Functional Analysis and Synergistic Application of CPVC Category VI Auxiliary Stabilizers

Chlorinated polyvinyl chloride (CPVC) is prone to thermal degradation during high-temperature processing, releasing HCl gas that further catalyzes material decomposition, resulting in discoloration, performance deterioration, and processing failure. To enhance the thermal stability and long-term service life of CPVC, auxiliary stabilizers have become key components in formulation design. This paper systematically analyzes six main types of auxiliary stabilizers—hydrotalcite, zeolite, epoxy compounds, polyols, β-diketones, and uracil—covering their synergistic enhancement mechanisms, key performance advantages, and applicable limitations, providing a technical basis for optimizing the thermal stability, processing performance, and environmental friendliness of CPVC products.

1. Hydrotalcite group 

- Mechanism: 

Surface hydroxyl groups absorb HCl, inhibiting its catalytic effect on the degradation of CPVC.

Interlayer CO₃²⁻ undergoes ion exchange with HCl, neutralizing acidic gases.

- Advantages:

- High transparency, excellent insulation, strong weather resistance, non-toxic, and synergistic effect with zinc stearate/organotin.

- Restrictions:

CPVC degradation produces a large amount of gas, so it is necessary to use it in combination with gas-absorbing stabilizers.

2. Zeolites

- FunctionNeutralize HCl with weak alkalinity to enhance long-term thermal stability and anti-yellowing capability.

- Key Parameters (Typical Zeolite Powder):

- Note:

The finer the particle size, the better the effect, but it will reduce the impact resistance of the product.

Lubricity may weaken the plasticizing performance of the system, so the formulation balance needs to be optimized.

3. Epoxy compound 

-Common typesEpoxidized soybean oil, epoxidized stearic acid ester, alicyclic epoxy resin, etc.

- Mechanism:

- Reacts with HCl to form chlorohydrin, where the unstable chlorine atom is substituted under the catalysis of metal soap.

- Inhibits CPVC yellowing, and shows a significant synergistic effect when compounded with phosphite esters.

- Disadvantages:The amount used in rigid CPVC needs to be controlled as it is prone to exudation.

4. Polyols

- Common types:

- Function: 

Chelate metal ions to prevent catalytic degradation; replace allyl chloride.

The hydroxyl group forms a colorless complex with metal ions, inhibiting "zinc burning."

- Note:

Some varieties are prone to dehydration, discoloration, or sublimation; modified products can improve these deficiencies.

When the amount of pentaerythritol exceeds 0.5 parts, precipitation is likely to occur.

5. β-Diketones

- Core varieties:

- Advantages:

- Significantly improves initial coloration, inhibits "zinc burning," and exhibits strong synergy with Ca/Zn systems.

- Mechanism: 

The active methylene group undergoes alkylation with allyl chloride, blocking the extension of the conjugated chain.

6. Uracil

Application:

- Compound zinc salts, lubricants, and antioxidants to produce a composite stabilizer specifically for CPVC pipes.

- Advantages:

- Improve thermal stability and processing fluidity, extend product lifespan.

- Free of heavy metals, simple process, and environmentally friendly.

Adaptation SystemCalcium-zinc stabilized system (not suitable for organotin).

Key Summary