Dave Hakkens has created Precious Plastics, a system for chopping up, heating and forming post consumer plastics. Like an exceptional citizen of the world he has made the plans available on line, and has tutorials aplenty. He really wants small localized recycling to form and gain momentum. Here is his tutorial on making planks and rods:

Turns out he's the guy behind Phoneblocks too!

Thank you Jesse for the tip.