If you believe Hank Green (
https://www.youtube.com/watch?v=325HdQe4WM4), a lot of recycled plastics aren't recycled the way I used to think they were (by shredding them, melting them down, and extruding them into new shapes). Rather, they're chemically decomposed into what's essentially raw feedstock, purified, and then re-synthesized into new polymers.
That's pretty energy intensive, to the point that it may be better to just use new feedstock (which is produced as a byproduct of oil and gas extraction). There are obviously higher-order effects to think about, but for me, plastic recycling isn't an obvious win for the environment.