The context of this work examines the influence of zinc sulfide (ZnS) and other inorganic substances (Sb2O3, Sb2S3, Sn, Zn ) on the cross-linking reactions of the conjugated double bond sequences, which are generated as a consequence of thermal dehydrochlorination reactions of poly(vinyl chloride) (PVC). With increasing cross-linking grade, the flammability of the corresponding PVC would be decreased due to the suppression of fragmentation reactions. In this work element balances of thermal degrading PVC samples with inorganic additives are analyzed, as well as thermogravimetric investigations are consulted. Apart from qualitative views a kinetic model of the dehydrochlorination reactions is developed using multivariate nonlinear regression analysis of thermogravimetric data. The changes in the thermally stressed polymer samples under argon and under oxygen admission are observed using different analytic techniques (visual video monitoring, infrared spectrometry, and scanning electron microscopy). It can be shown that during the thermal degradation of PVC the cross-linking reactions can be increased by several inorganic additives.