Material Analysis
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Performance Degradation Caused by Excessively High Regrind Ratio of Polypropylene
Problem Phenomenon
The mechanical properties of the product decline, the color is yellowish, and black specks appear on the surface.
After repeated thermal processing of the regrind, molecular chains break and antioxidants are consumed, and the performance gradually decreases.
Cause Analysis
(1) Each thermal processing of the regrind causes molecular chain breakage and a decrease in molecular weight
(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 not exceed 20% (by weight)
(2) The regrind is not used 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. 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 accumulated thermal history; the regrind ratio and the number of uses need to be strictly controlled.
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