Solvent-based methods have some unfortunate side-effects, and are difficult to scale [1]. Low and slow heat appears to work. I'm still trying to find reports of anyone who takes end user styrofoam and turns it back into desired styrofoam shapes with carbon dioxide as a foaming agent, entraining it into the closed cells. I've yet to hear of people who reduce styrofoam into polystyrene being able to turn it back into styrofoam again, but can't tell if that is an outcome of the chemistry/thermochemistry (very difficult to address), or lack of foaming equipment (addressable with enough expertise, space and capital).

Ideally, I'd like to figure out a way to take all styrofoam entering say a neighborhood as end user packing gets continuously turned into standardized insulation interlocking blocks that is continuously, incrementally installed into buildings that are pre-built with say, 2-4 meter thick wall cavities for incrementally build up the insulation over time. The styrofoam that enters our lives as packing material for a brief period and becomes unwanted detritus ends up in multi-decade and hopefully multi-century building insulation.

I want to do the same with the polyethylene used for most bags, though for those I'd want to turn them into sheets and use them for endlessly making Kaizen foam to organize, protect and store my tooling.

[1] https://davehakkens.nl/community/forums/topic/has-anyone-tri...