Preparation of high dilatability expandable graphite and its flame retardancy for LLDPE

Abstract

To prepare expandable graphite (EG) with high anti-flame property for Linear low density polyethylene (LLDPE), dosages of oxidant KMnO4, intercalation reagent H2SO4 and ancillary intercalation reagent Na4P2O7 were optimized during oxidation intercalation reaction of natural graphite. EG with an initiation expansion temperature of 148 ± 2 °C and expansion volume of 550 mL/g can be prepared according to the mass ratio of C:KMnO4:H2SO4(98%):Na4P2O7 = 1.0:0.4:5.0:0.6 (H2SO4 should be diluted to the mass concentration of 80% before intercalation reaction), the reaction time is 40 min at constant 40 °C. Addition of 30% of the prepared EG to LLDPE can improve its limiting oxygen index LOI from 17.5% to 29.4%, and the synergistic anti-flame LOI of 20% EG with 10 polyphosphate (APP II) can reach to 31.2%. TG and DTA analysis were completed to discuss the anti-flame mechanism. 70%LLDPE/10%APP(II)/20%EG synergistic anti-flame system can cause higher residual carbon and lower material surface temperature.