Preparation of highly dispersed expandable graphite/polystyrene composite foam via suspension polymerization with enhanced fire retardation

Expandable graphite (EG) is a common carbon-based fire retardant material. However, its low compatibility and tendency of agglomeration in polymeric material limit its application and potential efficiency. In this paper, polystyrene (PS) was applied as non-covalent compatiblizer for EG to disperse in styrene (St) through suspension polymerization. With appropriate pretreatments of EG and optimization of suspension polymerization conditions, EG was “pulled” and dispersed in oil phase by pre-dissolving PS itself in its monomer. Both glass transition temperature and temperature at maximum weight loss rate of the polymerized EG-PS composite increased, suggesting PS molecules were non-covalently attracted onto EG and confined. The EG-PS foam also maintained well dispersed EG particles, and have a more uniformed foam cell structure than the uncompatibled EG-PS as revealed by microscope and micro-CT. The foam reached V-0 rating in UL94 test. Limited oxidation index (LOI) of the foam increased from 18.2% to 31.3% and flame spreading speed was significantly inhibited to 25 times slower as measured in the test, in comparison to commercial Expandable Polystyrene (EPS). Effective reduction of heat release and suppression of smoke were confirmed by cone calorimeter, comprehensively showing EG as an intercalated graphite material alone could be effective retardant for styrenic foam.