Preparation and Antiflame Performance of Expandable Graphite Modified with Sodium Hexametaphosphate

Abstract

A kind of polyphosphate modified expandable graphite (EG p ) was prepared in graphite oxidation and intercalation reaction with KMnO 4 as oxidant, H 2 SO 4 as intercalator, and sodium hexametaphosphate (SHMP) as assistant intercalator. The feasible mass ratio of C : KMnO 4 : H 2 SO 4 (98%) : SHMP was determined as 1.0 : 0.3 : 4.5 : 0.6, H 2 SO 4 was diluted to 77 wt% before intercalation reaction, and the reaction lasted for 40 min at 40°C. Expanded volume and initial expansion temperature of the prepared EG p reached 600 mL/g (at 800°C) and 151°C, respectively. X-ray diffraction spectroscopy testified the intercalation and layer structure of EG p , and Fourier transform infrared spectroscopy illuminated the intercalated functional groups. Flame retardance of the prepared EG p and the referenced EG (with only H 2 SO 4 as intercalator) for linear low density polyethylene (LLDPE) was also investigated. Addition of 30 wt% EG p to the polymer improved the limiting oxygen index (LOI) from 17.5 to 27.3%. On the other hand, the LOI of the same amount of the referenced EG was only 24.6%. Assistant intercalation of SHMP improved the dilatability and flame retardancy.