Plastic is a long chain of tiny beads.
Thousands of beads, stuck together very tightly. That is why plastic lasts so long.
Normal recycling melts it and shapes it again.
But the chain breaks a little every time. After a few rounds, the plastic is too weak to use.
Chemical recycling cooks it in a hot box with no air.
With no air, the plastic cannot burn. The heat snaps the long chain into small pieces.
The small pieces become an oil.
A plastic factory can use this oil in place of oil from the ground. It makes plastic as good as new.
It can take the messy plastic.
Normal recycling cannot use these. PVC must stay out: when it is heated, it gives off an acid gas that damages the machine.
There are three problems.
Someone must sort the trash first. The raw oil must be cleaned before a factory will take it. And it costs more than oil from the ground, so it needs buyers who will pay extra.