Modified expandable graphite as an effective flame retardant for LLDPE/EVA composites filled with Mg(OH)2/Al(OH)3

Abstract

The flammability, thermal properties, and synergistic effects of modified expandable graphite (MEG) with magnesium hydroxide (MH) and aluminum hydroxide (ATH) on the linear low-density polyethylene/ethylene vinyl acetate (LLDPE/EVA) blends are investigated by Underwriters Laboratories-94 (UL-94) vertical combustion test, limiting oxygen index (LOI), thermogravimetric analysis (TGA), cone calorimeter test (CCT), and scanning electron microscopy (SEM). The results show that the MEG improves the flame-retardant efficiency of LLDPE/EVA blends. The addition of MEG apparently improves the LOI values and the UL-94 rating of LLDPE/EVA composites. The data obtained from the CCT show that the heat release rate (HRR), the total heat release (THR), and the gas production rate of composites with MEG decrease remarkably with increasing the content of MEG. When 10 phr of MEG is added, the char residues of LEMEG10 increase to 38.2% from 2.7% of LLDPE/EVA. The results of SEM and CCT present that MEG can improve the quality of char layers. The rate of char formation is enhanced also due to the existence of MEG, which plays an important role to improve the flame retardancy of the LLDPE/EVA composites.