Flax fibre-reinforced epoxy composites with gradient flame-retardant distribution and fire warning function

In general, epoxy resin (EP) mixed with a large number of flame-retardants is used to cover fiber layer by layer to prepare flame-retardant composites. However, the addition of flame-retardants not only increases the cost, but also obviously reduces the mechanical properties of the composite. In this study, a kind of fire-retardant composite was designed and prepared with gradient distribution mode and fire warning function. Unlike the traditional uniform distribution pattern of flame-retardants distributed evenly in each resin layer, the gradient pattern made the flame-retardant content concentrated in the surface layer, and the concentration gradually decreased along the thickness. The gradient model composite exhibited more significant flame retardancy than the uniform model composite to ensure repeated warning. The limiting oxygen index of the gradient model composite was 31.4%, and the UL-94 of the gradient model composite reached V0 class. At the same time, the maximum value of the heat release rate and total heat release of the gradient model composite were reduced by 34.8% and 27.1%, respectively. The mechanical properties of gradient model were better than those of uniform model distribution composites.