Heat Stabilizers :

One of the most critical additives is heat stabilizers which have a key role in minimizing loss of HCl, a degradation process that starts above 70 °C.

Once dehydrochlorination begins, it is autocatalytic. Many diverse agents have been used including, traditionally, derivatives of heavy metals (lead, cadmium).

Progressively, metallic soaps (metal "salts" of fatty acids) are preferred, species such as calcium stearate.

Addition levels differ usually from 2% to 4%.
The choice of the best heat stabilizer depends on its cost effectiveness in the end use application, performance specification requirements, processing technology and regulatory endorsements