system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why can't single-use plastics just be mixed together, melted down, and used to make any other plastic products?
gpt
Polymer Chemist here. Plastics which are single use plastics are normally commodity polymers such as Polyethylene, Polypropylene, PET, Polystyrene, PVC etc. Problem is that these different types of plastics cannot be mixed together because they tend to melt at different temperatures and also if you try to melt them together they all degrade and you are left with nothing but mess that is useless. 


Therefore, unless these plastics must be segregated based on their recycling class (the small triangle at the bottom of all recycling bottles for examples) and then melted together only with plastics which match same class you get useful recycling out of them.