON NANOTUBES IN GLASSFIBER/EPOXY COMPOSITES

Carolina Fernandez, Gonzalo Pincheira, Camila Scheel, Jaime Vergara, Paulo Flores

Mechanical Engineering Department – Faculty of Engineering – Universidad de ConcepciónEdmundo Larenas s/n, Barrio Universitario, Concepción, Chilee-mail: pfloresv@udec.cl, web page: http://www.dim.udec.cl

Key words: Epoxy-matrix composites, Vacuum infusion, Carbon nanotubes, Glass fiber,dispersion.

Summary: Carbon nanotubes (CNTs) in general are considered to be highly potential fillersto improve the material properties of polymers. However, their dispersion is the limitation formanufacturing nanocomposites for industral applications. The present work is focused on theevaluation of carbon nanotubes dispersion in glass fiber/epoxy composites, fabricated byvacuum infusion technique. Thermal and electrical test were made using an infrared cameraand a Megger, wich shows satisfactory the actual distribution of CNT on the matrix. SEMimages shows the size of the CNT agglomerations and FTIR-PAS allows to identify the CNTconcentration in the sample.

1 INTRODUCTIONEpoxy-fiber composites have demonstrated high ratio strength to weight and high ratiomodulus to weight, and showed numerous applications in several areas. In the last decade theresearch of carbon nanotubes addition in this composites have been incremented due to theirexceptional mechanical properties and thermal and electrical conductivity.The limitation in nanocomposites fabrication is associated with the CNTs poor dispersion inthe polymer matrix. Several authors have proposed different dispersion techniques such ascalendaring [1] and sonication [2] obtaining satisfactory results.This work is focused to the dispersion evaluation of the CNT in the nanocomposite bydifferent macro and micrometric techniques.

2 EXPERIMENTAL

The produced nanocomposites are based on an epoxy resin matrix cured with an aminehardener. The CNTs (MWNTs, 9.5 nm inner diameter, 1.5 µm length) were produced byNanocyl – Belgium. Two types of fiber are use in this research: unidirectional andbidirectional glass fiber. The weight percentages of CNTs used were 0.1, 0.3 and 0.5%wt,they were mixed in the epoxy matrix by a mechanical stirring for 10 minutes. Subsequently,the suspension was sonicated for 1.5 hrs. at 83 kHz at controlled temperature of 40°C. Themanufacturing technique was vacuum infusion at -0.8bar, and carried out at 40°C in order to

Gonzalo Pincheira, Carolina Fernandez, Camila Scheel, Paulo Flores

2

obtain low viscosity of the resin. The developed composite is 2 mm thickness and it has anestimated fiber content of 50%vf. The thermal gradient was measure by an infrared cameraand a black body equipment (Mikron M315) at 100°C. The electrical resistance was measuredirectly by a Megger and the samples were tested with a voltage amplitude of 1000 V.Microscopic images were taken with a scanning electron microscopy (JSM-6380, JEOL) priorgold – coating of the samples and through 20 acceleration voltage. The samples were alsotestes by a Fourier transform infrared photoacoustic spectroscopy (FTIR-PAS) in awavelength range of 4000-400 cm-1.

3 RESULTSDue to their properties, the addition of carbon nanotubes to the matrix increase the thermaland electrical conductivity in the composite. The infrared camera captures the heat flowthrough the composite and shows the heat distribution (figure 1-a) as evidence of the CNTsdistribution. Also, electric resistivity was measure in different points of the sample, showing asimilar gradient, wich demostrates the lack of dispersion homogenity.On the other hand, SEM image allows to visualize the carbon nanotubes agglomerations, wichshows clearly some concentrated areas and in some cases sizes exceeding the fiber diameter(Figure 1b and 1c).The FTIR-PAS test identificate the carbon nanotube concentration through the identificationof the functional groups of the sample.

b) c)

Figure 1: (a) Heat distribution in the sample (b) SEM image containing fiber and CNTs. (c) CNT aglomeration.

4 CONCLUSIONSThe described techniques allowed to evaluate the CNTs dispersion into the fiber/epoxymatrix. SEM images allows to measure the size of the agglomerations and evidence theinefficient dispersion technique wich leads to low CNTs dispersion in the nanocompossite.

REFERENCES[1] F. H. Gojny, M. H. Wichmannm, B. Fiedler, I. A. Kinloch, W. Bauhofer, A. Windle, K.

Schulte. “Evaluation and identification of electrical and thermal conduction mechanismsin carbon nanotubes/epoxy composites”, Polymer, 47, 2036-2045 (2006).

[2] Z. Yaping, Z. Aibo, C. Qinghua. “Functionalized effect on carbon nanotube/epoxy nano-composites”, Materials Science and Engineering A 435–436, 145–149, (2006).