Yellowing of PVC fittings after production is a common but troublesome problem, primarily affecting the product's appearance, especially when producing white or light-colored products. Yellowing not only lowers the product grade but can also lead to customer complaints.

Yellowing is not caused by a single factor but is the result of polymer degradation caused by the combined effects of multiple factors during the production process.

Excessive temperature is the most significant cause, including excessively high processing temperatures that directly lead to the thermal decomposition of PVC resin, or localized overheating causing local material temperatures to far exceed the set temperature.

An improper or ineffective stabilizer system is a key reason; insufficient stabilizer dosage will fail to fully capture the HCl released during processing. Additionally, an imbalance between lubricant and stabilizer can also lead to yellowing.

Solutions:

1. Temperature control and process optimization

2. High-performance composite calcium-zinc stabilizers must be selected.

3. A scientifically sound synergistic stabilization system must be constructed, requiring the addition of auxiliary stabilizers.

4. A balanced lubrication system.

By using a "mild processing technique" in conjunction with a "powerful stabilizer protection network," the yellowing problem of PVC pipe fittings can be effectively controlled to a minimum, producing high-quality products with a clean white appearance and long-term stability.

Email:Wong@htxchemical.com

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