Modified double base propellants with diisocyanate crosslinker
United States Patent 3894894
1. A propellant composition consisting of at least one of a member of nicelluloses selected from a group consisting of densified nitrocellulose, fluid ball powder nitrocellulose and plastisol nitrocellulose, at least one of a member of solid oxidizers selected from a group consisting of ammonium perchlorate, cyclotetramethylene tetranitramine, cyclotrimethylene trinitramine and nitroguanide, at least one of a member of explosive plasticizers selected from a group consisting of nitroglycerin, diethylene glycol dinitrate, triethylene glycol dinitrate and metriol trinitrate, at least one of a member of non-explosive plasticizers selected from a group consisting of triacetin, diallyl phthalate, di-n-propyl adipate, dimethyl sebacate, adiponitrile, isophorone (3,5,5-trimethyl-2-cyclohexen-1-one), o-chloronitrobenzene and dinitrotoluene, a stabilizer selected from a group consisting of 2-nitrodiphenylamine resorcinol diacetate and symmetrical diethyldiphenylurea, a crosslinking agent selected from a group consisting of 2,4-tolylene diisocyanate, hexamethylene diisocyanate, bitolylene diisocyanate, polyaryl polyisocyanate, 2,6-diisocyanate and 3,3'-dimethyl diphenylmethane 4,4'-diisocyanate, and a crosslinking catalyst selected from a group consisting of ferric acelylacetonate, lead 2-ethylhexoate, and di-n-butyl tin diacetate.
US Patent References:
Propellent powder
O'Neil, Jr. - December 1959 - 2916775
Method of manufacturing solid propellants having a polymeric fuel-binder using a plurality of crosslinking agents
Barr - October 1961 - 3002830
Propellent powder
O'Neil, Jr. - December 1959 - 2916775
Method of manufacturing solid propellants having a polymeric fuel-binder using a plurality of crosslinking agents
Barr - October 1961 - 3002830
Application Number:
04/202355
Publication Date:
07/15/1975
Filing Date:
06/08/1962
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Export Citation:
Assignee:
The United States of America as represented by the Secretary of the Navy (Washington, DC)
Primary Class:
Other Classes:
149/98, 149/38, 149/92, 149/19.920, 149/20, 149/19.800
International Classes:
C06B21/00; C06B23/00; C06B25/26; C08G18/64; C06B25/00; C08G18/00; C06D5/06
Field of Search:
149/19,76,98,103,92,38,19.4,19.8,19.92,20
Primary Examiner:
Padgett, Benjamin R.
Assistant Examiner:
Miller E. A.
Attorney, Agent or Firm:
Sciascia, Miller Roy R. S.
Claims:
What is claimed is
1. A propellant composition consisting of at least one of a member of nitrocelluloses selected from a group consisting of densified nitrocellulose, fluid ball powder nitrocellulose and plastisol nitrocellulose, at least one of a member of solid oxidizers selected from a group consisting of ammonium perchlorate, cyclotetramethylene tetranitramine, cyclotrimethylene trinitramine and nitroguanide, at least one of a member of explosive plasticizers selected from a group consisting of nitroglycerin, diethylene glycol dinitrate, triethylene glycol dinitrate and metriol trinitrate, at least one of a member of non-explosive plasticizers selected from a group consisting of triacetin, diallyl phthalate, di-n-propyl adipate, dimethyl sebacate, adiponitrile, isophorone (3,5,5-trimethyl-2-cyclohexen-1-one), o-chloronitrobenzene and dinitrotoluene a stabilizer selected from a group consisting of 2-nitrodiphenylamine resorcinol diacetate and symmetrical diethyldiphenylurea, a crosslinking agent selected from a group consisting of 2,4-tolylene diisocyanate, hexamethylene diisocyanate, bitolylene diisocyanate, polyaryl polyisocyanate, 2,6-diisocyanate and 3,3'-dimethyl diphenylmethane 4,4'-diisocyanate, and a crosslinking catalyst selected from a group consisting of ferric acelylacetonate, lead 2-ethylhexoate, and di-n-butyl tin diacetate.
2. A method for the preparation of a modified double base propellant grain comprising the steps of (1) adding while stirring at about 2 mm pressure nitrocellulose, ammonium perchlorate and aluminum to a solution composed of nitroglycerin, di-n-propyl adipate, 2-nitrophenylamine, resorcinol diacetate, 2,4-tolylene diisocyanate and ferric acetylacetonate, (2) transferring the resulting mixture under lower pressure to a container, and (3) curing for about seven days at a temperature ranging between 100° to 120° C.
3. A method for the preparation of modified double base propellants comprising the steps of (1) stirring 100 parts of the following mixture consisting of (a) 11 parts by weight nitrocellulose, (b) 22 parts by weight ammonium perchlorate, (c) 20 parts by weight aluminum, (d) 34.79 parts by weight nitroglycerin, (e) 11.13 parts by weight triacetin, (f) 1.03 parts by weight 2-nitrodiphenylamine and (g) 0.07 parts by weight lead 2-ethylhexoate, with 58 parts methylene chloride until the solids are well dispersed, (2) removing all but about 10% of the methylene chloride by heating to a temperature of about 40° - 45° C., (3) adding 0.3 parts by weight 2,4-tolylene diisocyanate, (4) transferring the mixture under pressure of about 15 psi. to a curing container and (5) curing for about 16 hours at about 50° C.
4. A propellant composition consisting of a binder composed of nitrocellulose, an oxidizer selected from the group consisting of ammonium perchlorate, nitroguanidine, cyclotetramethylene tetranitramine, and cyclotrimethylene tetranitramine, a solvent composed of a mixture selected from the group consisting of nitroglycerin, triacetin, nitrodiphenylamine, triethylene glycol dinitrate and diethylene glycol dinitrate, aluminum metal powder, a catalyst selected from the group consisting of lead-2-ethylhexoate and ferric acetylacetonate, and a crosslinking agent selected from the class of diisocyanates consisting of 2,4-tolylene diisocyanate, 3,3'-diisocyanate, hexamethylene diisocyanate and bitolylene diisocyanate.
5. A propellant composition consisting essentially of nitrocellulose, ammonium perchlorate, aluminum, nitroglycerin, di-n-propyl adipate, 2-nitrodiphenylamine, resorcinol diacetate, 2,4-tolylene diisocyanate and ferric acetylacetonate.
6. A propellant composition consisting essentially of from 10 to 20% nitrocellulose, about 20% ammonium perchlorate, about 20% aluminum, 28.4 to 36.2% nitroglycerin, 9 to 11.5% di-n-propyl adipate, 1% resorcinol diacetate, 1% 2-nitrodiphenylamine, 0.15 to 0.50% 2,4-tolylene diisocyanate and 0.007 to 0.05% ferric acetylacetonate; all percentages being by weight.
7. A propellant composition consisting essentially of 15 to 21.6% nitrocellulose of 70μ particle size, 20 to 20.2% ammonium perchlorate, 20 to 20.9% aluminum, 26.3 to 32.4% nitroglycerin, 8.4 to 10.15% triacetin, 1.0% 2-nitrodiphenylamine, 1.0% resorcinol, 0.10% calcium phosphate, 0.38 to 0.40% 2,4-tolylene diisocyanate, 0.01% ferric acetylacetonate and 0.03 to 0.04% dioctyl phthalate; all percentages being by weight.
8. A propellant composition consisting essentially of 15% plastisol nitrocellulose, 20% ammonium perchlorate, 20% aluminum, 32.1 to 32.25% nitroglycerin, 10.2 to 10.3% triacetin, 1.2 to 1.55% 2-nitrodiphenylamine, 0.4 to 0.8% symmetrical diethyldiphenylurea, 0.1% calcium phosphate, 0.30 to 0.45% 2,4-tolylene diisocyanate and 0.01% ferric acetylacetonate; all percentages being be weight.
1. A propellant composition consisting of at least one of a member of nitrocelluloses selected from a group consisting of densified nitrocellulose, fluid ball powder nitrocellulose and plastisol nitrocellulose, at least one of a member of solid oxidizers selected from a group consisting of ammonium perchlorate, cyclotetramethylene tetranitramine, cyclotrimethylene trinitramine and nitroguanide, at least one of a member of explosive plasticizers selected from a group consisting of nitroglycerin, diethylene glycol dinitrate, triethylene glycol dinitrate and metriol trinitrate, at least one of a member of non-explosive plasticizers selected from a group consisting of triacetin, diallyl phthalate, di-n-propyl adipate, dimethyl sebacate, adiponitrile, isophorone (3,5,5-trimethyl-2-cyclohexen-1-one), o-chloronitrobenzene and dinitrotoluene a stabilizer selected from a group consisting of 2-nitrodiphenylamine resorcinol diacetate and symmetrical diethyldiphenylurea, a crosslinking agent selected from a group consisting of 2,4-tolylene diisocyanate, hexamethylene diisocyanate, bitolylene diisocyanate, polyaryl polyisocyanate, 2,6-diisocyanate and 3,3'-dimethyl diphenylmethane 4,4'-diisocyanate, and a crosslinking catalyst selected from a group consisting of ferric acelylacetonate, lead 2-ethylhexoate, and di-n-butyl tin diacetate.
2. A method for the preparation of a modified double base propellant grain comprising the steps of (1) adding while stirring at about 2 mm pressure nitrocellulose, ammonium perchlorate and aluminum to a solution composed of nitroglycerin, di-n-propyl adipate, 2-nitrophenylamine, resorcinol diacetate, 2,4-tolylene diisocyanate and ferric acetylacetonate, (2) transferring the resulting mixture under lower pressure to a container, and (3) curing for about seven days at a temperature ranging between 100° to 120° C.
3. A method for the preparation of modified double base propellants comprising the steps of (1) stirring 100 parts of the following mixture consisting of (a) 11 parts by weight nitrocellulose, (b) 22 parts by weight ammonium perchlorate, (c) 20 parts by weight aluminum, (d) 34.79 parts by weight nitroglycerin, (e) 11.13 parts by weight triacetin, (f) 1.03 parts by weight 2-nitrodiphenylamine and (g) 0.07 parts by weight lead 2-ethylhexoate, with 58 parts methylene chloride until the solids are well dispersed, (2) removing all but about 10% of the methylene chloride by heating to a temperature of about 40° - 45° C., (3) adding 0.3 parts by weight 2,4-tolylene diisocyanate, (4) transferring the mixture under pressure of about 15 psi. to a curing container and (5) curing for about 16 hours at about 50° C.
4. A propellant composition consisting of a binder composed of nitrocellulose, an oxidizer selected from the group consisting of ammonium perchlorate, nitroguanidine, cyclotetramethylene tetranitramine, and cyclotrimethylene tetranitramine, a solvent composed of a mixture selected from the group consisting of nitroglycerin, triacetin, nitrodiphenylamine, triethylene glycol dinitrate and diethylene glycol dinitrate, aluminum metal powder, a catalyst selected from the group consisting of lead-2-ethylhexoate and ferric acetylacetonate, and a crosslinking agent selected from the class of diisocyanates consisting of 2,4-tolylene diisocyanate, 3,3'-diisocyanate, hexamethylene diisocyanate and bitolylene diisocyanate.
5. A propellant composition consisting essentially of nitrocellulose, ammonium perchlorate, aluminum, nitroglycerin, di-n-propyl adipate, 2-nitrodiphenylamine, resorcinol diacetate, 2,4-tolylene diisocyanate and ferric acetylacetonate.
6. A propellant composition consisting essentially of from 10 to 20% nitrocellulose, about 20% ammonium perchlorate, about 20% aluminum, 28.4 to 36.2% nitroglycerin, 9 to 11.5% di-n-propyl adipate, 1% resorcinol diacetate, 1% 2-nitrodiphenylamine, 0.15 to 0.50% 2,4-tolylene diisocyanate and 0.007 to 0.05% ferric acetylacetonate; all percentages being by weight.
7. A propellant composition consisting essentially of 15 to 21.6% nitrocellulose of 70μ particle size, 20 to 20.2% ammonium perchlorate, 20 to 20.9% aluminum, 26.3 to 32.4% nitroglycerin, 8.4 to 10.15% triacetin, 1.0% 2-nitrodiphenylamine, 1.0% resorcinol, 0.10% calcium phosphate, 0.38 to 0.40% 2,4-tolylene diisocyanate, 0.01% ferric acetylacetonate and 0.03 to 0.04% dioctyl phthalate; all percentages being by weight.
8. A propellant composition consisting essentially of 15% plastisol nitrocellulose, 20% ammonium perchlorate, 20% aluminum, 32.1 to 32.25% nitroglycerin, 10.2 to 10.3% triacetin, 1.2 to 1.55% 2-nitrodiphenylamine, 0.4 to 0.8% symmetrical diethyldiphenylurea, 0.1% calcium phosphate, 0.30 to 0.45% 2,4-tolylene diisocyanate and 0.01% ferric acetylacetonate; all percentages being be weight.
Description:
The present invention relates to the crosslinking of modified double base propellants by reacting the nitrocellulose binder with a suitable polyfunctional crosslinking agent such as a diisocyanate. Reaction occurs during cure and results in improved physical properties over non-crosslinked versions provided that the amount of nitrocellulose in the binder phase is sufficiently small.
Modified doubled base propellants contain a solid oxidizer such as ammonium perchlorate, a metal fuel such as aluminum, and a liquid organic nitrate plasticizer such as nitroglycerin in addition to the nitrocellulose binder and can be prepared in a number of ways. Most modified double base propellants are prepared using a casting process, wherein casting powder granules containing nitrocellulose, solid oxidizer, metal fuel and a plasticizer (usually nitroglycerin) are immersed in additional plasticizer and allowed to cure. during cure the granules expand and coalesce to form the cast propellant. These propellants have satisfactory physical properties if the nitrocellulose content in the binder phase is sufficiently high, about 23 volume percent. Specific impulse of the propellant would be improved if additional solid oxidizer could be substituted for a portion of the nitrocellulose. There are two reasons that the nitrocellulose content in propellants is kept above this level. First, high density casting powder containing small amounts of nitrocellulose is very difficult to prepare, and second, physical properties particularly modulus and tensile strength, would be quite low. The second disadvantage could be overcome by the use of crosslinking but there is no experimental evidence of this.
Other modified double base propellants are prepared using a slurry-cast process, wherein nitrocellulose in the form of very small, hard particles is mixed with the ingredients previously mentioned and the resulting slurry is poured into a container in which it is cured. During cure, the liquids plasticize the nitrocellulose and there is some swelling of the latter. The swelling, however, does not occur to the same extent as it does in cast propellants for the physical properties of cast propellants are better than those of slurry-cast propellants which are of similar composition. Crosslinked slurry-cast propellants do show increased tensile strength and elongation when compared to non-crosslinked versions and most of the experimental data in this invention is used to support this observation.
This invention also concerns solution cast propellants which comprise a third method of preparing modified double base propellants. In this method, a slurry of the previously mentioned ingredients is prepared and poured into a container and cured. The method is thus similar to slurry-cast propellants and differs from that type of propellant in that the nitrocellulose of the solution cast propellant is completely in solution prior to pouring. Solutions of normally used (military grade 10-18 sec.) nitrocellulose are quite viscous and a very low viscosity nitrocellulose (18-25 cp.) is crosslinked during the curing phase to convert the slurry to a solid mass. In this method the solid ingredients (nitrocellulose, solid oxidizer, and metal fuel) are added to a solution of casting solvent, stabilizer and crosslinking catalyst in methylene chloride. Nitrocellulose is essentially insoluble in this solution and thus may be well dispersed by stirring so that dissolution does occur readily as methylene chloride is gradually removed. When about 10% methylene chloride remains in this slurry, nitrocellulose is in solution. The crosslinker is added and dispersed at this time. The slurry is now transferred to a curing container under reduced pressure and heat is applied to facilitate removal of the remaining methylene chloride. The purpose of the diluent, methylene chloride, is thus twofold: a means of ensuring rapid dissolution of nitrocellulose and a means of increasing fluidity so that transfer can be more readily effected.
The primary purpose of the present invention is to improve the physical properties of slurry-cast propellants by crosslinking the nitrocellulose binder. Other purposes include the improvement by cross-linking of physical properties of cast propellants containing small amounts, less than about 23 volume percent, of nitrocellulose in the binder phase and a new method of preparing modified double base propellants, wherein a slurry containing nitrocellulose in solution is made more or less rigid by crosslinking that binder.
It is, therefore, an object of the present invention to improve physical properties of modified double base propellants.
Another object is the improvement of specific impulse.
Still another object is to provide a process for the production of propellant grains which has the economic advantages of reduced time, equipment and labor.
A further object of the present invention is the provision of a method for casting propellant grains which has the potential advantage of even greater simplicity and versatility than the standard casting procedure.
A still further object is the preparation of a propellant composition that can be poured into a motor and by suitable means polymerized to a solid bonded to the motor.
Other objects and many of the attendant advantages of this invention will be readily appreciated as the same become better understood in the following detailed description.
The mechanism of the crosslinking involves the reaction of the hydroxyl groups of the nitrocellulose with a polyfunctional crosslinker such as a diisocyanate. Commercial nitrocellulose has roughly 2.2 to 2.5 nitrate groups and 0.8 to 0.5 hydroxyl groups per monomer length. These hydroxyl groups can react more or less readily with difunctional molecules to form crosslinks which, in effect, increase the size of the molecule, change the structure from linear to branched, and alter the physical characteristics of the polymer. Crosslinking tends to increase the rigidity of the propellant matrix and the tendency for flow to occur at normal temperatures is decreased. Because of this change the tensile strength and modulus are increased and the elongation decreased at normal temperatures.
Crosslinking then improves the physical properties of solution cast propellants, which would flow if not crosslinked and should improve the physical properties of cast propellants containing small amounts of nitrocellulose by making the propellant matrices more rigid. Crosslinking apparently improves physical properties of slurry cast propellants by strengthening the nitrocellulose which has expanded into the areas immediately surrounding the metal fuel and solid oxidizer.
In addition to nitrocellulose, the ingredients involved in the crosslinking reaction are the crosslinker and crosslinking catalyst. In this invention 2,4-tolylene diisocyanate was the principal diisocyanate used because it was readily available. Hexamethylene diisocyanate and bitolylene diisocyanate have been used in other work and were shown to react at a similar rate and with similar effects. Polyaryl polyisocyanate was used as a substitute for 2,4-tolylene diisocyanate in a solution cast propellant with good results. Other diisocyanates such as 2,6-tolylene diisocyanate or 3,3'-dimethyl diphenylmethane 4,4-diisocyanate could also be used. The crosslinking catalyst for the diisocyanatehydroxyl reaction was either ferric acetylacetonate or lead 2-ethylhexoate. Other catalysts as di-n-butyl tin diacetate should also give satisfactory results. Other crosslinking systems that could be used include titanates, and anhydrides.
Any ingredient, which does not interfere with the crosslinking action or does not adversely affect propellant stability, may be used in crosslinked modified double base propellants. A metal powder, such as aluminum, is used as a fuel to obtain a high theoretical specific impulse. A liquid fuel, such as carboranylmethyl acrylate, has also been incorporated. A solid oxidizer such as ammonium perchlorate should also be present in the propellant to obtain acceptable delivered impulses. Nitroguanidine, cyclotetramethylene tetranitramine (HMX) and cyclotrimethylene trinitramine were also successfully incorporated as oxidizers into the crosslinked solution or slurry cast propellants. 2-Nitrodiphenylamine and resorcinol are usually used as stabilizers in modified double base propellants. That amine or ethyl Centralite (symmetrical diethyldiphenylurea) can be used in crosslinked versions but resorcinol does react with the diisocyanate. Resorcinol diacetate does not react with a diisocyanate and has been used as the second stabilizer.
The choice of a plasticizer, which is composed of explosive (an organic nitrate) and non-explosive (an ester, ketone, nitrile or nitro compound) components, is likewise only limited by consideration of reactivity and compatibility and the additional consideration of volatibility. In addition to nitroglycerin, other organic nitrates such as diethylene glycol dinitrate, triethylene glycol dinitrate and metriol trinitrate have been successfully used in crosslinked propellants. Esters such as triacetin (glycerol triacetate), diallyl phthalate, di-n-propyl adipate and dimethyl sebacate and a nitrile such as adiponitrile have been used and a ketone such as isophorone (3,5,5-trimethyl-2cyclohexen-1-one) or a nitro compound such as o-chloronitrobenzene or dinitrotoluene can be used.
A more comprehensive understanding of this invention is obtained by reference to the following examples:
EXAMPLE I ______________________________________ Composition (Parts by weight) ______________________________________ Nitrocellulose (12.2%N, 18-25 cp.) 11 Ammonium perchlorate 22 Aluminum (Alcoa 123) 20 Nitroglycerin 34.79 Triacetin 11.13 2-Nitrodiphenylamine 1.03 Lead 2-ethylhexoate 0.07 2,4-Tolylene diisocyanate 0.30 ______________________________________
The mixing procedure involves mixing all the ingredients above listed (100 parts) except for the crosslinker (2,4-tolylene diisocyanate) and 58 parts methylene chloride in a rotating container until the solids are well dispersed. Methylene chloride was gradually removed by heating and reduced pressure application as rotational stirring was continued. When only about 10% methylene chloride remained, the crosslinking agent, 2,4-toluene diisocyanate was added and mixed. The mixture was now transferred to a curing container under reduced pressure (1mm.) and heated to 40° - 45° C. to facilitate removal of the remaining methylene chloride. A curing time of 16 hours at 50° C. was adequate. Casting time of 1 to 3 hours and gel time of 6 to 16 hours were used. The gel time is the time required for the slurry to change to a nonfluid mass. Physical properties of a representative sample of this propellant at 77° F. showed tensile strength of 19 psi., a modulus of 130 psi. and an elongation value of 21%.
EXAMPLE II
The composition and procedure as described in Example I with 0.4 parts polyaryl polyisocyanate used as a crosslinking agent in lieu of 2,4-tolylene diisocyanate. The physical properties at 77° F. of a sample of this propellant showed a modulus value of 70 psi., a tensile strength of 13 psi. and elongation value of 19%.
EXAMPLE III ______________________________________ Composition (% by weight) ______________________________________ Nitrocellulose (densified, sub 40 mesh) 10 Ammonium perchlorate 20 Aluminum 20 Nitroglycerin 36.2 Di-n-propyl adipate 11.5 2-Nitrodiphenylamine 1.0 Resorcinol diacetate 1.0 2,4-Tolylene diisocyanate .25 Ferric acetylacetonate .05 ______________________________________
The mixing procedure of this composition involves mixing of the above ingredients (200 g) in a Morton stirring flask at a reduced pressure (2 mm.). The slurry was transferred under pressure into a glass container and subjected to reduced pressure to remove entrained and dissolved air. The propellane was not cured for 4 days at 140° F. This sample showed a low tensile strength of 24 psi., a modulus of 120 psi., and an elongation value of 81% at 77° F.
The stirring of the ingredients may also be accomplished in a modified Aseptic Dispersall Unit which is driven by a Waring Blendor.
EXAMPLE IV ______________________________________ Composition (% by weight) ______________________________________ Nitrocellulose (densified, sub 40 mesh) 15 Ammonium perchlorate 20 Aluminum 20 Nitroglycerin 32.25 Di-n-propyl adipate 10.32 2-Nitrodiphenylamine 1.0 Resorcinol diacetate 1.0 2,4-Tolylene diisocyanate 0.38 Ferric acetylacetonate 0.05 ______________________________________
The above ingredients (550 g) were all mixed in a stirring flask at reduced pressure as described in Example III. Physical properties at 77° F. were as follows: tensile strength 42 psi., modulus 220 psi. and elongation 42%.
EXAMPLE V ______________________________________ Composition (% by weight) ______________________________________ Nitrocellulose (densified, sub 60 mesh) 15 Ammonium perchlorate 20 Aluminum 20 Nitroglycerin 32.28 Di-n-propyl adipate 10.33 2-Nitrodiphenylamine 1.0 Resorcinol diacetate 1.0 2,4-Tolylene diisocyanate 0.38 Ferric acetylacetonate 0.01 ______________________________________
The batch size was 300 grams. Ingredients were mixed in a modified Aseptic Dispersall Unit which was driven by a Waring Blendor. To a solution of all ingredients (tolylene diisocyanate, resorcinol diacetate, and ferric acetylacetonate) which are soluble in the casting solvent (liquid organic nitrate and non-explosive plasticizer) was added the solid ingredients. These were added singly to minimize the amount of material that must be folded in at any one time. The order of addition was nitrocellulose, oxidizer, and then aluminum. Reduced pressure was applied after solids wetting was completed to remove most of the entrained air. The slurry was transferred into a glass container in which removal of entrained air was completed. The propellant was cured for 4 days at 120° F. Tests of this sample at 77° F. showed the modulus value at 450 psi.; tensile strength at 81 psi., and elongation at 57%.
EXAMPLE VI ______________________________________ Composition (% by weight) ______________________________________ Nitrocellulose (densified, washed) 20 Ammonium perchlorate 20 Aluminum 20 Nitroglycerin 28.64 Di-n-propyl adipate 9.17 2-Nitrodiphenylamine 1.0 Resorcinol diacetate 1.0 2,4-Tolylene diisocyanate 0.18 Ferric acetylacetonate 0.007 ______________________________________
The above ingredients were mixed together in a Aseptic Dispersall Unit, the solids being added singly to minimize the amount of material that must be folded in at any one time as described in Example V. The nitrocellulose was washed with methylene chloride to remove a small amount of methyl isobutyl ketone for the purpose of improving slurry pot life. Tests of samples of the propellant revealed the following physical properties at 77° F.: tensile strength, 72 psi., modulus, 800 psi., and elongation value 29%.
EXAMPLE VII ______________________________________ Composition (% by weight) ______________________________________ Nitrocellulose (densified sub 40 mesh) 15 Ammonium perchlorate 7 Cyclotetramethylene tetranitramine 14 Aluminum 16 Nitroglycerin 32.28 Di-n-propyl adipate 10.33 2-Nitrodiphenylamine 1.0 Resorcinol diacetate 1.0 2,4-Tolylene diisocyanate 0.38 Ferric acetylacetonate 0.01 Ferric oxide 3.0 ______________________________________
The above ingredients were rotationally mixed in an Aseptic Dispersall Unit as described in Example V. The product was then cured 4 days at 100° F. Tests were made which show the following physical characteristics at 77° F.: tensile strength, 46 psi.; modulus, 350 psi.; and elongation value 44%.
EXAMPLE VIII ______________________________________ Composition (% by weight) ______________________________________ Nitrocellulose (densified, sub 40 mesh) 15 Ammonium perchlorate 10 Nitroguanidine 10 Aluminum 20 Nitroglycerin 32.28 Di-n-propyl adipate 10.33 2-Nitrodiphenylamine 1.0 Resorcinol diacetate 1.0 2,4-Tolylene diisocyanate 0.38 Ferric acetylacetonate 0.01 ______________________________________
The above ingredients were rotationally mixed in the same manner as described in Example III. The product was cured for 6 days at 140° F. and tests show the following physical properties at 77° F.: tensile strength, 47 psi.; modulus, 590 psi.; and elongation 25%.
EXAMPLE IX ______________________________________ Composition (% by weight) ______________________________________ Nitrocellulose (densified, sub 40 mesh) 15 Ammonium perchlorate 20 Aluminum 20 Nitroglycerin 32.19 Triacetin 10.30 2-Nitrodiphenylamine 1.0 Resorcinol diacetate 1.0 2,4-Tolylene diisocyanate 0.50 Ferric acetylacetonate 0.01 ______________________________________
The above ingredients were mixed as described in Example V. The propellant was cured for 6 days at 140° F. and tests show the following physical properties at 77° F.: tensile strength, 38 psi.; modulus, 380 psi.; and elongation 28%.
EXAMPLE X ______________________________________ Composition (% by weight) ______________________________________ Nitrocellulose (70μ particles) 15 Ammonium perchlorate 20 Aluminum 20 Nitroglycerin 32.29 Triacetin 10.12 2-Nitrodiphenylamine 1.0 Resorcinol diacetate 1.0 Calcium phosphate 0.10 2,4-Tolylene diisocyanate 0.45 Ferric acetylacetonate 0.01 Dioctyl phthalate 0.03 ______________________________________
The above ingredients were rotationally mixed in an Aseptic Dispersall Unit, the dry ingredients being added singly; first the nitrocellulose, then the oxidizer and aluminum as described in Example V. After the solids were wetted by the remainder of the ingredients, the slurry was poured into a container and cured for a week at 120° F. The test results show the following physical characteristics at 77° F.; tensile strength, 66 psi.; modulus, 500 psi.; and elongation value 37%.
EXAMPLE XI ______________________________________ Composition (% by weight) ______________________________________ Nitrocellulose (70μ particles) 21.6 Ammonium perchlorate 20.2 Aluminum 20.9 Nitroglycerin 26.34 Triacetin 8.41 2-Nitrodiphenylamine 1.0 Resorcinol diacetate 1.0 Calcium phosphate 0.10 2,4-Tolylene diisocyanate 0.40 Ferric acetylacetonate 0.01 Dioctyl phthalate 0.04 ______________________________________
The above ingredients were mixed as described in Example IV and cured for 7 days at 120° F. The nitrocellulose was fluid ball powder with average particle size of 70μ. A test of the cured product shows the following physical characteristics at 77° F.: tensile strength, 95 psi.; modulus, 760 psi.; and elongation value 40%.
EXAMPLE XII ______________________________________ Composition (% by weight) ______________________________________ Nitrocellulose 15 Ammonium perchlorate 20 Aluminum 20 Nitroglycerin 32.15 Triacetin 10.29 2-Nitrodiphenylamine 1.54 Ethyl Centralite (symmetrical 0.46 diethyldiphenylurea) Calcium phosphate 0.10 2,4-Tolylene diisocyanate 0.45 Ferric acetylacetonate 0.01 ______________________________________
The above ingredients were mixed in the manner described in Example V. The nitrocellulose used was plastisol nitrocellulose with 10μ average particle size. The slurry was poured into a container and cured for a week at 120° F. A test of a sample of this composition shows the following physical characteristics at 77° F.: tensile strength, 148 psi.; modulus, 240 psi.; and elongation 118%.
EXAMPLE XIII ______________________________________ Composition (% by weight) ______________________________________ Nitrocellulose (plastisol, 10μ) 15 Ammonium perchlorate 20 Aluminum 20 Nitroglycerin 32.20 Diallyl phthalate 10.31 2-Nitrodiphenylamine 1.0 Resorcinol diacetate 1.0 2,4-Tolylene diisocyanate 0.38 Ferric acetylacetonate 0.01 ______________________________________
The ingredients were mixed in the manner described in Example V and cured for one day at 114° F. and 3 days at 120° F. A sample of this composition showed the following physical characteristics at 77° F.: tensile strength, 113 psi.; modulus, 165 psi.; and elongation of 91%.
EXAMPLE XIV ______________________________________ Composition (% by weight) ______________________________________ Nitrocellulose (densified, sub 40 mesh) 15 Ammonium perchlorate 20 Aluminum 20 Triethylene glycol dinitrate 42.86 2-Nitrodiphenylamine 1.0 Resorcinol diacetate 1.0 2,4-Tolylene diisocyanate 0.13 Ferric acetylacetonate 0.01 ______________________________________
These ingredients were mixed and cured in the manner described in Example III. A test of this propellant composition gives the following physical characteristics at 77° F.: tensile strength, 46 psi.; modulus, 320 psi.; and elongation 30%.
EXAMPLE XV ______________________________________ Composition (% by weight) ______________________________________ Nitrocellulose (70μ size) 20 Ammonium perchlorate 20 Aluminum 20 Diethylene glycol dinitrate 37.27 Nitroglycerin 0.08 2-Nitrodiphenylamine 1.36 Resorcinol diacetate 1.0 Calcium phosphate 0.10 2,4-Tolylene diisocyanate 0.15 Ferric acetylacetonate 0.002 Dioctyl phthalate 0.04 ______________________________________
The above ingredients were mixed in the manner described in Example V and cured for 7 days at 120° F. A sample of this composition was tested giving the following physical characteristics at 77° F.: tensile strength, 102 psi.; modulus, 740 psi.; and elongation value 34%.
The following table (page 15) shows the composition and physical properties of nineteen crosslinked slurry-cast propellants of this invention and nine non-crosslinked slurry-cast propellants to show by comparison the improvements in physical properties that were obtained by crosslinking. In this study tolylene diisocyanate (TDI) was the only crosslinker investigated because it was readily available. However, others such as polyaryl polyisocyanate and hexamethylene diisocyanate are as satisfactory.
The improvement in physical properties by crosslinking may be readily noted by comparing the physical properties of the following pairs of samples as set out in the above Table: 2 to 3, 4 to 5, 6 to 8, 11 to 12, 15 to 16, 17 to 18, 21 to 22, 24 to 25 and 26 to 28. In these pairs, a portion of the plasticizer in the non-crosslinked propellant was replaced
TABLE I ____________________________________________________________ ______________ Comparison of Physical Properties of Crosslinked and Non-crosslinked Propellants COMPOSITION Sample NC AP HMX NGD Al Nitrate Non Ex Pl NDPA EC Res RDA CP TDI FAA DOP FO No. (%) (%) (%) (%) (%) Name (%) Name (%) (%) (%) (%) (%) (%) (%) (%) (%) (%) ____________________________________________________________ ______________ 1 10 20 20 NG 36.2 DnPA 11.5 1 1 0.25 0.05 *2 15 20 20 NG 32.6 DnPA 10.4 1 1 3 15 20 20 NG 32.25 DnPA 10.32 1 1 0.38 0.05 *4 15 20 20 NG 32.6 DnPA 10.4 1 1 5 15 20 20 NG 32.28 DnPA 10.33 1 1 0.38 0.01 *6 20 20 20 NG 28.8 DnPA 9.2 1 1 7 20 20 20 NG 28.40 DnPA 9.09 1 1 0.50 0.01 8 20 20 20 NG 28.64 DnPA 9.17 1 1 0.18 0.007 9 15 7 14 16 NG 32.28 DnPA 10.33 1 1 0.38 0.01 3.0 10 15 10 10 20 NG 32.28 DnPA 10.33 1 1 0.38 0.01 *11 15 20 20 NG 32.6 TA 10.4 1 1 12 15 20 20 NG 32.19 TA 10.30 1 1 0.50 0.01 13 15 20 20 NG 32.34 TA 10.14 1 1 0.10 0.38 0.01 0.03 14 15 20 20 NG 32.29 TA 10.12 1 1 0.10 0.45 0.01 0.03 *15 20 20 20 NG 28.81 TA 9.15 1 1 0.04 16 20 20 20 NG 28.42 TA 9.03 1 1 0.10 0.40 0.01 0.04 *17 21.6 20.2 20.9 NG 26.64 TA 8.52 1 1 0.10 0.04 18 21.6 20.2 20.9 NG 26.34 TA 8.41 1 1 0.10 0.40 0.01 0.04 19 15 20 20 NG 32.21 TA 10.30 1.21 0.79 0.10 0.38 0.01 20 15 20 20 NG 32.15 TA 10.29 1.54 0.46 0.10 0.45 0.01 *21 15 20 20 NG 32.6 DAP 10.4 1 1 22 15 20 20 NG 32.28 DAP 10.33 1 1 0.38 0.01 23 15 20 20 NG 32.20 DAP 10.31 1 1 0.38 0.01 *24 15 20 20 TGDN 43 1 1 25 15 20 20 TGDN 42.86 1 1 0.13 0.01 *26 20 20 20 DGDN 37.50 1.36 1 0.10 0.04 27 20 20 20 DGDN 37.26 NG 0.08 1.36 1 0.10 0.15 0.01 0.04 28 20 20 20 DGDN 37.27 NG 0.08 1.36 1 0.10 0.15 0.002 0.04 PHYSICAL PROPERTIES Rate Mod Ten St Elong (in/min/in) (psi) (psi) (%) 0.1 120 24 81 1.0 500 33 21 0.74 220 42 42 1.0 390 37 26 1.0 450 81 57 0.1 860 48 14 0.1 860 60 19 0.1 800 72 29 0.74 350 46 44 0.1 590 47 25 0.1 150 7 24 0.1 380 37 28 1.0 200 37 44 1.0 500 66 37 1.0 550 52 32 1.0 850 103 55 0.74 620 83 29 0.74 760 95 40 0.74 190 117 134 0.74 240 148 118 0.1 190 15 13 0.74 250 54 43 0.1 165 113 91 0.1 230 16 20 0.1 320 46 30 0.74 670 68 19 0.74 510 59 16 0.74 740 102 34 ____________________________________________________________ ______________
In Table I (page 15) the abbreviations used refer to the following:
* - Propellant compositions without crosslinking agent
Nc - nitrocellulose
Ap - ammonium perchlorate that has been ground (25μ average particle size)
Hmx - cyclotetramethylene tetranitramine
Ngd - nitroguanidine
Al - Aluminum
Ng - nitroglycerin
Tgdn - triethylene glycol dinitrate
DGDN - Diethylene glycol dinitrate
Non Ex Pl - Non explosive plasticizer
DnPA - Di-n-propyl adipate
Ta - triacetin
Dap - diallyl phthalate
Ndpa - 2-nitrodiphenylamine
Ec - ethyl Centralite - summetrical diethyldiphenylurea
Res - Resorcinol
Rda - resorcinol diacetate
Cp - calcium phosphate (coating for ammonium perchlorate)
Tdi - 2,4-tolylene diisocyanate (a crosslinker)
Faa - ferric acetylacetonate (a crosslinking catalyst)
Dop - dioctyl phthalate (present in fluid ball powder to harden surface)
Fo - ferric oxide
Mod - Modulus
Ten St - Tensile strength
Elong - Elongation value
by crosslinker and catalyst in the crosslinked propellant and increases were obtained in both tensile strength and in elongation. a non-crosslinked version of Sample No. 1 shown in Table I would not have sufficient strength to maintain its shape.
There was also an improvement in physical properties when the nitrocellulose particle size was reduced. This can be shown by grouping Samples 2 through 5 as shown in Table I in the following Table designated II:
TABLE II ______________________________________ Tensile Sample Nitrocellulose Cross- Strength Elongation No. Particle Size (Mesh) linked (psi.) (%) ______________________________________ 2 sub 40 No 33 21 3 sub 40 Yes 42 42 4 sub 60 No 37 26 5 sub 60 Yes 81 57 ______________________________________
While there was some improvement in physical properties by reducing particle size in non-crosslinked versions (2 and 4), the improvement was more pronounced in the crosslinked versions (3 and 5).
Fluid ball powder and plastisol nitrocellulose are small, essentially spherical nitrocelluloses whose average particle sizes vary by a factor of seven. Again the material with the smaller particle size gave the better physical properties as is illustrated by the following Table III wherein the samples are the same as those compared in Table I.
TABLE III ______________________________________ Average Cross- Tensile Sample Nitro- Particle linker Strength Elongation No. cellulose Size (μ) (%) (psi.) (%) ______________________________________ 13 15% ball 70 0.38 37 44 14 15% ball 70 0.45 66 37 19 15% PNC 10 0.38 117 134 20 15% PNC 10 0.45 148 118 ______________________________________
Ball - fluid ball powder with average particle size of 70μ.
PNC - plastisol nitrocellulose with 10μ average particle size.
These samples 13, 14, 19 and 20, the composition of which is found in Table I, show the effect of crosslinker concentration on physical properties. An increase in crosslinker concentration gave an increase in tensile strength and a decrease in elongation.
Compositions containing other organic nitrates such as diethylene glycol dinitrate (see Table I, Samples 27 and 28) and triethylene glycol dinitrate (Table I, Sample 25) were incorporated into crosslinked propellants in this invention, and it was found necessary to decrease the crosslinker concentration from that used in the nitroglycerin based propellant from about 13 stoichiometric percent to about 4 - 5 stoichiometric percent to obtain satisfactory physical properties. A decrease in the catalyst level from 0.01 to 0.002% was also necessary for the propellant containing diethylene glycol dinitrate (Table I, Sample 28).
Solid oxidizers such as cyclotetramethylene tetranitramine and nitroguanidine were satisfactorily incorporated into the crosslinked propellants of this invention as shown in Samples No. 9 and 10 of Table I, respectively.
The casting of the propellants of this invention was accomplished by allowing the slurry with its crosslinking agent to flow into a suitable container while applying reduced pressure to that container to remove entrained air. Solution cast propellants contained methylene chloride and that diluent had to be removed while pouring. The sample size of solution cast propellants (Example I) was 200 to 300 g. These were cast in containers to a depth of from 3.5 to 6.5 inches. To obtain specimens for physical property testing, the propellant mixture was cast in a one-inch inside diameter glass test tube, which had been coated with a protective material that would permit the cured propellant mass to be removed intact, and type E tensile dumbbells were machined from the cured mass.
The sample size of slurry cast propellants (those described in Table I) was 200 - 600 g. Most of the specimens for physical property testing were obtained by casting and curing the slurry in a cellulose acetate beaker and then machining type 2 tensile dumbbells from the cured mass.
Although the invention has been described in detail in the foregoing specification it is to be understood that many variations can be made by those skilled in the art without departing from the scope thereof except as limited by the appended claims.
Modified doubled base propellants contain a solid oxidizer such as ammonium perchlorate, a metal fuel such as aluminum, and a liquid organic nitrate plasticizer such as nitroglycerin in addition to the nitrocellulose binder and can be prepared in a number of ways. Most modified double base propellants are prepared using a casting process, wherein casting powder granules containing nitrocellulose, solid oxidizer, metal fuel and a plasticizer (usually nitroglycerin) are immersed in additional plasticizer and allowed to cure. during cure the granules expand and coalesce to form the cast propellant. These propellants have satisfactory physical properties if the nitrocellulose content in the binder phase is sufficiently high, about 23 volume percent. Specific impulse of the propellant would be improved if additional solid oxidizer could be substituted for a portion of the nitrocellulose. There are two reasons that the nitrocellulose content in propellants is kept above this level. First, high density casting powder containing small amounts of nitrocellulose is very difficult to prepare, and second, physical properties particularly modulus and tensile strength, would be quite low. The second disadvantage could be overcome by the use of crosslinking but there is no experimental evidence of this.
Other modified double base propellants are prepared using a slurry-cast process, wherein nitrocellulose in the form of very small, hard particles is mixed with the ingredients previously mentioned and the resulting slurry is poured into a container in which it is cured. During cure, the liquids plasticize the nitrocellulose and there is some swelling of the latter. The swelling, however, does not occur to the same extent as it does in cast propellants for the physical properties of cast propellants are better than those of slurry-cast propellants which are of similar composition. Crosslinked slurry-cast propellants do show increased tensile strength and elongation when compared to non-crosslinked versions and most of the experimental data in this invention is used to support this observation.
This invention also concerns solution cast propellants which comprise a third method of preparing modified double base propellants. In this method, a slurry of the previously mentioned ingredients is prepared and poured into a container and cured. The method is thus similar to slurry-cast propellants and differs from that type of propellant in that the nitrocellulose of the solution cast propellant is completely in solution prior to pouring. Solutions of normally used (military grade 10-18 sec.) nitrocellulose are quite viscous and a very low viscosity nitrocellulose (18-25 cp.) is crosslinked during the curing phase to convert the slurry to a solid mass. In this method the solid ingredients (nitrocellulose, solid oxidizer, and metal fuel) are added to a solution of casting solvent, stabilizer and crosslinking catalyst in methylene chloride. Nitrocellulose is essentially insoluble in this solution and thus may be well dispersed by stirring so that dissolution does occur readily as methylene chloride is gradually removed. When about 10% methylene chloride remains in this slurry, nitrocellulose is in solution. The crosslinker is added and dispersed at this time. The slurry is now transferred to a curing container under reduced pressure and heat is applied to facilitate removal of the remaining methylene chloride. The purpose of the diluent, methylene chloride, is thus twofold: a means of ensuring rapid dissolution of nitrocellulose and a means of increasing fluidity so that transfer can be more readily effected.
The primary purpose of the present invention is to improve the physical properties of slurry-cast propellants by crosslinking the nitrocellulose binder. Other purposes include the improvement by cross-linking of physical properties of cast propellants containing small amounts, less than about 23 volume percent, of nitrocellulose in the binder phase and a new method of preparing modified double base propellants, wherein a slurry containing nitrocellulose in solution is made more or less rigid by crosslinking that binder.
It is, therefore, an object of the present invention to improve physical properties of modified double base propellants.
Another object is the improvement of specific impulse.
Still another object is to provide a process for the production of propellant grains which has the economic advantages of reduced time, equipment and labor.
A further object of the present invention is the provision of a method for casting propellant grains which has the potential advantage of even greater simplicity and versatility than the standard casting procedure.
A still further object is the preparation of a propellant composition that can be poured into a motor and by suitable means polymerized to a solid bonded to the motor.
Other objects and many of the attendant advantages of this invention will be readily appreciated as the same become better understood in the following detailed description.
The mechanism of the crosslinking involves the reaction of the hydroxyl groups of the nitrocellulose with a polyfunctional crosslinker such as a diisocyanate. Commercial nitrocellulose has roughly 2.2 to 2.5 nitrate groups and 0.8 to 0.5 hydroxyl groups per monomer length. These hydroxyl groups can react more or less readily with difunctional molecules to form crosslinks which, in effect, increase the size of the molecule, change the structure from linear to branched, and alter the physical characteristics of the polymer. Crosslinking tends to increase the rigidity of the propellant matrix and the tendency for flow to occur at normal temperatures is decreased. Because of this change the tensile strength and modulus are increased and the elongation decreased at normal temperatures.
Crosslinking then improves the physical properties of solution cast propellants, which would flow if not crosslinked and should improve the physical properties of cast propellants containing small amounts of nitrocellulose by making the propellant matrices more rigid. Crosslinking apparently improves physical properties of slurry cast propellants by strengthening the nitrocellulose which has expanded into the areas immediately surrounding the metal fuel and solid oxidizer.
In addition to nitrocellulose, the ingredients involved in the crosslinking reaction are the crosslinker and crosslinking catalyst. In this invention 2,4-tolylene diisocyanate was the principal diisocyanate used because it was readily available. Hexamethylene diisocyanate and bitolylene diisocyanate have been used in other work and were shown to react at a similar rate and with similar effects. Polyaryl polyisocyanate was used as a substitute for 2,4-tolylene diisocyanate in a solution cast propellant with good results. Other diisocyanates such as 2,6-tolylene diisocyanate or 3,3'-dimethyl diphenylmethane 4,4-diisocyanate could also be used. The crosslinking catalyst for the diisocyanatehydroxyl reaction was either ferric acetylacetonate or lead 2-ethylhexoate. Other catalysts as di-n-butyl tin diacetate should also give satisfactory results. Other crosslinking systems that could be used include titanates, and anhydrides.
Any ingredient, which does not interfere with the crosslinking action or does not adversely affect propellant stability, may be used in crosslinked modified double base propellants. A metal powder, such as aluminum, is used as a fuel to obtain a high theoretical specific impulse. A liquid fuel, such as carboranylmethyl acrylate, has also been incorporated. A solid oxidizer such as ammonium perchlorate should also be present in the propellant to obtain acceptable delivered impulses. Nitroguanidine, cyclotetramethylene tetranitramine (HMX) and cyclotrimethylene trinitramine were also successfully incorporated as oxidizers into the crosslinked solution or slurry cast propellants. 2-Nitrodiphenylamine and resorcinol are usually used as stabilizers in modified double base propellants. That amine or ethyl Centralite (symmetrical diethyldiphenylurea) can be used in crosslinked versions but resorcinol does react with the diisocyanate. Resorcinol diacetate does not react with a diisocyanate and has been used as the second stabilizer.
The choice of a plasticizer, which is composed of explosive (an organic nitrate) and non-explosive (an ester, ketone, nitrile or nitro compound) components, is likewise only limited by consideration of reactivity and compatibility and the additional consideration of volatibility. In addition to nitroglycerin, other organic nitrates such as diethylene glycol dinitrate, triethylene glycol dinitrate and metriol trinitrate have been successfully used in crosslinked propellants. Esters such as triacetin (glycerol triacetate), diallyl phthalate, di-n-propyl adipate and dimethyl sebacate and a nitrile such as adiponitrile have been used and a ketone such as isophorone (3,5,5-trimethyl-2cyclohexen-1-one) or a nitro compound such as o-chloronitrobenzene or dinitrotoluene can be used.
A more comprehensive understanding of this invention is obtained by reference to the following examples:
EXAMPLE I ______________________________________ Composition (Parts by weight) ______________________________________ Nitrocellulose (12.2%N, 18-25 cp.) 11 Ammonium perchlorate 22 Aluminum (Alcoa 123) 20 Nitroglycerin 34.79 Triacetin 11.13 2-Nitrodiphenylamine 1.03 Lead 2-ethylhexoate 0.07 2,4-Tolylene diisocyanate 0.30 ______________________________________
The mixing procedure involves mixing all the ingredients above listed (100 parts) except for the crosslinker (2,4-tolylene diisocyanate) and 58 parts methylene chloride in a rotating container until the solids are well dispersed. Methylene chloride was gradually removed by heating and reduced pressure application as rotational stirring was continued. When only about 10% methylene chloride remained, the crosslinking agent, 2,4-toluene diisocyanate was added and mixed. The mixture was now transferred to a curing container under reduced pressure (1mm.) and heated to 40° - 45° C. to facilitate removal of the remaining methylene chloride. A curing time of 16 hours at 50° C. was adequate. Casting time of 1 to 3 hours and gel time of 6 to 16 hours were used. The gel time is the time required for the slurry to change to a nonfluid mass. Physical properties of a representative sample of this propellant at 77° F. showed tensile strength of 19 psi., a modulus of 130 psi. and an elongation value of 21%.
EXAMPLE II
The composition and procedure as described in Example I with 0.4 parts polyaryl polyisocyanate used as a crosslinking agent in lieu of 2,4-tolylene diisocyanate. The physical properties at 77° F. of a sample of this propellant showed a modulus value of 70 psi., a tensile strength of 13 psi. and elongation value of 19%.
EXAMPLE III ______________________________________ Composition (% by weight) ______________________________________ Nitrocellulose (densified, sub 40 mesh) 10 Ammonium perchlorate 20 Aluminum 20 Nitroglycerin 36.2 Di-n-propyl adipate 11.5 2-Nitrodiphenylamine 1.0 Resorcinol diacetate 1.0 2,4-Tolylene diisocyanate .25 Ferric acetylacetonate .05 ______________________________________
The mixing procedure of this composition involves mixing of the above ingredients (200 g) in a Morton stirring flask at a reduced pressure (2 mm.). The slurry was transferred under pressure into a glass container and subjected to reduced pressure to remove entrained and dissolved air. The propellane was not cured for 4 days at 140° F. This sample showed a low tensile strength of 24 psi., a modulus of 120 psi., and an elongation value of 81% at 77° F.
The stirring of the ingredients may also be accomplished in a modified Aseptic Dispersall Unit which is driven by a Waring Blendor.
EXAMPLE IV ______________________________________ Composition (% by weight) ______________________________________ Nitrocellulose (densified, sub 40 mesh) 15 Ammonium perchlorate 20 Aluminum 20 Nitroglycerin 32.25 Di-n-propyl adipate 10.32 2-Nitrodiphenylamine 1.0 Resorcinol diacetate 1.0 2,4-Tolylene diisocyanate 0.38 Ferric acetylacetonate 0.05 ______________________________________
The above ingredients (550 g) were all mixed in a stirring flask at reduced pressure as described in Example III. Physical properties at 77° F. were as follows: tensile strength 42 psi., modulus 220 psi. and elongation 42%.
EXAMPLE V ______________________________________ Composition (% by weight) ______________________________________ Nitrocellulose (densified, sub 60 mesh) 15 Ammonium perchlorate 20 Aluminum 20 Nitroglycerin 32.28 Di-n-propyl adipate 10.33 2-Nitrodiphenylamine 1.0 Resorcinol diacetate 1.0 2,4-Tolylene diisocyanate 0.38 Ferric acetylacetonate 0.01 ______________________________________
The batch size was 300 grams. Ingredients were mixed in a modified Aseptic Dispersall Unit which was driven by a Waring Blendor. To a solution of all ingredients (tolylene diisocyanate, resorcinol diacetate, and ferric acetylacetonate) which are soluble in the casting solvent (liquid organic nitrate and non-explosive plasticizer) was added the solid ingredients. These were added singly to minimize the amount of material that must be folded in at any one time. The order of addition was nitrocellulose, oxidizer, and then aluminum. Reduced pressure was applied after solids wetting was completed to remove most of the entrained air. The slurry was transferred into a glass container in which removal of entrained air was completed. The propellant was cured for 4 days at 120° F. Tests of this sample at 77° F. showed the modulus value at 450 psi.; tensile strength at 81 psi., and elongation at 57%.
EXAMPLE VI ______________________________________ Composition (% by weight) ______________________________________ Nitrocellulose (densified, washed) 20 Ammonium perchlorate 20 Aluminum 20 Nitroglycerin 28.64 Di-n-propyl adipate 9.17 2-Nitrodiphenylamine 1.0 Resorcinol diacetate 1.0 2,4-Tolylene diisocyanate 0.18 Ferric acetylacetonate 0.007 ______________________________________
The above ingredients were mixed together in a Aseptic Dispersall Unit, the solids being added singly to minimize the amount of material that must be folded in at any one time as described in Example V. The nitrocellulose was washed with methylene chloride to remove a small amount of methyl isobutyl ketone for the purpose of improving slurry pot life. Tests of samples of the propellant revealed the following physical properties at 77° F.: tensile strength, 72 psi., modulus, 800 psi., and elongation value 29%.
EXAMPLE VII ______________________________________ Composition (% by weight) ______________________________________ Nitrocellulose (densified sub 40 mesh) 15 Ammonium perchlorate 7 Cyclotetramethylene tetranitramine 14 Aluminum 16 Nitroglycerin 32.28 Di-n-propyl adipate 10.33 2-Nitrodiphenylamine 1.0 Resorcinol diacetate 1.0 2,4-Tolylene diisocyanate 0.38 Ferric acetylacetonate 0.01 Ferric oxide 3.0 ______________________________________
The above ingredients were rotationally mixed in an Aseptic Dispersall Unit as described in Example V. The product was then cured 4 days at 100° F. Tests were made which show the following physical characteristics at 77° F.: tensile strength, 46 psi.; modulus, 350 psi.; and elongation value 44%.
EXAMPLE VIII ______________________________________ Composition (% by weight) ______________________________________ Nitrocellulose (densified, sub 40 mesh) 15 Ammonium perchlorate 10 Nitroguanidine 10 Aluminum 20 Nitroglycerin 32.28 Di-n-propyl adipate 10.33 2-Nitrodiphenylamine 1.0 Resorcinol diacetate 1.0 2,4-Tolylene diisocyanate 0.38 Ferric acetylacetonate 0.01 ______________________________________
The above ingredients were rotationally mixed in the same manner as described in Example III. The product was cured for 6 days at 140° F. and tests show the following physical properties at 77° F.: tensile strength, 47 psi.; modulus, 590 psi.; and elongation 25%.
EXAMPLE IX ______________________________________ Composition (% by weight) ______________________________________ Nitrocellulose (densified, sub 40 mesh) 15 Ammonium perchlorate 20 Aluminum 20 Nitroglycerin 32.19 Triacetin 10.30 2-Nitrodiphenylamine 1.0 Resorcinol diacetate 1.0 2,4-Tolylene diisocyanate 0.50 Ferric acetylacetonate 0.01 ______________________________________
The above ingredients were mixed as described in Example V. The propellant was cured for 6 days at 140° F. and tests show the following physical properties at 77° F.: tensile strength, 38 psi.; modulus, 380 psi.; and elongation 28%.
EXAMPLE X ______________________________________ Composition (% by weight) ______________________________________ Nitrocellulose (70μ particles) 15 Ammonium perchlorate 20 Aluminum 20 Nitroglycerin 32.29 Triacetin 10.12 2-Nitrodiphenylamine 1.0 Resorcinol diacetate 1.0 Calcium phosphate 0.10 2,4-Tolylene diisocyanate 0.45 Ferric acetylacetonate 0.01 Dioctyl phthalate 0.03 ______________________________________
The above ingredients were rotationally mixed in an Aseptic Dispersall Unit, the dry ingredients being added singly; first the nitrocellulose, then the oxidizer and aluminum as described in Example V. After the solids were wetted by the remainder of the ingredients, the slurry was poured into a container and cured for a week at 120° F. The test results show the following physical characteristics at 77° F.; tensile strength, 66 psi.; modulus, 500 psi.; and elongation value 37%.
EXAMPLE XI ______________________________________ Composition (% by weight) ______________________________________ Nitrocellulose (70μ particles) 21.6 Ammonium perchlorate 20.2 Aluminum 20.9 Nitroglycerin 26.34 Triacetin 8.41 2-Nitrodiphenylamine 1.0 Resorcinol diacetate 1.0 Calcium phosphate 0.10 2,4-Tolylene diisocyanate 0.40 Ferric acetylacetonate 0.01 Dioctyl phthalate 0.04 ______________________________________
The above ingredients were mixed as described in Example IV and cured for 7 days at 120° F. The nitrocellulose was fluid ball powder with average particle size of 70μ. A test of the cured product shows the following physical characteristics at 77° F.: tensile strength, 95 psi.; modulus, 760 psi.; and elongation value 40%.
EXAMPLE XII ______________________________________ Composition (% by weight) ______________________________________ Nitrocellulose 15 Ammonium perchlorate 20 Aluminum 20 Nitroglycerin 32.15 Triacetin 10.29 2-Nitrodiphenylamine 1.54 Ethyl Centralite (symmetrical 0.46 diethyldiphenylurea) Calcium phosphate 0.10 2,4-Tolylene diisocyanate 0.45 Ferric acetylacetonate 0.01 ______________________________________
The above ingredients were mixed in the manner described in Example V. The nitrocellulose used was plastisol nitrocellulose with 10μ average particle size. The slurry was poured into a container and cured for a week at 120° F. A test of a sample of this composition shows the following physical characteristics at 77° F.: tensile strength, 148 psi.; modulus, 240 psi.; and elongation 118%.
EXAMPLE XIII ______________________________________ Composition (% by weight) ______________________________________ Nitrocellulose (plastisol, 10μ) 15 Ammonium perchlorate 20 Aluminum 20 Nitroglycerin 32.20 Diallyl phthalate 10.31 2-Nitrodiphenylamine 1.0 Resorcinol diacetate 1.0 2,4-Tolylene diisocyanate 0.38 Ferric acetylacetonate 0.01 ______________________________________
The ingredients were mixed in the manner described in Example V and cured for one day at 114° F. and 3 days at 120° F. A sample of this composition showed the following physical characteristics at 77° F.: tensile strength, 113 psi.; modulus, 165 psi.; and elongation of 91%.
EXAMPLE XIV ______________________________________ Composition (% by weight) ______________________________________ Nitrocellulose (densified, sub 40 mesh) 15 Ammonium perchlorate 20 Aluminum 20 Triethylene glycol dinitrate 42.86 2-Nitrodiphenylamine 1.0 Resorcinol diacetate 1.0 2,4-Tolylene diisocyanate 0.13 Ferric acetylacetonate 0.01 ______________________________________
These ingredients were mixed and cured in the manner described in Example III. A test of this propellant composition gives the following physical characteristics at 77° F.: tensile strength, 46 psi.; modulus, 320 psi.; and elongation 30%.
EXAMPLE XV ______________________________________ Composition (% by weight) ______________________________________ Nitrocellulose (70μ size) 20 Ammonium perchlorate 20 Aluminum 20 Diethylene glycol dinitrate 37.27 Nitroglycerin 0.08 2-Nitrodiphenylamine 1.36 Resorcinol diacetate 1.0 Calcium phosphate 0.10 2,4-Tolylene diisocyanate 0.15 Ferric acetylacetonate 0.002 Dioctyl phthalate 0.04 ______________________________________
The above ingredients were mixed in the manner described in Example V and cured for 7 days at 120° F. A sample of this composition was tested giving the following physical characteristics at 77° F.: tensile strength, 102 psi.; modulus, 740 psi.; and elongation value 34%.
The following table (page 15) shows the composition and physical properties of nineteen crosslinked slurry-cast propellants of this invention and nine non-crosslinked slurry-cast propellants to show by comparison the improvements in physical properties that were obtained by crosslinking. In this study tolylene diisocyanate (TDI) was the only crosslinker investigated because it was readily available. However, others such as polyaryl polyisocyanate and hexamethylene diisocyanate are as satisfactory.
The improvement in physical properties by crosslinking may be readily noted by comparing the physical properties of the following pairs of samples as set out in the above Table: 2 to 3, 4 to 5, 6 to 8, 11 to 12, 15 to 16, 17 to 18, 21 to 22, 24 to 25 and 26 to 28. In these pairs, a portion of the plasticizer in the non-crosslinked propellant was replaced
TABLE I ____________________________________________________________ ______________ Comparison of Physical Properties of Crosslinked and Non-crosslinked Propellants COMPOSITION Sample NC AP HMX NGD Al Nitrate Non Ex Pl NDPA EC Res RDA CP TDI FAA DOP FO No. (%) (%) (%) (%) (%) Name (%) Name (%) (%) (%) (%) (%) (%) (%) (%) (%) (%) ____________________________________________________________ ______________ 1 10 20 20 NG 36.2 DnPA 11.5 1 1 0.25 0.05 *2 15 20 20 NG 32.6 DnPA 10.4 1 1 3 15 20 20 NG 32.25 DnPA 10.32 1 1 0.38 0.05 *4 15 20 20 NG 32.6 DnPA 10.4 1 1 5 15 20 20 NG 32.28 DnPA 10.33 1 1 0.38 0.01 *6 20 20 20 NG 28.8 DnPA 9.2 1 1 7 20 20 20 NG 28.40 DnPA 9.09 1 1 0.50 0.01 8 20 20 20 NG 28.64 DnPA 9.17 1 1 0.18 0.007 9 15 7 14 16 NG 32.28 DnPA 10.33 1 1 0.38 0.01 3.0 10 15 10 10 20 NG 32.28 DnPA 10.33 1 1 0.38 0.01 *11 15 20 20 NG 32.6 TA 10.4 1 1 12 15 20 20 NG 32.19 TA 10.30 1 1 0.50 0.01 13 15 20 20 NG 32.34 TA 10.14 1 1 0.10 0.38 0.01 0.03 14 15 20 20 NG 32.29 TA 10.12 1 1 0.10 0.45 0.01 0.03 *15 20 20 20 NG 28.81 TA 9.15 1 1 0.04 16 20 20 20 NG 28.42 TA 9.03 1 1 0.10 0.40 0.01 0.04 *17 21.6 20.2 20.9 NG 26.64 TA 8.52 1 1 0.10 0.04 18 21.6 20.2 20.9 NG 26.34 TA 8.41 1 1 0.10 0.40 0.01 0.04 19 15 20 20 NG 32.21 TA 10.30 1.21 0.79 0.10 0.38 0.01 20 15 20 20 NG 32.15 TA 10.29 1.54 0.46 0.10 0.45 0.01 *21 15 20 20 NG 32.6 DAP 10.4 1 1 22 15 20 20 NG 32.28 DAP 10.33 1 1 0.38 0.01 23 15 20 20 NG 32.20 DAP 10.31 1 1 0.38 0.01 *24 15 20 20 TGDN 43 1 1 25 15 20 20 TGDN 42.86 1 1 0.13 0.01 *26 20 20 20 DGDN 37.50 1.36 1 0.10 0.04 27 20 20 20 DGDN 37.26 NG 0.08 1.36 1 0.10 0.15 0.01 0.04 28 20 20 20 DGDN 37.27 NG 0.08 1.36 1 0.10 0.15 0.002 0.04 PHYSICAL PROPERTIES Rate Mod Ten St Elong (in/min/in) (psi) (psi) (%) 0.1 120 24 81 1.0 500 33 21 0.74 220 42 42 1.0 390 37 26 1.0 450 81 57 0.1 860 48 14 0.1 860 60 19 0.1 800 72 29 0.74 350 46 44 0.1 590 47 25 0.1 150 7 24 0.1 380 37 28 1.0 200 37 44 1.0 500 66 37 1.0 550 52 32 1.0 850 103 55 0.74 620 83 29 0.74 760 95 40 0.74 190 117 134 0.74 240 148 118 0.1 190 15 13 0.74 250 54 43 0.1 165 113 91 0.1 230 16 20 0.1 320 46 30 0.74 670 68 19 0.74 510 59 16 0.74 740 102 34 ____________________________________________________________ ______________
In Table I (page 15) the abbreviations used refer to the following:
* - Propellant compositions without crosslinking agent
Nc - nitrocellulose
Ap - ammonium perchlorate that has been ground (25μ average particle size)
Hmx - cyclotetramethylene tetranitramine
Ngd - nitroguanidine
Al - Aluminum
Ng - nitroglycerin
Tgdn - triethylene glycol dinitrate
DGDN - Diethylene glycol dinitrate
Non Ex Pl - Non explosive plasticizer
DnPA - Di-n-propyl adipate
Ta - triacetin
Dap - diallyl phthalate
Ndpa - 2-nitrodiphenylamine
Ec - ethyl Centralite - summetrical diethyldiphenylurea
Res - Resorcinol
Rda - resorcinol diacetate
Cp - calcium phosphate (coating for ammonium perchlorate)
Tdi - 2,4-tolylene diisocyanate (a crosslinker)
Faa - ferric acetylacetonate (a crosslinking catalyst)
Dop - dioctyl phthalate (present in fluid ball powder to harden surface)
Fo - ferric oxide
Mod - Modulus
Ten St - Tensile strength
Elong - Elongation value
by crosslinker and catalyst in the crosslinked propellant and increases were obtained in both tensile strength and in elongation. a non-crosslinked version of Sample No. 1 shown in Table I would not have sufficient strength to maintain its shape.
There was also an improvement in physical properties when the nitrocellulose particle size was reduced. This can be shown by grouping Samples 2 through 5 as shown in Table I in the following Table designated II:
TABLE II ______________________________________ Tensile Sample Nitrocellulose Cross- Strength Elongation No. Particle Size (Mesh) linked (psi.) (%) ______________________________________ 2 sub 40 No 33 21 3 sub 40 Yes 42 42 4 sub 60 No 37 26 5 sub 60 Yes 81 57 ______________________________________
While there was some improvement in physical properties by reducing particle size in non-crosslinked versions (2 and 4), the improvement was more pronounced in the crosslinked versions (3 and 5).
Fluid ball powder and plastisol nitrocellulose are small, essentially spherical nitrocelluloses whose average particle sizes vary by a factor of seven. Again the material with the smaller particle size gave the better physical properties as is illustrated by the following Table III wherein the samples are the same as those compared in Table I.
TABLE III ______________________________________ Average Cross- Tensile Sample Nitro- Particle linker Strength Elongation No. cellulose Size (μ) (%) (psi.) (%) ______________________________________ 13 15% ball 70 0.38 37 44 14 15% ball 70 0.45 66 37 19 15% PNC 10 0.38 117 134 20 15% PNC 10 0.45 148 118 ______________________________________
Ball - fluid ball powder with average particle size of 70μ.
PNC - plastisol nitrocellulose with 10μ average particle size.
These samples 13, 14, 19 and 20, the composition of which is found in Table I, show the effect of crosslinker concentration on physical properties. An increase in crosslinker concentration gave an increase in tensile strength and a decrease in elongation.
Compositions containing other organic nitrates such as diethylene glycol dinitrate (see Table I, Samples 27 and 28) and triethylene glycol dinitrate (Table I, Sample 25) were incorporated into crosslinked propellants in this invention, and it was found necessary to decrease the crosslinker concentration from that used in the nitroglycerin based propellant from about 13 stoichiometric percent to about 4 - 5 stoichiometric percent to obtain satisfactory physical properties. A decrease in the catalyst level from 0.01 to 0.002% was also necessary for the propellant containing diethylene glycol dinitrate (Table I, Sample 28).
Solid oxidizers such as cyclotetramethylene tetranitramine and nitroguanidine were satisfactorily incorporated into the crosslinked propellants of this invention as shown in Samples No. 9 and 10 of Table I, respectively.
The casting of the propellants of this invention was accomplished by allowing the slurry with its crosslinking agent to flow into a suitable container while applying reduced pressure to that container to remove entrained air. Solution cast propellants contained methylene chloride and that diluent had to be removed while pouring. The sample size of solution cast propellants (Example I) was 200 to 300 g. These were cast in containers to a depth of from 3.5 to 6.5 inches. To obtain specimens for physical property testing, the propellant mixture was cast in a one-inch inside diameter glass test tube, which had been coated with a protective material that would permit the cured propellant mass to be removed intact, and type E tensile dumbbells were machined from the cured mass.
The sample size of slurry cast propellants (those described in Table I) was 200 - 600 g. Most of the specimens for physical property testing were obtained by casting and curing the slurry in a cellulose acetate beaker and then machining type 2 tensile dumbbells from the cured mass.
Although the invention has been described in detail in the foregoing specification it is to be understood that many variations can be made by those skilled in the art without departing from the scope thereof except as limited by the appended claims.