METHOD FOR MANUFACTURING A NET-TYPE PRODUCT

Description

Technical Field

[0001] The invention relates to a method for manufacturing a crosslinked product having improved carbonization and thermal stability properties. This crosslinked product can in particular be used as an ablative resin for the constitution of a propellant nozzle or an atmospheric re-entry body. Prior art

[0002] It is known to produce ablative thermal protection for thruster nozzles or atmospheric reentry bodies from phenolic resins that are synthesized from formaldehyde and phenol, in order to obtain high aromatic and crosslinking densities, and therefore a high coke rate. However, formaldehyde and phenol are compounds classified as Carcinogenic Mutagenic Reprotoxic (CMR) category 1B and 2, the use of which should be limited, in particular to anticipate possible bans in the European Union. In addition, the reaction of phenol and formaldehyde is a polycondensation during which water is produced. This water can become trapped within the finished product, leading to a reduction in performance. With a view to solving this problem, developments have been pursued to obtain ablative resins by crosslinking benzoxazines.These developments reduce water entrapment in the finished product, but the solutions in the literature, providing a finished product with thermal stability and charring properties compatible with an application as an ablative resin, involve benzoxazines obtained by reaction of phenol with formaldehyde and an amine, and are therefore based on the use of compounds classified as CMR. Moreover, when these benzoxazines are synthesized without phenol, they have poor thermal stability and charring properties.

[0003] It would be desirable to have a new route for synthesizing materials with thermal stability and carbonization properties suitable for the production of ablative thermal protection for thruster nozzles or atmospheric re-entry bodies. Statement of the invention

[0004] The invention provides a method of manufacturing a crosslinked product comprising crosslinking a benzoxazine monomer of formula A provided below: in this formula: A 1 is a monocyclic or polycyclic aromatic or heterocyclic aromatic carbocyclic group, substituted by a crosslinkable group, said crosslinkable group is chosen from: a hydroxyl group, a carbonitrile group, a phthalonitrile group, R 1 a< is chosen from: furfuryl groups, substituted or unsubstituted.

[0005] The invention proposes the use of benzoxazine monomers having a crosslinkable group making it possible to obtain, after crosslinking, a product having high thermal stability and carbonization properties, compatible with an application as an ablative resin for the manufacture of a propellant nozzle or an atmospheric reentry body. The invention provides a new route for the synthesis of ablative resins limiting the use of CMR compounds, and in particular avoiding the use of formaldehyde.

[0006] A 1 is a monocyclic or polycyclic aromatic or heterocyclic aromatic carbocyclic group substituted by the crosslinkable group.

[0007] The choice of such groups advantageously makes it possible to obtain, after crosslinking the benzoxazine monomer, a product having improved thermal stability and carbonization properties.

[0008] In particular, A 1 may be a benzene ring substituted by the crosslinkable group. According to one example and whatever the embodiment considered, the crosslinkable group is a hydroxyl group.

[0009] R 1 a< is chosen from: furfuryl groups, substituted or unsubstituted.

[0010] The choice of such groups advantageously makes it possible to obtain, after crosslinking the benzoxazine monomer, a product having improved thermal stability and carbonization properties.

[0011] The presence of oxygen in the furfuryl ring allows, by accepting hydrogen bonds, to provide increased stabilization of the crosslinked network, and thus to further increase the carbonization rate.

[0012] In one example, the method comprises, prior to crosslinking the benzoxazine monomer of formula A, condensing an amine of formula A11 with an aldehyde of formula A12 to obtain the benzoxazine monomer of formula A, wherein formulas A11 and A12 are provided below:

[0013] In particular, the process may comprise, before condensation, obtaining the amine of formula A11, this obtaining comprising: an addition reaction of an amine of formula A21 to an aldehyde of formula A22 to form an imine of formula A23, and a reduction reaction of the imine of formula A23 to an amine of formula A11, formulas A21, A22 and A23 being provided below:

[0014] The amine of formula A21 is for example chosen from the following compounds: furfurylamine.

[0015] The aldehyde of formula A22 is salicylaldehyde. The aldehyde of formula A22 is a monoaldehyde, that is, it contains only one aldehyde function.

[0016] The aldehyde of formula A12 is for example chosen from the following compounds: hydroxybenzaldehyde, for example para-hydroxybenzaldehyde, vanillin, syringaldehyde or phthalonitrile-benzaldehyde, for example para-phthalonitrile-benzaldehyde.

[0017] In another example, the method comprises, prior to crosslinking the benzoxazine monomer of formula A: the condensation of the amine of formula A11 with an aldehyde of formula A13 to obtain a benzoxazine precursor of formula A14, formula A11 being defined above and formulas A13 and A14 being provided below: where A 3 denotes a precursor group making it possible to obtain the function A 1 carrying the crosslinkable group after a functionalization reaction, and carrying out the functionalization reaction of the benzoxazine precursor of formula A14 in order to obtain the benzoxazine monomer of formula A.

[0018] The aldehyde of formula A13 is for example chosen from the following compounds: hydroxybenzaldehyde, for example para-hydroxybenzaldehyde, vanillin, syringaldehyde, aminobenzaldehyde, for example para-aminobenzaldehyde.

[0019] The hydroxyl and amine groups may be crosslinkable groups as described above or the hydroxyl and amine groups may constitute precursor groups of other crosslinkable groups.

[0020] Regardless of the example considered, the condensation can be carried out by bringing the mixture of amine and aldehyde to reflux. The condensation can be carried out in toluene, methanol, ethanol or even without solvent.

[0021] The invention also relates to a propellant nozzle obtained by using a crosslinked product obtained by the method described above. The invention also relates to a method for manufacturing a propellant nozzle in which the nozzle is manufactured by using a crosslinked product obtained by the method described above.

[0022] The propellant nozzle may be made of a composite material. In this case, the manufacture of the nozzle may include a first step of forming a fibrous preform of the nozzle to be obtained impregnated with the benzoxazine monomer of formula A described above. This manufacture may further include a second step of heat treatment of the impregnated fibrous preform so as to crosslink the benzoxazine monomer of formula A and obtain the propellant nozzle.

[0023] The fiber preform may, for example, comprise fibers of carbon, silica, glass, or a ceramic material, for example silicon carbide. The fiber preform intended to form the fiber reinforcement of the nozzle may be formed in various ways (draping of pre-impregnated fabric layers, for example). In particular, it is possible to drape or wind impregnated two-dimensional or three-dimensional fabric layers onto a form having a surface reproducing the desired geometry of an internal or external surface of the nozzle to be produced in order to obtain the impregnated preform.

[0024] Alternatively, the fibrous preform of the nozzle to be obtained can first be obtained and then this preform can be placed in an injection cavity and then the benzoxazine monomer of formula A can be injected into the cavity so as to impregnate the preform. In this case, a resin transfer molding technique can be used to impregnate the fibrous preform.

[0025] Crosslinking can be carried out by imposing a temperature greater than or equal to 130°C, for example between 180°C and 250°C.

[0026] Alternatively, the invention also relates to an atmospheric reentry body obtained by using a crosslinked product obtained by the method described above. The invention also relates to a method for manufacturing an atmospheric reentry body in which the atmospheric reentry body is manufactured by using a crosslinked product obtained by the method described above.

[0027] Whatever the embodiment considered, the crosslinking implemented to obtain the crosslinked product can be a homo-crosslinking of the benzoxazine monomer of formula A on itself. Brief description of the drawings

[0028] [ Fig. 1 ] There figure 1 is a thermogram obtained by differential scanning calorimetry (“Differential Scanning Calorimetry”; “DSC”) of a first example of benzoxazine monomer according to the invention. Fig. 2 ] There figure 2 is a thermogravimetric analysis (TGA) result of a crosslinked product obtained by crosslinking this first example of benzoxazine monomer. Fig. 3 ] There figure 3 is a DSC thermogram of a second example of benzoxazine monomer according to the invention. Fig. 4 ] There figure 4 is a result of thermogravimetric analysis of a crosslinked product obtained by crosslinking this second example of benzoxazine monomer. Description of the embodiments Examples Example 1: Synthesis of a benzoxazine monomer from furfurylaminomethylphenol and para-hydroxybenzaldehyde followed by subsequent crosslinking

[0029] Furfurylamine is reacted with salicylaldehyde in stoichiometric proportions in refluxing methanol for 2 h, to form the corresponding imine. The imine is reduced to the amine with 1 equivalent of NaBH 4 added at 0 °C in a solution of the imine in MeOH, followed by refluxing for 2 h. The synthesized furfurylaminomethylphenol is dissolved in toluene with 1 equivalent of para-hydroxybenzaldehyde, then refluxed in a Dean Stark apparatus, to remove the water generated during the condensation reaction. The reaction is stopped when the conversion of aldehydes has reached its maximum, followed by proton NMR. After evaporation of the solvent under reduced pressure, the isolated benzoxazine is a pale yellow solid. The product has been characterized by NMR and infrared spectroscopy and the structure has been confirmed.

[0030] Thermal characterization by DSC revealed a melting temperature of 130°C and an exothermic reaction between 140°C and 250°C corresponding to crosslinking, representing 283J / g of enthalpy compared to the reference, with a ramp of 10°C / min in high-pressure sealed steel crucibles. The obtained DSC thermogram is provided at figure 1 .

[0031] Thermogravimetric analysis showed a coke rate after polymerization in situ of 64% under nitrogen atmosphere, as well as a degradation temperature of 10% of the total mass of 402°C (heating ramp: 10°C / min). This shows excellent thermal stability for this resin. The thermogravimetric analysis graph obtained is provided at figure 2 . Example 2: Synthesis of a benzoxazine monomer from furfurylaminomethylphenol and para-phthalonitrile-benzaldehyde followed by subsequent crosslinking

[0032] Para-hydroxybenzaldehyde is reacted with 1 equivalent of K 2 CO 3 in dimethylformamide at 0°C. 1.1 equivalents of 4-nitrophthalonitrile are gradually added at 0°C. The mixture is left stirring at room temperature overnight. The reaction medium is then precipitated in 50 times the volume of ice water. The yellow heterogeneous medium is then filtered under vacuum, and an off-white viscous solid is obtained. This solid is dissolved in dichloromethane and washed 3 times with saturated sodium chloride solution. The organic phase is isolated, dried over magnesium sulfate and the product recovered by evaporation of the solvent under reduced pressure. The product is an off-white powder.

[0033] Furfurylamine is reacted with salicylaldehyde in stoichiometric proportions in refluxing methanol for 2 h, to form the corresponding imine. The imine is reduced to the amine with 1 equivalent of NaBH 4 added at 0 °C in a solution of the imine in MeOH, followed by refluxing for 2 h. The synthesized furfurylaminomethylphenol is dissolved in toluene with 1 equivalent of para-phthalonitrile-benzaldehyde, then refluxed in a Dean Stark apparatus, to remove the water generated during the condensation reaction. The reaction is stopped when the conversion of aldehydes has reached its maximum, followed by proton NMR. After evaporation of the solvent under reduced pressure, the isolated benzoxazine is an off-white viscous solid. The product was characterized by NMR and the structure confirmed.

[0034] Thermal characterization by DSC revealed an exothermic reaction between 170°C and 278°C, representing 430J / g of enthalpy compared to the reference, with a ramp of 10°C / min in high-pressure sealed steel crucibles. The obtained DSC thermogram is provided at figure 3 .

[0035] Thermogravimetric analysis showed a coke rate after polymerization in situ of 62% under nitrogen atmosphere, as well as a degradation temperature of 10% of the total mass of 444°C (heating ramp: 10°C / min). The thermogravimetric analysis graph obtained is provided at figure 4 .

Claims

1. A process for manufacturing a cross-linked product comprising the cross-linking of a benzoxazine monomer of formula A provided below: in this formula: A1 is selected from aromatic carbocyclic or heterocyclic, monocyclic or polycyclic, groups, substituted by a cross-linkable group, said cross-linkable group is selected from: a hydroxyl group, a carbonitrile group, a phthalonitrile group, R1a is selected from: substituted or unsubstituted furfuryl groups.

2. The process as claimed in claim 1, wherein A1 is a benzene ring substituted by the cross-linkable group.

3. The process as claimed in claim 1 or 2, wherein the cross-linkable group is a hydroxyl group.

4. A rocket nozzle obtained by using a cross-linked product obtained by the process as claimed in any one of claims 1 to 3.

5. A re-entry vehicle obtained by using a cross-linked product obtained by the process as claimed in any one of claims 1 to 3.