Preparation of low initial expansion temperature expandable graphite and its flame retardancy for LLDPE

Abstract

To get expandable graphite (EG) flame retardant for Liner Low-Density Polyethylene (LLDPE) with low initial expansion temperature and high dilatability, the effects of various factors on dilatability were investigated including the dosages of oxidant KMnO₄, intercalating reagent H₂SO₄, assistant intercalating reagent acetic acid (HAc) and reaction temperature. Feasible conditions were obtained according to the results of L₉ (3⁴) experiments and single factor experiments. EG with an initial expansion temperature of 160°C and expansion volume of 460 mL g⁻¹ could be prepared according to the mass ratio of material graphite C: KMnO₄: 100% H₂SO₄: HAc = 1.0: 0.4: 5.0: 1.0 (H₂SO₄ should be diluted to the mass concentration of 75% before the intercalation reaction); the reaction time was 1.0 hour at 25°C. It was found that reaction temperature and H₂SO₄ dosage were the most important influence factors for dilatability. The limiting oxygen index could be improved to 28.1% by adding 30% of the prepared EG to LLDPE, and the synergistic anti-flame capability of 20% EG with 10% Ammonium polyphosphate (APP) (I) can reach to 33.9%. According to thermal gravimetric and differential thermal analysis results, 70% LLDPE /10% APP (I) /20% EG synergistic anti-flame system shows higher residual carbon and thermal stability.