Aging in PP 1

[cholladay]

Hi,
Has anyone ever had problems with shelf-life in injection-molded PP parts? I'm looking at high flow PP, UV resistant PP, or metallocene PP and I would like a shelf-life of 2 years. Specifically interested in surface chemistry changes.
Cheers!

 

[Demon3]

PP is very sensitive to oxidation. Having said that, it is normally stabilized sufficiently to survive processing and several years in service. It is possible to make parts that survive for decades. This has been studied in detail. Very thin parts and those in contact with fluids suffer most because the antioxidant is then extracted, leaving the PP unprotected. If you are concerned, it is possible to have the PP analyzed.

If you are seeing an increase in surface energy over time, that does not mean that oxidation has taken place. Migration of additives to the surface can give the same effect. It is possible to distinguish the two.

You mention high flow PP. Sometimes PP is vis cracked to increase flow. That is done using peroxides which encourage oxidation as well as chain breakage.

We don't know enough detail to give a definitive answer but I would not expect a normal injection molded PP part to oxidize indoors at room temperature in two years.

Dr. Chris DeArmitt
President

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