GB2159166A - Combustion inhibitor compositions for coating solid propellants - Google Patents
Combustion inhibitor compositions for coating solid propellants Download PDFInfo
- Publication number
- GB2159166A GB2159166A GB08512548A GB8512548A GB2159166A GB 2159166 A GB2159166 A GB 2159166A GB 08512548 A GB08512548 A GB 08512548A GB 8512548 A GB8512548 A GB 8512548A GB 2159166 A GB2159166 A GB 2159166A
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- GB
- United Kingdom
- Prior art keywords
- polymer
- composition according
- molecular weight
- hydroxy groups
- combustion
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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Classifications
-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
- C08G18/00—Polymeric products of isocyanates or isothiocyanates
- C08G18/06—Polymeric products of isocyanates or isothiocyanates with compounds having active hydrogen
- C08G18/28—Polymeric products of isocyanates or isothiocyanates with compounds having active hydrogen characterised by the compounds used containing active hydrogen
- C08G18/40—High-molecular-weight compounds
- C08G18/48—Polyethers
- C08G18/4804—Two or more polyethers of different physical or chemical nature
-
- C—CHEMISTRY; METALLURGY
- C06—EXPLOSIVES; MATCHES
- C06B—EXPLOSIVES OR THERMIC COMPOSITIONS; MANUFACTURE THEREOF; USE OF SINGLE SUBSTANCES AS EXPLOSIVES
- C06B23/00—Compositions characterised by non-explosive or non-thermic constituents
-
- 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
- C06B45/12—Compositions or products which are defined by structure or arrangement of component of product having contiguous layers or zones
-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
- C08G18/00—Polymeric products of isocyanates or isothiocyanates
- C08G18/06—Polymeric products of isocyanates or isothiocyanates with compounds having active hydrogen
- C08G18/28—Polymeric products of isocyanates or isothiocyanates with compounds having active hydrogen characterised by the compounds used containing active hydrogen
- C08G18/40—High-molecular-weight compounds
- C08G18/4009—Two or more macromolecular compounds not provided for in one single group of groups C08G18/42 - C08G18/64
- C08G18/4018—Mixtures of compounds of group C08G18/42 with compounds of group C08G18/48
Abstract
A combustion inhibitor composition for coating solid propellants comprises an aliphatic polyurethane formed by the reaction of (a) at least on polyisocyanate with (b) a mixture comprising (i) at least one polyetherpolyol (A) containing at least three hydroxy groups per molecule, and (ii) at least one lactone polymer and/or tetrahydrofuran polymer (B) containing two hydroxy groups per molecule, the mole ratio of A:B ( gamma A: gamma B) being such that <IMAGE> where MWA, gamma A, and fA denote molecular weight, mole fraction, and a number of hydroxy groups respectively of the polymer A, and MWB, gamma B, and fB denote molecular weight, mole fraction, and number of hydroxy groups respectively of the polymer B.
Description
SPECIFICATION
Combustion inhibitor compositions for coating solid propellants
This invention is concerned with combustion inhibitor compositions suitable for coating solid propellants and, more particularly, with compositions of this kind based on aliphatic polyurethane elastomers.
Combustion inhibitors are materials used to cover the the surfaces of propellant blocks other than the combustion surface. These materials protect the surfaces of the block against any unintended ignition which could occur, especially as a result of the effect of the hot gases produced by combustion of the block. Combustion inhibitors therefore enable the rate of combustion of a propellant block to be controlled by defining a limited zone where uniform combustion can take place.
In the case of tactical weapons which are generally guided by signals from the firing post, it is necessary that the combustion of the propellant block which propels the weapon, should not produce fumes or gases which would obscure the rear zone of the weapon and interfere with its guidance from the firing post. This condition, referred to as "discreteness", is determined by the degree of transparency of the emitted combustion gases to the guidance signals, particularly infrared and visible radiations.
So-called "double-base" propellants are inherently discrete; their combustion gases contain very few or no solid particles and are consequently transparent to the radiations used to guide weapons. This condition of discreteness is also important for the materials employed to produce the inhibition coating of double-base propellant blocks.
For an inhibitor to be discrete it is necessary that the material employed satisfies several requirements.
These include:
(i) Longitudinal and transverse transparency of the gases produced by the combustion to the radiations used to guide the weapon,
(ii) endothermic decomposition of the inhibitor layer in contact with the hot combustion gases in order to "cool" the layer and thereby improve its thermal resistance;
(iii) uniformity of continuous combustion of the propellant over the entire combustion surface and, particularly, absence of a hypervelocity effect on the side edges of the propellant block; and
(iv) absence of migration of the nitroglycerine present in the double-base propellant into the inhibitor.
To satisfy these requirements, a combustion inhibitor must have, in particular, the following properties:
(i) no emission of radiation-obscuring fumes during the combustion of the propellant,
(ii) good adhesion to the propellant block; and
(iii) resistance to nitroglycerine migration.
One solution which satisfies these requirements is to use a material which is ablated during the combustion of the propellant, producing transparent gases. Thus the material is vaporised by the hot gases produced by combustion of the propellant. A second solution is to use materials which have excellent thermal resistance, such as materials with a silicone binder, which remain in the combustion chamber and do not emit radiation- obscuring particles.
The inhibitor compositions of the present invention correspond to materials of the first type and are therefore referred to as vaporisable. Such materials have already been described, for example in French
Patent 2275425 in which the material consists of an aliphatic polyurethane based on a polyetherpolyol, an aliphatic polyisocyanate and a filler. However, in view of the affinity of the aliphatic polyurethane for nitroglycerine in the propellant, it is necessary with these compositions to place a barrier layer consisting of a polyurethane based on a triisocyanate, in order to produce a layer containing an extremely tightlyknit lattice, between the inhibitor and the propellant.
In order to dispense with this barrier layer, it has been proposed in French Patent 2444689 that the degree of cross-linking of the polyurethane material be increased by using polyols of low molecular weight. However, the radiation transparency characteristics of these materials are still not wholiy satisfactory and significant edge effects occur with some of these compositions during combustion.
We have now developed combustion inhibitor compositions which are also based on aliphatic oxygenated polyurethanes, but which have improved characteristics of transparency to guidance radiations and of control of propellant combustion.
According to the present invention, therefore, there is provided a combustion inhibitor composition for coating a solid propellant, which comprises an aliphatic polyurethane formed by the reaction of
(a) at least one polyisocyanate with
(b) a mixture comprising
(i) at least one polyetherpolyol (A) containing at least three hydroxy groups per molecule, and
(ii) at least one lactone polymer and/or tetrahydrofuran polymer (B) containing two hydroxy groups per molecule, the mole ratio of A:B (A 78) being such that::
where MWA, m, and fA denote molecular weight, mole fraction, and number of hydroxy groups respectively of the polymer A, and MWs, r,, and fB denote molecular weight, mole fraction, and number of hydroxy groups respectively of the polymer B.
The invention also includes a propellant block, at least a part of the surface of which is coated with an inhibitor composition according to the invention.
The compositions of the present invention have high discreteness and their melting points are higher than those of compositions comprising a polyurethane based solely on polyetherpolyols. As a result, during combustion of a propellant block having a combustion inhibitor according to the present invention, only ablation of the inhibitor occurs, whereas with an inhibitor comprising a polyurethane based solely on polyetherpolyols, in addition to ablation, melting of the inhibitor takes place and this results in liquid flows in the combustion chamber which can give rise to irregularities in the combustion of the block and also a reduction in radiation transparency due to the entrainment of liquid particles in the emitted combustion gases.
The term "aliphatic polyurethane" is used herein to mean a polyurethane which contains substantially no aromatic moieties. However, these polyurethanes may contain a small proportion of aromatic moieties, but this proportion should not exceed 10% in order not to affect the discreteness characteristics of the inhibitor.
In order for the compositions of the invention to be vapourisable, the polyurethane component is oxygen-rich. The ratio of carbon atoms to oxygen atoms in the polyurethanes of the invention is preferably less than 6, more preferably from 4 to 5.5.
The polyetherpolyols used to prepare the compositions of the invention have at least three hydroxy groups and preferably have a molecular weight of from 400 to 4500, more preferably from 400 to 1000.
Suitable polyetherpolyols include, for example, polyethylene glycol, polypropylene glycol, polypropylene ethylene glycol, polytetramethylene glycol and the like, and the products of addition of polyoxypropylene glycol to ethylene glycol, diethylene glycol, propylene glycol, glycerol, sorbitol, pentaerythritol, trimethylolpropane; it is also possible to use polyesterpolyols derived from dicarboxylic acids, such as adipic, succinic or sebacic acid, and from low molecular weight glycols, such as ethylene glycol, propylene glycol, diethylene glycol, 1,4-butanediol, 1,6-hexanediol, or the like.
The lactone polymers used to prepare the compositions of the invention preferably have a molecular weight of from 500 to 300û, more preferably from 1100 to 1700. Suitable lactone polymers are formed by successive ring opening of lactone monomers using polyfunctional initiators.
Preferred lactone monomers are those of the formula:
where n is equal to or less than 4. Particularly preferred lactone polymers are poly-S-caprolactone and
poly-y-butyrolactone.
The tetrahydrofuran polymers used to prepare the compositions of the invention preferably have a mo
lecular weight of from 600 to 2000, more preferably about 1000. The preferred tetrahydrofuran polymer is
polytetrahydrofuran itself.
Suitable polyisocyanates for preparing the compositions of the invention are aliphatic diisocyanates,
such as 4,4'-diisocyanatodicyclohexylmethane (MDCI), 1,6- diisocyanate-2,2,3-trimethylhexane, isopho
rone diisocyanate, and hexamethylenediisocyanate The cross-linking is preferably carried out in the pres
ent of known catalysts such as those based on tin, for example, dibutylin diacetate or dibutyltin dilaurate.
The ratio of NCO groups to OH groups in the polyisocyantate is preferably 1 or slightly greater than 1.
The composition of the invention may also comprise aliphatic plasticisers, such as triacetin or tri-nbutyl acetylcitrate. Up to 50 parts by weight of plasticiser may be added to 100 parts of polyurethane.
The compositions according to the invention may also contain a vapourisable organic filler, provided the filler has a melting temperature equal to or higher than that of the polyurethane. Suitable fillers include, for example, oxamide, ammonium oxalate, polyoxyethylen, polyoxypropylene, polyoxymethylene, and ammonium oxalate polyacetal. Preferably, these fillers should be non- hygroscopic, to avoid the presence of water which interferes with cross-linking of the polymer, and be oxygen-rich. The ratio of carbon atoms to oxygen atoms in the fillers is preferably about 1, in order to promote oxidation reactions relative to polymerisation reactions and thereby reduce ash formation.
Up to 300 parts by weight of filler may be added to 100 parts of polyurethane, the upper limit being determined by the castability of the resulting composition and by the minimum mechanical properties which are acceptable for a combustion inhibitor. A preferred filler is oxamide which has a very high melting point (approximately 400"C).
The composition of the invention may also include a chain extender, such as a low molecular weight glycol, for example 1,4-butanediol, a diamine, such as ethylenediamine, or very low molecular weight polyols, such as trimethylolpropane. The quantity of trimethylolpropane which is added is determined by the required mechanical properties of the inhibitor and may be as much as 20 parts by weight of trimethylolpropane to 100 parts of polyol(s).
The compositions of the invention may also include heat-stable organic or inorganic fibres, such as polyphenylene terephthalamide fibres, for example those sold by du Pont de Menours & Co. under the trade name "Kevlar".
The compositions of the invention are used in accordance with known procedures employed in coating of propellant blocks. A preferred procedure for applying the composition of the invention to the surface of a block of propellant will now be described in detail.
A block of double-base propellant is arranged concentrically in a cylindrical mould so as to leave a uniform space between the surface of the block and the inner wall of the mould. The constituents of the polyurethane composition according to the invention, together with any optional fillers, plasticisers, chain extenders, or fibres, are thoroughly mixed using a mixer. When the mixture is homogeneous, the propellant block is inhibited by casting the composition into the space provided in the mould or, according to a particularly preferred procedure, by injection-moulding the composition into this space.
In order that the invention may be more fuily understood, the following examples are given by way of illustration only.
Tests of several inhibitor compositions according to the invention were carried out using the following propellant composition, expressed in percentages by weight:
Nitrocellulose: 40.2%
Nitroglycerine 36.5%
Triacetin: 8.2%
Hexogen: 9.1%
Additives (combustion and
polymerisation catalysts,
ballistic modifiers): 6%
Examples of formulations of inhibitor compositions in accordance with the invention are shown in Table 1.
Table 1 - Formulation of the composition
Composition no.
Constituents 1 2 γ % C/O R γ % C/O R Glycerol polyoxypropylene (1) 0,340 13,80 0,302 13,80 Poly- -caprolactone (2) 0,056 12,40 5,3 1,34 0,048 12,00 5,1 1,29 PHTF (6) MDCI (3) 0,605 16,10 0,608 18,10 Chain extender (5) 0,044 0,65 Oxamide 52,40 50,20 Triacetin 5,20 5,00 Catalyst (4) 0,05 0,05 Table 1 - Formulation of the compositions (continued)
Composition no.
Constituents 3 4 γ % C/O R γ % C/O R Glycerol polyoxypropylene (1) 0,344 14,31 0,228 10,90 Poly- -caprolactone (2) 0,042 9,60 5,3 1 PHTF (6) 0,109 13,10 5,9 1,79 MDCI (3) 0,614 16,20 0,634 20,10 Chain Extender (5) 0,029 10,20 Oxamide 54,25 19,65 Triacetin 5,30 5,45 Catalyst (4) 0,04 0,013 γ : Mole fraction of the constituents in the polyurethane
% : Weight % of the constituents in the inhibitor composition
C/O :Number of carbon atoms/number of oxygen atoms in the polyurethane R:
(1) : Polyetherpolyol sold by "Ugine Kuhlman" under the name $Pluracol 3130", MW = 400.
(2) : Lactone polymer sold by "Hooker Chemical" under the designation "S10363-55",
MW = 2170.
(3) : 4,4'- diisocyanatodicyclohexylmethane, MW = 262.
(4) : Dibutyltin dilaurate (5) : Trimethylolpropane, MW = 134.
(6) : Polytetrahydrofuran sold by BASF, MW = 1000.
The mechanical properties of these compositions were evaluated after ageing for 15 days at 20 C. The results obtained are shown in Table 2.
TABLE 2
Mechanical Properties
Composition Sm (bar) % E (bar) e, 1%1 no.
1 50 8,5 607 102
2 90 8,7 1025 128
3 55 9,2 598 98
4 34 11,5 297 118
SM : maximum tensile stress at 20"C E : elastic elongation at 20"C E : Young's modulus at 20"C : : maximum elongation at break at 20"C Furthermore, the absorption of nitroglycerine from the propellant into each of the inhibitor compositions was low.
The four compositions were tested by firing cylindrical blocks (height 200mm, (2i : 90 mm) of doublebase propellant, of the composition given above, which had been inhibited with a layer of the inhibitor composition which was 2.55mm thick. From these firings it was possible to evaluate, on the one hand, the transverse and longitudinal transparencies of the emitted combustion gases to radiations, in order to assess the discreteness of the inhibitor composition, and, on the other hand, the thermal resistance of these compositions, by determining the extent of ablation by visual inspection of the combustion chamber after each firing.
The results are shown in Table 3.
TABLE 3
Results of the firing trials
transmission
Composition extent of transverse longitudinal
no. ablation (%) (%) 1 20-22 91 40
2 16.5 90 > 40
3 18.5 92 > 50
4 18-20 > 90 > 40
Furthermore, no indication of any trace of melting of the composition in the combustion chamber was found after firing, in contrast to that found when using inhibitor compositions which do not contain lactone or tetrahydrofuran polymers.
Thus the compositions of the invention have good discreteness characteristics and excellent mechanical and combustion control properties.
Claims (12)
1. A combustion inhibitor composition for coating a solid propellant, which comprises an aliphatic polyurethane formed by the reaction of
(a) at least one polyisocyanate with
(b) a mixture comprising
(i) at least one polyetherpolyol (A) containing at least three hydroxy groups per molecule, and
(ii) at least one lactone polymer and/or tetrahydrofuran polymer (B) containing two hydroxy groups per molecule, the mole ratio of A:B (A : Ws) being such that:
where MWA, YAI and fA denote molecular weight, mole fraction, and number of hydroxy groups respectively of the polymer A, and MEW,, WE, and fB denote molecular weight, mole fraction, and number of hydroxy groups respectively of the polymer B.
2. A composition according to claim 1, in which the dihydroxy polymer is a lactone polymer having a molecular weight from 500 to 3000.
3. A composition according to claim 1 or 2, in which the lactone polymer is poly--caprolactone or poly-z-butyrolactone.
4. A composition according to claim 1, in which the dihydroxy polymer is a tetrahydrofuran polymer having a molecular weight of from 600 to 2000.
5. A composition according to any of claims 1 to 4, in which the polyetherpolyol has a molecular weight of from 400 to 4500.
6. A composition according to any of claims 1 to 5, in which the ratio of carbon atoms to oxygen atoms in the polyurethane is greater than 4.
7. A composition according to any of claims 1 to 6, which also comprises one or more chain extenders.
8 A composition according to any of claims 1 to 7, which also comprises trimethylolpropane.
9. A composition according to any of claims 1 to 8, which also comprises heat-stable organic or inorganic fibres.
10. A composition according to any of claims 1 to 9, which additionally comprises a gasifiable organic filler and/or an aliphatic plasticiser.
11. A combustion inhibitor composition substantially as herein described in any of the Examples
12. A solid propellant block, at least a part of the surface of which is coated with a combustion inhibitor composition as claimed in any of the preceding claims.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| FR8407657A FR2564457B1 (en) | 1984-05-17 | 1984-05-17 | COMBUSTION INHIBITOR BASED ON ALIPHATIC POLYURETHANE ELASTOMER FOR PROPERGOL, AND BLOCK COATED WITH THIS INHIBITOR |
| JP59103657A JPS60248713A (en) | 1984-05-24 | 1984-05-24 | Preparation of fluorine-contained copolymer |
Publications (3)
| Publication Number | Publication Date |
|---|---|
| GB8512548D0 GB8512548D0 (en) | 1985-06-19 |
| GB2159166A true GB2159166A (en) | 1985-11-27 |
| GB2159166B GB2159166B (en) | 1987-06-24 |
Family
ID=26223966
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB08512548A Expired GB2159166B (en) | 1984-05-17 | 1985-05-17 | Combustion inhibitor compositions for coating solid propellants |
Country Status (1)
| Country | Link |
|---|---|
| GB (1) | GB2159166B (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2200362A (en) * | 1986-12-23 | 1988-08-03 | Bayern Chemie Gmbh Flugchemie | An intermediate layer between a rocket solid propellant composition and an insulating layer thereof |
Citations (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB1336842A (en) * | 1971-03-03 | 1973-11-14 | Olin Corp | Urethane coating composition and process |
| GB1376839A (en) * | 1971-07-12 | 1974-12-11 | Pechiney Ugine Kuhlmann | Polyurethane polymers |
| GB1432239A (en) * | 1972-04-05 | 1976-04-14 | Pechiney Ugine Kuhlmann | Polyurethane-polyurea materials |
-
1985
- 1985-05-17 GB GB08512548A patent/GB2159166B/en not_active Expired
Patent Citations (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB1336842A (en) * | 1971-03-03 | 1973-11-14 | Olin Corp | Urethane coating composition and process |
| GB1376839A (en) * | 1971-07-12 | 1974-12-11 | Pechiney Ugine Kuhlmann | Polyurethane polymers |
| GB1432239A (en) * | 1972-04-05 | 1976-04-14 | Pechiney Ugine Kuhlmann | Polyurethane-polyurea materials |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2200362A (en) * | 1986-12-23 | 1988-08-03 | Bayern Chemie Gmbh Flugchemie | An intermediate layer between a rocket solid propellant composition and an insulating layer thereof |
| GB2200362B (en) * | 1986-12-23 | 1990-01-24 | Bayern Chemie Gmbh Flugchemie | Intermediate layer between solid propellant charge and insulating layer thereof |
Also Published As
| Publication number | Publication date |
|---|---|
| GB8512548D0 (en) | 1985-06-19 |
| GB2159166B (en) | 1987-06-24 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| PE20 | Patent expired after termination of 20 years |
Effective date: 20050516 |