Molds & Tooling
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PVDF Yellowing and Thermal Degradation Discoloration
Problem Phenomenon
【Problem phenomenon】White PVDF products turn yellow after processing, yellowing of heat-shrink tubing intensifies after irradiation, and appearance and transparency are impaired
Cause Analysis
During PVDF thermal processing, the de-HF reaction generates conjugated double bond structures that cause yellowing; the higher the temperature, the longer the residence, and the greater the irradiation dose, the heavier the yellowing; yellowing-resistant patents use alkaline macromolecules and silicon-containing substances as HF scavengers to suppress this reaction
Solution
Control melt temperature and residence time to suppress de-HF; when necessary, select yellowing-resistant grades with added HF scavengers; for irradiated products, optimize electron beam energy to reduce dehalogenation; for yellowed batches, trace temperature records to locate the overtemperature section
Key Takeaway
The essence of yellowing is de-HF generating conjugated double bonds; lowering temperature, shortening time, and adding HF scavengers are applied together; After confirming effectiveness, fix the parameters and practices into the work instruction to prevent recurrence
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