First of all, I am in high school[to tell that I don't know much physics].

And the second thing is that, I am not sure whether this question is specifically related to physics.

What I want to achieve for now is a thing that can differentiate between poly bags[polyethylene] and other stuffs. Or a thing that could detect polyethylene.

The reason I mentioned mechanical waves or IR is lame. I have to built a robot and therefore we have only a few method accessible.

Anyway any knowledge provided by you, about this topic would be welcomed by me.

  • $\begingroup$ That sounds potentially like a difficult problem. Usually polymers like polyethylene are highly configurable beasts with lots of questions like "are neighboring strands crosslinked at all?" and "how long are the strands?" and "how does the strand length vary?" and so forth. I would not be surprised if there were ways to mimic almost every mechanical feature of polyethylene with some other polymer. If you just want to differentiate between plastic and not-plastic, then there may be some other options (e.g. check if stretching creates irreversible deformations which stiffen the substance). $\endgroup$
    – CR Drost
    Commented Apr 9, 2015 at 15:25
  • $\begingroup$ If you are just separating plastics, you can do it how they do it at recycling centers: by floating them in liquids with different densities. See siena.edu/assets/files/general/… $\endgroup$
    – pentane
    Commented Apr 9, 2015 at 19:05


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