Material Drying
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PC Brittleness Caused by Hydrolytic Degradation
Fenómeno do problema
The product appearance is acceptable but the impact strength drops sharply, it breaks when bent, performance tests fail, appearance inspection is hard to find it, it is a hidden failure.
Análise das causas
Water-containing PC undergoes hydrolysis reaction at processing temperature, carbonate bonds break and molecular weight decreases irreversibly; hydrolysis has no obvious appearance characteristics, but the mechanical properties are already seriously damaged, and the products break in batches in actual use, which is far more harmful than appearance defects.
Solução
①Strictly dry to make the moisture content meet the grade requirements (generally ≤0.02%); ②Verify moisture content with the Karl Fischer method before starting the machine; ③Avoid exposing the dried material to humid environments, keep the hopper sealed and insulated; ④Material that has absorbed moisture must not be used directly at a degraded level, re-dry it fully and evaluate the molecular weight before deciding; ⑤Shorten the melt residence time in the barrel to reduce thermal cumulative degradation.
Conclusão principal
PC hydrolysis is an irreversible 'invisible killer': products with normal appearance may already be performance-scrapped; drying for PC is not a suggestion but a hard threshold, moisture content verification must be incorporated into the startup SOP, otherwise it is handing unqualified products directly to the customer.
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