Many pipe and profile plants are considering a move from lead stabilizers to calcium-zinc (CaZn). The reasons vary: customer demand, project specifications, export plans, or regulations for specific applications such as drinking water pipes.
What is often overlooked is that switching to CaZn is not simply swapping one material for another. They work differently, so the formulation and process settings need to change as well.
How lead stabilizers work
Lead stabilizers are known for good heat ageing and a wide processing window. They capture the HCl that PVC releases when heated, and process viscosity tends to stay stable. Their weakness is a small lubricating effect, so lead formulations usually carry a purpose-built lubricant package.
How CaZn stabilizers work
In a CaZn system the two metals have different roles. Zinc does most of the work keeping early color, while calcium captures HCl. The catch is that zinc reactions produce zinc chloride, which can trigger sudden degradation. On the shop floor this is known as zinc burning: product that looked fine suddenly turns black.
That is why modern CaZn systems almost always use co-stabilizers, such as polyols and epoxides, together with enough calcium stearate. The calcium to zinc ratio, plus the choice of co-stabilizers, decides whether stability holds through the whole process.
What else changes when you switch
- Lubricant package: internal and external lubricant needs usually differ from a lead formulation
- Fusion: fusion speed can shift, so the temperature profile may need adjusting
- Early color and long-term stability: check them with stepwise heat testing
- For cables: heat ageing and moisture sensitivity matter because they affect insulation properties
A safe transition
We recommend a stepwise transition. First, compare your current lead formulation with several CaZn candidates in the lab: fusion time on a rheometer and oven heat-stability strips. Second, take the best candidate to a trial on your production line with a clear evaluation plan agreed with QC. Third, once the trial succeeds, ramp up production gradually while monitoring color, impact and output.
For regulated applications such as drinking water pipes, always check the current requirements before choosing a stabilizer system.