Composite propellant with reduced combustion rate

Abstract

The invention relates to a solid composite propellant comprising: 5.0% to 20.0% by mass of a polyurethane crosslinked binder, which is the reaction product of a polyester polyol and a polyisocyanate crosslinking agent, in the presence of a crosslinking catalyst; 20.0% to 90.0% by mass of ammonium perchlorate; optionally up to 25.0% by mass of aluminum; optionally up to 5.0% by mass of a ballistic catalyst; optionally up to 20.0% by mass of at least one additive.

Description

[0001] Composite propellant with reduced combustion rate

[0002] Technical field of the invention

[0003] The present invention lies in the technical field of solid propellant propulsion and more specifically relates to composite solid propellants with reduced combustion speed. The invention also relates to the use of these propellants.

[0004] State of the art

[0005] Rocket propulsion is a propulsion method used in space applications (satellite launchers, satellites, orbital stations) and military applications (missiles). In the aerospace field, solid propellant engines are highly valued for their performance and small footprint. Indeed, solid propellants are by nature very dense, and therefore generate a greater quantity of propellant gases for the same on-board volume than a liquid propellant, which results in a reduction in the weight of the structure. In addition, these engines are relatively easy to install, giving them a lower structural mass than a cryogenic engine. Finally, their operation does not require any moving parts, thus reducing the risk of breakdown. For these reasons, this type of engine remains a preferred option when designing a launcher such as the Ariane 5 launcher.

[0006] Propellants can be divided into two families based on their composition. The first family, historically the oldest, includes propellants composed of nitrocellulose, a solid cellulose that absorbs liquid nitroglycerin, as well as additives. These homogeneous propellants are known as "double base." Indeed, each of these two energetic materials combines both the oxidizing agent and the reducing agent. Their performance is not very high, but they are generally non-smoke-producing (except in the presence of metallic additives), which has contributed to their use in the design of tactical missiles. The second family of propellants is known as "composite." They are typically composed of a solid phase (oxidizer crystals and fuel) held in place by a synthetic rubber, the binder (typically polybutadiene), the whole forming a heterogeneous whole.The addition of metal powder (aluminum or iron for example) makes it possible to increase the density of the propellant as well as its performance. Composite propellants have much better performance than double-base propellants, and are widely used for space applications. Application FR-A-3 017 615 describes a monolithic charge, of essentially cylindrical external shape, with a cylindrical central channel, of composite solid propellant containing in a crosslinked inert binder of polyurethane type: an oxidizing charge of ammonium perchlorate distributed in three monomodal distributions, and a reducing charge of aluminum having a median diameter (D. 50 ) less than or equal to 30 pm.

[0007] The combustion speed of a solid propellant depends on the pressure P prevailing in the combustion chamber and classically follows a law (called Vieille's law) expressed in the form:

[0008] Vc= aP n .

[0009] The said combustion speed Vc and the pressure exponent n of the propellant are fundamental parameters for the ballistic adjustment of a solid propellant motor (combustion time, thrust, combustion stability, etc.). They determine the stationary operating point of the motor at any time of firing.

[0010] Typically, polyurethane-bound composite propellants, comprising an aluminum reducing charge, such as those described in application FR-A-3 017 615, have a combustion speed of the order of 10 mm / s, in an operating pressure range of 8-10 MPa.

[0011] It is understood that a reduction in the combustion rate of a solid propellant could be advantageous in terms of, for example, the combustion time of the propellant, provided that the energy and mechanical performance of the fuel are not impacted. Several solutions could contribute to achieving this objective. One solution would be to not use a ballistic catalyst; another solution would be to use, as an oxidizing charge, ammonium perchlorate of larger particle size than that commonly used; another solution would be to identify an advantageous isocyanate as a precursor of the polyurethane matrix. However, these potential solutions are either not sustainable (in terms of raw material supply), or do not a priori allow maintaining a satisfactory level of energy and / or mechanical performance.

[0012] US patent application 2019 / 016645 describes a solid propellant comprising a reaction product between a PBHT (hydroxytelechelic polybutadiene) or PEHT (hydroxytelechelic polyether) prepolymer, a diol dimer and a curative isocyanate. The propellants tested have a combustion rate of the order of 0.3 ips (inches per second) or about 7.6 mm / s. The pressure at which the combustion rate was determined is not mentioned, however. US patent application 2019 / 077725 describes a solid propellant comprising PBHT, a diol dimer and an isocyanate.

[0013] It is to the credit of the inventors to propose composite solid propellants having a combustion speed of the order of 6 to 7 mm / s in a pressure range from approximately 5 MPa to approximately 10 MPa, and having the usual properties desired for space and strategic applications (performance, mechanical properties, etc.). Summary of the invention

[0014] According to one aspect, the invention relates to a composite solid propellant comprising:

[0015] - about 5.0% to about 20.0% by mass of a polyurethane-type crosslinked binder, which is the reaction product of a polyester polyol and a polyisocyanate-type crosslinking agent, in the presence of a crosslinking catalyst;

[0016] - about 20.0% to about 90.0% by mass of ammonium perchlorate;

[0017] - 0% to about 25.0% by mass of aluminum;

[0018] - 0% to about 5.0% by mass of a ballistic catalyst;

[0019] - 0% to about 20.0% by mass of at least one additive.

[0020] In some embodiments, the polyester polyol has a weight average molecular weight of between about 1000 g / mol and about 4000 g / mol. In some embodiments, the polyester polyol comprises from 50 to 300 carbon atoms.

[0021] According to another aspect, the invention relates to the use of the above-mentioned composite solid propellant as fuel for a rocket, satellite or missile engine. Description of the figures

[0022] Figure 1 represents the volume electrical resistivity of polymers and corresponding binders.

[0023] Figure 2 represents the mechanical properties at break of binders based on PBHT or polyester polyol.

[0024] Figure 3 shows the comparative combustion rates of typical compositions with PBHT or polyester polyol binder.

[0025] Figures 4A-4C represent the comparative tensile curves of typical compositions with PBHT or polyester polyol binder obtained after cooking or after aging. Description of the invention

[0026] According to one aspect, the invention relates to a composite solid propellant comprising:

[0027] - about 5.0% to about 20.0% by mass of a polyurethane crosslinked binder, which is the reaction product of a polyester polyol and a polyisocyanate crosslinking agent, in the presence of a crosslinking catalyst; - about 20.0% to about 90.0% by mass of ammonium perchlorate;

[0028] - 0% to about 25.0% by mass of aluminum;

[0029] - 0% to about 5.0% by mass of a ballistic catalyst;

[0030] - 0% to about 20.0% by mass of at least one additive.

[0031] Of course, the sum of the quantities of the different constituents of the composite solid propellant is equal to 100%.

[0032] The polyurethane-type crosslinked binder is obtained by crosslinking the polyester polyol with at least one polyisocyanate-type crosslinking agent, which generally occurs in a controlled quantity, i.e. in a quantity such that the NCO / OH bridging ratio (Rp) is between 0.7 and 1.5, advantageously this ratio is equal to 1. The OH functions are, as will be understood, provided by the polyester polyol.

[0033] In some embodiments, the polyester polyol has a weight average molecular weight of between about 1000 g / mol and about 4000 g / mol, for example between about 1500 g / mol and about 2500 g / mol.

[0034] In some embodiments, the polyester polyol comprises from 50 to 300 carbon atoms, for example from 100 to 200 carbon atoms.

[0035] Examples of polyester polyols that may be used in the context of the present invention include those marketed by the company Croda under the trade name Priplast™.

[0036] In some embodiments, the polyester polyol is obtained from an acid monomer (preferably a diacid) and an alcohol monomer (preferably a diol). In some embodiments, the acid monomer comprises 4 to 50 carbon atoms, preferably 4 to 10 carbon atoms. In some embodiments, the alcohol monomer comprises 30 to 50 carbon atoms, preferably 32 to 40 carbon atoms.

[0037] For example, in the simplified scheme below of a polyester synthesis, the rectangular block of the diol is a hydrocarbon structure of 30 to 50 carbons. The polyisocyanate crosslinking agent is suitable for crosslinking such polyester polyols. In certain embodiments, the crosslinking agent, known per se, is a polyisocyanate selected from methyl diisocyanate (MDI), toluene diisocyanate (TDI), isophorone diisocyanate (IPDI), dicyclohexyl methylene diisocyanate (MDCI), hexamethylene diisocyanate (HDI), the trimer of said hexamethylene diisocyanate (in particular sold by the company Bayer under the trade name Desmodur® N 3300), biuret trihexane isocyanate (BTHI), 3,5,5-trimethyl-1,6-hexamethylene diisocyanate and mixtures thereof. Such crosslinking agents are conventionally used (i) in a quantity necessary and sufficient to ensure the crosslinking of the polyester polyol (not excessive so as not to pollute the crosslinked product obtained) and (ii) in a quantity such that the bridging ratio Rp is as defined above.The reaction between the polyester polyol and the polyisocyanate crosslinking agent is carried out in the presence of a crosslinking catalyst, which is generally used in an amount of between about 0.1 ppm and about 10 ppm, advantageously between about 0.1 ppm and about 1 ppm, this amount being expressed relative to the mass of composite solid propellant. In certain embodiments, the crosslinking catalyst is chosen from triphenylbismuth, dibutyltin dilaurate (BDTL), a bismuth carboxylate such as bismuth octoate or bismuth neodecanoate (as described in application FR-A-3 102 476), and mixtures thereof.

[0038] The composite solid propellant according to the invention comprises about 20.0% to about 90.0% by mass, such as for example about 60% by mass to about 75% by mass, of ammonium perchlorate (oxidizing charge).

[0039] In some embodiments, the ammonium perchlorate comprises, per 100% of its mass, the following proportions of different fillers:

[0040] - 40 to 80% by mass of class A filler;

[0041] - 5 to 35% by mass of class B filler;

[0042] - 1 to 35% by mass of class C filler.

[0043] In this disclosure, the term "class A filler" means a filler whose monomodal particle size distribution has a value of D 10 between 100 pm and 110 pm, a value of D 50 between 170 pm and 220 pm and a value of D 90 between 315 pm and 340 pm.

[0044] In this disclosure, the term "class B filler" means a filler whose monomodal particle size distribution has a value of D 10 between 15 pm and 20 pm, a value of D 50 between 60 pm and 120 pm and a value of D90 between 185 pm and 220 pm.

[0045] In this disclosure, the term "class C filler" means a filler whose monomodal particle size distribution has a value of D i0 between 1.7 pm and 3.6 pm, a value of D 50 between 6 pm and 12 pm and a value of D 90 between 8 pm and 12 pm.

[0046] D values i0 , D 50 and D 90 represent the diameter for which the cumulative volume percentage is respectively equal to 10%, 50% or 90%. These granulometric values ​​are taken from measurements carried out using a laser granulometer (Mastersizer™ 3000 type or equivalent), according to a procedure defined by standard NF 11-666.

[0047] The composite solid propellant according to the invention also comprises 0% to about 25.0% by mass, such as for example about 15% by mass to about 20% by mass, of aluminum (reducing charge).

[0048] In some embodiments, the aluminum reducing filler has a value of D 50 less than or equal to 30 pm.

[0049] The composite solid propellant according to the invention also comprises 0% to about 5.0% by mass of a ballistic catalyst.

[0050] In certain embodiments, the ballistic catalyst is chosen from conventional ballistic catalysts, such as lead salts and oxides, and bismuth citrate. The Applicant has described, in patent application WO 2016 / 066245, the advantageous use of said bismuth citrate as a ballistic catalyst.

[0051] The composite solid propellant according to the invention may also comprise up to approximately 20.0% by mass of at least one additive.

[0052] In certain embodiments, said at least one additive is chosen from plasticizers, anti-glare agents, adhesion agents between the binder and the oxidizing filler, antioxidants, energy fillers.

[0053] Examples of plasticizers include dioctyl azelate, diisooctyl sebacate, isodecyl pelargonate, polyisobutylene, dioctyl phthalate, and also energy-based plasticizers such as triethylene glycol dinitrate.

[0054] Examples of anti-glow agents include compounds based on alkali metals, sodium (Na2SO4, etc.) and especially potassium (K2SO4, KNO3, K3AIF6, C4H5KO6, etc.), particularly potassium salts such as potassium cryolite (K3AIF6) or monobasic potassium tartrate (C4H5KO6), said monobasic potassium tartrate being able to be in the form of L- or D- enantiomer or in racemic form. These specific potassium salts are commercially available, in conventional particle sizes (powders with grains generally having a D 50 between 1 and 300 pm).

[0055] Examples of adhesion agents between the binder and the oxidizing filler include bis(2-methylaziridinyl)-methylaminophosphine oxide (methyl BAPO) or triethylene pentamine acrylonitrile (TEPAN).

[0056] Examples of antioxidants include those from the rubber industry, such as ditertiobutylparacresol (DBC) or 2,2'-methylene-bis(4-methyl-6-tertio-butylphenol) (MBP5).

[0057] Examples of energy charges include hexogen (RDX) or octogen (HMX).

[0058] In a non-limiting manner, the composite solid propellants according to the invention can be prepared by a process comprising the following steps:

[0059] - the constitution of a homogeneous paste by: a) incorporation, with stirring, at a temperature between approximately 30°C and approximately 70°C, into a polyester polyol as defined above, of the other constituent ingredients of the desired composite solid propellant with the exception of the crosslinking agent and the crosslinking catalyst, and b) stirring of the resulting mixture, under partial vacuum, at a temperature between approximately 30°C and approximately 70°C;

[0060] - incorporation into said homogeneous paste formed, under partial vacuum and at a temperature between approximately 30°C and approximately 50°C, of ​​said crosslinking agent and from approximately 0.1 ppm to approximately 10 pm of said crosslinking catalyst, followed by stirring of the formed mixture;

[0061] - casting said mixture into at least one structure; and

[0062] - the heat treatment of said stirred mixture cast into said at least one structure.

[0063] The partial vacuum mentioned is intended for degassing the medium above which it is applied. It is generally about 10 mm Hg. It should be noted incidentally that it is not necessarily of constant intensity.

[0064] The heat treatment (for crosslinking the polyester polyol) is generally carried out at a temperature of between approximately 30°C and approximately 60°C (30°C < T < 60°C), for several days. The composite solid propellants in accordance with the invention advantageously have a combustion rate of less than approximately 10 mm / s, for example of the order of approximately 6 mm / s to approximately 7 mm / s, and pressure exponents of between 0.2 and 0.5, over an operating pressure range of approximately 5 MPa to approximately 10 MPa. They are particularly suitable as fuel for rocket, satellite or missile engines. Their use for this purpose is particularly recommended. It forms an integral part of the present invention and constitutes another aspect thereof.

[0065] Another aspect of the invention lies in the use, in a solid propellant containing an oxidizing charge of ammonium perchlorate, a reducing charge of aluminum and a crosslinked binder of polyurethane type, of a polyester polyol as defined above as a precursor ingredient of said binder.

[0066] According to another aspect, the invention relates to a propellant load containing at least one composite solid propellant as defined above. Such a load is suitable not only for satellite or missile engines, but also for engines for space launchers such as, for example, those of the Ariane 5 rocket. The propellant loads contained in these engines have a mass ranging from a few hundred kilograms to several hundred tonnes.

[0067] According to another aspect, the invention relates to a rocket, satellite or missile engine comprising a propellant charge as defined above.

[0068] The invention will be better understood with the aid of the examples below, given for illustrative purposes.

[0069] Example 1

[0070] A binder was prepared from a polyisocyanate and a polymer (PBHT, R45HT™, marketed by the company Cray Valley, or polyester polyol according to the invention, Priplast™ 1838, marketed by the company Croda) optionally in the presence of a plasticizer, dioctyl azelate (DOZ), according to the following protocol:

[0071] - stirring, under partial vacuum, at a temperature of 70°C of the polymer and the plasticizer for 60 minutes;

[0072] - incorporation after cooling to a temperature of 50°C, of ​​the crosslinking agents MDCI and Desmodur N3300 and 3 pm of DBTL, followed by stirring of the resulting mixture;

[0073] - pouring said mixture into a mold;

[0074] - heat treatment for 10 days at 50°C.

[0075] Then the volume electrical resistivity (expressed in ohm.m) at 20°C and the stress (Sm, expressed in MPa) of the binders thus obtained were determined. The stress measurements were carried out by uniaxial traction at 50 mm / min, in accordance with the NFT70-315 standard. The results are presented in Figures 1 and 2. As can be seen in these figures, interesting properties are obtained by using a polyester polyol instead of a conventional PBHT: lower electrical resistance and similar mechanical properties in tension.

[0076] Example 2

[0077] Propellants were prepared in the following manner, from either a conventional PBHT or a polyester polyol according to the invention:

[0078] - incorporation, with stirring, at a temperature of 70°C, into the polymer, of the constituent ingredients of the composite solid propellant (mainly 68% ammonium perchlorate (of composition A or B depending on the proportions of ammonium perchlorate classes used) and 20% aluminium) with the exception of the crosslinking agent and the crosslinking catalyst;

[0079] - stirring the resulting mixture, under partial vacuum, at a temperature of 70°C for 60 minutes;

[0080] - incorporation into said homogeneous paste constituted, under partial vacuum and at a temperature of 50°C, of ​​the crosslinking agents MDCI and Desmodur® N3300 and 0.15 pm of DBTL, followed by stirring of the constituted mixture;

[0081] - pouring said mixture into a mold;

[0082] - 2-week heat treatment at 50°C.

[0083] The burning rate (Vc) of these propellants was measured. The results are shown in Figure 3. The dotted curves represent the Vc of a propellant comprising ammonium perchlorate of composition A and either PBHT (top curve) or a polyester polyol (bottom curve). The solid curves represent the Vc of a propellant comprising ammonium perchlorate of composition B and either PBHT (top curve) or a polyester polyol (bottom curve).

[0084] Over the operating pressure range of 5 MPa to 10 MPa, a reduction in combustion speed (approximately -1 mm / s) of the propellant containing polyester polyol compared to the propellant containing PBHT is observed, regardless of the type of ammonium perchlorate used.

[0085] The energy performance of the propellants was also determined. The results are presented in the table below. Table 1

[0086] Is: specific impulse / Is p: specific impulse volume /

[0087] T: combustion temperature / Tvol: charge rate in % by volume

[0088] It can be noted that the energy performances of the two propellants are similar. The polyester polyol according to the invention, which is a bio-sourced product, with a low density (0.96), a low Tg (-63°C), and less insulating than PBHT, can therefore be used advantageously as a substitute for PBHT.

[0089] Example 3

[0090] The mechanical properties of the propellants obtained in Example 2 were measured after baking and after accelerated aging. The results are shown in Figure 4. The dotted curves represent the tensile curves of a PBHT binder propellant. The solid curves represent the tensile curves of a polyester polyol binder propellant with the same load distribution. While the mechanical properties of the polyester polyol binder propellant are lower than those of the PBHT binder propellant at the initial time t0, it is observed after accelerated aging of 3 months at 60°C in dry or humid conditions that the mechanical properties of the polyester polyol binder propellant become higher than the mechanical properties of the PBHT binder propellant aged under the same conditions.

Claims

Claims 1. Composite solid propellant comprising: - 5.0% to 20.0% by mass of a polyurethane-type crosslinked binder, which is the reaction product of a polyester polyol and a polyisocyanate-type crosslinking agent, in the presence of a crosslinking catalyst; - 20.0% to 90.0% by mass of ammonium perchlorate; - 0% to 25.0% by mass of aluminum; - 0% to 5.0% by mass of a ballistic catalyst; - 0% to 20.0% by mass of at least one additive; said polyester polyol being obtained from an alcohol monomer comprising from 30 to 50 carbon atoms, preferably from 32 to 40 carbon atoms.

2. Composite solid propellant according to claim 1, wherein the polyester polyol has a mass average molecular weight of between about 1000 g / mol and about 4000 g / mol, preferably between about 1500 g / mol and about 2500 g / mol.

3. Composite solid propellant according to one of the preceding claims, in which the polyester polyol comprises from 50 to 300 carbon atoms, preferably from 100 to 200 carbon atoms.

4. Composite solid propellant according to one of the preceding claims, in which the crosslinking agent is chosen from methyl diisocyanate, toluene diisocyanate, isophorone diisocyanate, dicyclohexyl methylene diisocyanate, hexamethylene diisocyanate, hexamethylene diisocyanate trimer, biuret trihexane isocyanate, 3,5,5-trimethyl-1,6-hexamethylene diisocyanate and mixtures thereof.

5. Composite solid propellant according to one of the preceding claims, in which the crosslinking catalyst is chosen from triphenylbismuth, tin dibutyldilaurate, a bismuth carboxylate, and mixtures thereof.

6. Composite solid propellant according to one of the preceding claims, in which the ballistic catalyst, when present, is chosen from lead salts and oxides and bismuth citrate.

7. Use of a composite solid propellant as defined in any one of the preceding claims as rocket, satellite or missile engine fuel.

8. Use, in a solid propellant containing an oxidizing charge of ammonium perchlorate, a reducing charge of aluminum and a crosslinked binder of polyurethane type, of a polyester polyol as defined in any one of claims 1 to 3 as a precursor ingredient of said binder.

9. Propellant charge comprising at least one composite solid propellant as defined in any one of claims 1 to 6.

10. A rocket, satellite or missile engine comprising a propellant charge according to claim 9.

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