Polypropylene question: "high heat tolerance"

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Discussion Overview

The discussion revolves around the heat tolerance of polypropylene (PP), particularly in relation to its melting point and suitability for various applications, including food containers and lab items. Participants explore the properties of PP as a thermoplastic and its behavior under heat, as well as concerns about chemical leaching and decomposition.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Some participants question the claim that PP has a "high heat tolerance," noting its melting point of around 100-120 degrees Celsius and its unsuitability for microwave use.
  • Others suggest that the term "high heat tolerance" may refer to the ability of thermoplastics like PP to be reheated without significant degradation, contrasting with thermoset plastics.
  • One participant raises the point that while PP softens when heated, it does not decompose, prompting further inquiry into the meaning of "decompose" in this context.
  • Concerns are expressed about the odor from new PP containers, with questions about whether it is due to PP itself or other substances from the manufacturing process.
  • Another participant notes that polypropylene is used in lab items that can withstand autoclaving at 121 °C, while polyethylene has a lower melting point and is less suitable for such applications.

Areas of Agreement / Disagreement

Participants express varying views on the definition of "high heat tolerance" and the implications of PP's thermal properties. There is no consensus on the appropriateness of PP for certain applications or the nature of its decomposition.

Contextual Notes

Some discussions involve assumptions about the definitions of terms like "decompose" and the conditions under which PP may leach chemicals. The conversation reflects a range of perspectives on the material properties of polypropylene without resolving these complexities.

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 celsius. 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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