The present work revealed three important and novel findings regarding the effect of ferrous chloride (FeCl2) on thermal properties of polyvinyl chloride (PVC). First, the glass transition temperature of PVC upon composite with FeCl2 exhibited a noticeable increase, along with improvement of crystallization degree and modification of surface morphology. Second, a much lower degradation temperature and an almost entire degradation of PVC occurred in the presence of FeCl2 in nitrogen. Third, the thermal degradation products of the PVC in the composite were greatly changed compared to free PVC, indicating that FeCl2 could prevent the cleavage of PVC chains under mass spectrometry conditions. It is very interesting that FeCl2 plays an opposite role in modifying the thermal stability of PVC in the two experiments. We believe that this work is of general significance because our findings will be helpful for improving PVC materials. (c) 2013 Elsevier B.V. All rights reserved.