[Ege Artan]

Why do most plastic smell after you physically deform it? I am coming from a physics background and I thought maybe the deformation causes fibres to undergo exothermic reaction while breaking up which in turn makes it heat up, which we can observe as well. I am assuming this excess heat is allowing some activation energy for the plastic to chemically react with air which causes the smell. Is this hypothesis correct?

[Borek]

Definitely friction inside of the material produces some heat, so technically it is not impossible for some thermal decomposition, but I doubt temperatures produced are high enough for substantial effect.

But my bet is there are some small sealed pockets of unreacted monomers/solvent or whatever remains of the process, that mechanically open up when you deform the element, freeing whatever was closed. Or even you are just moving occluded molecules closer to the surface so that they can leave the solid.

[marquis]

It depends on the plastic and the additives.  In the case of PVC, one of the most notable degradation products is HCl, so there is usually a faint acid smell. But the different additives can dramatically change the odor.

[marquis]

We were mainly a medical/ pharm  company.  So many of the potential additives were not possible, for toxicological reasons.  Most of the PE and PP stuff was relatively pure, except for a few antioxs( which did sometimes give problems). Likewise with polystyrene.  The elastomer were more interesting and more smelly.  The cured were often nervous based.  You would smell that.  Also the same for latex based cures, if not worse.  Latex has to cure very quickly.  So the cures must be more active and usually smellier.  Sll,of course, while meeting USP rewuirements.  Good luck.

[marquis]

My apologies for spell checkers.  The previous post says the cures were often nervous based.  That should have been mercaptan based.  This often was used In addition to pure elemental sulfur to cure many elastomers.  The results can be smelly.