USH1341H - High energy propellant formulation - Google Patents
High energy propellant formulation Download PDFInfo
- Publication number
- USH1341H USH1341H US07/627,169 US62716990A USH1341H US H1341 H USH1341 H US H1341H US 62716990 A US62716990 A US 62716990A US H1341 H USH1341 H US H1341H
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- US
- United States
- Prior art keywords
- propellant
- cellulose acetate
- polyethylene glycol
- butyrate
- hexamethylene diisocyanate
- 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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- 239000003380 propellant Substances 0.000 title claims abstract description 90
- 239000000203 mixture Substances 0.000 title claims description 32
- 238000009472 formulation Methods 0.000 title description 4
- 239000002202 Polyethylene glycol Substances 0.000 claims abstract description 82
- 229920001223 polyethylene glycol Polymers 0.000 claims abstract description 82
- 229920002301 Cellulose acetate Polymers 0.000 claims abstract description 40
- UGZICOVULPINFH-UHFFFAOYSA-N acetic acid;butanoic acid Chemical compound CC(O)=O.CCCC(O)=O UGZICOVULPINFH-UHFFFAOYSA-N 0.000 claims abstract description 30
- ZHXAZZQXWJJBHA-UHFFFAOYSA-N triphenylbismuthane Chemical compound C1=CC=CC=C1[Bi](C=1C=CC=CC=1)C1=CC=CC=C1 ZHXAZZQXWJJBHA-UHFFFAOYSA-N 0.000 claims description 20
- SNIOPGDIGTZGOP-UHFFFAOYSA-N 1,2,3-propanetrioltrinitrate Chemical group [O-][N+](=O)OCC(O[N+]([O-])=O)CO[N+]([O-])=O SNIOPGDIGTZGOP-UHFFFAOYSA-N 0.000 claims description 18
- RRAMGCGOFNQTLD-UHFFFAOYSA-N Hexamethylene diisocyanate Chemical compound O=C=NCCCCCCN=C=O RRAMGCGOFNQTLD-UHFFFAOYSA-N 0.000 claims description 18
- 239000005057 Hexamethylene diisocyanate Substances 0.000 claims description 18
- 229960003711 glyceryl trinitrate Drugs 0.000 claims description 18
- 229920000642 polymer Polymers 0.000 claims description 18
- HHEFNVCDPLQQTP-UHFFFAOYSA-N Ammonium perchlorate Chemical compound [NH4+].[O-]Cl(=O)(=O)=O HHEFNVCDPLQQTP-UHFFFAOYSA-N 0.000 claims description 16
- 239000000006 Nitroglycerin Substances 0.000 claims description 16
- 229940014995 Nitroglycerin Drugs 0.000 claims description 16
- 229910052751 metal Inorganic materials 0.000 claims description 16
- 239000002184 metal Substances 0.000 claims description 16
- 239000002245 particle Substances 0.000 claims description 16
- XIFJZJPMHNUGRA-UHFFFAOYSA-N N-methyl-4-nitroaniline Chemical compound CNC1=CC=C([N+]([O-])=O)C=C1 XIFJZJPMHNUGRA-UHFFFAOYSA-N 0.000 claims description 14
- 229910052782 aluminium Inorganic materials 0.000 claims description 14
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminum Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 claims description 14
- -1 nitrate ester Chemical class 0.000 claims description 14
- OHJMTUPIZMNBFR-UHFFFAOYSA-N biuret Chemical compound NC(=O)NC(N)=O OHJMTUPIZMNBFR-UHFFFAOYSA-N 0.000 claims description 12
- UZGLIIJVICEWHF-UHFFFAOYSA-N octogen Chemical compound [O-][N+](=O)N1CN([N+]([O-])=O)CN([N+]([O-])=O)CN([N+]([O-])=O)C1 UZGLIIJVICEWHF-UHFFFAOYSA-N 0.000 claims description 12
- RUKISNQKOIKZGT-UHFFFAOYSA-N 2-Nitrodiphenylamine Chemical compound [O-][N+](=O)C1=CC=CC=C1NC1=CC=CC=C1 RUKISNQKOIKZGT-UHFFFAOYSA-N 0.000 claims description 10
- IQPQWNKOIGAROB-UHFFFAOYSA-N [N-]=C=O Chemical compound [N-]=C=O IQPQWNKOIGAROB-UHFFFAOYSA-N 0.000 claims description 10
- 229920001727 cellulose butyrate Polymers 0.000 claims description 10
- ZJCCRDAZUWHFQH-UHFFFAOYSA-N Trimethylolpropane Chemical compound CCC(CO)(CO)CO ZJCCRDAZUWHFQH-UHFFFAOYSA-N 0.000 claims description 4
- 229910052790 beryllium Inorganic materials 0.000 claims description 4
- ATBAMAFKBVZNFJ-UHFFFAOYSA-N beryllium(0) Chemical compound [Be] ATBAMAFKBVZNFJ-UHFFFAOYSA-N 0.000 claims description 4
- ZOXJGFHDIHLPTG-UHFFFAOYSA-N boron Chemical compound [B] ZOXJGFHDIHLPTG-UHFFFAOYSA-N 0.000 claims description 4
- 229910052796 boron Inorganic materials 0.000 claims description 4
- PEDCQBHIVMGVHV-UHFFFAOYSA-N glycerine Chemical compound OCC(O)CO PEDCQBHIVMGVHV-UHFFFAOYSA-N 0.000 claims description 4
- 235000011187 glycerol Nutrition 0.000 claims description 4
- 229940113165 trimethylolpropane Drugs 0.000 claims description 4
- 125000002887 hydroxy group Chemical group [H]O* 0.000 claims 12
- QTBSBXVTEAMEQO-UHFFFAOYSA-M acetate Chemical compound CC([O-])=O QTBSBXVTEAMEQO-UHFFFAOYSA-M 0.000 claims 4
- FERIUCNNQQJTOY-UHFFFAOYSA-M butyrate Chemical compound CCCC([O-])=O FERIUCNNQQJTOY-UHFFFAOYSA-M 0.000 claims 4
- 239000003431 cross linking reagent Substances 0.000 claims 4
- 239000011230 binding agent Substances 0.000 abstract description 22
- 239000000446 fuel Substances 0.000 description 40
- 230000000694 effects Effects 0.000 description 18
- 239000004014 plasticizer Substances 0.000 description 16
- 239000007787 solid Substances 0.000 description 16
- 229920001451 Polypropylene glycol Polymers 0.000 description 12
- 239000003054 catalyst Substances 0.000 description 12
- 238000004132 cross linking Methods 0.000 description 12
- 229920000570 polyether Polymers 0.000 description 10
- 239000004721 Polyphenylene oxide Substances 0.000 description 8
- 239000000945 filler Substances 0.000 description 8
- 239000007800 oxidant agent Substances 0.000 description 8
- 238000002156 mixing Methods 0.000 description 6
- 239000003381 stabilizer Substances 0.000 description 6
- LYAGTVMJGHTIDH-UHFFFAOYSA-N Diethylene glycol dinitrate Chemical compound [O-][N+](=O)OCCOCCO[N+]([O-])=O LYAGTVMJGHTIDH-UHFFFAOYSA-N 0.000 description 4
- AGCQZYRSTIRJFM-UHFFFAOYSA-N Triethylene glycol dinitrate Chemical compound [O-][N+](=O)OCCOCCOCCO[N+]([O-])=O AGCQZYRSTIRJFM-UHFFFAOYSA-N 0.000 description 4
- IPPYBNCEPZCLNI-UHFFFAOYSA-N Trimethylolethane trinitrate Chemical compound [O-][N+](=O)OCC(C)(CO[N+]([O-])=O)CO[N+]([O-])=O IPPYBNCEPZCLNI-UHFFFAOYSA-N 0.000 description 4
- 239000007789 gas Substances 0.000 description 4
- 150000002513 isocyanates Chemical class 0.000 description 4
- 150000002739 metals Chemical class 0.000 description 4
- 238000000034 method Methods 0.000 description 4
- 230000004048 modification Effects 0.000 description 4
- 238000006011 modification reaction Methods 0.000 description 4
- 229920005862 polyol Polymers 0.000 description 4
- 150000003077 polyols Chemical class 0.000 description 4
- 239000000126 substance Substances 0.000 description 4
- XTFIVUDBNACUBN-UHFFFAOYSA-N 1,3,5-trinitro-1,3,5-triazinane Chemical group [O-][N+](=O)N1CN([N+]([O-])=O)CN([N+]([O-])=O)C1 XTFIVUDBNACUBN-UHFFFAOYSA-N 0.000 description 2
- 239000004971 Cross linker Substances 0.000 description 2
- 235000015842 Hesperis Nutrition 0.000 description 2
- 235000012633 Iberis amara Nutrition 0.000 description 2
- 240000004804 Iberis amara Species 0.000 description 2
- 239000000020 Nitrocellulose Substances 0.000 description 2
- 239000004743 Polypropylene Substances 0.000 description 2
- 230000004308 accommodation Effects 0.000 description 2
- 229920001400 block copolymer Polymers 0.000 description 2
- 238000006243 chemical reaction Methods 0.000 description 2
- 239000003795 chemical substances by application Substances 0.000 description 2
- 238000002485 combustion reaction Methods 0.000 description 2
- 150000001875 compounds Chemical class 0.000 description 2
- 238000010790 dilution Methods 0.000 description 2
- 230000002708 enhancing Effects 0.000 description 2
- 150000002430 hydrocarbons Chemical class 0.000 description 2
- 239000004615 ingredient Substances 0.000 description 2
- 230000002452 interceptive Effects 0.000 description 2
- 238000004519 manufacturing process Methods 0.000 description 2
- 239000000463 material Substances 0.000 description 2
- 230000000051 modifying Effects 0.000 description 2
- 150000002823 nitrates Chemical class 0.000 description 2
- 229920001220 nitrocellulos Polymers 0.000 description 2
- 125000000962 organic group Chemical group 0.000 description 2
- 239000004033 plastic Substances 0.000 description 2
- 229920003023 plastic Polymers 0.000 description 2
- 229920001155 polypropylene Polymers 0.000 description 2
- 230000035945 sensitivity Effects 0.000 description 2
- 239000000779 smoke Substances 0.000 description 2
- WYURNTSHIVDZCO-UHFFFAOYSA-N tetrahydrofuran Chemical group C1CCOC1 WYURNTSHIVDZCO-UHFFFAOYSA-N 0.000 description 2
- 230000002588 toxic Effects 0.000 description 2
- 231100000331 toxic Toxicity 0.000 description 2
- FPYOWXFLVWSKPS-UHFFFAOYSA-N triethylbismuthane Chemical compound CC[Bi](CC)CC FPYOWXFLVWSKPS-UHFFFAOYSA-N 0.000 description 2
Images
Definitions
- This invention relates to propellants for rockets and more particularly, this invention relates to a rocket propellant having about 22 to 27 weight percent binder and about 73 to 78 weight percent solids. Still more particularly, but without limitation thereto, this invention relates to a propellant having a binder using a specific range of ratios of cellulose acetate butyrate (CAB) to polyethylene glycol (PEG).
- CAB cellulose acetate butyrate
- PEG polyethylene glycol
- This invention provides a very high performance nitrate ester plasticized polyether (NEPE) propellant based upon a unique cellulose acetate butyrate (CAB) polyethylene glycol (PEG) binder system.
- NEPE nitrate ester plasticized polyether
- CAB unique cellulose acetate butyrate
- PEG polyethylene glycol
- this invention provides a propellant with a long pot life, improved efficiency, low burn rate pressure sensitivity, excellent mechanical properties, high critical impact velocity, and a high delivered specific impulse.
- An object of this invention is to develop an improved high energy propellant.
- a further object of this invention is to develop an improved high energy propellant having optimal mechanical and ballistic properties.
- the propellant binder has a cellulose acetate butyrate: polyethylene glycol ratio in the range of about 0.01 to 0.03 on a weight basis.
- FIG. 1 shows graphs of the effect of PEG molecular weight on propellant mechanical properties.
- the general composition of the high energy propellant is about 22 to 27 weight percent binder and about 73 to 78 weight percent solids.
- the binder itself has several components: two polymers, a plasticizer, is a curative, and two stabilizers.
- the binder also contains a trace amount of catalyst.
- the solids component of the propellant is comprised of a metanized fuel, an energetic filler, and an oxidizer.
- Table I illustrates four examples of preferred propellant compositions, by weight percent. Examples I and II exemplify the most preferred formulations. It is to be understood that the values specified in Table I are approximate, and some variations from those shown are still within the scope of this invention.
- the preferred polymers are polyethylene glycol (PEG) and cellulose acetate butyrate (CAB).
- PEG polyethylene glycol
- CAB cellulose acetate butyrate
- the polymer PEG functions to give physical strength to the binder when crosslinked with itself and/or CAB.
- Polypropylene glycol can be used for some PEG but the plasticizers are less soluble in it so that in most cases it is preferred to use PEG as the polyol polymer.
- PEG and CAB also serve as sources of fuel in the propellant.
- CAB as a crosslinker provides physical strength by improving tensile strength and the modulus of elasticity.
- such chemicals as cellulose acetate, cellulose butyrate, trimethylol propane, or glycerin can be substituted in part or in whole for the CAB component of the inventive fuel.
- a mixture of cellulose acetate and cellulose butyrate are used in combination as substitutes for CAB rather than either alone.
- the mechanical properties of the propellant can be modified by varying the molecular weight of the PEG employed in the propellant formulation.
- Molecular weight of the polyether and the modulus of elasticity vary inversely but the elongation varies directly.
- increasing the molecular weight of the polyether causes a steady drop in the modulus of elasticity and increases the elongation in the resultant fuel.
- the molecular weight of the PEG has a direct bearing on the crosslink density and gelling efficiency of the present propellant, particularly at the higher Pl:P0 (i.e. plasticizer: polymer) levels due to the dilution of the polymer.
- Pl:P0 i.e. plasticizer: polymer
- FIG. 1 also demonstrates the effects of PEG molecular weight on the mechanical properties of the propellant.
- various mechanical properties of the propellant can be modified by adjustment of the ingredients (i.e. ones selected and the amounts) to meet the particular requirements of a specific missile system, and thereby optimize its efficiency.
- PEG with molecular weights of 1000-8000 can be used depending on the desired mechanical properties.
- the preferred PEG has a nominal molecular weight of about 3500.
- the mechanical properties of the propellant also vary with the ratio of CAB to PEG. It is desirable to have both high elongation and high tensile strength. However, while tensile strength is proportional to the CAB:PEG ratio, elongation is inversely proportional to said ratio. Taking this into consideration, it has been found that a CAB:PEG weight ratio in the range of about 0.001 to 0.05 is suitable. Where nitrocellulose is used for CAB, we have found the ratios of 0.001 to 1.0 to be suitable. We have found ratios of CAB in the range of about 0.01 to 0.03 to be preferred as producing on balance overall good results.
- Another embodiment of the present invention allows a modification of the mechanical properties of the manufactured fuel by blending polyethers of various molecular weights. This effect is shown in Table IV.
- PEG polypropylene glycol
- the mechanical properties can be modified by blending the PEG component of the fuel with various amounts of polypropylene glycol (PPG) to form block copolymers.
- PPG polypropylene glycol
- Table V the use of PEG/PPG tends to yield a poor modulus.
- the inclusion of polypropylene for PEG tends to reduce the solubility of plasticizers and thus in most cases PEG alone is preferred and used.
- the preferred plasticizer is nitroglycerin (NG), a high energy compound.
- NG nitroglycerin
- the mixing of CAB and NG results in a material that is formable and plastic. Its use in the present invention results in improved mechanical properties and higher performance for the binder.
- nitrate esters generally may serve as suitable plasticizers.
- Butanethol trinitrate (BTTN), triethylene glycol dinitrate (TEGDN), diethylene glycol dinitrate (DEGDN), and trimethylolethane trinitrate (TMETN) are examples of plasticizers that can be utilized within the purview of the present invention.
- the crosslinking curative of the subject invention is responsible for crosslinking the various components of the fuel.
- a polyfunctional isocyanate containing the biuret trimer of hexamethylene diisocyanate is preferred. It has an NCO functionality of at least 3.
- Desmodur N-100 commercially available from Mobay Chemical Co., which is a complex mixture of biurets, uretediones, isocyanurates and unreacted hexamethylene diisocyanate.
- Optimal crosslinking and mechanical properties are obtained when the stabilizer for NG, N-methyl-p-nitroaniline (MNA), which is discussed later, acts to stabilize the complete propellant.
- MNA N-methyl-p-nitroaniline
- Pentaerythritol tetraisocyanate is a chemical which can be considered as an alternative curing agent.
- Difunctional isocyanates tend to increase the elasticity of the resulting fuel to a great degree, and so are generally less preferred.
- Triphenyl bismuth is the preferred cure catalyst in the present invention. It functions to speed up the crosslinking process and helps to provide a very long pot life or working life (i.e., until a viscosity of about 40 kilopoise is reached). Because TPB functions as a relatively slow reacting cure catalyst, it is particularly advantageous with large missiles where the set time for the fuel is longer. Competing and interfering reactions are minimized in this system.
- organo metal cure catalysts can be employed in place of TPB.
- TPB organo metal cure catalysts
- examples are trialkyl bismuths, such as triethyl bismuth.
- Other metals can be used but they can have adverse effects unrelated to cure. The choice depends on the final fuel qualities desired, and accommodations to be made to the exigencies of the particular production process employed. The considerations involved include the size of the missile for which the fuel is being manufactured.
- the metal used to form the metallized fuel used in the preferred embodiment of the present invention is free metal aluminum (Al).
- Al reacts with the oxidizers primarily to provide heat as a product of the combustion process. This fuel is particularly useful in larger missiles, and may be eliminated in smaller tactical missiles, or for minimum smoke missiles.
- metallized fuels can be employed with that of the preferred embodiment or as substitutes for it, depending on the nature of the fuel desired.
- Suitable other metals for use in metallized fuels are boron and beryllium (although the latter is quite toxic).
- the energetic filler employed in the preferred embodiment of the present invention is cyclotetramethylene tetranitramine (HMX), which generates heat and gases. Also useful in this capacity is cyclotrimethylene trinitramine (RDX).
- HMX size affects the mechanical properties of the propellant. The modulus of elasticity is not dramatically affected by HMX diameter. However, tensile strength and especially percent elongation increase dramatically as the particle size decreases. The particle size is varied to obtain a proper viscosity for processing, but the optimum mechanical properties are achieved with the finest possible HMX.
- the preferred oxidizer in the present invention is ammonium perchlorate (AP), which functions to oxidize all of the hydrocarbons and the metal, aluminum, to generate heat and gases.
- AP is also used to control the burning rate of the propellant.
- Table I the particle size and ratio of the oxidizer can be varied to fit the needs of a particular fuel requirement.
Abstract
A high energy rocket propellant can be formed wherein the propellant binder has a cellulose acetate butyrate: polyethylene glycol ratio of about 0.01 to 0.03 on a weight basis.
Description
This invention relates to propellants for rockets and more particularly, this invention relates to a rocket propellant having about 22 to 27 weight percent binder and about 73 to 78 weight percent solids. Still more particularly, but without limitation thereto, this invention relates to a propellant having a binder using a specific range of ratios of cellulose acetate butyrate (CAB) to polyethylene glycol (PEG).
There is a constant search for improved propellants that are easier to process, have improved mechanical properties, and are higher performance. This invention provides a very high performance nitrate ester plasticized polyether (NEPE) propellant based upon a unique cellulose acetate butyrate (CAB) polyethylene glycol (PEG) binder system.
Further, this invention provides a propellant with a long pot life, improved efficiency, low burn rate pressure sensitivity, excellent mechanical properties, high critical impact velocity, and a high delivered specific impulse.
An object of this invention is to develop an improved high energy propellant.
A further object of this invention is to develop an improved high energy propellant having optimal mechanical and ballistic properties.
These and other objects have been demonstrated by the present invention wherein the propellant binder has a cellulose acetate butyrate: polyethylene glycol ratio in the range of about 0.01 to 0.03 on a weight basis.
FIG. 1 shows graphs of the effect of PEG molecular weight on propellant mechanical properties.
The general composition of the high energy propellant is about 22 to 27 weight percent binder and about 73 to 78 weight percent solids. The binder itself has several components: two polymers, a plasticizer, is a curative, and two stabilizers. The binder also contains a trace amount of catalyst. The solids component of the propellant is comprised of a metanized fuel, an energetic filler, and an oxidizer.
Table I illustrates four examples of preferred propellant compositions, by weight percent. Examples I and II exemplify the most preferred formulations. It is to be understood that the values specified in Table I are approximate, and some variations from those shown are still within the scope of this invention.
TABLE I __________________________________________________________________________ Percentage by Weight COMPONENTS Example I Example II Example III Example IV __________________________________________________________________________ BINDER Polymers Polyethylene Glycol (PEG) 6.25 6.25 11.65 5.02 Cellulose Acetate Butyrate (CAB) 0.06 0.06 .00 0.20 Plasticizer Nitroglycerin (NG) 19.02 19.02 8.06 20.18 Crosslinking Curative Desmodur N-100 0.88 0.88 1.74 0.80 Stabilizer 2 nitrodiphenylamine (2NDPA) 0.19 0.19 0.08 0.20 N-methyl-p-nitroaniline (MNA) 0.60 0.60 0.47 0.60 Cure Catalyst Triphenyl bismuth (TPB) 0.02 0.02 0.02 0.02 SOLIDS Fuel Aluminum 18.00 18.00 24.00 16.00 Energetic Filler Cyclotetramethylene 47.00 46.00 12.00 57.00 Tetranitramine (HMX) Particle Size 2μ-11μ 2μ-11μ 2μ 57μ/2μ Ratio 1:1 1:1 -- 34:23 Oxidizer Ammonium Perchlorate (AP) 8.00 9.00 42.00 Particle Size 20μ-50μ 5μ-20μ 200μ Ratio 1:1 1:1 -- -- __________________________________________________________________________
Examples I and II in the Table, which represent the most preferred embodiments of the present invention, have the following mechanical properties:
______________________________________ Example I Example II ______________________________________ Modulus (psi) 430 545 Tensile strength (psi) 92 99 Elongation (%) 270 273 ______________________________________
These values are determined at a 2 in/min pull rate at 80° F. The above values were obtained from a 600 gallon mixed batch.
The preferred polymers are polyethylene glycol (PEG) and cellulose acetate butyrate (CAB). The polymer PEG functions to give physical strength to the binder when crosslinked with itself and/or CAB. Polypropylene glycol can be used for some PEG but the plasticizers are less soluble in it so that in most cases it is preferred to use PEG as the polyol polymer. PEG and CAB also serve as sources of fuel in the propellant.
CAB as a crosslinker provides physical strength by improving tensile strength and the modulus of elasticity. In other embodiments, such chemicals as cellulose acetate, cellulose butyrate, trimethylol propane, or glycerin can be substituted in part or in whole for the CAB component of the inventive fuel. Preferably a mixture of cellulose acetate and cellulose butyrate are used in combination as substitutes for CAB rather than either alone.
In the present invention, the mechanical properties of the propellant can be modified by varying the molecular weight of the PEG employed in the propellant formulation. Molecular weight of the polyether and the modulus of elasticity vary inversely but the elongation varies directly. Thus, increasing the molecular weight of the polyether causes a steady drop in the modulus of elasticity and increases the elongation in the resultant fuel. The molecular weight of the PEG has a direct bearing on the crosslink density and gelling efficiency of the present propellant, particularly at the higher Pl:P0 (i.e. plasticizer: polymer) levels due to the dilution of the polymer. The various effects of PEG molecular weight modulation can be seen in Tables II and III.
TABLE II ______________________________________ EFFECT OF PEG MOLECULAR WEIGHT 70% Solids, 2.8 Pl:Po Approx. σ ε E MW (psi) (%) (psi) ______________________________________ 430 64 37 680 1020 70 56 728 1376 77 100 510 3240 65 292 296 4100 67 411 204 ______________________________________
TABLE III ______________________________________ EFFECT OF POLYETHER MOLECULAR WEIGHT ON MECHANICAL PROPERTIES 75% Solids, 1.2 NCO:OH Approx. .sup.σ m .sup.ε m .sup.ε f E MW PL:Po (psi) (%) (%) (psi) ______________________________________ 1000 2.1 123 25 25 1040 1500 2.1 130 23 23 1100 3100 2.1 77 29 145 685 4000 2.1 72 260 260 425 7800 2.1 81 970 970 185 9400 2.1 82 1170 1170 215 1000 2.8 111 24 24 880 1500 2.8 114 25 25 810 3100 2.8 59 24 93 550 4000 2.8 54 295 295 455 7800 2.8 68 1000 1000 160 8100 2.8 69 1100 1100 130 9400 2.8 57 1130 1130 105 ______________________________________
FIG. 1 also demonstrates the effects of PEG molecular weight on the mechanical properties of the propellant. Thus, various mechanical properties of the propellant can be modified by adjustment of the ingredients (i.e. ones selected and the amounts) to meet the particular requirements of a specific missile system, and thereby optimize its efficiency. PEG with molecular weights of 1000-8000 can be used depending on the desired mechanical properties. The preferred PEG has a nominal molecular weight of about 3500.
The mechanical properties of the propellant also vary with the ratio of CAB to PEG. It is desirable to have both high elongation and high tensile strength. However, while tensile strength is proportional to the CAB:PEG ratio, elongation is inversely proportional to said ratio. Taking this into consideration, it has been found that a CAB:PEG weight ratio in the range of about 0.001 to 0.05 is suitable. Where nitrocellulose is used for CAB, we have found the ratios of 0.001 to 1.0 to be suitable. We have found ratios of CAB in the range of about 0.01 to 0.03 to be preferred as producing on balance overall good results.
Another embodiment of the present invention allows a modification of the mechanical properties of the manufactured fuel by blending polyethers of various molecular weights. This effect is shown in Table IV.
TABLE IV ______________________________________ EFFECT OF POLYMER BLENDS 70% Solids, 2.1 Pl:Po, 1.2 NCO:OH .sup.σ m .sup.ε m .sup.(ε f E Approx. MW (psi) (%) (%) (psi) ______________________________________ 4000 72 260 260 425 4000/7800 74 530 530 350 7800 81 970 970 185 3100 77 29 145 685 3100/8100 76 745 745 295 8100 85 960 960 315 1500 130 23 23 1095 1500/3100 88 26 58 795 3100 77 29 145 685 1500 130 23 23 1095 1500/8100 56 485 485 325 8100 85 960 960 315 ______________________________________ All blends were OH equivalent ratio of 1:1.
In alternate embodiments, other long chain polyols may be used in part or in whole in place of PEG. For instance, the mechanical properties can be modified by blending the PEG component of the fuel with various amounts of polypropylene glycol (PPG) to form block copolymers. This effect is demonstrated in Table V. However, the use of PEG/PPG tends to yield a poor modulus. The inclusion of polypropylene for PEG tends to reduce the solubility of plasticizers and thus in most cases PEG alone is preferred and used.
The preferred plasticizer is nitroglycerin (NG), a high energy compound. The mixing of CAB and NG results in a material that is formable and plastic. Its use in the present invention results in improved mechanical properties and higher performance for the binder.
In alternate embodiments, other nitrate esters generally may serve as suitable plasticizers. Butanethol trinitrate (BTTN), triethylene glycol dinitrate (TEGDN), diethylene glycol dinitrate (DEGDN), and trimethylolethane trinitrate (TMETN) are examples of plasticizers that can be utilized within the purview of the present invention.
The crosslinking curative of the subject invention is responsible for crosslinking the various components of the fuel. A polyfunctional isocyanate containing the biuret trimer of hexamethylene diisocyanate is preferred. It has an NCO functionality of at least 3.
An especially suitable curative is Desmodur N-100, commercially available from Mobay Chemical Co., which is a complex mixture of biurets, uretediones, isocyanurates and unreacted hexamethylene diisocyanate. Optimal crosslinking and mechanical properties are obtained when the stabilizer for NG, N-methyl-p-nitroaniline (MNA), which is discussed later, acts to stabilize the complete propellant.
TABLE V ______________________________________ COMPARISON OF PEG WITH PEG/PPG COPOLYMERS ______________________________________ Parameter % Solids 73 73 73 75 75 75 Wt % PEG/ 100/0 10/90 40/60 50/50 50/50 70/30 Wt % PPG Pl:Po 2.1 1.8 1.72 2.1 2.8 2.8 NCO:OH 1.2 1.2 1.3 1.2 1.2 1.2 Mechanical Properties, 2 ipm σ (psi) 95 62 69 52 53 62 ε (%) 500 698 706 685 890 1000 E (psi) 350 135 202 165 105 140 ______________________________________
In additional embodiments of the present invention, other polyfunctional isocyanates may be successfully employed as crosslinking curatives. Pentaerythritol tetraisocyanate is a chemical which can be considered as an alternative curing agent. Difunctional isocyanates tend to increase the elasticity of the resulting fuel to a great degree, and so are generally less preferred.
Organo bismuth compounds are used as cure catalysts. Triphenyl bismuth (TPB) is the preferred cure catalyst in the present invention. It functions to speed up the crosslinking process and helps to provide a very long pot life or working life (i.e., until a viscosity of about 40 kilopoise is reached). Because TPB functions as a relatively slow reacting cure catalyst, it is particularly advantageous with large missiles where the set time for the fuel is longer. Competing and interfering reactions are minimized in this system.
Other organo metal cure catalysts can be employed in place of TPB. Examples are trialkyl bismuths, such as triethyl bismuth. Other metals can be used but they can have adverse effects unrelated to cure. The choice depends on the final fuel qualities desired, and accommodations to be made to the exigencies of the particular production process employed. The considerations involved include the size of the missile for which the fuel is being manufactured.
The metal used to form the metallized fuel used in the preferred embodiment of the present invention is free metal aluminum (Al). Al reacts with the oxidizers primarily to provide heat as a product of the combustion process. This fuel is particularly useful in larger missiles, and may be eliminated in smaller tactical missiles, or for minimum smoke missiles.
In other embodiments, different metallized fuels can be employed with that of the preferred embodiment or as substitutes for it, depending on the nature of the fuel desired. Suitable other metals for use in metallized fuels are boron and beryllium (although the latter is quite toxic).
The energetic filler employed in the preferred embodiment of the present invention is cyclotetramethylene tetranitramine (HMX), which generates heat and gases. Also useful in this capacity is cyclotrimethylene trinitramine (RDX). As can be seen in Table 6, the particle size and ratio of the energetic filler can be varied to fit the needs of a particular fuel requirement. An increase in quantity enhances the energetic nature of the fuel. HMX size affects the mechanical properties of the propellant. The modulus of elasticity is not dramatically affected by HMX diameter. However, tensile strength and especially percent elongation increase dramatically as the particle size decreases. The particle size is varied to obtain a proper viscosity for processing, but the optimum mechanical properties are achieved with the finest possible HMX.
TABLE VI ______________________________________ Effect of HMX Size on Mechanical Properties ______________________________________ HMX Size (μ) 4 2 Tensile Strength (psi) 90 97 Elongation (%) 290 450 Modulus (psi) 430 370 ______________________________________
The preferred oxidizer in the present invention is ammonium perchlorate (AP), which functions to oxidize all of the hydrocarbons and the metal, aluminum, to generate heat and gases. AP is also used to control the burning rate of the propellant. As can be seen in Table I, the particle size and ratio of the oxidizer can be varied to fit the needs of a particular fuel requirement.
The propellants provided in Examples I and II specified in Table I have the following typical properties:
TABLE VII ______________________________________ Example I Example II ______________________________________ Density (lb/in.sup.3) 0.0665 0.0665 Burning rate (1000 psi, 80° F., in/sec) 0.42 0.49 Specific impulse, 1bf-sec/1bm 271.5 271.4 ______________________________________
This invention has been described in detail with particular reference to certain preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention.
Claims (18)
1. A propellant composition comprising:
polyethylene glycol;
a nitrate ester;
the biuret trimer of hexamethylene diisocyanate;
2-nitrodiphenylamine;
N-methyl-p-nitroaniline;
an organo-bismuth compound;
a metal selected from aluminum, boron and beryllium;
cyclotetramethylene tetranitramine;
ammonium perchlorate; and,
optionally at least one crosslinking agent selected from the group consisting of trimethylol propane, glycerin, cellulose acetate butyrate, cellulose acetate and cellulose butyrate alone, or said acetate and butyrate in combination.
2. The propellant according to claim 1 wherein said organo bismuth compound is triphenyl bismuth.
3. The propellant of claim 1 wherein the crosslinking agent is chosen from the group consisting of cellulose acetate butyrate, cellulose acetate, cellulose butyrate, or a combination of the acetate and the butyrate, the weight ratio of cellulose acetate butyrate, cellulose acetate, cellulose butyrate or a combination thereof to said polyethylene glycol being about 0.01 to 0.03.
4. The propellant according to claim 1 wherein said metal is aluminum.
5. The propellant of claim 1 wherein said bioret trimer of hexamethylene diisocyanate is a polyfunctional isocyanate having an NCO functionality of at least 3.
6. The propellant according to claim 1 wherein said nitrate ester is nitroglycerine.
7. The propellant of claim 1 wherein said polyethylene glycol has a hydroxyl functionality of about 2.
8. The propellant according to claim 1 wherein said polyethylene glycol is in the form of a polymer having a molecular weight of between about 1000 and 8000.
9. The propellant of claim 1 wherein said cellulose acetate butyrate has a hydroxyl equivalent weight of about 1100.
10. The propellant of claim 1 wherein the ratio of isocyanate functional groups of said biuret trimer of hexamethylene diisocyanate to the combined hydroxyl functionality of said polyethylene glycol and cellulose acetate butyrate is about 1.1 to 1.3.
11. The propellant of claim 1 wherein said cyclotetramethylene tetranitramine has an average particle size of about 6.5 μ.
12. A propellant composition comprises by weight percent:
about 6.25 polyethylene glycol,
about 0.06 cellulose acetate butyrate,
about 19.02 nitroglycerin,
about 0.88 biuret trimer of hexamethylene diisocyanate,
about 0.19 2-nitrodiphenylamine,
about 0.60 N-methyl-p-nitroaniline,
about 0.02 triphenyl bismuth,
about 18.0 aluminum,
about 46.0 cyclotetramethylene tetranitramine, and
about 9.0 ammonium perchlorate.
13. The propellant of claim 2 which further comprises a trace amount of triphenyl bismuth.
14. The propellant of claim 12 wherein said polyethylene glycol has nominal molecular weight of 3500.
15. The propellant of claim 12 wherein said bioret trimer of hexamethylene diisocyanate is a polyfunctional isocyanate having an NCO functionality of at least 3, and wherein said polyethylene glycol has a hydroxyl functionality of about 2 and said cellulose acetate butyrate has a hydroxyl equivalent weight of about 1100.
16. The propellant of claim 12 wherein the ratio of isocyanate functional groups in said biuret trimer of hexamethylene diisocyanate to the combined hydroxyl functionality of said polyethylene glycol and cellulose acetate butyrate is about 1.1 to 1.3.
17. The propellant of claim 12 wherein said cyclotetramethylene tetranitramine has an average particle size of about 6.5μ.
18. A propellant composition comprising by weight percent:
About 6.25 polyethylene glycol,
about 0.06 cellulose acetate butyrate,
about 19.02 nitroglycerin,
about 0.88 biuret trimer of hexamethylene diisocyanate,
about 0.19 2-nitrodiphenylamine,
about 0.60 N-methyl-p-nitroaniline,
about 0.02 triphenyl bismuth,
about 18.0 aluminum,
about 47.0 cyclotetramethylene tetranitramine, and
about 8.0 ammonium perchlorate.
Publications (1)
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USH1341H true USH1341H (en) | 1994-08-02 |
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EP0790476A3 (en) * | 1996-02-15 | 1997-12-29 | Dynamit Nobel GmbH Explosivstoff- und Systemtechnik | Selfpropelled missile |
US6168677B1 (en) * | 1999-09-02 | 2001-01-02 | The United States Of America As Represented By The Secretary Of The Army | Minimum signature isocyanate cured propellants containing bismuth compounds as ballistic modifiers |
US6969434B1 (en) * | 2002-12-23 | 2005-11-29 | The United States Of America As Represented By The Secretary Of The Navy | Castable thermobaric explosive formulations |
US20140338803A1 (en) * | 2013-05-14 | 2014-11-20 | Agency For Defense Development | Smokeless propellant composition containing bismuth-based compound and method of preparing the same |
CN114591126A (en) * | 2022-03-17 | 2022-06-07 | 西安近代化学研究所 | Thermocuring intelligent gunpowder and preparation method thereof |
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EP0790476A3 (en) * | 1996-02-15 | 1997-12-29 | Dynamit Nobel GmbH Explosivstoff- und Systemtechnik | Selfpropelled missile |
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US20140338803A1 (en) * | 2013-05-14 | 2014-11-20 | Agency For Defense Development | Smokeless propellant composition containing bismuth-based compound and method of preparing the same |
US9133070B2 (en) * | 2013-05-14 | 2015-09-15 | Agency For Defense Development | Smokeless propellant composition containing bismuth-based compound and method of preparing the same |
CN114591126A (en) * | 2022-03-17 | 2022-06-07 | 西安近代化学研究所 | Thermocuring intelligent gunpowder and preparation method thereof |
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