Simultaneous reactions of sulfonation and condensation for high-yield conversion of polystyrene into carbonaceous material

Abstract

Polystyrene (PS) was chemically treated with sulfuric acid to prepare stabilized precursors, which were converted into carbonaceous materials with high yield via subsequent carbonization. In addition to sulfuric acid, paraformaldehyde (PFA) was used to increase the crosslink density within the sulfonated PS chain networks by forming methylene bridges between phenyl rings via condensation. This transformed PS into a black glassy powder with increased crosslinking points. The carbon yield of the stabilized PS obtained after carbonization showed was considerably higher (45.3 wt%) than those of pristine PS (0 wt%) and sulfonated PS without PFA (22.4 wt%). This was attributed to its superior degree of crosslinks and the additional contribution of sulfur bridges to its thermal stability during carbonization. Further thermal treatment up to 2800 °C resulted in the formation of an intermediate structure between hard and soft carbons, which was directly revealed by microscopic images. These simultaneous reactions of sulfonation and condensation can be universally applied to various PS wastes, regardless of their shape and morphology. This suggests that the solid-to-solid transformation from PS to carbonaceous substances can be an effective and affordable method of upcycling general PS wastes.