Polypropylene question: "high heat tolerance"

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Polypropylene (PP) is commonly used in yogurt containers, deli food containers, and winter clothing insulation due to its high heat tolerance. However, its melting point typically ranges from 100-120 degrees Celsius, raising questions about its suitability for microwave use and the claim of high heat tolerance. The discussion highlights that thermoplastics like PP can be reheated without significant degradation, allowing for recycling, unlike thermoset plastics which can only be heated once. Concerns are raised about the odor from new PP containers, with inquiries into whether it results from manufacturing residues or chemical leaching. It is noted that while PP does not decompose significantly, it can be autoclaved at 121 °C, making it suitable for lab items, unlike polyethylene, which has a lower melting point. The conversation also touches on the potential for mold release compounds and plasticizers to leach from the plastic over time.
kenny1999
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The following red highlight is quoted from a website

"
5. PP: polypropylene.

PP is used to make yogurt containers, deli food containers and winter clothing insulation. PP actually has a high heat tolerance and as such, does not seem to leach many of the chemicals other plastics do."

However, as far as I understand, the melting point of PP is usually only around 100-120 degree celcius. And PP made container is not suitable for microwave oven, in that case, why it is considered to be "high heat tolerance"
 
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Good point. One must wonder if that website is objective.

I do find similar mentions elsewhere, though they do not go into any explanation as to the rationale.

Here's one possible rationale:

"A major useful attribute about thermoplastics is that they can be heated to their melting point, cooled, and reheated again without significant degradation. Instead of burning, thermoplastics like polypropylene liquefy, which allows them to be easily injection molded and then subsequently recycled. By contrast, thermoset plastics can only be heated once (typically during the injection molding process)."
 
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What about: easily gets soft, but doesn't decompose.
 
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Borek said:
What about: easily gets soft, but doesn't decompose.

Does "Decompose" mean changing to some other substance of different chemical structure?
 
DaveC426913 said:
Good point. One must wonder if that website is objective.

I do find similar mentions elsewhere, though they do not go into any explanation as to the rationale.

Here's one possible rationale:

"A major useful attribute about thermoplastics is that they can be heated to their melting point, cooled, and reheated again without significant degradation. Instead of burning, thermoplastics like polypropylene liquefy, which allows them to be easily injection molded and then subsequently recycled. By contrast, thermoset plastics can only be heated once (typically during the injection molding process)."

Do you know what is the odor / smell coming from the new PP made container? Are they vapor form of PP or any other substances during manufacturing of the products?
 
kenny1999 said:
Does "Decompose" mean changing to some other substance of different chemical structure?

Yes. Not only does it not decompose, it doesn't even degrade significantly when reheated multiple times.
 
Polypropylene is used for a lot of lab items that can be autoclaved (121 °C (250 °F)).
Ployethylene on the other hand has a lower melting point and does not survive autoclaving.

If it is just a mold release compound on the surface, it should wash off.
Plastisizers and unreacted chemical components leach out slowly from the interior of the plastic parts.
 

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