Heating Elements based on PVC and Carbon Fillers

Composites based on PVC containing 8 vol % carbon black (CB), 8 vol % carbon fibers (CF), and their mixture in the ratio 4 vol %/4 vol % (CB/CF) were studied. The filler creates an ordered, segregated structure as a framework in the polymer matrix. A lattice model is proposed that describes the characteristics of the framework. Conductivity versus filler content demonstrates percolation behavior, with values of the percolation threshold of 0.02 for PVC-CB and 0.01 for PVC-CF. The pyroresistive properties of composites have been studied; the conductive filler releases Joule heat when electric voltage U is applied in the range of 9–13 V, and equilibrium temperature increases with the quadratic law Te = T0 + a·U2 and reaches 102–112 °C. A comparative calculation of the energy amount Q required to heat a composite sample and the amount of Joule heat energy A released in the sample showed that energy QCF is 15% of the released Joule heat ACF for the PVC-CF composite, which means that the main part of Joule heat is dissipated into the environment. Resistance welding using a heating element (HE) has been tested as a possible application. A welded joint was formed by overlapping two PVC parts with a HE between them; during testing, the joint showed maximal adhesive strength.