Polypropylene (PP)/intumescent flame retardant (IFR) filled PP (PPFR) alternating multilayered composites with different layer numbers (2

4

16 and 64) were fabricated through a layer-multiplying coextrusion technology.The influence of the number of layers on the flame-retarding and mechanical properties of the multilayered specimens was investigated.Polarized light micrographs displayed that PP and PPFR layers were distributed alternatively along the thickness direction of the multilayered specimen

and interfaces between PP and PPFR layers were enriched with increasing the number of layers.The non-isothermal crystallization curve of the specimen with more layers tended to become similar to that of the conventional IFR-filled system

which was ascribed to the heterogeneous crystallization of PP layers induced by IFR particles located around interfaces.This suggested that the distribution of IFRs could be controlled by changing the number of layers.The results of vertical burning test

LOI and MCC showed that increasing the number of layers could play a positive role in accelerating the self-extinguishment of an ignited specimen and decreasing its heat release rate.Compared with that of the 2-layer specimen

the LOI of 64-layer specimen was increased from 19.5 to 25.Tensile properties displayed that increasing the number of layers little influenced the tensile strength of multilayered specimens

while induced a significant increase of the elongation at break.It was considered that the multilayered distribution of IFRs could not only promote the formation of continuous char layers

but also retard the propagation of crazes in the whole composites.Thus

it would be a novel route to fabricate polymer composites with both excellent flame retardancy and mechanical properties.