HIGH PERFORMANCE COMPOSITE PYROTECHNIC PRODUCT WITHOUT Pb IN ITS COMPOSITION, AND PREPARATION THEREOF

Abstract

A high performance composite pyrotechnic product without lead in its composition, and that can be obtained on an industrial scale without encountering a problem of potlife for the intermediate paste, the product containing organic energetic charges and a combustion catalyst in a plasticized binder including a cured energetic polymer and at least one energetic plasticizer. In characteristic manner, the cured energetic polymer consists of a glycidyle azide polymer (GAP) having number average molecular weight (Mn) lying in the range 700 g/mol to 3000 g/mol, cured via its hydroxyl terminal functions with at least one curing agent of polyisocyanate type; and the combustion catalyst consists of bismuth citrate.

Claims

1. A composite pyrotechnic product containing organic energetic charges and a combustion catalyst in a plasticized binder comprising a cured energetic polymer and at least one energetic plasticizer, wherein: said cured energetic polymer consists of a glycidyle azide polymer (GAP) having number average molecular weight (Mn) lying in the range 700 g/mol to 3000 g/mol, cured via its hydroxyl terminal functions with at least one curing agent of polyisocyanate type; and said combustion catalyst consists of bismuth citrate.

2. The composite pyrotechnic product according to claim 1, wherein said glycidyle azide polymer (GAP) has number average molecular weight (Mn) lying in the range 1700 g/mol to 2300 g/mol.

3. The composite pyrotechnic product according to claim 1, wherein said at least one energetic plasticizer is of the nitrate and/or nitramine type.

4. The composite pyrotechnic product according to claim 1, wherein said organic energetic charges are selected from: hexogen, octogen, hexanitrohexaazaisowurtzitane, nitroguanidine, ethylene dinitramine, N-guanylurea dinitramide, 1,1 -diamino-2,2-dinitro ethylene, bis(triaminoguanidinium)-5,5-azotetrazolate, dihydrazinium 5,5-azotetrazolate, 5,5-bis(tetrazolyl)hydrazine, bis(2,2-dinitropropyl) nitramine, and nitropyrazole charges, and mixtures of such charges.

5. The composite pyrotechnic product according to claim 1, containing 1% to 6% by weight, of said bismuth citrate.

6. The composite pyrotechnic product according to of claim 1, further containing at least one additive.

7. The composite pyrotechnic product according to claim 6, wherein said at least one additive comprises at least one curing catalyst and/or at least one stabilizer agent for said at least one energetic plasticizer.

8. The composite pyrotechnic product according to claim 1, wherein in that its composition contains the following, expressed in percentages by weight: 50% to 70% of said organic energetic charges; 10% to 14% of said cured energetic polymer; 10% to 30% of said at least one energetic plasticizer; 1% to 6%, of said bismuth citrate; and 0 to 4%, of at least one additive.

9. A method of preparing a composite pyrotechnic product according to claim 1, comprising: preparing a homogeneous paste by: a) incorporating, at a temperature lying in the range 35 C. to 55 C., in said glycidyle azide polymer, said at least one energetic plasticizer, organic energetic charges, and other ingredients constituting said desired composite pyrotechnic product with the exception of any curing agent and any curing catalyst; and b) stirring the resulting mixture under a partial vacuum at a temperature lying in the range 35 C. to 55 C.; under a partial vacuum, at a temperature lying in the range 35 C. to 55 C., incorporating in said resulting homogeneous paste, said at least one curing agent and optionally at least one curing catalyst, followed by stirring the resulting mixture; casting said stirred resulting mixture in at least one structure; and heat treating said cast stirred resulting mixture in said at least one structure.

10. The composite pyrotechnic product according to claim 5, containing 3% to 5% by weight of said bismuth citrate.

11. The composite pyrotechnic product according to claim 8, wherein its composition contains, expressed in percentages by weight, 55% to 65% of said organic energetic charges.

12. The composite pyrotechnic product according to claim 8, wherein its composition contains, expressed in percentages by weight 15% to 25% of said at least one energetic plasticizer.

13. The composite pyrotechnic product according to claim 8, wherein its composition contains, expressed in percentages by weight, 3% to 5% of said bismuth citrate.

14. The composite pyrotechnic product according to claim 8, wherein its composition contains, expressed in percentages by weight, 0.1% to 4% of said at least one additive.

Description

[0062] The invention is illustrated below by the following examples. More precisely, there follow Examples A, B1, and B2 illustrating the prior art, Examples 1 and 2 illustrating the invention, and comparative Examples C1 and C2.

[0063] Examples 1 and 2 relate to propellants of the invention that include in their composition hexogen (RDX) charges, a binder based on an energetic polymer of hydroxytelechelic PAG type (sold by the supplier Eurenco (Mn (number average molecular weight)=1900 (g/mol) that has been cured (by hexamethylene diisocyanate trimer sold by the supplier Bayer under the trade name Desmodur N 3300), and plasticized (by a mixture of two energetic plasticizers (BTTN/TMETN; 30/70 (% by weight), stabilizer agents for said plasticizers (MNA/2-NDPA; 75/25 (% by weight)), and bismuth citrate as ballistic catalyst (at a content by weight of 1% in Example 1 and a content by weight of 4% in Example 2).

[0064] Said propellants of Examples 1 and 2 have been compared with reference propellants, one of which (Ref. 1) had no ballistic catalyst in its composition (Example A), and the other of which (Ref. 2) had lead citrate as ballistic catalyst in its composition at contents by weight of 1% (Example B1) and of 3.5% (Example B2).

[0065] Two comparative examples are also described with propellants similar to the propellant of Example 2 of the invention, but including, as ballistic catalysts, bismuth subsalicylate (C1) and bismuth carbonate (C2), replacing bismuth citrate.

[0066] The compositions of these propellants (more precisely the compositions of their pastes prior to curing) are set out in Table 1 below.

[0067] The same ingredients were naturally used for all of the examples. Concerning the RDX charges, they were constituted by 68% by weight of an RDX having a grain size class of 0-100 micrometers (m) and 32% by weight of RDX having a grain size class of 2.5 m-5 m.

TABLE-US-00001 TABLE 1 Propellants (% by weight) Comparative Ref. 1 Ref. 2 Examples examples Ingredients (% by weight) A B1 B2 Ex. 1 Ex. 2 C1 C2 Plasticized Energetic polymer PAG 10.63 10.63 9.63 10.63 9.63 9.63 9.63 binder Curing agent Desmodur N 3300 2.01 2.01 2.01 2.01 2.01 2.01 2.01 Plasticizers BTTN/TMETN 20.7 20.7 19.7 20.7 19.7 19.7 19.7 Plasticizer stabilizer agents MNA/2-NDPA 0.8 0.8 0.8 0.8 0.8 0.8 0.8 (additive) Charges Organic energetic charges RDX 64 63 62.5 63 62 62 62 Combustion Combustion catalyst Pb citrate 1 3.5 additive Bi citrate 1 4 Bi subsalicylate 4 Bi carbonate 4 Other Processing auxiliaries 1.86 1.86 1.86 1.86 1.86 1.86 1.86 additive

[0068] Composite pyrotechnic products (propellants) were thus prepared presenting the compositions by weight given in Table 1 above. For that purpose, the method set out below was performed (see the following paragraph headed Preparation).

[0069] Attention was paid to the pot lives of the propellant pastes (intermediates) that were prepared. Said potlife was determined by performing viscosity measurements as described below (see the paragraph below headed Determining the potlife). The results appear in the first portion of Table 2 below.

[0070] In its second portion, said Table 2 also contains the burn rate results as measured at different pressures, on the propellants as finally obtained.

Preparation

[0071] The following were introduced into a mixer: glycidyl azide polymer (GAP) as a binder precursor polymer; followed by the plasticizers (BTTN/TMETN) and the stabilizing agents (MMA/2-NDPA) for said plasticizers. The mixture was mixed for 15 minutes (min) at a temperature of 40 C.

[0072] Thereafter, the following were added to said mixture under stirring: the organic energetic charges (RDX) in portions; followed by the additives (other than the curing agent and catalyst (Desmodur N 3330 and DBTL)); and the combustion catalyst. Stirring was then continued for 2 h 30 min, still at the temperature of 40 C. and under a vacuum of 10 mmHg (to enable the medium to degas), in order to obtain a homogeneous paste.

[0073] The curing catalyst (DBTL (55 ppm)) was then added to said homogeneous paste and the medium continued to be stirred for 30 min prior to adding the curing agent for the binder. Said curing agent (Desmodur N 3300) was finally added, and the medium continued to be stirred for 15 min (still at 40 C. and under a vacuum).

[0074] Propellant paste was thus prepared in 2 kilogram (kg) batches.

[0075] A sample was taken of each of the propellant pastes as prepared in that way in order to determine potlife.

[0076] The remainder of each of the prepared propellant pastes was then cast into a suitable structure and subjected to the following heat treatment: baking for 75 h at a temperature of 50 C.

Determining the Potlife of the Pastes

[0077] Potlife was determined by measuring the viscosity of the propellant paste in question (containing the curing agent and the curing catalyst) over time, by using a Brookfield viscosity meter (using the No. 3 body (mobile C) rotating at 1 revolution per minute (rpm)), at a temperature of 40 C. The time for the viscosity to reach 15 kPo was measured in order to determine whether the propellant satisfied the criterion for industrialization, i.e. whether the measured time was greater than 15 h.

TABLE-US-00002 TABLE 2 Ref. 1 Ref. 2 Invention Comparative examples A B1 B2 Ex. 1 Ex. 2 C1 C2 Combustion / Lead citrate Bismuth citrate Bismuth Bismuth carbonate catalyst subsalicylate % by weight 0 1 3.5 1 4 4 4 Time for paste >24 h >24 h >24 h >24 h >16 h <1 h <1 h viscosity to reach 15 kPo at 40 C. Ballistic properties Pressure (MPa) Burn rate (millimeters per second) 7 6.6 9.5 15.6 8.9 12.7 10 8.8 11.7 16.4 11.3 14.8 13 11.1 14.0 17.9 13.6 16.2 18 15.3 17.6 20.4 17.5 18.4

[0078] The following comments are made on the topic of the results of Table 2.

Potlife

[0079] As expected, pastes of the reference propellants, without ballistic catalyst (Example A) or containing lead citrate as ballistic catalyst (Examples B1 and B2) reached the viscosity value of 15 kPo after longer than 24 h, thus satisfying the criterion for industrial castability.

[0080] The propellant paste of Example 1 (of the invention) incorporating bismuth citrate at a content by weight of 1% presented castability properties equivalent to those of the propellants of reference A (no ballistic catalyst) and B1 (containing 1% by weight of Pb citrate).

[0081] Example 2 (of the invention) shows that even with a high content by weight (4%) of bismuth citrate, the propellant paste conserved viscosity less than or equal to 15 kPo for at least 16 h, which is more than the minimum time of 15 h (required for performing the operations of casting the paste industrially).

[0082] The viscosity of the propellant pastes of the comparative Examples C1 and C2 exceeded the maximum acceptable viscosity value (15 kPo) in less than one hour (which is much less than the required 15 h). This shows that selecting the pair comprising PAG and bismuth citrate in accordance with the invention is particularly pertinent).

Burn Rates

[0083] Table 2 also shows that the ballistic catalyst (combustion catalyst), i.e. bismuth citrate, imparts burn rates to propellants of the invention as a function of pressure that are much greater than those of reference propellant A (without ballistic catalyst in its composition), and close to those propellants B1 and B2 of composition including lead citrate (toxic product) as the combustion catalyst.