Hydrotalcite in PVC stabilizer systems
Polyvinyl chloride (PVC), is the most produced plastic polymer in the world after polyethylene and polypropylene. The polymer was discovered in 1872 by Eugen Baumann when he observed that some vinyl chloride in a flask had started to polymerize in a white solid during exposure to the sun. However, the use of PVC in commercial products became more widespread only after the B.F. Goodrich Company had developed a method to plasticze the rigid, brittle polymer by blending PVC with several additives.
PVC is a relatively low cost polymer with good chemical and biological resistance and excellent workability. However, the unmodified polymer must always be converted into a compound by blending it with additives such as heat and UV stabilizers, flame retardants, smoke surpressants, plasticizers, processing aids, impact modifiers, thermal modifiers, pigments and fillers. The choice of additives depends on the required functionality, dictated by the respective application.
When exposed to heat (> 100o C), HCl is eliminated from the polymer backbone. This HCl triggers a further autocatalytic degradation process, causing rapid discoloration and embrittlement of the PVC. Heat stabilizers can greatly increase the heat stability by various mechanisms, such as scavenging of released HCl molecules. The type of heat stabilizer that is used depends on the application and required heat stability. Lead compounds were among the first stabilizers to be adopted by the PVC industry but due to health concerns, the industry has voluntarily committed to phasing out of lead compounds (VinylPlus voluntary commitment) in the EU-27 by latest end 2015. Hydrotalcite-like materials, such as the Alcamizer products from Kisuma Chemicals, are a crucial for the heat stabilisation of non-toxic alternatives for heavy metal compounds for PVC, such as Calcium Organic Stabilizer systems. This makes Hydrotalcites especially popular in high end applications such as high temperature automotive cables.