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Wisdom For Polyethylene

Bleed-out of additives

2024-09-24
Bleed-out of additives
Organic additives such as antioxidants and lubricants always have the problem of bleed-out. Inorganic additives such as anti-blocking agents have the problem of release from the film.
 
・What is bleed-out?
 
Bleed-out is the aggregation and solidification of various additives in the film volume over time, causing them to bleed onto the film surface and form a powder.
You may have seen powdery substances or white spots on the surface of bags during long-term storage.
This phenomenon is more noticeable with LLDPE, which is catalyst polymerization.
As mentioned in the previous section, LLDPE is catalytically polymerized, so stearic acid and calcium chloride are separately present in the film volume.
 
In addition, LLDPE has a smoother film surface than LDPE so the amount of added lubricants and AB agents tends to be higher than in LDPE.
Therefore, LLDPE is more often complained of due to bleed-out during long-term stocking.
 
・Problems of size and amount of bleed-out powder
 
The particle size of the powder is not constant depending on the agglomeration situation, but varies from submicron order to more than 40 μm in size.
We have measured the number of particles inside a bag, which is generally around 500 mm wide and 700 mm long, and found that LLDPE bags contain several million particles of 2 μm or larger on the entire inner surface, and LDPE bags contain several hundred thousand particles of 2 μm or larger. (However, these figures vary depending on the bag size, raw material production conditions, melt temperature, inflation air control, and raw material grade.)
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