Material Analysis
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Performance Degradation Caused by Excessively High Regrind Usage Ratio of High-Density Polyethylene
Problem Phenomenon
The mechanical properties of the product decline, the color turns yellowish, and black spots appear on the surface.
After multiple thermal processing cycles, the molecular chains of the regrind break, the antioxidants are 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 antioxidants 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 no more than 20% (by weight)
（2）Use the regrind no more than 2 times; regrind used more than 2 times is downgraded for use
（3）Fully and uniformly mix the regrind with the new material before use
（4）Remove flash, impurities, etc. from the regrind before crushing
（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 degradation of regrind is the result of accumulated thermal history, and the regrind ratio and the number of uses need to be strictly controlled.
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