Material Drying
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PP Regrind-Induced Embrittlement
Problembeschreibung
After increasing regrind ratio, part toughness drops significantly, breaking easily on drop or bending; meanwhile melt index abnormally rises and flowability improves.
Ursachenanalyse
After multiple heat processing cycles, PP molecular chains break and molecular weight drops, manifesting as increased flowability but degraded mechanical properties; pulverized material contains much fine powder with uneven plasticization, and if regrind contains moisture or impurities, performance fluctuation is further amplified.
Lösung
①Control regrind ratio within 30%—use virgin material for critical load-bearing parts as much as possible; ②sieve regrind to remove fines and mix thoroughly and uniformly with virgin material; ③re-dry regrind; ④appropriately lower melt temperature and shorten residence time to reduce secondary degradation; ⑤establish a ledger correlating regrind batches with properties (melt index/impact).
Wichtigste Erkenntnis
PP regrind requires 'control ratio, control heat history, control drying' simultaneously, monitored with melt index and impact data; better flowability does not equal better usability—it is often exactly the signal of molecular weight drop and performance degradation.
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