Thermoplastic composite material made from natural fibers

A process for producing a composite material, wherein the composite material comprises a fibrous assembly of one or more natural reinforcing fibers, impregnated with at least one amorphous or semicrystalline thermoplastic polymer to form a thermoplastic matrix and wherein said process comprises:

• i) a step of impregnation of said fibrous assembly with a precursor composition in the molten state, the precursor composition comprising:
• a) at least one prepolymer P(X)n of said thermoplastic polymer, comprising a molecular chain P having, at its ends, n reactive functions X, with n ranging from 1 to 3, said prepolymer P(X)n having a number-average molecular weight Mn ranging from 500 to 10 000,
• b) at least one chain extender Y-A-Y comprising functions Y which react with at least one of said functions X,
• ii) a step of bulk polymerization by poly(addition), in the molten state, of said prepolymer with said chain extender,
• wherein:
• said thermoplastic polymer of the thermoplastic matrix is the result of said bulk polymerization by polyaddition of said precursor composition;
• and
• said impregnation i) and polymerization ii) steps take place at a temperature below 230° C.