In this work, multiwalled carbon nanotubes (MWCNT) were oxidized in a mixture of sulfuric and nitric acid (3:1 v/v) using two distinct times (9 and 18 hours). The effects of different oxidation levels and concentrations of MWCNT on curing kinetics, thermal, and mechanical properties of bisphenol A diglycidyl ether nanocomposites were studied. The nanocomposites were produced using in situ polymerization technique at two different volume fractions (0.15% and 0.50% v/v) without using solvents. X-ray photoelectron spectroscopy results indicated that MWCNT were in fact oxidized and just 9 hours of acid treatment showed a greater amount of oxygen on the MWCNT surfaces. Results of differential scanning calorimetry and dynamic mechanical analysis showed small variations in the glass transition temperatures of the nanocomposites, indicating alterations in the quality of the interphase matrix/ carbon nanotubes. Concerning the thermogravimetric analysis results, the most thermally stable samples were those containing 0.15% v/v of pristine and 18 hours of oxidized MWCNT, which also had the highest stiffness of all nanocomposites. Finally, the cure kinetics of nanocomposites is fairly represented by Kamal and Sourour's semiempirical model with an autocatalytic behavior at 100 C and 120 C, but decelerated at 140 C.

Percolation threshold is an important phenomenon to be addressed when producing nanocomposites, especially because the literature suggests a depression of properties near this region. In this study, epoxy matrix nanocomposites were produced with different volume fractions of multi-walled carbon nanotubes and were characterized according to their electrical, thermal, and mechanical properties. In addition, digital image correlation (DIC) was used to measure the strain of nanocomposites and to show how it behaves in different percolation states. Electrical conductivity indicated a percolation threshold near 0.22% v/v of nanoparticles. Differential scanning calorimetry analysis showed a depression followed by an increase in glass transition temperature near the percolation threshold. Tensile strength tests presented a depression followed by an increasing near percolation threshold. DIC images showed that nanocomposites present a different behavior when near the percolation threshold, with a more distributed strain over the surface of the sample under stress and fracture toughness decreased near the percolation threshold.