Microscopic Mechanism of Hydrogen Generation During Pyrolysis of the High-Voltage Cable PVC Outer Sheath

Polyvinyl chloride (PVC), owing to its excellent insulation and flame-retardant properties, is widely used in cable outer sheath materials. However, under thermal fault conditions such as overloading or partial discharge, PVC readily undergoes pyrolysis and releases flammable gases, including hydrogen (H₂), which serve as critical indicators of early cable failure. Although H₂ has been identified as one of the major products of PVC pyrolysis, its microscopic formation pathway remains insufficiently quantified. In this study, a syndiotactic PVC model with a degree of polymerization of 4 was constructed based on density functional theory (DFT). Through analysis of key bond dissociation energies, a two-step reaction pathway involving terminal β-position C–H bond cleavage followed by hydrogen radical recombination was identified. The results indicate that C–Cl bond scission can induce activation of β-hydrogens, subsequently triggering H₂ formation. This work proposes and quantitatively characterizes a representative bonding mechanism for H₂ formation during PVC pyrolysis, providing theoretical support for thermal fault identification in cables based on hydrogen signal monitoring.