Material Analysis
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Excessive regrind ratio of general-purpose polyethylene causing performance decline
Problem Phenomenon
The mechanical properties of the product decrease, the color is yellowish, and black spots appear on the surface.
After multiple thermal processing, the molecular chains of the regrind break and the antioxidant is consumed, and the performance gradually decreases.
Cause Analysis
（1）Each thermal processing of the regrind causes molecular chain breakage and molecular weight reduction
（2）The antioxidant and other additives in the regrind have been partially consumed
（3）The regrind may be mixed with impurities or other materials
（4）The regrind particle size is uneven, and the plasticization quality fluctuates
（5）The regrind ratio is too high or the regrind is used too many times
Solution
（1）Control the regrind ratio to not exceed 20% (by weight)
（2）The regrind should not be used more than 2 times, and regrind used more than 2 times should be downgraded
（3）Fully mix the regrind with the new material before use
（4）Remove flash, impurities, etc. before crushing the regrind
（5）Regularly test the MFR of the regrind, and stop using it when the deviation from the new material exceeds 20%
Key Takeaway
The performance decline of regrind is the result of heat history accumulation, and the regrind ratio and number of uses need to be strictly controlled.
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