Material Analysis
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Performance degradation caused by excessive regrind ratio in low density polyethylene
Problem Phenomenon
Product mechanical properties decrease, color turns yellowish, and black specks appear on the surface.
After repeated thermal processing, regrind undergoes molecular chain breakage and antioxidant consumption, with gradually decreasing performance.
Cause Analysis
(1) Each thermal processing of regrind causes molecular chain breakage and molecular weight reduction
(2) Antioxidants and other additives in regrind have been partially consumed
(3) Regrind may be mixed with impurities or other materials
(4) Uneven regrind particle size, fluctuating plasticizing quality
(5) Regrind ratio too high or too many times of regrind use
Solution
(1) Control regrind ratio not exceeding 20% (by weight)
(2) Use regrind no more than 2 times; regrind used more than 2 times is downgraded
(3) Fully mix regrind and virgin material evenly before use
(4) Remove flash, impurities, etc. before crushing regrind
(5) Regularly test regrind MFR; stop using when deviation from virgin material exceeds 20%
Key Takeaway
Regrind performance degradation is the result of accumulated heat history; regrind ratio and number of uses need to be strictly controlled.
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