The molecular structure of PVC is made of continuous carbon- carbon single bonds in the main chain.
As this main chain is highly flexible, PVC products have the disadvantage of having a low heat distortion temperature (softening temperature) compared with other plastics of the similar molecular structure.
These Charts show the thermal deformation temperature and the softening temperature (called the “Vicat softening temperature”) of major plastics.
The heat distortion temperature is the temperature when the test piece placed in the heat medium with bending load applied reaches a specified deflection as temperature rises. The Vicat softening temperature is defined as the temperature where the needle shaped penetrator sinks into the test piece to a specified depth as temperature of the heating medium rises and specified vertical load is applied to the test piece.