[ska]

   Do they use deep learning yet?

"yet" ? Deep learning is no panacea - it's not clear why this would even be on a top 5 list of approaches to try on a putative ML part of the process. There seems to be a lot of confusion on this, generally.

Most likely they just use cheap labor for sorting

[rvense]

I'd think once you have built sensors that can digitize the whatever properties of the plastic that are relevant to sorting them, actually recognizing the different types of plastics would be rather simple.