Effect of thermomechanical history on final properties of carbon nanotube-polymer composites

Abstract

We present here results of a Master thesis [1] carried out in the frame of EURHEO: the Erasmus Mundus Master in Engineering Rheology, which is a Master programme funded by the European Union (EACEA) and described elsewhere in these proceedings. One of the key technological issues in nanocomposites is the effective dispersion of carbon nanotubes (CNT) into the polymeric matrix. The lack of nano scale dispersion is at the origin of the observed gap between predicted enhanced physical properties and actual nanocomposites performances. Despite successful efforts in improving CNT dispersion by chemically functionalizing them or by the study of the interplay between processing conditions and final nanocomposite structure, there is a phenomenon called “re-agglomeration” responsible for dispersion recovery and destruction of the CNTs inside the matrix, which occurs during the shaping of nanocomposite batches into final products. Theory suggests that re-agglomeration process highly depends on the processing conditions and more important on the thermo-mechanical history of the material in its compounding step prior to processing. Here, efforts have been made in order to study the effect of thermo mechanical history on the nanocomposite structure and properties, thus contributing to a better understanding of the reagglomeration process [1]. In order to study the evolution of the CNT dispersion during the processing and the re-processing of the nanocomposite, a special set up has been used to obtain data in different mixing times and conditions. CNT-Polypropylene composites have been produced, and then submitted to reprocessing under controlled conditions, using a modified Capillary Rheometer. Optical microscopy, SEM and electrical conductivity tests have been performed for dispersion assessment. Results of the microscopy and electrical conductivity tests show a “percolation time” during the processing and reprocessing sections, which corresponds to an abrupt change in dispersion state as well as electrical properties. Furthermore it has been proved that applied shear rate in first processing is the main responsible parameter in re-agglomeration mechanism.