Lead based stabilizers are being used from the very beginning to stabilize rigid PVC across the world. The decomposition temperature of PVC is much lower than its processing temperature. Thus, the processing of PVC requires heat stabilizers that do not allow HCl molecules to leave the polymer chain and increases the decomposition temperature.

Lead based heat stabilizers provide excellent heat and light stability. They also provide good mechanical and electrical properties and display a very wide processing range. They are the best kind of stabilizers in terms of cost to performance ratio.

Apart from these benefits, lead based heat stabilizers have a major drawback of toxicity. A small amount of lead leaching can also cause potential health problems in a young infant. The concern of toxicity has brought an initiative to phase out lead from PVC manufacturing.

Lead stabilizers are being replaced by non-toxic calcium (Ca) and zinc (Zn) based stabilizers. The PVC market is now diverted towards heavy metal free stabilizers based on a mixture of Ca-Zn soap and other organic and inorganic compounds. Similar to lead stabilizers, these are also available in One Pack Systems in powder, flake and paste forms.

Other than being harmless, Ca-Zn stabilizers  provide good aesthetic and electrical properties. They improve color stability during the processing of PVC and provide excellent outdoor weathering performance in comparison to lead based stabilizers. A well-adjusted system of stabilizers, co-stabilizers and lubricants improves heat stability, color hold and surface gloss. They do not discolor the product after coming in contact with sulfur, whereas sulfur blackening is a very common issue in lead stabilizers. The Ca-Zn stabilizers show synergistic effects, thus an increase in calcium content may not necessarily increase heat stability. In terms of processing properties, Ca-Zn stabilizers show more or less similar performance to that of lead stabilizers. Based on the application, region and requirement we can customize the stabilizer systems to achieve specific performance.

The Ca-Zn stabilizers seem to be costlier than lead stabilizers, but they come up with a higher yield than lead stabilizers. Therefore, considering the overall cost to performance ratio Ca-Zn stabilizers are similar to Lead stabilizers.