Material Analysis
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Performance decline caused by excessive regrind proportion in random copolymer polypropylene
Problem Phenomenon
Product mechanical properties decline, color turns yellowish, and black spots appear on the surface.
After repeated thermal processing, molecular chains in the regrind break and antioxidants are consumed, and performance gradually decreases.
Cause Analysis
(1) Each thermal processing of regrind causes molecular chain breakage and molecular weight reduction
(2) Antioxidants and other additives in the regrind have been partially consumed
(3) Regrind may be mixed with impurities or other materials
(4) Regrind particle size is uneven, and plasticizing quality fluctuates
(5) The regrind proportion is too high or regrind is used too many times
Solution
(1) Control the regrind proportion to no more than 20% (by weight)
(2) Use regrind no more than 2 times; regrind used more than 2 times is downgraded
(3) Fully and uniformly mix regrind with new material before use
(4) Remove flash, impurities, etc. from regrind before crushing
(5) Regularly test the MFR of regrind; stop using it when the deviation from new material exceeds 20%
Key Takeaway
Regrind performance decline is the result of thermal history accumulation; the regrind proportion and number of uses need to be strictly controlled.
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