Polymer degradation of polystyrene through chain scission, if I recall correctly. Phosphoric acid results in a whole bunch of H+ ions floating around in the cok

Polymer degradation of polystyrene through chain scission, if I recall correctly. Phosphoric acid results in a whole bunch of H+ ions floating around in the coke. Those can attach to the C of both ends of each piece of a broken polymer chain or to the aromatic rings on the chain. So the styrofoam breaks into shorter and shorter chains until they are simply floating in solution invisible to the naked eye.