Many many years ago I worked in a machine shop that specialized in making plastic parts. Of course, there was no market for the chips, except one.
That one was PTFE, better known as Teflon®. When we ran PTFE parts we would carefully clean the machine and build a box around the work area. We would then box up the chips and sell them. Even with all of that trouble, it was worth it. This stuff was much more valuable than steel or brass, and may even have been more expensive than exotics like zircon and titanium.
We did machine plastics that cost more than PTFE, but they were mostly thermosets. As such, they couldn't be melted down and recycled.