A Guide to PVC Product Yellowing: Causes, Prevention, and Solutions

创建于05.29

Yellowing in PVC products is a common challenge for material engineers and manufacturers. Beyond affecting appearance, it can lead consumers to perceive products as "aged," "toxic," or low-quality, potentially causing returns and brand trust issues. While reworking yellowed products is possible, remelting increases energy use by 30%, and adding over 15% recycled material can trigger secondary yellowing.

 PVC, a chlorine-based polymer, degrades under heat, light, shear, or oxidation to release HCl, which accelerates chain breakdown and forms yellowing double bonds. This article breaks down causes and offers cost-effective, easy-to-implement solutions.

I. Main Types and Causes of Yellowing

01 Processing-Induced Yellowing

Causes: High temperatures, long processing time, excessive shear stress
Symptoms: Immediate yellowing at extrusion, starting at edges

02 Light-Induced Yellowing

Causes: UV radiation leading to structural aging
vSymptoms: Gradual surface yellowing, worse on sun-exposed areas

03 Oxidation-Induced Yellowing

Causes: Degradation from oxygen or air pollutants
Symptoms: Discoloration during storage, concentrated on edges/exposed surfaces

04 Heat Aging Yellowing

Causes: Long-term use in high-temperature environments
Symptoms: Uniform yellowing or brittleness

05 Formulation Issues

Causes: Insufficient stabilizers, incompatible additives
Symptoms: Yellowing in new products, inconsistent batches

II. Practical Strategies to Prevent Yellowing

1. Formulation Optimization – Key Defense

· Use efficient heat stabilizers (e.g., Ca-Zn, tin-based) – avoid lead salts for poor stability and environmental risks.
· Add antioxidants (e.g., BHT) and UV absorbers (e.g., UV-531, UV-327).
· Balance lubricants to prevent heat buildup and shear stress.
· Choose heat/light-resistant pigments (e.g., rutile titanium dioxide for white products).

2. Processing Control – Reduce Triggers

· Maintain optimal temperature and processing time; avoid overheating or prolonged material 滞留.
· Adjust screw speed and compression ratio to minimize shear heat.
· Clean equipment to remove carbon deposits that cause yellow spots.

3. Packaging & Storage – Block Degradation Triggers

· Seal products and store in dark, cool environments (below room temperature) to prevent UV/oxygen exposure.
· Ship promptly to avoid slow yellowing during long-term storage.

How to Identify Normal vs. Abnormal Yellowing?

· Normal: Initial discoloration that stabilizes after molding.
· Abnormal: Progressive yellowing or blackening during storage (indicates unstable ).
· Batch Variations: Investigate raw material changes, stabilizer levels, or pigment dispersion issues.

PVC yellowing is manageable. By understanding its mechanisms, optimizing formulations, and controlling processes, manufacturers can produce durable, visually stable PVC products.

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