Figure 1 shows polyethylene (PE) filled with 1.8% carbon black. The first Decomposition reactionA decomposition reaction is a thermally induced reaction of a chemical compound forming solid and/or gaseous products. decomposition step (DTG peak at 479°C) refers to the decomposition of PE. After switching from an inert gas atmosphere (nitrogen) to an oxidizing atmosphere (synthetic air), the added carbon black totally burns to carbon dioxide.
The surface of the carbon black determines the combustion behavior (in oxygen atmosphere). The larger the surface area, the smaller the particle size, the lower the combustion temperature or the faster the combustion takes place at a defined temperature (see figure 2).
Due to this combustion behavior, it is in many cases possible to distinguish between added carbon black and pyrolytic carbon. Therefore, the TGA can be used to determine the carbon black content – even in polymers which form pyrolytic soot.