The use of calcium/zinc stabiliser systems has been common in PVC applications for over 25 years.
These materials are generally based on metal carboxylates and will sometimes incorporate other elements to boost performance such as aluminium or magnesium.
Because the heat stability in some applications may require some enhancement when using calcium/zinc, organic co-stabilisers will also often be added to this type of formulation.
These materials include polyols, epoxydised soya bean oil, antioxidants and organic phosphites.
Properties and Applications
Because of the characteristics of calcium/zinc stabilised materials they are widely used in many flexible and rigid PVC applications. This type of stabilising system can give products which have a high degree of clarity, good mechanical and electrical properties, excellent organoleptic properties and good outdoor weatherability.
The performance of more recent developments in calcium/zinc stabilisers also makes them potential technical alternatives to most other stabilising systems, including lead and barium/zinc. As a result of pressures on the continuing use of heat stabilisers based on lead compounds, considerable development work has been carried out on new, improved systems for applications including cable covering, pipe and window profile and many of these are have been in commercial use for several years.
These newer forms of calcium/zinc stabiliser are in general more complex and expensive than the traditional soaps mainly because of the specialised co-stabilisers required to meet the specific requirements of these applications. The rate of introduction of such stabilising systems is slowed down by the extensive evaluation work required and the need for acceptance by the specifier.
So far, the penetration of calcium/zinc stabilisers in these three sectors is almost complete in drinking water pipes, well advanced in cables but still limited in other pipes and profiles.
Further growth is expected as a result of the progressive phasing out of lead-based systems. In the sector of flexible foils where the main stabiliser used is a barium/zinc soap, substitution by calcium/zinc materials is also taking place although, again, there are technical issues which need to be overcome.
