Extrusion & Post
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PPA stabilizes surface quality in recycled material extrusion
Problem Phenomenon
When HDPE recycled material containing impurities is used for pipe extrusion, a large number of pits and scratches appear on the product surface, and the surface roughness Ra>2 μm makes it unable to be used in applications without appearance requirements.
Cause Analysis
Tiny impurity particles (metal chips/sand particles, etc.) mixed in the recycled material generate abnormal stress at the interface with the melt at the die exit, damaging the surface; the recycled material has a wide molecular weight distribution and contains degraded low-molecular parts, causing uneven flow; the PPA coating is worn by impurities and consumed quickly.
Solution
Increase the PPA addition to 0.06-0.08% (recycled material requires more PPA to compensate for impurity wear); install a magnetic frame and a screen of 80 mesh or above at the feed section to intercept impurities; select a PPA grade containing wear-resistant fillers to extend the die coating life; increase the PPA replenishment frequency by adding 0.02% every 4 hours to maintain coating integrity.
Key Takeaway
Recycled material extrusion causes more severe wear on PPA, and it is necessary to increase the addition amount and coating maintenance frequency to ensure surface quality.
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