Heat Stabilizers for PVC: Ca-Zn, OBS and Organotin Systems
Heat Stabilizers for PVC: Ca-Zn, OBS and Organotin Systems
PVC begins to degrade at 160–200°C by elimination of HCl, causing discoloration (yellowing → blackening) and embrittlement. Heat stabilizers work by replacing labile allylic chloride sites and neutralizing released HCl.
Ca-Zn Systems
Calcium-zinc (Ca-Zn) stabilizers are the dominant REACH- and RoHS-compliant choice. Zinc stearate reacts rapidly with labile chloride; calcium stearate acts as HCl scavenger and prevents "zinc burn."
Typical formulation for flexible PVC (wire & cable):
- Ca stearate: 0.5–1.0 phr
- Zn stearate: 0.2–0.5 phr
- Antioxidant (DSTDP): 0.3–0.5 phr
Total: 1–2.5 phr, giving 30–50 min stability at 200°C (Congo red test).
Organotin Systems
Organotin stabilizers offer superior thermal stability and color hold — the default choice for rigid PVC profiles, pipes, and bottles in North America. Typical loading: 0.5–2.0 phr.
Selection Guide
| Parameter | Ca-Zn | Organotin |
|---|---|---|
| Initial color | Good | Excellent |
| Long-term stability | Good (with co-stabilizers) | Excellent |
| Regulatory | EU food-contact approved | REACH registration needed |
| Cost | Low | Higher |
HMEChem offers Ca-Zn stabilizer concentrates for flexible and semi-rigid PVC applications.
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