The multilayered distribution of intumescent flame retardants and its influence on the fire and mechanical properties of polypropylene

The multilayered distribution of intumescent flame retardants (IFRs) was obtained by fabricating a series of alternating multilayered composites consisting of polypropylene (PP) and IFR-filled PP (PPFR) layers through a layer-multiplying coextrusion technology. With increasing the layer numbers, the limiting oxygen index (LOI) and elongation at break (εb) of the multilayered composites were enhanced, accompanied with the gradually decreased values of the peak heat release rate and the total heat release. When the layer numbers beyond 16, the LOI and εb values were even larger than those of the PP/IFR conventional composite filled with the same content of IFRs. The layer interfaces and confined layer spaces in the multilayered system were considered to play a crucial role in retarding the spread of fire as well as the propagation of crazes. The significance of this work was providing an optimal route to fabricate flame-retarding composites with excellent mechanical properties.