Effect of processing on rheological properties and structure development of EPOXY/MWCNT nanocomposites

Polymer nanocomposites of epoxy resin containing multiwall carbon nanotubes (external diameter ~30 ± 10 nm, approximate length 10–20 μm) are studied using a rheological approach to determine the stage of debundling of the nanofiller in the epoxy matrix and the development of the rheological properties and structure with time. The role of processing for nanotube dispersion and structure formation is also determined by polarized microscopy and Raman spectrometry. Functionalization with amine groups is applied for part of the samples (mixing the nanotubes in amine hardener followed by mixing in appropriate amounts of epoxy resin). Further on the experimental procedure has been optimized and samples within the concentration range from 0 to 1.0 wt% have been prepared by applying high speed mechanical mixing and ultrasonic treatment with power of 250 W. The results show that chemical functionalization with amine groups contributes to significant changes in the rheological properties and hence in the structure of the composites, as proved by Raman and POM results, indicating better deaggregation of the carbon nanotubes in the amine hardener and chemical bonding of the amine groups attached to the functionalized nanotube surface with the epoxy matrix. The evolution of the dynamic viscosity in the process of polymerization reveals some interesting aspects as retarded curing in the viscometer cell, compared to the control sample under the same conditions, prolonged polymerization time owing to the applied shear rates and carbon nanotube content.