Composite structure

1 - 28 . (canceled)

29 . A composite structure comprising at least:

a structural layer C1;

a weight-reducing layer C2 of rigid or semi rigid foam; and

optionally a structural layer C3

wherein the foam is a polyamide-class foam.

30 . The composite structure as claimed in claim 29 , being a sandwich structure comprising two outer structural layers C1 and C3, and a weight-reducing internal layer C2.

31 . The composite structure as claimed in claim 30 , wherein at least one structural layer is a plate or a sheet.

32 . The composite structure as claimed in claim 31 , wherein the plate or sheet of metal is of a metal alloy, optionally steel.

33 . The composite structure as claimed in claim 29 , wherein the structural layer has a thickness of between 0.2 and 3 mm.

34 . The composite structure as claimed in claim 29 , wherein the composite layer has a thickness of between 3 and 50 mm.

35 . The composite structure as claimed in claim 29 , having a density of the foam of less than 300 kg/m 3 , and optionally between 30 and 200 kg/m 3 .

36 . The composite structure as claimed in claim 29 , wherein the foam has a Young's modulus (modulus of elasticity in compression) greater than or equal to 30 MPa.

37 . The composite structure as claimed in claim 29 , wherein the polyamide foam is obtained by injecting gas into the polyamide and/or by incorporating volatile compounds, blowing agents and/or a compound reacting with the polyamide to form gas, in the polyamide.

38 . The composite structure as claimed in claim 37 , wherein the foam is obtained from a mixture of polyamide and polycarbonate.

39 . The composite structure as claimed in claim 38 , wherein the polycarbonate is a polycarbonate comprising aromatic rings of formula:

in which R 1 and R 2 , which are identical or different, are hydrogen atoms, halogen atoms or alkyl or haloalkyl radicals having between 1 and 5 carbon atoms, and each aromatic ring optionally being substituted by alkyl or haloalkyl radicals having between 1 and 5 carbon atoms; and n is an integer between 40 and 300.

40 . The composite structure as claimed in claim 39 , wherein the polycarbonate has a molecular weight of between 5000 and 80000.

41 . The composite structure as claimed in claim 38 , wherein the mixture contains 0.5 to 20 wt. % of polycarbonate relative to the polyamide, optionally 5 to 15 wt. %.

42 . The composite structure as claimed in claim 38 , wherein the foam is obtained by heating the mixture of polyamide and polycarbonate at a temperature greater than or equal to the melting point of the polyamide.

43 . The composite structure as claimed in claim 29 , wherein at least one structural layer is a plate or a sheet comprising a thermoplastic or thermosetting polymer matrix.

44 . The composite structure as claimed in claim 43 , wherein at least one structural layer is a plate or a sheet comprising a thermoplastic or thermosetting polymer matrix and reinforcing fibers, optionally glass, carbon, aramid, polyimide, quartz, sisal, hemp, or flax fibers.

45 . The composite structure as claimed in claim 43 , wherein the matrix comprises a star-structured polyamide comprising:

star-structured macromolecular chains comprising one or more cores and at least three arms or three polyamide segments connected to the core, and

optionally, linear macromolecular polyamide chains.

46 . The composite structure as claimed in claim 45 , wherein the star-structured polyamide is of the type of polyamides obtained by copolymerization of a mixture of monomers comprising at least:

a) monomers of the following general formula (I):

b) monomers of the following general formulas (IIa) and (IIb):

c) and optionally monomers of the following general formula (III):

Z-R 3 -Z   (III)

wherein:

R 1 is a hydrocarbon radical having at least 2 carbon atoms, linear or cyclic, aromatic or aliphatic optionally containing heteroatoms,

A is a covalent bond or an aliphatic hydrocarbon radical optionally containing heteroatoms and has from 1 to 20 carbon atoms,

Z represents a primary amine function or a carboxylic acid function,

Y is a primary amine function when X represents a carboxylic acid function

or

Y is a carboxylic acid function when X represents a primary amine function,

R 2 and R 3 , which are identical or different, represent optionally substituted aliphatic, cycloaliphatic or aromatic hydrocarbon radicals having from 2 to 20 carbon atoms optionally containing heteroatoms, and

m represents an integer between 3 and 8.

47 . A method of production of the composite structure as defined in claim 29 , comprising the step of assembly of at least the following elements:

(C1′): a structural layer or a precursor of said layer;

(C2′): a weight-reducing layer of polyamide-based foam or a precursor of said foam; and

optionally (C3′): a structural layer or a precursor of said layer.

48 . The method as claimed in claim 47 , wherein the precursor of the foam is a powder or an article comprising an expandable polyamide composition containing polyamide and an expanding agent.

49 . The method as claimed in claim 48 , wherein the expanding agent is a polycarbonate.

50 . The method as claimed in claim 47 , wherein the precursor of at least one structural layer is an article containing reinforcing fibers.

51 . The method as claimed in claim 50 , wherein the precursor of at least one structural layer comprises:

an article containing reinforcing fibers; and

a polymer matrix

52 . The method as claimed in claim 50 , wherein the precursor of at least one structural layer is an article containing reinforcing threads and/or fibers and threads and/or fibers of polymer matrix.

53 . The method as claimed in claim 52 , wherein the article is in the form of continuous threads, cut threads, strips, mats, of braided, woven fabrics, knitted fabrics, fleece, multiaxial materials, or nonwovens.

54 . The method as claimed in claim 47 , wherein the assembly is carried out by thermoforming or calendering of the various elements (C1′), (C2′) and optionally (C3′), the various elements being thermoformed or calendered simultaneously or successively.

55 . The method as claimed in claim 53 , wherein the thermoplastic polymer matrix of the precursor of at least one structural layer is a thermoplastic matrix and in that the temperature during thermoforming or calendering is greater than or equal to the melting point of the thermoplastic matrix.