Preparation of Ferric Nitrate Modified Expandable Graphite and Its Flame Retardance for Polyethylene

Author(s): Shuxia Ren, Xiuyan Pang*, Weishu Chang, Ruinian Lin

A ferric nitrate modified expandable graphite (written as EGFe) was prepared through flake graphite intercalation reaction with H2SO4 as main intercalator and ferric nitrate as assistant intercalator simultaneously. The feasible mass ratio of C:KMnO4:H2SO4(98 wt.%):ferric nitrate was determined as 1.0:0.27:5.0:0.17, H2SO4 was diluted to 75 wt.% before intercalation reaction, and the reaction lasted 40 min at 40°C. Expanded volume and initial expansion temperature of the prepared EGFe reached 533 mL·g-1 (at 800ºC) and 170ºC respectively. X-ray diffraction spectroscopy testified the intercalation reaction and layer structure of EG, and Fourier transform infrared spectroscopy illuminated the intercalated functional groups. Flame retardance of the prepared EGFe and the referenced EG (with only H2SO4 as intercalator) for linear low density polyethylene (LLDPE) was also investigated. Addition of 30 wt.% the normal EG to the polymer improved the limiting oxygen index (LOI) from 17.5 to 25.5%. While, the LOI of the same amount of the prepared EGFe reached 27.5%. Furthermore, the combination of EGFe and ammonium polyphosphate (II) (APP) made the 70LLDPE/15APP/15EGFe system present a LOI of 30.5%. Assistant intercalation of ferric nitrate improved the EGFe dilatability and flame retardance.

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