Classifications

• • C—CHEMISTRY; METALLURGY
  • C06—EXPLOSIVES; MATCHES
  • C06B—EXPLOSIVES OR THERMIC COMPOSITIONS; MANUFACTURE THEREOF; USE OF SINGLE SUBSTANCES AS EXPLOSIVES
  • C06B45/00—Compositions or products which are defined by structure or arrangement of component of product
  • C06B45/04—Compositions or products which are defined by structure or arrangement of component of product comprising solid particles dispersed in solid solution or matrix not used for explosives where the matrix consists essentially of nitrated carbohydrates or a low molecular organic explosive
  • C06B45/06—Compositions or products which are defined by structure or arrangement of component of product comprising solid particles dispersed in solid solution or matrix not used for explosives where the matrix consists essentially of nitrated carbohydrates or a low molecular organic explosive the solid solution or matrix containing an organic component
  • C06B45/10—Compositions or products which are defined by structure or arrangement of component of product comprising solid particles dispersed in solid solution or matrix not used for explosives where the matrix consists essentially of nitrated carbohydrates or a low molecular organic explosive the solid solution or matrix containing an organic component the organic component containing a resin
  • C06B45/105—The resin being a polymer bearing energetic groups or containing a soluble organic explosive
• • C—CHEMISTRY; METALLURGY
  • C06—EXPLOSIVES; MATCHES
  • C06B—EXPLOSIVES OR THERMIC COMPOSITIONS; MANUFACTURE THEREOF; USE OF SINGLE SUBSTANCES AS EXPLOSIVES
  • C06B21/00—Apparatus or methods for working-up explosives, e.g. forming, cutting, drying
  • C06B21/0008—Compounding the ingredient
  • C06B21/0025—Compounding the ingredient the ingredient being a polymer bonded explosive or thermic component

Definitions

• the present invention relates to composite pyrotechnic products, which are suitable especially as propellant powders for barrel weapons (more particularly for tank artillery). It concerns composite pyrotechnic products, containing a high content of energetic charges in an energetic crosslinked binder. Said products are particularly advantageous, especially in terms of force (of energetic power), of vulnerability (see below a reminder regarding this notion, which is familiar to those skilled in the art), and of field of application as regards the nature of the charges they may contain. They may conveniently be optimized in terms of erosivity.
• a subject of the present invention is also a process for preparing said composite pyrotechnic products. Said process is particularly easy to perform. It does not require any solvent or any precipitation to carry out forming while the crosslinking begins, or any pre-crosslinking step.
• “Homogeneous” propellant powders constituted by one or more gelatinized energetic bases having a homogeneous appearance are known.
• “smokeless” powders based on nitrocellulose alone or based on a nitrocellulose-nitroglycerine mixture In order to improve the energy performance of these “homogeneous” powders, it is sought to incorporate therein organic (pulverulent) energetic charges. These charged powders no longer have a homogeneous appearance, but a heterogeneous appearance in which are distinguished, on the one hand, the energetic binder, and, on the other hand, the charges.
• Such charged powders are referred to as “composite” or “heterogeneous” powders. Such charged powders are described, for example, in French patent application FR 2 488 246.
• Vulnerability refers to the property that the powders have of being able to ignite and deflagrate under the effect of an undesired, random physical phenomenon, for instance the impact of a projectile. Vulnerability is a major defect for powders intended to be transported on combat tanks. The development of modern combat machines thus led those skilled in the art to seek sparingly vulnerable propellant powders.
• composite powders with an inert binder were proposed (constituted mainly of organic energetic charges in a synthetic resin). Such powders are markedly less vulnerable than homogeneous or composite powders with an energetic binder (nitrocellulose). However, since they contain an inert binder, these powders must, in order to deliver the necessary energy during their ignition, contain very high levels of charges, often in the region of 80% of the total weight of the powder. Composite powders with an inert binder thus have the characteristic of containing very little binder relative to their pulverulent charge.
• the precursor mixtures of these powders must, however, be able to be worked (in particular be able to be calendered or drawn through a die of relatively small diameter, usually comprising pins intended to create channels present in the final powder strand), and the powders must conserve their geometrical shape over time. It is particularly in reference to the production of these composite propellant powders with an inert binder for barrel weapons that those skilled in the art came up against and are still coming up against serious difficulties.
• thermoplastic binders thermosetting binders obtained from oligomers
• thermoplastic inert binders allow, in theory, while raising temperature, mechanical working of the product to give it the desired geometry.
• the working temperature at which the binder is deformable
• Patent application EP 0 036 481 describes a process for manufacturing composite explosives with a thermoplastic binder.
• Patent application IN 498/DEL/2001 describes a process for preparing propergol containing hexogen charges (RDX) in a thermoplastic binder.
• Composite products with a thermoplastic binder are generally not entirely satisfactory, since their mechanical properties are too sensitive to thermal variations.
• thermosetting inert binders obtained from oligomers
• polyurethane binders such as (crosslinkable) polyurethane binders
• thermosetting binders
• the first which consists in mixing in a blender the constituents of the resin with the energetic charges, in initiating crosslinking of the resin and, during crosslinking, in forming the product, within a very short space of time, as described, for example, in French patent applications FR 1 409 203 and FR 2 159 826.
• This technique requires precise control of the crosslinking kinetics in order to be able to work the paste and, as a result, it is difficult to manage at the industrial scale;
• the composite pyrotechnic products obtained via this second technique are constituted mainly, on the one hand, by a polymeric binder (for example polyurethane) obtained by reaction of a polyhydroxylated prepolymer (polymer) (with a number-average molecular weight of between 2000 and 5000 and a mean functionality of hydroxyl groups (OH greater than 2 and less than 3) (PBHT, polyether or polyester, for example) with a crosslinking agent (diisocyanate), and, on the other hand, by an energetic charge, preferentially of octogen (HMX) or of hexogen (RDX), in a content of about 80% by weight.
• a polymeric binder for example polyurethane
• PBHT polyhydroxylated prepolymer
• PBHT polyether or polyester, for example
• a crosslinking agent diisocyanate
• Said second technique consists:
• the technique under consideration thus comprises two polymerization or crosslinking steps, more precisely a first step of pre-crosslinking (or first crosslinking phase) with an amount of isocyanate that allows the production of a partially polymerized (crosslinked) paste, having mechanical strength and cohesion suitable for the implementation of the rest of the process (especially extrusion) and a second step of crosslinking leading to the final product with the desired crosslinked binder.
• said technique overcomes the two types of difficulty mentioned above (difficulty due to the lack of mechanical strength and cohesion of the product to be extruded and problem of the “pot life”).
• novel composite pyrotechnic products that are especially suitable as propellant powders for barrel weapons, containing a high content of charges in an energetic crosslinked binder.
• Said novel composite pyrotechnic products are optimized in terms of force (they contain a high content of energetic charges in an energetic binder), of vulnerability (they do not contain any nitrocellulose and may advantageously contain sparingly vulnerable energetic charges) and of production process (said process is easy to perform: without solvent, without precipitation for carrying out forming while the crosslinking begins, without pre-crosslinking) and they may also be optimized in terms of erosivity (they may advantageously contain EDNA charges in total or partial replacement for RDX charges).
• the present invention thus relates to novel composite pyrotechnic products. They are of the type comprising a crosslinked binder containing organic energetic charges (see above). Characteristically, their compositions, expressed as weight percentages, contain:
• the composite pyrotechnic products of the invention thus contain a high content of organic energetic charges: from 78% to 90% by weight, advantageously from 80% to 86% by weight.
• organic charges mineral charges having been set aside insofar as they generate solid particles
• organic energetic charges that are known per se and, for the most part, are already conditioned according to the prior art in a conventional organic polymeric binder (such as PBHT), especially crosslinked.
• the charges are advantageously hexogen (RDX), octogen (HMX), nitroguanidine (NGU), ethylene dinitramine (EDNA), N-guanylurea dinitramide (FOX 12 (GUDN)), 1,1-diamino-2,2-dinitroethylene (FOX 7 (DADE)), bis(triaminoguanidinium) 5,5′-azotetrazolate (TAGZT), dihydrazinium 5,5′-azotetrazolate (DHDZT), 5,5′-bis(tetrazolyl)hydrazine (HBT), bis(2,2-dinitropropyl)nitramine (BDNPN), a nitropyrazole, or a mixture of these energetic charges.
• RDX hexogen
• HMX octogen
• NGU nitroguanidine
• EDNA ethylene dinitramine
• GUDN N-guanylurea dinitramide
• FOX 7 DADE
• EDNA organic energetic charges are preferably found therein.
• a mixture of EDNA charges and of RDX charges is particularly preferably found therein. It is in no way excluded to find only RDX charges or only EDNA charges, but, as indicated above, mixtures of EDNA charges and of RDX charges make it possible to achieve an optimum with reference to the force/erosivity compromise. It has been understood that the more said mixtures contain RDX, the more energetic they are, but the more erosive they are.
• Energetic charges are in the form of solid grains homogeneously distributed in the crosslinked binder. These solid grains advantageously have, in a manner known per se, several particle size distributions.
• the binder This is present in a proportion of from 10% to 22% by weight, these 10% to 22% by weight including the 1% to 5% of gum.
• thermoset crosslinked
• binder which is obtained from a thermosetting (crosslinkable) polymer placed in contact with a gum. It is such an energetic binder, obtained from such an energetic polymer.
• a polymer should be understood as meaning “at least one polymer” throughout the present text. Specifically, it is in no way excluded from the context of the invention for a mixture of at least two polymers (each of the type indicated and having different molecular weights and/or different degrees of branching) to be used.
• the energetic polymer under consideration is a polyglycidyl azide (PGA).
• Mn number-average molecular weight
• Mn number-average molecular weight
• it must not be too liquid, so that a reasonable amount of gum suffices to thicken said mixture, which allows it to be formed (minimum mechanical strength and cohesion) before any crosslinking.
• Said polymer is a polyazide, whence 1) its energetic properties and 2) its capacity to be crosslinked with crosslinking agents other than isocyanates.
• crosslinking involves only 8% to 12% of its azide functions (such a low degree of crosslinking, performed on the polymer having the above molecular weight, allows the production of the final product with suitable mechanical properties). Said crosslinked polymer thus conserves its energetic properties.
• the binder for the composite pyrotechnic products of the invention is thus, as indicated above, an energetic binder. The force of said composite pyrotechnic products of the invention (containing a high content of energetic charges in a (crosslinked) energetic binder) is better understood.
• the crosslinked binder of the invention is thus obtained by crosslinking a prepolymer, as pointed out aboye, with at least one crosslinking agent containing alkyne functions, i.e. via triazole rings of formula:
• the at least one crosslinking agent used is a compound containing at least two propargyl functions in its chemical formula (”a polypropargyl“); it generally consists of a di- and/or tri-propargyl.
• it consists of dipropargyl succinate (DPS), dipropargyl maleate (DPM), tripropargyl tricarballylate (TCATP), the benzene ester of tripropargyl (BETP), and a dipropargyl poly(ethylene glycol) (PEG) with a number-average molecular weight of between 200 and 1500 g/mol.
• DPS dipropargyl succinate
• DPM dipropargyl maleate
• TCATP tripropargyl tricarballylate
• BETP the benzene ester of tripropargyl
• PEG dipropargyl poly(ethylene glycol)
• PEG dipropargyl poly(ethylene glycol)
• composition of the composite pyrotechnic products of the invention also contains a polymeric gum (“crude rubber”) of the stated type.
• Said gum a polymeric gum
• Such a gum is perfectly suitable for the purposes of the invention, insofar as it allows forming of the mixture to be crosslinked at a temperature below 100° C. (which is entirely compatible with the charges present), and does so without the use of solvent, without precipitation (for carrying out said forming while the crosslinking begins) and without any pre-crosslinking.
• Said gum is miscible with the polymer (PGA) (the gum/polymer mixture is “stable”, no exudation is observed). It exerts its (beneficial) action while being present in small amount (it represents a maximum of only 5% of the total weight of the product): its presence is therefore not detrimental in reference to the force of said products.
• the inventors have, to their credit, identified (selected) this type of gum, which is perfectly suitable for the purposes of the invention.
• Said gum generally consists of a polyurethane-polyester or a polyurethane-polyether gum, but mixtures of at least two gums (at least two polyurethane-polyester gums, at least two polyurethane-polyether gums or at least one polyurethane-polyester gum and at least one polyurethane-polyether gum; such mixtures of gums (gums within the meaning of the invention) constituting a gum within the meaning of the invention) having the required properties (recalled above) may be used.
• Said gum advantageously consists of a polyurethane-polyester gum.
• This gum thus participates upstream of the crosslinking process, upstream of the forming step, as a manufacturing auxiliary. It is the gum which gives, without danger, to the charged polymer, by virtue of its properties (sufficient molecular weight and adequate viscosity), the required cohesion and mechanical strength. It is this gum which allows the easy preparation, without solvent, without precipitation (for carrying out forming while the crosslinking begins) and without pre-crosslinking, of the composite pyrotechnic products of the invention. It acts, at suitable temperatures (below 100° C.), as a thickener and cohesion agent for said charged polymer. By intervening upstream of any crosslinking, said gum, a manufacturing auxiliary, thus allows the easy manufacture of the composite pyrotechnic products of the invention. It is finally found interlaced in the crosslinked polymer (PGA) network.
• PGA crosslinked polymer
• the crosslinked binder is thus the product resulting from the reaction, between the polymer (PGA) and the at least one crosslinking agent, performed in the presence of the gum and that it thus contains, besides said polymer crosslinked via triazole rings, said gum.
• composition of the composite pyrotechnic products of the invention is thus constituted essentially of the energetic charges and of the crosslinked binder (containing said gum). It may be constituted to 100% by weight of said energetic charges and of said crosslinked binder (containing said gum). It is generally thus constituted to at least 95% by weight, more generally to at least 98% by weight. In effect, it cannot be excluded for it to contain in addition at least one other additive; said gum, present in small amount, may quite rightly be considered as an additive: it is not an essential constituent of the binder, it is a manufacturing auxiliary whose intervention allows simple production of the desired product (according to the process described later in the present text).
• Such an at least one other additive when it is present, is generally present in a proportion of from 0.1% to 5% by weight, more generally in a proportion of from 0.1% to 2% by weight. It may especially be at least one other additive, chosen from formulation agents (candelilla wax and/or paraffin wax), (energetic or non-energetic) plasticizers and stabilizers.
• the composite pyrotechnic products of the invention are entirely suitable as propellant powders for barrel weapons. Said composite pyrotechnic products of the invention thus consist advantageously of such powders.
• the composite pyrotechnic products of the invention, as described above, are also suitable, especially, as tactical propergol, explosive composition and gas generator.
• the major advantage of the products of the invention becomes apparent from the foregoing text.
• the products are advantageous per se (in terms of force, vulnerability and wide field of application with reference to the nature of the charges) and insofar as they may be obtained via a process that is simple to perform (much easier to perform than the processes of the prior art).
• Said process constitutes the second subject of the present invention. It comprises:
• Said process thus comprises the provision of the (essential) constituent ingredients of the desired composite pyrotechnic products: the charges+the components, from which the crosslinked binder is obtained, i.e. the polymer, the at least one crosslinking agent and the gum. It has been indicated that the charges represent between 78% and 90% of the weight of the desired product, whereas the crosslinked binder represents between 10% and 22%, said 10% to 22% including the 1% to 5% of said gum (the remainder of said 1% to 5% corresponding to the product of reaction of the polymer and of the at least one crosslinking agent).
• Said at least one crosslinking agent is incorporated in an amount suitable for crosslinking the 8% to 12% of the azide functions of the polymer; it is generally incorporated to less than 5% by weight (more generally between 0.5% and 4%) of the reaction mixture. It is recalled here incidentally that additives, other than said gum, are liable to be incorporated.
• a pasty mixture is thus prepared, which is the precursor of the targeted final product (crosslinked).
• a pasty mixture is advantageously prepared with a twin-screw extruder (by extrusion) or with a two-roll mill, depending on the amounts to be used. It is generally prepared at a temperature of between 15° C. and 45° C. It may thus be prepared at room temperature or at a temperature above room temperature. In any case, incorporation of the gum allows said pasty mixture to be obtained, which can be manipulated and formed.
• At least one element is prepared (n elements are thus generally prepared) in a desired form (directly that desired for the final product(s) or an “intermediate” form from which, after crosslinking (and generally chopping), said final product(s) having the desired form are obtained).
• Said third step is thus analyzed as a step of forming the paste.
• This forming may especially comprise spinning or calendering. After such spinning (performed in a press cylinder, having an outlet orifice of more or less substantial diameter), a spun product is obtained. This spun product is generally heat-treated for crosslinking and then chopped into strands (of the desired length).
• Such strands which are suitable as propellant powders for barrel weapons, generally have a length of from 2 to 20 mm, for a diameter of from 1 to 20 mm (more generally for a diameter of from 2 to 15 mm). However, it is not excluded to chop the spun product (as strands which are thus not crosslinked) and then to crosslink said strands. On conclusion of such calendering, the calendered product, in the form of a plate (such a plate generally has a thickness of from 10 to 20 mm), may be chopped directly into platelets or heat-treated for crosslinking and then chopped into platelets.
• steps b and c of said process may comprise:
• the pasty mixture, formed into the desired form for the final product or into an intermediate form, is then heat-treated.
• the heat treatment must make it possible to ensure the expected result (crosslinking of the polymer) at a temperature that is not excessive (compatible with the presence of the energetic charges in a high content). Generally, said temperature is above 45° C. and remains below 80° C.
• the crosslinking is performed at 55° C. ( ⁇ 5° C.).
• Said at least one heat-treated element corresponds to the at least one desired product of the invention or makes it possible to obtain same, generally by chopping.
• EDNA ethylene dinitramine
• nitric acid was introduced into a jacketed 50 cm 3 reactor. The nitrating bath was then cooled to a reaction temperature of 0° C. Once said bath reached 0° C., the introduction of imidazolidone was commenced. This reagent was introduced slowly so as not to exceed 20° C. The DNEU precipitated as soon as its concentration in the medium was greater than 23% by weight. The introduction of imidazolidone into the heterogeneous medium (nitrating bath+solid DNEU) was continued.
• the mixture was poured into a bath of cold water at about 5° C. with stirring.
• the solid was then separated from the mother liquors by filtration, and washed several times with distilled water to neutral pH, then drained by suction. It was then taken up, in wet form, for the synthesis of EDNA.
• the decarboxylation step was performed by addition of DNEU to a hot aqueous solution buffered with sodium acetate. Evolution of gas (of CO 2 ) was observed, which necessitated portionwise introduction of the powder.
• the reaction medium was then cooled to make the EDNA precipitate.
• the suspension was then filtered and then dried. A yield of 85% was obtained.
• PEG-1000 50 g was first introduced into a 100 mL three-necked flask; this flask was heated to a temperature of 45-50° C. to be able to be stirred. Next, sodium hydroxide at 40% by weight (6 g) was added, followed by dropwise addition of propargyl bromide, as a solution at 80% by weight in toluene (13.36 ml, 0.12 mol), with stirring. The medium was maintained at 65° C. for a period of 36 hours. At the end of reaction, 150 ml of dichloromethane were added to the reaction medium, cooled to room temperature. The resulting medium was then washed with water until a pH of the washing waters equal to 7 was obtained. The organic solution was then dried and the solvent was evaporated off.
• the recovered product (35 g) was in the form of a wax.
• Composite pyrotechnic products of the invention of two types were prepared and tested. Their weight composition and their force (measured) are given, respectively, in Tables 1 and 2 below. Below each of said Tables 1 and 2, other characteristics of said products are indicated.
• Step b of the process of the invention the pasty mixtures were obtained in a two-roll mill, in a manner known per se.
• the gum was first introduced between the rollers of the two-roll mill (rolling mill), brought to a temperature of 38° C. It was thus softened.
• a charges+PGA mixture prepared beforehand in a container
• Candelilla wax formulating agent
• the crosslinking agent were then successively added to the resulting mixture (in a —C ⁇ CH/—N 3 ratio equal to 10).
• Step c of the process of the invention the pasty mixtures obtained were introduced into a press cylinder heated to 38° C. to perform spinning at a pressure of between 180 and 220 bar.
• Step d of the process of the invention the heat treatment of the spun product was performed at 50° C. for 5 days. After chopping (of the crosslinked spun product), powder strands were obtained (diameter: 10 mm, length: 11 mm).
• Weight per unit volume 1.619 g/cm 3 .
• Weight per unit volume 1.635 g/cm 3 .

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• 2013
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