Composite propellant with reduced burning rate

Abstract

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

Description

[Technical Field]

[0001] The present invention relates to the field of solid propellants, and more particularly to composite solid propellants with reduced burn rates. The present invention also relates to the use of these propellants. [Background technology]

[0002] Rocket propulsion is a propulsion method used in space applications (satellite rockets, orbital stations) and military applications (missiles). In the aerospace field, solid propellant engines are highly valued for their performance and compact size. Indeed, because solid propellants are inherently very dense, they generate more propellant gas than liquid propellants for the same payload volume, which reduces the weight of the structure. In addition, these engines are relatively easy to install and result in a lower structural mass than cryogenic engines. Finally, they require no moving parts to operate, reducing the risk of failure. For these reasons, this type of power plant remains the preferred choice when designing rockets, such as the Ariane 5.

[0003] Propellants can be divided into two groups based on their composition. The first group, historically the oldest, includes propellants composed of nitrocellulose, a solid cellulose that absorbs liquid nitroglycerin, and additives. These homogeneous propellants are known as "double-base" propellants. These two energetic materials each serve as both an oxidizer and a reductant. Although their performance is not particularly high, they are generally non-smoking (except in the presence of metal additives), contributing to their use in tactical missile design. The second group of propellants is known as "composite" propellants. These typically consist of a solid phase (oxidizer crystals and fuel) held together by synthetic rubber, a binder (typically polybutadiene), and a heterogeneous overall group. The addition of metal powders (e.g., aluminum or iron) increases the propellant's density and improves its performance. Composite propellants perform much better than double-base propellants and are widely used in space applications.

[0004] French Patent No. 3 017 615 describes a monolithic charge, essentially of cylindrical external shape with a cylindrical central channel, of a composite solid propellant in a cross-linked inert binder of polyurethane type, comprising: an ammonium perchlorate oxide charge distributed in three monomodal distributions, and a median diameter (D) of less than 30 μm. 50 ) an aluminum reducing charge having

[0005] The burning rate of a solid propellant depends on the pressure P in the combustion chamber and is classically governed by the following law (known as Vieille's law): Vc=aP n

[0006] The burn rate Vc and the propellant pressure exponent n are fundamental parameters for ballistic control of solid propellant engines (burn time, thrust, combustion stability, etc.). They determine the steady-state operating point of the engine at any launch time.

[0007] Typically, polyurethane-bonded composite propellants containing reduced aluminum charges, such as those described in French Patent No. 3 017 615, have a burn rate of about 10 mm / s in the operating pressure range of 8-10 MPa.

[0008] It is understood that reducing the burn rate of a solid propellant can be advantageous, for example, in terms of the burn time of the propellant, as long as it does not affect the energy and mechanical performance of the fuel. To achieve this goal, several solutions are conceivable. One solution would be to not use a combustion catalyst; another would be to use ammonium perchlorate with a larger particle size than that commonly used as an oxidizing charge; and another would be to identify advantageous isocyanates as precursors to the polyurethane matrix. However, these potential solutions are unlikely to be sustainable (in terms of raw material supply) or to maintain satisfactory levels of energy and / or mechanical performance.

[0009] U.S. Patent Application Publication No. 2019 / 016645 describes a solid propellant containing the reaction product of an HTPB (hydroxyl-terminated polybutadiene) or HTPE (hydroxyl-terminated polyether) type prepolymer, a dimer diol, and a curable isocyanate. The burn rate of the tested propellant is about 0.3 ips (inches per second) or about 7.6 mm / s. However, the pressure at which the burn rate was determined is not mentioned. U.S. Patent Application Publication No. 2019 / 077725 describes a solid propellant containing HTPB, a dimer diol, and an isocyanate. Summary of the Invention [Problem to be solved by the invention]

[0010] The inventors' achievement is the development of a composite solid propellant that has a burning rate of about 6 to about 7 mm / s in the pressure range of about 5 MPa to about 10 MPa and has the typical properties (performance, mechanical properties, etc.) desired for space and strategic applications. [Means for solving the problem]

[0011] In one aspect, the present invention relates to a composite solid propellant comprising: - about 5.0% to about 20.0% by weight of a polyurethane-type crosslinked binder which is the reaction product of a polyester polyol and a polyisocyanate-type crosslinker in the presence of a crosslinking catalyst; about 20.0% to about 90.0% by weight of ammonium perchlorate; - 0% to about 25.0% by weight of aluminum; - 0 wt. % to about 5.0 wt. % combustion catalyst; - 0% to about 20% by weight of at least one additive.

[0012] In some embodiments, the polyester polyol has a weight average molecular weight of about 1000 g / mol to about 4000 g / mol, hi some embodiments, the polyester polyol contains 50 to 300 carbon atoms.

[0013] According to another aspect, the present invention relates to the use of the composite solid propellant described above as a fuel for a rocket, satellite or missile engine. [Brief explanation of the drawings]

[0014] [Figure 1] FIG. 1 shows the volume electrical resistivity of polymers and their corresponding binders. [Figure 2] FIG. 2 shows the mechanical properties at break of binders based on HTPB or polyester polyols. [Figure 3] FIG. 3 shows the comparative burn rates of typical HTPB or polyester polyol binder compositions. [Figure 4A] FIG. 4A shows the comparative tensile curves of a typical HTPB or polyester polyol binder composition obtained after baking or aging. [Figure 4B]FIG. 4B shows the comparative tensile curves of a typical HTPB or polyester polyol binder composition obtained after baking or aging. [Figure 4C] FIG. 4C shows the comparative tensile curves of a typical HTPB or polyester polyol binder composition obtained after baking or aging. DETAILED DESCRIPTION OF THE INVENTION

[0015] In one aspect, the present invention relates to a composite solid propellant comprising: - about 5.0% to about 20.0% by weight of a polyurethane-type crosslinked binder which is the reaction product of a polyester polyol and a polyisocyanate-type crosslinker in the presence of a crosslinking catalyst; about 20.0% to about 90.0% by weight of ammonium perchlorate; - 0% to about 25.0% by weight of aluminum; - 0 wt. % to about 5.0 wt. % combustion catalyst; - 0% to about 20% by weight of at least one additive.

[0016] Of course, the sum of the amounts of the various components of a composite solid propellant equals 100%.

[0017] Crosslinked binders of polyurethane type are obtained by crosslinking polyester polyols with at least one crosslinking agent of polyisocyanate type, which is generally present in controlled amounts, i.e. such that the NCO / OH crosslinking ratio (Rp) is between 0.7 and 1.5, advantageously such that this ratio is equal to 1. The OH functions are provided by the polyester polyol.

[0018] In some embodiments, the polyester polyol has a weight average molecular weight of from about 1000 g / mol to about 4000 g / mol, for example, from about 1500 g / mol to about 2500 g / mol.

[0019] In some embodiments, the polyester polyol contains from 50 to 300 carbon atoms, for example, from 100 to 200 carbon atoms.

[0020] Examples of polyester polyols suitable for use in the present invention include those sold under the trade name Priplast™ by Croda.

[0021] In some embodiments, the polyester polyol is derived from an acid monomer (preferably a diacid) and an alcohol monomer (preferably a diol). In certain embodiments, the acid monomer contains 4 to 50 carbon atoms, preferably 4 to 10 carbon atoms. In certain embodiments, the alcohol monomer contains 30 to 50 carbon atoms, preferably 32 to 40 carbon atoms.

[0022] For example, in the following simplified scheme of polyester synthesis, the rectangular blocks of diols are hydrocarbon structures with 30 to 50 carbon atoms. [ka]

[0023] Polyisocyanate-type crosslinking agents are suitable for crosslinking such polyester polyols. In some embodiments, known crosslinking agents are polyisocyanates selected from methyl diisocyanate (MDI), toluene diisocyanate (TDI), isophorone diisocyanate (IPDI), dicyclohexylmethylene diisocyanate (MDCI), hexamethylene diisocyanate (HDI), the trimer of the aforementioned hexamethylene diisocyanate (notably sold by 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 in (i) an amount necessary and sufficient to ensure crosslinking of the polyester polyol (but not in excess so as not to contaminate the resulting crosslinked article), and (ii) an amount such that the crosslinking ratio Rp is as defined above.

[0024] The reaction between the polyester polyol and the polyisocyanate-type crosslinker is carried out in the presence of a crosslinking catalyst, generally in an amount of about 0.1 ppm to about 10 ppm, preferably about 0.1 ppm to about 1 ppm, expressed relative to the weight of the composite solid propellant. In some embodiments, the crosslinking catalyst is selected from triphenylbismuth, dibutyltin dilaurate (TDBL), bismuth carboxylates such as bismuth octoate or bismuth neodecanoate (described in French Patent No. 3 102 476), and mixtures thereof.

[0025] The composite solid propellant according to the present invention includes about 20.0% to about 90.0% by weight, for example, about 60% to about 75% by weight, of ammonium perchlorate (oxidizing charge).

[0026] In some embodiments, the ammonium perchlorate contains the following different charges per 100% by weight: - 40-80% by weight of class A charge; - 5-35% by weight of class B charge; - 1-35% by weight of Class C charge.

[0027] In this disclosure, a "Class A charge" refers to a charge having a monomodal particle size distribution of D between 100 μm and 110 μm. 10 Value, D of 170 μm to 220 μm 50 value, and D of 315 μm to 340 μm 90 It means a charge having a value.

[0028] In this disclosure, a "Class B charge" refers to a charge having a monomodal particle size distribution of D between 15 μm and 20 μm. 10 Value, D of 60 μm to 120 μm 50 value, and D of 185 μm to 220 μm 90 It means a charge having a value.

[0029] In this disclosure, a "Class C charge" refers to a charge having a unimodal particle size distribution of D between 1.7 μm and 3.6 μm. 10 Value, D of 6 μm to 12 μm 50 value, and D of 20 μm to 32 μm 90 It means a charge having a value.

[0030] Value D 10 , D 50 , and D 90 denotes the diameter at which the cumulative volume percentage is equal to 10%, 50%, or 90%, respectively. These particle size values ​​are obtained from measurements carried out using a laser particle sizer (Mastersizer™ 3000 type or equivalent) according to the procedure defined by standard NF 11-666.

[0031] The composite solid propellant according to the present invention also includes 0% to about 25.0% by weight, such as about 15% to about 20% by weight, of aluminum (reducing charge).

[0032] In some embodiments, the aluminum reducing charge has a D of 30 μm or less. 50 It has a value.

[0033] The composite solid propellant according to the present invention also includes from 0% to about 5.0% by weight of a combustion catalyst.

[0034] In some embodiments, the combustion catalyst is selected from conventional combustion catalysts, such as lead salts and oxides, and bismuth citrate, the advantageous use of which as a combustion catalyst has been described by the applicant in WO 2016 / 066245.

[0035] Composite solid propellants according to the present invention may also include up to about 20.0% by weight of at least one additive.

[0036] In some embodiments, the at least one additive is selected from a plasticizer, an antiglare agent, an adhesive between a binder and an oxidizing charge, an antioxidant, and an energetic charge.

[0037] Examples of plasticizers include dioctyl azelate, diisooctyl sebacate, isodecyl pelargonate, polyisobutylene, and dioctyl phthalate, as well as energetic plasticizers such as triethylene glycol dinitrate.

[0038] Examples of antiglare agents include alkali metal-based compounds, sodium-based compounds (such as Na2SO4), especially potassium-based compounds (such as K2SO4, KNO3, K3AlF6, C4H5KO6), especially potassium salts such as potassium cryolite (K3AlF6) or potassium tartrate monobasic (C4H5KO6), the latter in the form of the L- or D-enantiomer or in racemic form. These particular potassium salts are suitable for use in conventional particle sizes (D1-300 μm). 50 It is commercially available in various forms (typically powders with particles having

[0039] Examples of adhesives between the binder and the oxidizing charge include bis(2-methylaziridinyl)methylaminophosphine oxide (methyl BAPO) or triethylenepentamine acrylonitrile (TEPAN).

[0040] Examples of antioxidants include those from the rubber industry, such as di-tertiarybutyl-paracresol (DBC) or 2,2'-methylene-bis(4-methyl-6-tert-butylphenol) (MBP5).

[0041] Examples of energetic charges include hexogen (RDX) or octogen (HMX).

[0042] Without limitation, composite solid propellants according to the present invention may be produced by a process including the following steps: - Forming a homogeneous paste by: (a) blending, by stirring, the components of the desired composite solid propellant, except for the crosslinking agent and crosslinking catalyst, into a polyester polyol as defined above at a temperature of about 30°C to about 70°C; and (b) stirring the resulting mixture under partial vacuum at a temperature of about 30°C to about 70°C; - incorporating into the formed homogeneous paste, under partial vacuum and at a temperature of about 30°C to about 50°C, the crosslinking agent and about 0.1 ppm to about 10 ppm of the crosslinking catalyst, and then stirring the resulting mixture; placing the mixture into at least one structure; and Heat treating the stirred-formed mixture that is introduced into the at least one structure.

[0043] The partial vacuum mentioned is intended to evacuate the medium to which it is applied. It is generally of the order of 10 millimeters of mercury (mmHg), although it is not necessarily of a constant strength.

[0044] The heat treatment (to crosslink the polyester polyol) is generally carried out at a temperature of about 30° C. to about 60° C. (30° C.≦T≦60° C.) for several days.

[0045] The solid composite propellants according to the present invention advantageously have a burning rate of less than about 10 mm / s, for example, about 6 mm / s to about 7 mm / s, and a pressure exponent of 0.2 to 0.5 over an operating pressure range of about 5 MPa to about 10 MPa. They are particularly suitable as rocket, satellite, or missile engine fuels. Their use for this purpose is particularly recommended. This is an important part of the present invention and constitutes another aspect thereof.

[0046] Another aspect of the present invention is the use of a polyester polyol as defined above as a precursor component of a polyurethane-type crosslinked binder in a solid propellant containing an ammonium perchlorate oxidizing charge, an aluminum reducing charge, and said binder.

[0047] According to another aspect, the present invention relates to a propellant charge containing at least one composite solid propellant as defined above. Such a charge is suitable for engines of satellites or missiles, as well as for engines for space launchers, such as those of the Ariane 5 rocket. The propellant charges contained in these engines have weights ranging from several hundred kilograms to several hundred tons.

[0048] According to another aspect, the invention relates to a rocket, satellite or missile engine comprising a propellant charge as defined above.

[0049] The invention will be better understood with the aid of the following examples, given by way of illustration. [Example]

[0050] Example 1

[0051] Binders were prepared from polyisocyanates and polymers (HTPB, R45HT™ (available from Cray Valley) or polyester polyols according to the invention, Priplast™ 1838 (available from Croda)), optionally in the presence of a plasticizer, dioctyl azelate (DOZ), according to the following procedure: - Stirring the polymer and plasticizer under partial vacuum at a temperature of 70°C for 60 minutes; - after cooling to a temperature of 50°C, combining the crosslinking agents MDCI and Desmodur N3300 with 3 pm of TDBL, then stirring the mixture formed; - Pouring the mixture into a mold; - Heat treatment at 50°C for 10 days.

[0052] The volume electrical resistivity (unit: Ω·m) and stress (expressed in MPa, Sm) of the resulting binders were then determined at 20 °C. Stress measurements were carried out according to standard NFT 70-315 using a uniaxial traction of 50 mm / min. The results are shown in Figures 1 and 2. As can be seen from these figures, interesting properties are obtained by using polyester polyol instead of conventional PBHT: the electrical resistivity is relatively low and the mechanical properties in tension are comparable.

[0053] Example 2

[0054] Propellants were produced using either conventional HTPB or polyester polyols according to the present invention in the following manner: - blending, with stirring, the components of the composite solid propellant (mainly 68% ammonium perchlorate (of composition A or B depending on the proportion of the ammonium perchlorate class used) and 20% aluminum) into the polymer, except for the crosslinking agent and crosslinking catalyst, at a temperature of 70°C; - stirring the resulting mixture under partial vacuum at a temperature of 70°C for 60 minutes; - combining the crosslinkers MDCI and Desmodur® N3300 with 0.15 pm of TDBL into a homogeneous paste formed under partial vacuum and at a temperature of 50°C, then stirring the mixture; - Pouring the mixture into a mold; - Heat treatment at 50°C for 2 weeks.

[0055] The burn rates (Vc) of these propellants were measured. The results are shown in Figure 3. The dotted curves represent the Vc of propellants containing ammonium perchlorate of composition A and either HTPB (upper curve) or polyester polyol (lower curve). The solid curves represent the Vc of propellants containing ammonium perchlorate of composition B and either HTPB (upper curve) or polyester polyol (lower curve).

[0056] Over the operating pressure range of 5 MPa to 10 MPa, a reduction in the burn rate (approximately -1 mm / s) for propellants containing polyester polyol is observed compared to propellants containing HTPB, regardless of the type of ammonium perchlorate used. The propellant energy performance was also determined. The results are shown in the table below.

[0057] [Table 1]

[0058] It should be noted that the energy performance of the two propellants is similar. The polyester polyol used in the present invention is a bio-based product with low density (0.96), low Tg (-63°C), and relatively poorer barrier properties (insulation) than HTPB, and can be advantageously used as a replacement for HTPB.

[0059] Example 3

[0060] The mechanical properties of the propellant obtained in Example 2 were measured after firing and accelerated aging. The results are shown in Figure 4. The dotted line shows the tensile curve of the propellant containing an HTPB binder. The solid line shows the tensile curve of the propellant containing a polyester polyol binder with the same charge distribution. While the mechanical properties of the propellant containing the polyester polyol binder are lower than those of the propellant containing the HTPB binder at the initial time t0, after accelerated aging at 60°C for 3 months under dry or humid conditions, the mechanical properties of the propellant containing the polyester polyol binder are higher than those of the propellant containing the HTPB binder aged under the same conditions.

Claims

1. Composite solid propellants comprising: - 5.0% to 20.0% by weight of a crosslinked binder of polyurethane type, which is the reaction product of a polyester polyol with a crosslinking agent of polyisocyanate type in the presence of a crosslinking catalyst; 20.0 to 90.0% by weight of ammonium perchlorate; - 0% to 25% by weight of aluminium; - 0% to 5.0% by weight of a combustion catalyst; - 0% to 20% by weight of at least one additive; wherein the polyester polyol is derived from alcohol monomers containing 30 to 50 carbon atoms, preferably 32 to 40 carbon atoms.

2. 2. The composite solid propellant of claim 1, wherein the polyester polyol has a weight average molecular weight of about 1000 g / mol to about 4000 g / mol, preferably about 1500 g / mol to about 2500 g / mol.

3. 3. A composite solid propellant according to claim 1 or 2, wherein the polyester polyol comprises from 50 to 300 carbon atoms, preferably from 100 to 200 carbon atoms.

4. 4. The composite solid propellant according to claim 1, wherein the crosslinking agent is selected from the group consisting of methyl diisocyanate, toluene diisocyanate, isophorone diisocyanate, dicyclohexylmethylene diisocyanate, hexamethylene diisocyanate trimer, biuret trihexane isocyanate, 3,5,5-trimethyl-1,6-hexamethylene diisocyanate, and mixtures thereof.

5. 5. The composite solid propellant according to claim 1, wherein the crosslinking catalyst is selected from the group consisting of triphenylbismuth, dibutyltin dilaurate, bismuth carboxylate, and mixtures thereof.

6. 6. A composite solid propellant according to any one of claims 1 to 5, wherein the combustion catalyst, if present, is selected from lead salts and oxides, and bismuth citrate.

7. Use of the composite solid propellant according to any one of claims 1 to 6 as a rocket, satellite or missile engine fuel.

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

9. A propellant charge comprising at least one composite solid propellant according to any one of claims 1 to 6.

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

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