Multifuncionalidade em compósitos poliméricos de nanotubos de carbono de paredes múltiplas em matriz epóxi

Abstract

A strategy to obtain multifunctional materials of high performance is the use of carbon nanotubes (CNT) as a filler in polymeric composites , to improve thermal and mechanical properties of these materials. Several parameters influence these properties, but it is the effective interaction between filler and matrix, as well as a uniform dispersion, which define the final properties of a polymeri c composite. A common practice employed in the search for an appropriate interaction and dispersion is the chemical modification of these nanomaterials. However, the direct characterization of these interfacial interactions has not yet been explored, and no consensus has been reached on what would be the chemical nature of the interactions between the polymeric chains and the functional groups attached on the surface of carbon nanomaterials. In order to evaluate how this interaction between filler and matrix occurs, Differential Scanning Calorimetry (DSC) measurements were performed by on a mixture containing only epoxy resin (DGEBA) and 10% w/w of CNT prepared rapidly, functionalized or not, without the addition of curing agent. Well-defined exothermic peaks were observed in the DSC curves only for samples containing modified CNT. This is a strong indication that the functional groups , added to the surface of the CNT, interact with the epoxy rings with the formation of covalent bonds. Thermogravimetric analysis, X-ray photoelectron spectroscopy and transmission electron microscopy were performed, to support this interpretation. Different polymeric composites involving DGEBA/oxidized or amino- functionalized CNT were prepared, with concentrations of 0.1; 0.25 a nd 0.5% w/w of CNT, and characterized as to their thermal and mechanical behavior. Increases in properties such as elastic modulus and impact, tensile and flexural strength, indicating that a good dispersion as well as good filler-matrix interaction were achieved in some cases . For instance, the sample containing 0.25% w/w of oxidized NTCs, and whose hardener was based on triethylenetetramine, showed increases of 56% in impact strength, 27% in elastic modulus, and 5% in flexural strength, when compared to pure epoxy.