Are there sensor of PET plastic to arduino ?
No.
Answer remains the same without the "for Arduino" part.
Recognizing plastic types is notoriously difficult.
To determine the kind of plastic you need a destructive method typically, chemical analysis of the
thermal breakdown products, for instance (humans are good at this, using their noses, when plastics
burn).
Most types of plastic come in multiple formulations varying in density, mechanical properties, optical
properties. Co-polymers are essentially mixes of differ plastics so the properties can be continuously
varied.
I suspect if you have identically sized samples you could get some reasonably useful information from
the elastic behaviour and tensile strength, but again some plastic samples may already have aligned
molecules, others random... PET as used in pop bottles is very strong and usually has the molecules aligned
sheet-style (which gives the strength for containing the pressure).
Perhaps the best sensor is a camera using computer vision to detect recycling labels!
MarkT:
Perhaps the best sensor is a camera using computer vision to detect recycling labels!
The most reliable way to sort plastics (mixed post consumer, that is), is by people sorting it by product type (bottles, butter cups, CD casings, carrier bags, etc). Many plastics don't have recycling labels, or they're obscured, or dirty, and there are only six types of plastic recognised with everything else being type 7 ("other").
To make matters worse, lots of food wrappers are multi-layer film. So a fictional PET plastic sensor may go off on a cookie wrapper because it contains PET, but it may contain several more layers. PET is nice and strong, a layer of PE makes it sealable, and other layers for food contact, oxygen barrier, etc.