Abstract:

The synergistic flame-retardant effects of expandable graphite(EG) with ammonium polyphosphate (APP) in wood flour/polypropylene composites were investigated by cone calorimeter (CONE) under a heat flux 50 kW·m^-2. The CONE results showed that both APP and EG decreased the heat release rate (HRR), total heat release(THR), release smoke rate(RSR) and increased the residual char of wood flour/polypropylene system, which indicate APP and EG are effective fire retardants for wood flour/polypropylene composites. However, EG flame retardant displayed the better smoke suppressing performance than that of APP. When the mass ratio of EG and APP was 2 : 1, the incorporation of EG and APP had a positive effect on forming a compact and intumescent char layer with stabilized structure, and showed a good synergistic effect in flame inhibition and smoke suppression. The mechanical test results showed that, even in the presence of maleic anhydride grafted polypropylene copolymer (MAPP), the addition of APP and EG flame retardant also decreased the impact and flexural strength of composites, but EG improved the flexural modulus.

Key words: wood flour, polypropylene, ammonium polyphosphate, expandable graphite, flame retardants, cone calorimeter