Polyethylene terephthalat PET or PETE plastic code 1 is made from carbon, hydrogen and oxygen, just like paper.
It is claimed that, just like paper, it can be safely burnt and will only produce carbon dioxide and water leaving no toxic residue.
I came across this nuggets out there in google land and as you know panning in tham thar rivers often finds you only fools gold.
So lets see if I am richer than Midas or talking through my arsk no questions.
Google MSDS followed by the product name ie MSDS Polyethylene terephthalat
This pulls up the Material Safety Data Sheet for PET
Solid pellets with slight or no odor. Spilled pellets create slipping hazard. Can burn in a fire creating dense toxic smoke. Molten plastic can cause severe thermal burns. Fumes produced during melt processing may cause eye, skin and respiratory tract irritation.
Secondary operations, such as grinding, sanding or sawing, can produce dust which may present a respiratory hazard. Product in pellet form is unlikely to cause irritation
A useful guide for crafters on burning and melting plastic can be found here.