Influence of carbon nanofiber heat treatment on thermal, mechanical, and electrical properties of structural epoxy resins

Carbon nanofibers (CNFs) were heat treated at 1100°C (CNF1100) and 2500°C (CNF2500) respectively and embedded as fillers into a mixture of epoxy precursors. The heat-treatment at a higher temperature removes defects from CNFs and determines a relevant modification in the hybridization state of the bonded carbon atoms, thus causing a strong increase in their structural perfection and thermal stability. Thermogravimetric analysis (TGA) indicates that CNFs annealed at 2500°C are more air stable than CNFs treated at 1100°C. The oxidative stability enhancement of the sample CNF2500 is about 200°C. The TGA curves in air indicate that the first oxidation stage of both nano-filled samples cured up to 200°C substantially occurs in the temperature range of 380–480°C, highlighting that the different thermal treatment of CNFs does not influence the temperature of beginning degradation. A strong influence of the different thermal treatment is instead revealed with respect to the electrical conductivity and mechanical properties.