Thermal, mechanical and electrical performance of structural epoxy resins filled with carbon nanofibers

Abstract

Carbon nanofibers (CNFs) were heat-treated at 1100 °C (CNF1100) and 2500 °C (CNF2500), respectively, and embedded as fillers at different mass percentages into an epoxy mixture. The paper aims at evaluating, through a comparison between the two different types of resulting nanocomposites, the influence of the CNF heat treatment on the thermal, mechanical, and electrical performance of the formulated samples. Thermogravimetric analysis (TGA) showed oxidative stability in the air of CNF2500 approximately 200 °C higher than the CNF1100 ones. The first oxidation stage of the resins embedding the two typologies of CNFs falls between 380 and 480 °C. This means that the temperature of the heat treatment of the nanofiller does not influence the temperature at which the thermodegradation of the nanocomposites starts. Differential Scanning Calorimetry (DSC) data show that the highest degree of cure (DC) was recorded for the epoxy samples filled with CNF2500. CNF thermal treatment increases the direct current (dc) conductivity of the nanocomposite by 3 orders of magnitude around the electrical percolation threshold (EPT) and increases the storage modulus of the CNF2500-based resins up to 60 °C compared with the unfilled resin. The peculiar wall structure of CNF1100 determines a further slight enhancement. Tunneling Atomic Force Microscopy (TUNA) reveals that the CNFs are evenly distributed on the nanodomains showing higher electric current values for samples loaded with CNF2500.