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A calcium–zinc stabilizer is a “composite additive system.” It does not have a single CAS number, molecular formula, or molecular weight. It is typically formulated by blending calcium salts, zinc salts, lubricants, antioxidants, and other components.
- Appearance and physical properties:
Powder form: white powder, with no obvious mechanical impurities.
Granular form: white, cylindrical or irregularly shaped particles.
Liquid form: pale yellow or clear oily liquid.
Odor: Typically odorless or with a slight oily smell, with no pungent odor.
-Physical parameters
Due to the different formulations, the parameter ranges are relatively broad:
Density:
Powder: approximately 1.0–1.1 g/cm³
Liquid: approximately 0.9–1.0 g/cm³
Melting point / Softening point:
Powders: typically between 100°C and 140°C (depending on the stearate content).
Solubility: Insoluble in water; partially soluble in hot organic solvents (such as mineral oil and plasticizers).
- Chemical properties
The mechanism of action of calcium–zinc stabilizers is rather complex and is primarily based on the following chemical reactions:
Capture of HCl: During the thermal decomposition of PVC, hydrogen chloride (HCl) is released. The metal soaps (calcium soap and zinc soap) in calcium–zinc stabilizers react with HCl to form metal chlorides, thereby terminating the autocatalytic degradation of PVC.
Replacement of unstable chlorine atoms: Zinc soaps can replace the unstable chlorine atoms on the PVC polymer chain, thereby inhibiting the dehydrochlorination reaction.
Synergy:
Calcium soap: exhibits excellent long-term thermal stability, but has significant initial coloration (prone to yellowing).
Zinc soap: exhibits very little initial coloration (remaining transparent), but has poor long-term stability and is prone to “zinc burning,” which causes the finished product to turn black.
After compounding: When used in combination, calcium soap inhibits the “zinc burn” phenomenon associated with zinc soap, while zinc soap enhances the initial color tone, resulting in excellent initial whiteness and superior long-term stability.
Antioxidation: The formulation typically includes antioxidants that decompose hydroperoxides, thereby preventing PVC oxidation.
Uses
Calcium-zinc stabilizers are primarily used in the polyvinyl chloride (PVC) processing industry, particularly in applications with stringent environmental requirements:
1. Food packaging materials:
Used in the production of PVC cling film, disposable infusion sets, food-grade flexible tubing, and other applications (must comply with FDA or GB 9685 standards).
2. Children’s toys:
A lead-salt-free stabilizer for the production of non-toxic children’s toys and stationery.
3. Wires and Cables:
Insulating and sheathing materials for the production of low-smoke, halogen-free, or environmentally friendly wires and cables.
4. Pipes and Profiles:
Used in construction materials such as PVC water supply pipes, drainage pipes, and custom-shaped profiles for doors and windows.
5. Transparent products:
Liquid calcium–zinc stabilizers are commonly used in the production of highly transparent PVC sheets and bottle-grade resins.