On the pyrolysis characteristic parameters of four flame-retardant classes of PVC sheathless cable insulation materials

Flame retardant cables are widely used today, while the comparison of thermal degradation behavior between PVC cable insulation materials with different flame-retardant levels has not been extensively studied so far. The thermal degradation behaviors of four flame-retardant and one non-flame-retardant PVC cable insulation materials were studied using thermogravimetric (TG) analysis and a combination of TG-Fourier transform infrared analysis. Generally, TG data differ at the first peaks but are similar at the second peaks for various types of insulation materials. This is because the reaction mechanisms of the first pyrolysis stage vary with the change of flame-retardant level, while the second pyrolysis stage is similar regardless of the flame-retardant level. Besides, the flame-retardant performance level cannot solely be evaluated based on the activation energy of these insulation materials. The coupled Fourier transform infrared spectroscopy (FTIR) shows that during the pyrolysis of flame-retardant PVC insulation materials (ZA-BV, ZB-BV, ZC-BV, and ZR-BV), the amount of the seven major released components, arranged in order from most to least, is C-H bending > H2O > C-H stretching > CO2 > C-H aliphatic bending > CH2 deformation > C-Cl stretching. While for the non-flame-retardant PVC insulation material (BV), the series is CO2 > C-H bending > C-H stretching> H2O > C-H aliphatic bending > CH2 deformation > C-Cl stretching. The reported results provide a basis to evaluate the thermal degradation behavior of typical PVC cable insulation materials at present and can also provide essential data for the numerical simulation of an electrical fire.