EP3812356A1 - Composite solid propellant - Google Patents

Abstract

The invention relates to a composite solid propellant comprising, in a crosslinked inert binder of polyurethane type, an oxidizing charge of ammonium perchlorate and optionally a reducing charge of aluminum, the inert binder being crosslinked with an organic salt of bismuth.

Description

Field of the invention

The present invention relates to the field of rocket engine propulsion, and more particularly to composite solid propellants based on an inert binder of the polyurethane type.

State of the art

Today, in the space field, the propellants used in the propulsion of space launchers are composite propellants with a crosslinked inert binder of the polyurethane type and conventionally contain charges of ammonium perchlorate (oxidizing charge) and aluminum ( reducing charge).

The crosslinked inert binder of polyurethane type is conventionally obtained by crosslinking a liquid polymer polyol with at least one crosslinking agent, in the presence of at least one crosslinking catalyst. The crosslinking agent is generally chosen from polyisocyanates, and the crosslinking catalyst is generally chosen from iron or copper acetylacetonate, or advantageously tin dibutyldilaurate (DBTL) which is the reference catalyst for the type of application envisaged. The crosslinking is typically carried out by heating the propellant paste at a temperature of about 50 ° C for 10 days. These crosslinking conditions, however, generate a non-negligible cost, corresponding to the curing step and the associated material investments, as well as significant residual stresses on thermal shrinkage.

It is therefore desirable to be able to reduce the duration and / or the crosslinking temperature in order, on the one hand, to limit the occupancy time of the reaction wells as much as possible and, on the other hand, to reduce the thermal shrinkage and therefore the specifications on the reaction well. propellant loading design.

It is in this context that the present invention was carried out, and it is to the credit of the inventors to have developed a catalytic system for crosslinking the liquid polymer polyol which can be implemented at low temperature without affecting the properties of the liquid. resulting solid propellant.

Summary of the invention

According to a first aspect, the invention relates to a composite solid propellant containing, in a crosslinked inert binder of polyurethane type, an oxidizing charge of ammonium perchlorate and optionally a reducing charge of aluminum, the crosslinked inert binder. being obtained by crosslinking a liquid polymer polyol in the presence of at least one crosslinking agent of polyisocyanate type, in an amount such that the NCO / OH bridging ratio is between 0.75 and 1, and at least a crosslinking catalyst chosen from organic salts of bismuth.

According to another aspect, the invention relates to the use of an organic salt of bismuth in the preparation of a composite solid propellant.

According to another aspect, the invention relates to a rocket launcher (or rocket) engine comprising a charge of propellant as defined above.

Brief description of the figures

• The figure 1 represents the stress of an inert crosslinked binder used in the context of the invention.
• The figure 2 represents the elongation at break of a crosslinked inert binder used in the context of the invention.
• The figure 3 represents the consumption of the NCO functions of a crosslinked inert binder used in the context of the invention and of an inert reference binder.
• The figure 4 represents the evolution over time of the hardness of a composite propellant in accordance with the invention.

Legend of figures

• DBTL = dibutyldtin dilaurate
• OZn = zinc octoate
• OBi = bismuth octoate
• IPDI = isophorone diisocyanate

Description of the invention

According to a first aspect, the invention relates to a composite solid propellant containing, in a crosslinked inert binder of polyurethane type, an oxidizing charge of ammonium perchlorate and optionally a reducing charge of aluminum, the crosslinked inert binder being obtained by crosslinking of 'a liquid polymer polyol in the presence of at least one crosslinking agent chosen from polyisocyanates, in an amount such that the NCO / OH bridging ratio is between 0.75 and 1, and at least one crosslinking catalyst chosen from organic salts of bismuth. The mass of oxidizing charge represents about 60% to about 86% of the total mass of the composite solid propellant. The mass of reducing charge represents up to about 20% of the total mass of the composite solid propellant.

In one embodiment, the liquid polymer polyol is a hydroxytelechelic polybutadiene (PBHT), such as, for example, those sold under the Poly bd® range by the company Cray Valley.

In one embodiment, the crosslinking agent is an alicyclic polyisocyanate, such as advantageously dicyclohexylmethylene diisocyanate (MDCI) or isophorone diisocyanate (IPDI). The polyisocyanate (s) is (are) used in an amount such that the NCO / OH bridging ratio is advantageously between 0.75 and 1.0, preferably this ratio is equal to approximately 0, 85.

dans laquelle R₁, R₂ et R₃ représentent chacun indépendamment un alkyle en C₅-C₁₁ linéaire ou ramifié, de préférence R₁, R₂ et R₃ sont identiques.In one embodiment, the crosslinking catalyst is a bismuth carboxylate. It will easily be understood that since the valence of bismuth is +3, the organic salt of bismuth will have three “carboxylate” units bonded to the bismuth atom, as represented by the formula:

wherein R ₁ , R ₂ and R ₃ each independently represent linear or branched _{C 5} -C _{11 alkyl, preferably R 1} , R ₂ and R ₃ are the same.

Preferably, the organic salt of bismuth is bismuth octoate or bismuth neodecanoate.

The composite solid propellant can also comprise at least one plasticizer and / or at least one additive.

In one embodiment, the plasticizer is chosen from dioctyl azelate (DOZ), diisooctyl sebacate (DOS), dioctyl adipate (DOA), isodecyl pelargonate, polyisobutylene, dioctyl phthalate (DOP).

In one embodiment, the additive is chosen from adhesion agents, such as for example bis (2-methylaziridinyl) - methylaminophosphine (methyl BAPO) or triethylene pentamine acrylonitrile (TEPAN) oxide, antioxidants derived from those from the rubber industry, such as ditertiobutylparacresol (DBPC) or 2,2'-methylene-bis (4-methyl-6-tertio-butylphenol) (MBP5), combustion catalysts such as for example iron oxide.

• environ 60% à environ 75% en masse de charge oxydante de perchlorate d'ammonium,
• environ 15% à environ 20% en masse de charge réductrice d'aluminium,
• environ 5% à environ 15% en masse de liant inerte réticulé ;
• éventuellement, le complément à 100% en masse d'au moins un plastifiant et/ou d'au moins un additif, avantageusement la quantité de plastifiant(s) et/ou d'additif(s) ne dépasse pas 10% en masse.

In one embodiment, the composite solid propellant contains from about 15% to about 20% by weight of reducing aluminum filler. In an advantageous variant, the composite solid propellant contains:

• about 60% to about 75% by mass of ammonium perchlorate oxidizing charge,
• about 15% to about 20% by mass of reducing aluminum filler,
• about 5% to about 15% by weight of crosslinked inert binder;
• optionally, the remainder to 100% by mass of at least one plasticizer and / or at least one additive, advantageously the amount of plasticizer (s) and / or additive (s) does not exceed 10% by mass.

• environ 60% à environ 86% en masse de charge oxydante de perchlorate d'ammonium,
• moins de 4% en masse de charge réductrice d'aluminium (c'est-à-dire de 0% à < 4%),
• environ 5% à environ 15% en masse de liant inerte réticulé ;
• éventuellement, le complément à 100% en masse d'au moins un plastifiant et/ou d'au moins un additif, avantageusement la quantité de plastifiant(s) et/ou d'additif(s) ne dépasse pas 10% en masse.

In one embodiment, the composite solid propellant contains less than 4% by weight of reducing aluminum filler. In an advantageous variant, the composite solid propellant contains:

• about 60% to about 86% by mass of ammonium perchlorate oxidizing charge,
• less than 4% by mass of reducing aluminum filler (i.e. from 0% to <4%),
• about 5% to about 15% by weight of crosslinked inert binder;
• optionally, the remainder to 100% by mass of at least one plasticizer and / or at least one additive, advantageously the amount of plasticizer (s) and / or additive (s) does not exceed 10% by mass.

In one embodiment, the reducing aluminum filler has a median diameter (D ₅₀ ) less than or equal to 30 μm. Advantageously, the aluminum charge consists of a single charge whose monomodal distribution has a median diameter value (D ₅₀ ) of less than 15 μm (D ₅₀ <15 μm) or that it is distributed according to the two monomodal distributions.

• * une première charge dont la distribution granulométrique monomodale présente une valeur de D₁₀ comprise entre 100 µm et 110 µm, une valeur de D₅₀ comprise entre 170 µm et 220 µm et une valeur de D₉₀ comprise entre 315 µm et 340 µm,
• * une seconde charge dont la distribution granulométrique monomodale présente une valeur de D₁₀ comprise entre 15 µm et 20 µm, une valeur de D₅₀ comprise entre 60 µm et 120 µm et une valeur de D₉₀ comprise entre 185 µm et 220 µm ; et
• * une troisième charge dont la distribution granulométrique monomodale présente une valeur de D₁₀ comprise entre 1,7 µm et 3,6 µm, une valeur de D₅₀ comprise entre 6 µm et 12 µm et une valeur de D₉₀ comprise entre 20 µm et 32 µm.

In one embodiment, the oxidizing charge of ammonium perchlorate is distributed according to the three monomodal distributions specified below:

• * a first charge whose monomodal particle size distribution has a D ₁₀ value between 100 µm and 110 µm, a D ₅₀ value between 170 µm and 220 µm and a D ₉₀ value between 315 µm and 340 µm,
• * a second filler whose monomodal particle size distribution has a value of D ₁₀ between 15 μm and 20 μm, a value of D ₅₀ between 60 μm and 120 μm and a value of D ₉₀ between 185 μm and 220 μm; and
• * a third load, the monomodal particle size distribution of which has a D ₁₀ value between 1.7 µm and 3.6 µm, a D ₅₀ value between 6 µm and 12 µm and a D ₉₀ value between 20 µm and 32 µm.

• D₁₀ représente le diamètre pour lequel le pourcentage volumique cumulé est égal à 10% ;
• D₅₀ représente le diamètre pour lequel le pourcentage volumique cumulé est égal à 50% ;
• D₉₀ représente le diamètre pour lequel le pourcentage volumique cumulé est égal à 90%.

As indicated in the request WO 2011/001107 , the results of the particle size measurements of a particle size class are conventionally expressed in the form of curves giving, on the one hand, the histogram of the volume percentages of particles (also called passing volume percentages) as a function of the diameter (equivalent spherical) particles and, on the other hand, the accumulation of the volume percentages of particles as a function of the diameter (equivalent spherical) of the particles, accumulation carried out according to the increasing diameters. So :

• D ₁₀ represents the diameter for which the cumulative volume percentage is equal to 10%;
• D ₅₀ represents the diameter for which the cumulative volume percentage is equal to 50%;
• D ₉₀ represents the diameter for which the cumulative volume percentage is equal to 90%.

These particle size data are obtained from measurements carried out by means of a laser particle size analyzer (Mastersizer ™ 3000 type or equivalent), according to an operating mode defined by standard NF 11-666.

The composite solid propellant of the invention is particularly advantageous, in particular if one considers the combustion residues that it generates. In particular, the aforementioned distribution of the oxidizing charge of ammonium perchlorate in the solid propellant makes it possible to minimize, during the combustion of the latter in a rocket engine, combustion instabilities of the thermo-acoustic type (cf. WO 2011/001107 ).

Thus, according to another aspect, the invention relates to a rocket launcher (or rocket) engine comprising a charge of composite solid propellant as defined above; such a propellant loading is particularly suitable for launchers of the Ariane 5 rocket.

dans laquelle R₁, R₂ et R₃ représentent chacun indépendamment un alkyle en C₅-C₁₁ linéaire ou ramifié, de préférence R₁, R₂ et R₃ sont identiques.According to another aspect, the invention relates to the use of an organic salt of bismuth as a catalyst for crosslinking a composite solid propellant containing a binder based on liquid polymer polyol. The organic salt of bismuth is advantageously a bismuth carboxylate, in particular represented by the formula:

wherein R ₁ , R ₂ and R ₃ each independently represent linear or branched _{C 5} -C _{11 alkyl, preferably R 1} , R ₂ and R ₃ are the same.

The use of an organic bismuth salt, in the preparation of a composite solid propellant containing a binder based on liquid polymer polyol, makes it possible to simplify the manufacture of said propellant, without altering the mechanical properties of the latter, by operating at crosslinking temperatures less than or equal to 50 ° C, in particular less than or equal to 40 ° C. Moreover, the fact of being able to lower the crosslinking temperature results in an energy gain, in particular when working on large quantities of propellant paste (of the order of around one hundred kilograms or more).

The invention will be better understood with the aid of the examples below, given purely by way of illustration. In these examples, the percentages indicated are percentages by weight, unless otherwise indicated.

Example 1

A mixture of 74.04% Poly bd® R45HT, 24.43% DOZ plasticizer and 1.53% antioxidant (DBPC + MBP5) was mixed under vacuum and then the mixture was degassed at 70 ° C, still under vacuum for 1 hour. MCDI was then added at 50 ° C. so as to have an NCO / OH bridging ratio equal to 0.9, then 3 ppm of DBTL as crosslinking catalyst. The mixture obtained was poured into plate molds 4 mm thick for baking at 30 ° C. for at least 1.5 months in order to reach a stabilized state. H2 specimens were cut to test the mechanical properties (stress (Sm), elongation at break (em)) of the crosslinked binder. The measurements were carried out by uniaxial traction at 50 mm / min, in accordance with Standard NFT70-315. The results are presented on the figures 1 and 2 .

Example 2

The procedure of Example 1 was repeated but using 2000 ppm zinc octoate as the reaction catalyst instead of DBTL and allowing the crosslinking reaction to continue at 30 ° C. The result of the evaluation of the mechanical properties of the crosslinked binder is presented on the figures 1 and 2 .

Example 3

The procedure of Example 1 was repeated but using 15 ppm of bismuth octoate as the reaction catalyst in place of DBTL and allowing the crosslinking reaction to continue at 30 ° C. The result of the evaluation of the mechanical properties of the crosslinked binder is presented on the figures 1 and 2 .

Example 4

The procedure of Example 1 was repeated but replacing MDCI with IPDI and using 5 ppm DBTL, and allowing the crosslinking reaction to continue at 30 ° C. The result of the evaluation of the mechanical properties of the crosslinked binder is presented on the figures 1 and 2 .

As can be seen on the figures 1 and 2 , the use of a reaction catalyst of organic bismuth salt type (Example 3) makes it possible to obtain a crosslinked binder with a higher stress (Sm) associated with a lower strain (em). These mechanical properties appear earlier (before 20 days) compared to the other binders tested.

Example 5

• soit 3 ppm de DBTL, en laissant la réaction de réticulation se poursuivre à 50°C,
• soit 5 ppm d'octoate de bismuth, en laissant la réaction de réticulation se poursuivre à 30°C.

A mixture of 98% Poly bd® R45HT and 2% antioxidant (DBPC + MBP5) was mixed under vacuum and then the mixture was degassed at 65 ° C., still under vacuum, for 1 hour 30 minutes. MDCI was then added so as to have an NCO / OH bridging ratio equal to 0.9 then:

• or 3 ppm of DBTL, allowing the crosslinking reaction to continue at 50 ° C,
• or 5 ppm of bismuth octoate, allowing the crosslinking reaction to continue at 30 ° C.

Fourier transform infrared spectroscopy (IRTF) was monitored in order to understand the characteristic reaction time on these mixtures. To use the measurements, the response studied was normalized by a stable spectrum band, ie the band of aliphatic functions at 2100 cm ^-1 . As can be seen on the figure 3 , quite similar results are obtained with the two mixtures.

Example 6

A mixture of Poly bd® R45HT, DOZ plasticizer, antioxidant (DBPC + MBP5) and 40 μm aluminum was mixed under vacuum, then the mixture was degassed at 70 ° C., still under vacuum, for 1 hour. Ammonium perchlorate was then added, the medium was kneaded under vacuum for 1 hour at 70 ° C, was cooled to 50 ° C and then MCDI was added at 50 ° C so as to have a bridging ratio NCO / OH equal to 0.82, then 5 ppm of bismuth octoate, as crosslinking catalyst. The proportions of the various constituents of the mixture (before addition of the MCDI and of the crosslinking catalyst) are reported in Table 1. The mixture was then poured into capsules as well as in the form of test tubes, then the whole was placed in cooking at 30 ° C. The hardness was measured on the capsules once a day after the first week of cooking. As can be seen on the figure 4 , the hardness no longer changes after 20 days of cooking at 30 ° C. The mechanical properties (hardness (E), stress (Sm), elongation at break (em)) of the test pieces after firing are collated in Table 2.

Example 7

The procedure of Example 6 was repeated but using DBTL as the reaction catalyst in place of bismuth octoate. The mechanical properties of the test pieces were tested after 10 days of baking at 50 ° C; the results are collated in Table 2. Table 1 Component % Poly bd® R45HT 9.7 DOZ 3.2 DBPC + MBP5 0.2 aluminum 20.0 ammonium perchlorate 66.9 Example E (MPa) Sm (MPa) em (%) 6 7.2 1.0 38.7 7 8.8 1.12 37.1

Claims (11)

Composite solid propellant containing, in a crosslinked inert binder of polyurethane type, an oxidizing filler of ammonium perchlorate and a reducing aluminum filler, the crosslinked inert binder being obtained by crosslinking a liquid polymer polyol in the presence of at least a crosslinking agent chosen from polyisocyanates, in an amount such that the NCO / OH bridging ratio is between 0.75 and 1, and at least one crosslinking catalyst chosen from organic salts of bismuth. A composite solid propellant according to claim 1, wherein the liquid polymer polyol is a hydroxytelechelic polybutadiene. A composite solid propellant according to claim 1 or claim 2, wherein the crosslinking agent is an alicyclic polyisocyanate. A composite solid propellant according to any one of claims 1 to 3, wherein the crosslinking agent is used in an amount such that the NCO / OH bridging ratio is between 0.75 and 1.0. A composite solid propellant according to any one of claims 1 to 4, wherein the crosslinking catalyst is a bismuth carboxylate. A composite solid propellant according to claim 5, wherein the bismuth carboxylate is bismuth octoate or bismuth neodecanoate. A composite solid propellant according to any one of claims 1 to 6, which contains: - from 60 to 75% by mass of ammonium perchlorate oxidizing charge, - from 15 to 20% by mass of reducing aluminum filler, - from 5 to 15% by mass of crosslinked inert binder; - optionally, the remainder to 100% by mass of at least one plasticizer and / or at least one additive. A composite solid propellant according to any one of claims 1 to 6, which contains: - from 60 to 86% by mass of ammonium perchlorate oxidizing charge, - less than 4% by mass of reducing aluminum filler, - from 5 to 15% by mass of crosslinked inert binder; - optionally, the remainder to 100% by mass of at least one plasticizer and / or at least one additive. A rocket or rocket launcher engine comprising a composite solid propellant charge as defined in any one of claims 1 to 8. Use of an organic bismuth salt as a catalyst for crosslinking a composite solid propellant containing a binder based on liquid polymer polyol. Use according to claim 10, wherein the organic salt of bismuth is a bismuth carboxylate, preferably bismuth octoate or bismuth neodecanoate.

Images