US3036939A - Cast gas-producing charge containing nitrocellulose and vinyl polymers - Google Patents

Description

3,036,939 Patented May 29, 1962 lice 3,036,939 CAST GAS-PRODUCING CHARGE CONTAINWG NITROCELLULOSE AND VINYL POLYMERS Albert T. Camp, Frosthurg, Md, assignor to Hercules Powder Company, Wilmington, Del., a corporation of Delaware No Drawing. Filed Mar. 3, 1949, Ser. No. 79,528 8 Claims. (Cl. 14919) This invention relates to cast gas-producing charges and more particularly to cast gas-producing charges of improved physical strength and stability having useful burning characteristics.

The initial demand for relatively large grains of smokeless powder suitable for propelling military rockets or for actuating sizable jet devices such a jet-assisted take-off units for airplanes, was met by charges manufactured by the well-known solventless extrusion process. While the solvent-less process is intrinsically hazardous due to the high temperatures and pressures involved and the constant danger of fire associated with the rolling process, it is now considered feasible for manufacturing grains up to 7 or 8 inches in diameter. With the steadily increasing demand for much larger charges, however, solventless extrusion has become undesirable because of the massive and expensive equipment required to produce such grains. Consequently, most large diameter gasproducing grains are currently produced by one of several casting techniques.

In general, a cast double-base (or multi-base) gasproducing charge is fabricated by combining a casting powder, usually granulated in solid cylinders of approximately 0.03 inch in length and 0.03 inch in diameter with a casting liquid comprising nitroglycerin and suitable desensitizing plasticizers such as dimethyl phthalate or triacetin. The combination may be achieved by the addition to a suitable mold of alternate increments or a continuous and simultaneous flow of casting powder and casting liquid. The preferred method, however, is by the basal addition technique disclosed in the copending application, Serial No. 28,218, of Gordon W. McCurdy. The McCurdy process comprises loading the casting powder into a metal or plastic mold to a uniform density. The pressurized casting liquid is then introduced into the base of the mold through a base assembly comprising an air trap feature designed to prevent entrained air from rising into the matrix and a manifold distributor plate designed to evenly distribute the incoming liquid across the cross-sectional area at the base of the mold. Regardless of the method utilized to combine the casting powder and the casting liquid, the mixture is cured at a suitable curing temperature (usually about 140 F.). During curing, the plasticizers partially dissolve and swell the granules of casting powder, and in effect, bond them together to provide a consolidated mass.

While the grains produced by these casting techniques exhibit few shortcomings and have great utility, several important problems are still present which, when solved, will allow fabrication of even better gas-producing charges.

Probably an attribute most desired in a gas-producing charge is increased compressive, tensile and shear strength. Such enhanced structural qualities, particularly increased compressive strength, are especially advantageous in firing a charge, which is itself at a high temperature, and heretofore have not been achieved. 7

Another problem encountered in large diameter grains of large Web is that of internal cracking during storage, especially at elevated temperatures. Most of such cracking' is believed to result from two contributing causes, viz., the formation of gases from the decomposition of nitro-compounds such as nitrocellulose and nitroglycerin which are not absorbed by the stabilizers incorporated during manufacture, and, to some degree, from the abovediscusscd lack of optimum structural strength. When such internal cracking occurs, the obvious result in rocket charges and jet gas-producing charges generally is increased tendency to break up during combustion and consequent aberration in ballistics.

An additional problem encountered with conventional cast or extruded charges lies in the fact that calorific output and burning rate are directly proportional. When the calorific output of a charge is below about 700 cal/g, smoke is produced. Consequently, a burning rate lower than that obtained at about 700 cal./ g. cannot be achieved in a unitary charge without substantial smoke production. Lower burning rates without smoke production, however, are often desirable in applications where a more gradual gas production is preferred. This is particularly true in such applications as small gasproducing cartridges for actuating mechanical devices. A lower burning rate in the smokeless high potential charges is also desirable in some applications since it permits greater latitude in charge geometry to achieve greater neutrality in burning.

Therefore, an object of the present invention is a cast gas-producing charge of greatly enhanced structural strength.

Another object of the invention is a cast gas-producing charge of greatly increased stability which will exhibit a greatly increased resistance to internal cracking during storage at elevated temperatures.

A further object of this invention is a substantially smokeless cast gas-producing charge of increased structural strength and stability which exhibits lower burning rates than those obtained with conventional charges of the same potential,

Generally described, the present invention is a cast gas-producing charge comprising a smokeless powder dispersed in not more than 30% by weight of a polymerized vinyl material compatible therewith. The smokeless powder may be either singleor multiple-based depending on the particular application. The amount of polymerized material present in a particular gas-producing charge prepared in accordance with the invention depends on the nature of the polymerized material itself, the desired calorific output of the charge and the amount of polymerizable material which will polymerize in situ in the presence of the other components of the composition. If the polymerized material is itself explosive or semiexplosive, it will contribute to the potential of the gasproducing charge and may be used, depending on the particular application, in as large a proportion as will polymerize or copolymerize in situ. It has been found that the nonexpl-osive polymerizable materials will polymerize or copolymerize in proportion up to at least 30% by weight of the composition. If the gas-producing charge i to be used in rocket or jet applications where excessive smoke is undesirable, then the upper limit of nonexplosive polymer should generally be set at 18% in order to maintain the calorific output above the necessary 700 caL/g. below which level excessive smoke generation is generally encountered.

The polymerization products of the gas-producing charges of this invention may be formed by the polymerization in situ of polymerizable vinyl monomers or the copolymerization in situ of such monomers with other vinyl compounds which by themselves are not polymerizable in the propellent system. It is, of course, essential that the polymerization product and its constituent or constituents are compatible with the smokeless powder employed, are polymerizable in situ, and do not generate water vapor or other gaseous products during the poly- I which renders the charge worthless, especially in propellent applications. Operable vinyl materials are monomers such as vinyl, vinylene, and vinylidene compounds having the general formula of where R R and R may be hydrogen, an alkyl group or an a-lkenyl group and R may be an alkyl group. Examples of such monomers which are polymerizable and compatible with the various components of smokeless powder are: methyl acrylate, methoxy ethyl acrylate, ethyl acrylate, butyl and isobutyl acrylate, Z-ethyl hexyl acrylate, methyl methacrylate, ethyl methacrylate, butyl and isobutyl methacrylate and lauryl methacrylate.

Operable copolymers may be formed by copolymerizing in situ any of the suitable monomers, such as those above set forth, with compatible, unsaturated vinyl-type compounds such as styrene, alkyd'polyesters, divinyl benzene, allyl, diglycol carbonate and diallyl maleate. 7

All of the above materials may be readily polymerized or copolymerized in situ at temperatures of not more than 140 F. with conventional polymerization catalysts such as benzoyl peroxide, lauroyl peroxide, di-tert-butyl peroxide, tertiary butyl hydroperoxide, cumene hydroperoxide, methyl ethyl ketone peroxide, di-tert-butyl diperphthalate and tert-butyl perbenzoate.

The cast gas-producing charges of this invention are prepared by incorporating the desired polymerizable compound or compounds and a suitable polymerization catalyst in the casting liquid and then combining the casting liquid with a casting powder of predetermined composition according to any suitable casting technique. The polymerizable material may replace all or part of the conventional plasticizers and nitroglycerin desensitizers as may be desired. If the polymerizable material is explosive or semiexplosive, it may also replace part or all of the nitroglycerin or other explosive plasticizer. V The casting powder may be a single-base powder or may contain any desired amount of nitroglycerin or other explosive plasticizer. It has been found that to obtain a satisfactory gas-producing charge, the nitrocellulose content of the charge should be between 40 and 65% by weight.

In planning the formulation of a gas-producing charge in accordance with this invention, it should be borne in mind that while the disclosed polymerizable substances are compatible with the normal components of a smokeless powder including dinitrotoluene, the presence of a substantial quantity of dinitrotoluene may somewhat inhibit the polymerization of acrylic monomers with the exception of methyl methacrylate. While a substantial polymerization still takes place with the remaining acrylics, it is preferred to employ a methacrylate monomer when it is desirable to incorporate a substantial amount of dinitrotoluence. As shown by Examples 1, 6, 7, 8, 9 and 13, methyl methacrylate polymerizes readily in the presence of substantial amounts of dinitrotoluene.

Having generally described the invention, the following.

examples are presented for purposes of more specific illustration. These examples set forth a number of formulations, the preferred casting techniques, and the many novel properties resulting from the polymer content. The various parent powders referred to in the examples are the conventional formulations incorporating conventional plasticizers in place of the polymerizable material. In order to permit a ready comparison of all the formulations described in-the examples and a comparison between those formulations and their parent compositions, Table 1 is included following Example 13 in which is shown the results of physical, chemical and thermal tests of all the powders set forth and their parent compositions. Total polymer, by analysis, was considered to be thatportion of the powder (less carbon) which did not dissolve in the conventional extraction with methylene chloride. Total volatiles were determined by the well-known, solution-evacuation technique. Ultimate compressive strength at the loading rate of 10,000 p.s.i./sec. and at various temperatures was measured in a high-rate compression tester using cylinders either 0.375 in. 'diameter'by 0.75 in. length or 0.50 in. diameter by 1.0 in. length. The work required to cause rupture by compression of cylinders 1.125 in. diameter by 2.25 in. length was measured at +25 C. on the powder described in Example 5 and on its parent powder. The apparatus was a Southwark-Tate-Emery Universal Testing Machine operated at a compression rate of 0.1 in./ min/in. Work was computed as thetotal area under the stress-straincurve. in general, thermal stability of the powders was compared by heating 2 in.-cubes at C., with daily radiographic inspection, until internal cracks appeared. A fewpowders were also tested in a'modified Taliani' apparatus operating at C. under nitrogen atmosphere. Although this test showed stability improvements of smaller magnitude than the 80 C. test of cubes, the reduction in rate of gassing'at 110 C. is also significant in the examples given.

' EXAMPLE 1 Cast double-base grains of the following nominal composition were prepared by suitably combining in a 67:33

1 Contained 0.006% of hydroquinone.

The casting powder was prepared in the form of cylinders 0.03 inch in diameter and 0.03 inch in length by a conventional, single-base solvent process well known to the art and the solvent removed therefrom. The casting powder was loaded with vibration into cellulose acetate molds 4 inches in diameter and 12 inches in length to a uniform bulk density of 0.036 lb./cu. in. The loaded molds were placed in vacuum desciccators for 16 hours at an absolute pressure of less than 10 mm. of mercury. The casting liquid was prepared' by dissolving 1.25% of ethyl central'ite and 25% of dimethyl phthalate in 73.75% of nitroglycerin and evacuating the resulting solution according to standard practice at an absolute pressure of less than 10 mm. of mercury for a period of three hours. Vacuum was released and the methyl methacrylate and benzoyl peroxide catalyst were admixed just prior to use in casting.

The molds of casting powder were removed from vacuum and were fitted at their base with the air trap base assemblies which have previously been discussed and are fully described in copending application No. 28,218.

Cheesecloth over the bottoms of the molds prevented loss 5 to the top of the grain to insure good consolidation, the pinch clamp was tightened to prevent leakage, the top of the cellulose acetate mold was tightly covered with masking tape, the liquid supply system was detached and the mold and base assembly were placed in a forced air oven maintained at a temperature of 140 F. for 100 hours.

After curing, the grains were sectioned near each end for purposes of inspection. Specimens for physical and chemical testing were then machined from the remaining powder.

Consolidation of the powder was excellent. As shown in Table 1, ultimate compressive strength was approximately 45% higher than that of the parent powder, thermal stability was equivalent to that of the unmodified powder, and chemical analysis indicated virtually complete polymerization of the methyl methacrylate and no inordinate volatiles content in the finished powder.

EXAMPLE 2 Cast double base grains of the following nominal composition were prepared by suitably combining, in a 65 :35 weight ratio, casting powder and casting liquid having the formulas shown in adjoining columns.

Cast Casting Casting Ingredients matrix, powder, liquid,

percent percent percent Nitrocellulose (13.15% N) Nitroglyoerin Ethyl Oentralite Dinitrotoluena. Triaeetin Graphite (glaze) Methyl mcthaerylate Benzoyl peroxide (added) l Contained 0.006% of hydroquinone.

EXAMPLE 3 Cast doublebase grains of the following nominal composition were prepared by suitably combining in a 67:33 weight ratio, casting powder and casting liquid having the formulas shown in the adjoining columns.

Cast Casting Casting Ingredients matrix, powder, liquid,

percent percent percent Nitrocellulose (12.6% N) 66. 3 99.

' t- 21. 8 65. 8 1. 0 1. 0 1. O 4. 3 13. 2 0v 02 0. 03 Graphite (glaz 0. 03 0. 05 Methyl methaerylate 6. 6 20 0 Benzoyl peroxide (added) 0. 05 0.

1 Contained 0.006% of hydroquinone.

The casting powder and casting liquid were prepared, loaded, and evacuated according to procedures described in Example 1. Combination of the powder and liquid, curing, and machining were also in accordance with the methods used in Example 1.

Consolidation of the powder was excellent and ultimate compressive strength was approximately 85% higher than that of the parent powder. Thermal stability was at least equivalent to that of the parent powder and polymerization appeared to be virtually complete.

6 EXAMPLE 4 Cast double-base grains of the following nominal composition were prepared by suitably combining in a 65:25 weight ratio, casting powder and casting liquid having the formulas shown in the adjoining columns.

Cast Casting Casting Ingredients matrix, powder, liquid, percent percent percent Nitrocellulose (12.6% N) 64. 3 99. 0 Nitroglycerin 20. 7 59.0 Ethyl Centralite 1.0 1.0 1.0 Dimethyl phthalat 7.0 20.0 Carbon black (added). 0. 13 0.2 Graphite (glaze) 0.03 0.05 Ethyl acrylate 7. 0 20.0 Benzoyl peroxide (added) 0.02 0.06

EXAMPLE 5 Cast double-base grains of the following nominal composition were prepared by suitably combining in approximately a 66:34 weight ratio, casting powder and casting liquid having the formulas shown in the adjoining columns.

Cast Casting Casting Ingredients matrix, powder, liquid.

percent percent percent Nitrocellulose (12.6% N) 63. 30 99. 0

N itroglyeerin 24. 2 70. 0

Ethyl Oentra1ite 1.0 1.0 1.0

Ethyl acrylate 9. 5 29.0 Carbon black (added)- 0. 13 0.2 Graphite (glaze) 0. 03 0. 05 Lupersol l DDM (added) 0.09 0.25

1 60% methyl ethyl ketone peroxide in dimethyl phthalate.

The casting powder was prepared, loaded and evacuated according to conventional procedures as described in Example 1. The casting liquid was prepared by adding nitroglycerin to a mixture of distilled ethyl acrylate, ethyl centralite and peroxide catalyst. The liquid was not evacuated before casting. Combination of the casting powder and casting liquid, and curing and machining of the cast grain were in accordance with the methods used in Example 1.

Consolidation of the powder was excellent, being much superior to that of a conventionally formulated cast powder made with unevaeuated casting liquid (70% nitroglycerin, 29% dimethyl phthalate, 1% ethyl centralite) and equivalent to that of conventional powder made with evacuated solvent containing 70% nitroglycerin, 29% dimethyl phthalate, 1% ethyl centralite.

Ultimate compressive strength at a loading rate of 10,000 p.s.i./sec. was higher than that of a powder containing dimethyl phthalate in place of all of the ethyl acrylate. The work required to produce rupture by co1npression of 1% in. diameter, 2% in. length cylinders at the compression rate of 0.1 in./min./in. Was 207 ft./lb./cu. in. of powder, this being nearly four times the work required for cylinders of the parent powder shown in Table l and from two to seven times as great as the work required to produce rupture of similar cylinders of other known cast powders containing no polymerizable material. Thermal stability of the powder was considerably better than that of the parent powder.

Strands of the cast powder were cut to a 4;" x Ma cross section and 7 length-and after application of a restrictive coating were end-burned in a bomb containing nitrogen at various pressure levels. The powder burned very satisfactorily giving'a burning rate of 0.23 in./sec. at 1000 p.s.i. pressure. The calculated-specific impulse of the powder also showed that it was a satisfactory rocket propellant. The measured energy of explosion of the powder was 880 ca./g. which would insure a virtually smokeless propellant. The low burning rate of this propellant is useful in the design of charges for certain jet-assisted take-off applications.

EXAMPLE 6 A cast, double-base grain of the following nominal composition was prepared by combining in a 65:35 weight ratio casting powder and casting liquid having the formulas shown in the adjacent columns.

Cast Casting Casting Ingredients matrix, powder, liquid,

percent percent percent Nitrocellulose (12.6% N) 57. 9 89.0 Nitroglycerin 23. 2 66. 5 Ethyl Centre-lite. 1.0 1.0 1.0 Dinitrotoluene. 6. 5 10. Dlrnethyl phalate... 7. 9 22. Methyl methacrylate 3. 5 10.0 Carbon black (added). 0. 13 0. 2 Graphite (glaze) 0. 03 0.05 Benzoyl peroxide (added) 0.03 0.08

1 Containing 0.006% of hydroquinone.

EXAMPLE 7 Cast, double-base grains of the following nominal composition were prepared by combining in a 67:33 weight ratio casting powder and casting liquid having the formulas shown in the adjoining columns.

l Contained 0.006% hydroquinone.

The casting powder was prepared, loaded, and evacuated according to procedures described in Example 1. The casting liquid was prepared by adding the allyl diglycol carbonate to a casting liquid composed of 74% nitroglycerin, 25 dimethyl phthalate, 1% ethyl centralite, and evacuating this mixture for 3 hours at an absolute pressure of less than 10 mm. of mercury. Vacuum was released and methyl methacrylate and catalyst were admixed just prior to use in casting. Combination of the powder and solvent, and curing and machining of the cast grains were in accordance with the methods described in Example 1.

Consolidation and degree of homogeneity of the powder were excellent, Ultimate compressive strength was approximately 24% higher than that of the parent cast powder and thermal stability was considerably better as measured both by a modified Taliani test at 110 C. under nitrogen atmosphere, and by a heating test of 2 in. cubes at 80 C. Chemical analysis of the powder indicated that most of the allyl diglycol carbonate had copolymerized with the methyl methacrylate. No ob= jectionable increase in volatiles content of the finished powder was noted.

EXAMPLE 8 *Cast, double-base grains having the nominal composition of powder described in Example 7, with the exception that diallyl maleate was substituted for allyl diglycol carbonate, were prepared by identical techniques.

Physical pnoperty measurements showed, a 22% increase in compressive strength over the parent powder. Consolidation was very satisfactory and thermal stability tests showed improvements over the parent powder which were slightly greater than those of the Example 7 powder.

EXAMPLE 9 Cast, double-base brains of the following nominal composition were prepared by combining in a 67 :33 weight ratio casting powder and casting liquid having the formulas shown in adjoining columns.

Cast Casting Casting Ingredients matrix, powder, liquid,

percent percent percent Nitrocellulose (12.6% N) 59. 6 Nitroglyoerin -t 19. 5 Ethvl Centralite 1.0 Dinitroluene 6. 7 Dlmethyl phthalat 6. 6 Methyl methacrylat 4. 9 Divinyl benzene 1.7 Carbon black (added) 0. 13 I Graphite (glaze) 0.03 Lnpersol DDM (added) 3 0. 08

1 Containing 0.006% of hydroquinone.

Z Supplied by Koppers Company, Inc., as a 40% solution of DVB 1n related monofunctional monomers.

3 60% methyl ethyl lretone peroxidein dimethyl phthalate,

The casting powder was prepared, loaded, and evacuated according to procedures described in Example 1. The casting liquid was. prepared by adding the methyl rnet-hac-rylate, catalyst, and divinyl benzene solution to a previously evacuated (three hours at 10 mm. of mercury) solution composed of 74% nitroglycerin, 25% dimethyl phthalate, and 1% ethyl centralite. Combination of the powder and solvent, and curing and machining of the cast grains were in accordance with the methods described in Example 1.

Physical tests of cylinders of the cured propellant showed a 43% increase in compressive strength over the parent powder. Consolidation and degree of homogeneity were highly satisfactory and the result of an C. storage test of 2 in. cubes showed some improvement over the parent powder. Crosslinking of the acrylic with divinyl benzene was confirmed by an acetone-solubility test of the powder, which was shown to contain 6.3% of acetone-insoluble polymer.

Strands of the powder, x x 7 in. were coated with plastic solutions to restrict burning to a single end and were burned at various pressure levels in a nitrogen filled bomb. The powder burned in a regular manner giving a rate of 0.18 in./ sec. at 1000 p.s.i. which fact gives the propellant utility in the design of charges for certain jetassisted take-off applications.

EXAMPLE 10 Cast, double-base grains of the following nominal composition were prepared by combining in a 65:35 weight 1 60% methyl ethyl ketone peroxide in dimethyl phthalate. The casting powder was prepared by a solvent process,

' dn'edin ai-r'at 140 F. for 6 days, and glazed with graphite and screened. It was loaded into cellulose acetate molds and evacuated according to the procedure described in Example 1. The casting liquid was prepared by adding the nitroglycerin to a mixture of the methoxy ethyl acrylate and the ethyl cent-ralite and evacuating the solution for 3 hours at a pressure of mm. of mercury. The peroxide catalyst was admixed just prior to casting. Addition of the casting liquid to the powder was accomplished by the basal addition technique described previously. Curing and machining operations were as described in Example 1.

Consolidation of the powder was excellent. The powder exhibited unusually high flex strength on the basis of the comparatively large number of times it could he folded and twisted Without breaking. The thermal stability of the powder was much superior to that of the parent cast powder containing dimethyl phthalate in place of methoxy ethyl acrylate.

EXAMPLE 11 Cast, double-base grains of the following nominal composition were prepared by combining in a 67:33 ratio, casting powder and casting liquid having the formulas shown in the accompanying columns.

l 60% methyl ethyl ketone peroxide in dlmethyl phthalate.

The casting powder was prepared, loaded, and evacuated in the manner described in Examples 1 and 10. The casting solvent was prepared by adding the butyl methacrylate and peroxide catalyst to 'a previously evacuated solution of casting liquid containing 74% of nitroglycerin, 25% of dimethyl phthalate and 1% of ethyl centralite. The resulting casting liquid was not again evacuated prior to use. The casting powder and liquid were combined by methods previously described and the castings were cured and machined according to standard techniques.

Consolidation of the cast propellant was excellent and the ultimate compressive strength was approximately 28% higher than that of the parent cast powder containing additional nitroglycerin and dimethyl phthalate in place of the polymerizable material. A thermal stability test of 2 in. cubes of the modified powder at 80 C. showed marked improvement over the parent composition.

EXAMPLE 12 A cast, triple-base grain of the following composition was prepared by combining in a 67:33 weight ratio, cast- 10 ing powder and casting liquid having the formulas shown in the adjoining columns.

Cast Casting Casting Ingredients matrix, powder, liquid, percent percent percent Nitrocellulose (12.6% N) 49. 5 74. 0 Nitroglyceriu 25. 6 19. 0 39 0 Ethyl Centrallte 1. 0 1. O 1 0 Dlmethyl phthalate. 4. 0 6. 0 Methyl methacr; late 9. 9 30. 0 Allyl pentaerythritcl trinit 9. 9 30. 0 Carbon black (added) 0.3 0. 5 Graphite (glaze) 0. 03 0.05 Benzoyl peroxide (added)- 0. 05 0. 15

1 Containing 0. 006% of hydroqulnone.

The casting powder wasprepared, loaded and evacuated as in Examples 1 and 9. The casting liquid was prepared by adding the nitroglycerin to a mixture of the methyl methacrylate, ethyl centralite, benzoyl peroxide and allyl pentaerythr-itol trinitrate, and evacuating the mixture for ten minutes at an absolute pressure of about 15 mm. of mercury. The casting liquid and powder were combined by the standard techniques described previously. Curing of the grain consisted of storage for 40 hours at F. and 65 hours at F. in a forced-air oven. The grain was machined into samples for physical and chemical tests, and strands of /s x A; x 7 in. were cut for ballistic tests in a nitrogen-pressurized bomb.

Consolidation of the casting was excellent; ultimate compressive strength of 0.5 in diameter, 1.0 in. length cylinders of the powder at the loading rate of 10,000 p.s.i./sec. was 75% higher than that of an unmodified powder prepared with the same casting powder and a casting liquid containing 69% nitroglycerin, 30% dimethyl phthalate and 1% ethyl centralite.

The modified powder in the strand form mentioned above burned in a regular manner and is suitable for general use as a rocket propellant or as a charge for any gas-generating device.

EXAMPLE 13 Cast, double-base grains of the following composition were prepared by combining in a 65 :35 weight ratio, casting powder and casting liquid having the formulas shown in the accompanying columns.

Cast Casting Casting Ingredients matrix, powder, liquid, percent percent percent Nitrocellulose (12.6% N) 57. 8 89.0 N itroglycerln 25. 8 74. 0 Ethyl Centrallte 1.0 1. 0 1. 0

1 Containing 0.006% of hydroqulnone. 2 60% methyl ethyl ketone peroxide in dlmethyl phthalate.

The casting powder was prepared according to procedures described in Example 1 and was loaded into an 8.4 in. diameter by 30 in. length multi-core mold through aperforated plate (V8 in. holes on V2 in. diameters). The mold and contents were then evacuated for 16 hours at an absolute pressure of less than 10 mm. of mercury and the vacuum was released with dried air just prior to addition of the casting liquid. The casting liquid was prepared by adding the nitroglycerin to a solution of the other ingredients and evacuating the mixture for 10 minutes at an absolute pressure of 15 mm. of mercury. Basal addition of the casting liquid was accomplished by pressurizing the casting liquid container with nitrogen gas. The gas pressure was 5 p.s.i. at the start of flow and was gradually raised to 8 p.s.i. during filling in order to maintain a nearly uniform rate of flow. Solvent addition time was approximately 3 minutes as compared with a filling time of about 6 minutes for parent type cast Processing of the grains after casting may be identical grains of the same dimensions with a casting liquid which to the treatment used with conventional, cast double-base did not contain the polymerizable material' The grains powder. However,modification in curing temperature or were tightly covered after casting and were cured for time may be made, provided such changes do not affect 100 hours at 140 F. The brass cores were removed by powder stability or have other undesirable effects. Coverpulling, a Silicone grease having been applied to the cores ing of the grains during curing is essential to prevent exoriginally to prevent sticking, and the grains were sawed cessive loss of volatile monomers. However, this pracinto the proper lengths for firing.- tice is ordinarily followed with conventional cast powders The firing charge consisted of 74 lb. of powder in to prevent loss of plasticizers and to avoid premature gelatwo sections, one 8 long and the'other 24.5 in. long. tion at the top of the casting. The grains were fired in a 9' in. diameter rocket motor in alt will be noted from the formulations of the forecomparison with a similar charged the parent powder. going examples, with the exception of Example 12, that Both rounds were conditioned to a temperature of 150 the content of polymer formed in situ does not exceed F. before firing. The charge of unmodified powder pro: 10% by weight of the total composition. It has been duced an excessively high pressure at the beginning of found that while amounts up to 18% are operable in the shot and was very regressive burning thereafter. The rocket and jet applications where substantially smokeless irregular appearance of powder slivers ejected from the propellants are desired and while up to 30% of polymer nozzle at the end of firing indicated failure'of the charge formed in situ may be used in gas-producing charges apparently because of excessive softness at the 150 F. where smoke is nota serious problem, the advantages conditioning temperatures. The round containing acrylic- 20 of the invention can usually be obtained with a polymer modified powder showed the nearly neutral burning decontent of 10%'or less.; The examples have been prisired. Recovered slivers were regular in appearance and marily directed to propellants for rocket and jet appliindicated that no powder break-up had occurred. The cations because it is in thisfield that the gas-producing firing produced little smoke and was considered satisfaccharges of the invention find greatest utility. It is to tory in respects. be understood, however, that the invention is not limited Table I APPROXIMATE PERCENTAGE COMPOSITIONS AND'PHYSICAL AND THERMAL PROPERTIES OF CAST POWDERS DE- SCRIBED IN EXAIMPLES 1-13 Formula (percent) Powder reference NC N NG EC DN T DMP TA Carbon 1 Polymerlzable materials Parent powder for Examples 1, 6, 7, 8 9 13-- 57.8 12. 6 24.5 110 6; 5 0.13 None. Examp 1 59. 6 12. 6 19. 5 1. 0 6. 7 0.13 MMA 6.6. Example 6. 57. 9 12. 6 2312 1. 0 6. 5 0.13 MMA 3.5. Example 7- 59. 5 a 12. 6 19. 5 1.0 6. 7 0.13 MINIA 3.3, ADGO 3.3. Example 8- 59v 5 12. 6 19. 5 1. 0 6. 7 0.13 MMA 3.3, DAM 3.3. Example 9 59. 5 12. 6 19. 5 1.0 6. 7 0.13 MMA 4.9, DVB 1.7. Parent powder for Example 58. 5 13.15 22. 5 8.0 2. 5 one. Example 2 I 58. 5 13.15 20. 7 6. 5 0. 3 MMA 7 0 Parent powder for Example 3 65.0 12; 6 25. 2 1. 0 8. 8 0.02 None. Example 3 66. 3 12. 6 21.8 1. 0 4. 3 0.02 MMA 6 6 Parent powder for Examples 4 an 64. 3 12. 6 25. 7 1. 0 9.0 0.13 None.

xamp 64. 3 12. 6 20. 7 1. 0 7. 0 0.13 EA 7.0. Example 5 65. 3 12. 6 24. 2 1. 0 0.13 EA 9.5. Parent powder for Example 49.1 12.6 35.8 1. 0 14.1 0.33 None. Examp 48. 0 12. 6 36. 8 1. 0 4.0 0.33 MOEA 9 9 Example 11. 49. 5 12. 6 29. 9 1. 0 10. 3 0. 33 BMA 9.3. Example 12- 49. 5 12.6 25.6 1.0 4.0 0.33 MLIA 9.9, APETN, 9.9. Example 13 57. 8 12. 6 25. 8 1. 0 1. 8 0.13 MMA 7.0.

Total Total Ultimate compressive strength -Ta-liani test at 110 polymer volatiles (p.s.i.) loading rate: 10,000 p.s.l./ C. under nitrogen 7 Energy sec. 80 0. Powder reference of explocracking slon cal./ test) S1 1 g (days ope l inutes Analyzed -10 0 +25 0. C. at 100 to 100 7 mm mm Parent powder for Examples 1, 6, 7, 8, 9, 13 57. 9 0. 35 799 19, 250 12, 700 7,800 xample 1 66.0 0. 48 680 25, 800 18, 350 13, 450 Example 6-- 61. 2 0.42 757 20,200 15, 400 10, 500 Example 7.- 64. 8 0.52 688 20, 600 15, 700 10, 150 Example 8- 65. 0 0. 48 685 20, 500 15, 450 10, 800 Example 9 65. 9 0. 37 660 24, 600 18, 150 14, 050 Parent. powder for Example 2- 58. 3 0.37 700 12, 800 6, 850 3, 450 Example 2 65.0 0. 46 620 18, 700 11, 900 7, 900 Parent powder for Example 3- 64. 8 0. 915 15,800 9,000 6, 300 E ole 3 72. 6 0.95 832 25, 900 16, 750 11,800 Parent powder for Examples 4 and 5 64. 2 0.53 910 15, 400 6, 700 3,950 Example 4 72. 2 0.85 742 26, 900 18, 500 11,300 Example 5 73. 9 1.01 881 27, 200 18,650 13,600 Parent powder for Examples 10, 11, 12.- 49.1 0.24 861 15, 200 9, 300 4, 600 56. 6 0.39 862 14, 300 7, 950 5, 57.9 0. 72 620 20; 300 11, 950 7, 850 Example 12-- 69.0 0.43 762 20,800 16, 300 11,100 12 Example 13 64.5 0. 50 840 Not tested because of similarlilty 1%) Example 1. Fired in rocket 0 am er 1 As added ingredient. 2 Powder cylinders either 0.50 in. diam. by 1.0 in. length or 0.375 in. diam. lay-0.75 in. length were used. Graphite glaze only. Glaze of 0.05% graphite applied to all casting powder.

No'rE.Code: ADGC-Al1yl diglycol carbonate NCNitrocellulose (percent nitration as shown) EA-Ethyl acrylate NG-Nitroglycerin, MOEABeta-methoxyethyl aerylate E CE th yl Centralite B M An-Butyl meth'acrylate DNT-Dinitrotoluene D AMDiallyl maleate DMP--Dimethylpl1tha1ate DVBDivinyl benzene (40% soln in monofunctlonal monomers) 'IA-Triacetin APETN-Ally1 pentaerytnritol trinitrate M MA-Methyl methacrylate to propellent charges but applies to gas-producing charges generally.

From the examples, it is clear that the invention has attained the objects initially set forth. The gas-producing charges of the invention clearly have a greatly enhanced structural strength due to the presence of the polymerized material. This increase in structural strength offers increased resistance to internal cracking due to the pressure of decomposition gases; increased resistance to charge breakup during firing, especially at high temperatures; and increased resistance to breakage or cracking during handling and machining. A further desirable result of the increased physical strength lies in the fact that less elaborate and weighty trapping systems are necessary in rockets and jet-actuated devices employing the gas-producing charges of the invention.

It has become apparent that internal cracking is greatly diminished not only by the increased structural strength of the gas-producing charge brought about by the presence of the polymerization product, but is also due to a chemical action of the polymerizable material itself in some instances. While it is not desired to be bound by the following theory, it is possible that the small amount of polymerizable material which does not polymerize or copolymerize, actually reacts with nitrogen oxides at the point of unsaturation. This stabilizing eifect of the polymerization product has been noted generally, but the effect is greatest when a copolymer is employed and particularly when the substance copolymerized with the monomer is allyl diglycol carbonate or diallyl maleate.

From the examples, it is also obvious that gas-producing charges may be formulated in accordance with this invention which have the necessary calorific output to make them substantially smokeless and still have a compartively low burning rate which allows greater latitude in interior geometry of gas-producing grains, the exterior dimensions of which are controlled by aerodynamic consideration. This property of relatively slow burning in a relatively high potential charge also renders the gasproducing charges of this invention very useful for such diversified applications as the inflation of life rafts, and as the gas-producing charge of jet engine starter units.

In addition to these primary advantages, several other very definite advantages accompanying use of polymerizable material in the casting liquid in accordance with the invention. For example, the operable polymerizable substances are generally considerably less viscous than the conventional casting liquids and, consequently, the overall viscosity of the liquid is generally reduced in proportion to the amount of their incorporation. This reduced viscosity, especially where the polymerizable substance is also a solvent for the powder, greatly increases the solvent action of the casting liquid, thus making possible an improved degree of homogeneity in the casting charge and a higher degree of coalescence of the solvated granules. As a result of this improved coalescence, the curing time of the charges is proportionally decreased, thus contributing substantially to the speed and economy of manufacture. Furthermore, the reduction of viscosity in the casting liquid results in substantially more rapid addition of the liquid to the powder-filled mold by the preferred basal addition technique and, as illustrated, effects a substantial diminution in the filling time required for a particular grain size. This property is especially important in large-scale production of tall grains, not only from the standpoint of the time required for casting liquid addition but also in the amount of pressure necessary to fill the mold. Many additional advantages of this invention will be readily appreciated by those skilled in the art.

Many modifications of the gas-producing charges of this invention may obviously be made without departing from the scope of the inventive concept involved. Therefore, the invention is to be considered as limited only by the scope of the appended claims.

The term vinyl material as referred to in the specification and claims is meant to include vinyl, vinylene, and vinylidene compounds.

What I claim and desire to protect by Letters Patent is:

1. An improved gas-producing charge of enhanced structural strength and stability which consists of the cured product of a mixture comprising a smokeless powder, the major explosive components of which are selected from the group consisting of nitrocellulose and nitroglycerin dispersed in not more than 30% by weight of vinyl material having the structural formula where R R and R are selected from the group consisting of hydrogen, an alkyl group and an alkenyl group R is an alkyl group; said gas-producing charge being essentially free from volatile substituents.

2. An improved gas-producing charge of enhanced structural strength and stability which consists of the cured product of a mixture comprising a smokeless powder comprising essentially nitrocellulose dispersed in not more than 30% by weight of vinyl material having the structural formula Ra OOOR4 where R R and R are selected from the group consisting of hydrogen, an alkyl group and an alkenyl group and R is an alkyl group; said gas-producing charge being essentially free from volatile substituents.

3. An improved gas-producing charge of enhanced structural strength and stability which consists of the cured product of a mixture comprising a smokeless powder comprising nitrocellulose and nitroglycerin dispersed in not more than 30% by weight of vinyl material having the structural formula where R R and R are selected from the group consisting of hydrogen, an alkyl group and an alkenyl group and R is an alkyl group; said gas-producing charge being essentially free from volatile substituents.

4. A gas-producing charge according to claim 3 in which the vinyl material is monomeric ethyl acrylate.

5. A gas-producing charge according to claim 3 in which the vinyl material is monomeric methyl acrylate.

6. A gas-producing charge according to claim 3 in which the vinyl material is monomeric methyl methacrylate.

7. A gas-producing charge according to claim 3 in which the vinyl material is monomeric methyl methacrylate and is in solution With allyl diglycol carbonate.

8. A gas-producing charge according to claim 3 in which the vinyl material is monomeric methyl methacrylate and is in solution with allyl pentaerythritol trinitrate.

References Cited in the file of this patent UNITED STATES PATENTS 2,165,263 Holrn July 11, 1939 2,171,379 3.111. Aug. 29, 1939 2,407,131 Bruson et al Sept. 3, 1946 2,468,027 Britton et a1 Apr. 26, 1949 FOREIGN PATENTS 572,790 Great Britain Oct. 24, 1945 579,057 Great Britain July 22, 1946 580,409 Great Britain Sept. 6, 1946

Claims (1)

1. AN IMPROVED GAS-PRODUCING CHARGE OF ENHANCED STRUCTURAL STRENGTH AND STABILITY WHICH CONSISTS OF THE CURED PRODUCT OF A MIXTURE COMPRISING A SMOKELESS POWDER, THE MAJOR EXPLOSIVE COMPONENTS OF WHICH ARE SELECTED FROM THE GROUP CONSISTING OF NITROCELLULOSE AND NITROGLYCERIN DISPERSED IN NOT MORE THAN 30% BY WEIGHT OF VINYL MATERIAL HAVING THE STRUCTURAL FORMULA