US2952530A

US2952530A - Method of mixing propellant com-

Info

Publication number: US2952530A
Authority: US
Publication date: 1960-09-13
Anticipated expiration: 1977-09-13

Description

Willard M. St. John, Jr., Waco, Tex., assignor to Phillips Petroleum Company, a corporation of Delaware No Drawing. Filed Nov. 27, 1957, Ser. No. 699,424 7 Claims. (Cl. 52-.5)

This invention relates to a new propellant composition. In a further aspect this invention relates to a method of mixing the components of a propellant composition.

It has been established that certain physical properties are desired in rocket propellant compositions of the JATO, ICBM, and IRBM types. At the present time, it is believed that the propellant composition should have an elongation of at least about percent and a tensile strength of at least about 125 p'.s.i. It also appears desirable to have a modulus as low as 1000 although this iigure can range up to a few thousand.

I have discovered that good propellant compositions can be made using a rubbery binder of the type exemplified by a rubbery copolymer of 1,3-butadiene and 2- methyl-S-vinylpyridine, a solid inorganic oxidizing salt, and, the new ingredient, a chlorinated paraflin Wax. The exast basis upon which the chlorinated wax improves the composition is not known but, in view of the work reported herein, it is apparent that several advantages are obtained. Products can be made which cure rapidly and show substantially no change in aging at elevated temperatures. The recipes shown simplify production in that the number of ingredients involved is reduced. A further advantage is that it is possible to provide a sulfur-free propellant unit.

The following are objects of our invention.

An object of my invention is to provide new propellant compositions. A further object of my invention is to provide propellant compositions having especially desirable physical properties. A further object of my invention is to provide a sulfur-free propellant composition. A further object of my invention is to provide a new and improved method of preparing propellant compositions.

Other objects and advantages of my invention will become apparent to one skilled in the art upon reading the accompanying disclosure.

Broadly, my invention is based upon the discovery that a good propellant composition is obtained when a chlorinated paraflin wax is incorporated with a solid inorganic oxidizing salt in a rubbery binder, said rubbery binder comprising a polymer of a conjugated diene and a compound of pyridine and quinoline series containing a substituent where R is selected from the group consisting of hydrogen and methyl.

The chlorinated paraifins used in my invention are thosejcontaining 25 to 70 weight percent of chlorine and they are used in amounts ranging from 10 to 50 parts by weight per 100 parts of rubbery binder. The

' Patented Sept. 13, 1960 chlorinated parafiins are commercially available, representative types being Cerechlor, Paroil 143, Paroil 163 and Paroil 173, Clorafin, Chlorowax LV, Chlorowax 40, Chlorowax 50 and Chlorowax 70. The chlorinated paraflins are frequently considered as representing three different classes. The materials with low chlorine content, say 25 to 30 weight percent, are considered the low chlorine containing members; those containing 40 to 55 percent chlorine the middle group; and paraflins containing around weight percent chlorine as the high chlorine content parafiins. The materials range from liquid materials through resinous materials, the materials becoming harder as the chlorine content is increased. A method for producing these materials is disclosed in Hardie et a1. 2,130,952 (1938).

The chlorinated parafr'ins used in the Work reported in this disclosure included Chlorowax 40 and Chlorowax 70. The first of these materials is a clear, almost colorless liquid material cont-aining approximately 40 percent combined chlorine by weight which has a specific gravity of about 1.15 and a viscosity of 20 to 25 poises at 25 C. Chlorowax 70 is a cream-colored, powdered, resinous material with a specific gravity of 1.6 to 1.7 and a melting point of to C. The chlorine con tent is approximately 70 Weight percent.

As those skilled in the art will understand, the conjugated dienes which can be employed are, in addition to butadiene, those which contain from 4 to 6, inclusive, carbon atoms per molecule and include 1,3-butadiene, isoprene (Z-methyl-1,3-butadiene), piperylene, 2-methyl- 1,3-pentadiene, 2,3-dimethyl-1,3-butadiene, and others. Mixtures of conjugated dienes can be used.

The polymen'zable heterocyclic nitrogen bases which are applicable in our invention are those of the pyridine and quinoline series which are copolymerizable with a conjugated diene and contain one and only one substituent wherein R is either hydrogen or a methyl group. That is, the substituent is either a vinyl or an alpha-methylvinyl (isopropenyl) group. Of these compounds, the pyridine derivatives are of the greatest interest commercially at present. Various substituted derivatives are also applicable but the total number of carbon atoms in the nuclear substituted groups, such as alkyl groups, in addition to the vinyl or alpha-methylvinyl group, should not be greater than 12 because the polymerization rate decreases somewhat with increasing size of the alkyl group. Compounds where, the alkyl r substituents are methyl and/or ethyl are available commerciall-y.

These heterocyclic nitrogen bases have the formula 0 where R is selected from the group consisting of hydroaryl, and combinations of these groups such as haloalkyl, alkylaryl, hydroxyaryl, and the like; one and only one of said groups being selected from the group consisting of vinyl and alpha-methylvinyl; and the total number of carbon atoms in the nuclear substituted groups in addition to the vinyl or alpha-methylvinyl group, being not greater than 12. Examples of such compounds are 2-vinylpyridine; 2-vinyl S-ethylpyridine; 2-methyl-5-vinylpyridine; 4-vinylpyridine; 2,3,4-trimethyl--vinylpyridine; 3,4,5,6-tetramethyl-2-vin ylpyridine; 3-et-hyl5-vinylpyridine; 2,6-diethyl-4-vinylpyridine; 2-isopropyl-4-nonyl-5-vinylpyridine; Z-methyl- 5 undecyl 3 vinylpyridine; 2,4 dimethyl 5,6- dipentyl 3 vinylpyridine; 2 decyl 5 (alpha methylvinyDpyridine; 2-vinyl-3-methyl-5-ethylpyridine; 2- methoxy-4 chloro-6-vinylpyridine; 3-vinyl-5-ethoxyp-yridine; 2 vinyl 4,5 dichloropyridine; 2 (alpha methylvinyl) 4 hydroxyl 6 cyanopyridine; 2 vinyl- 4 phenoxy 5 methylpyridine; 2 cyano 5 7 (alpharnethylvinyl)pyridine; 3 vinyl 5 phenylpyridine; 2- (para methylphenyl) 3 vinyl 4 methylpyridine; 3 vinyl 5 (hydroxyphenyl) pyridine; 2 vinylquinoline; 2 vinyl 4 ethylquinoline; 3 vinyl 6,7- di n propylquinoline; 2 methyl 4 nonyl 6 vinylquinoline; 4 (alpha methylvinyl) S dodecylquinoline; 3 vinylisoq-uinoline; 1,6 dimethyl 3 vinylisoquinoline; 2 vinyl 4 benzylquinoline; 3 vinyl- 5 chloroethylquinoline; 3 vinyl 5,6 dichloroisoquinoline; 2 vinyl 6 ethoxy 7 methylquinoline; 3-vinyl-6-hydroxymethylisoquinoline; and the like. Mixtures can be used.

The copolymers are prepared by polymerizing a major amount of the diene with a minor amount of the heterocyclic nitrogen base by any suitable method. Preferably, the ultimate product has a Mooney viscosity (ML-4) of 10 to 40 although higher Mooney polymers are frequently made and then mixed with extender oils.

In my invention, the usual pigments, fillers, reinforcing agents,.and antioxidants commonly used in rubbery compositions can be employed. The usual solid inorganic oxidizing agents are used, probably the best known thereof being ammonium nitrate and ammonium perchlorate, although a great many others, potassium nitrate, etc. are known and the particular oxidant does not constitute a feature of the present invention. Obviously, mixtures of oxidants can be used.

Based upon 100 parts by weight of the binder, suitable propellants are made using the following recipe:

Parts by weight The mixing procedure for the compositions of the present invention was one in which a solvent was employed, this representing an improvement over prior mixing procedure wherein the dry ingredients are incorporated in the binder by a dry mixingprocedure such as a roll mill or a Banbury mixer. In the present work the rubber and black master batch was milled for a short time and then dissolved in a solvent. Solution of the polymer can be carried out in any type of mixer which provides rapid agitation and comminution of the rubbery material. The best dispersions are made when sufiicient solvent is used to provide a mixture containing approximately 30 weight percent of binder in the solvent. Immediately prior to the addition of other ingredients, it is convenient to determine the solid content by oven drying a small sample of the material. The 'binder solvent mixture is then transferred to a mixer equipped with dispersion blades, such as a Baker-Perkins mixer. As the additional ingredients are added, cooling is usually required in order. to prevent excessive temperature rise 4 and loss of solvent prior to obtaining a good dispersion. The next step is to add all of the other binder ingredients. Since the quantity of these -materials is small a short mixing time of 1 to 5 minutes is frequently satisfactory. Finally, the solid inorganic oxidizing salt is added and mixing is continued until a uniform mixture is obtained. Due to the large quantity of salt, a mixing time of 30 to 120 minutes or more is required. The solvent is then removed and this is preferably done by raising the temperature and applying a vacuum. The temperature should be in the neighborhood of the boiling point of the solvent under the conditions of removal. The time,

of removal, of course, varies greatly depending upon the physical conditions but, usually, a time of 20 to 120 minutes will be satisfactory.

Following the additionof the oxidant the system is adaptable to remote control and I have found that infra red analysis of the off-gas from the mixture provides a convenient method for determining when all of the sol vent is removed. A large variety of solvents can be used, the only requirement being that it be capable of dissolving the rubbery binder and non-reactive with the binder and the rest of the components in the propellant composition. Normal hexane wasthe solvent used inthe work reported in the example of this application and other hydrocarbons such as pentane, cyclohexane, isooctane, etc. can be used. Halogenated hydrocarbons are also suitable as well as ethers, ketones, etc. Mixtures of solvent materials can be used. The choice of solvent will frequently be determined by the ability of the apparatus used to maintain suitable temperatures. During the mixing, considerable heat is evolved and cooling is required. After the mixing, the mixture is warmed to permit removal of the solvent. The worker in the field will have little difliculty in choosing a solvent which will not be excessively volatile at the temperature of mixing and yet will be easily removed at the end of the mixing operation.

The followingexample illustrates my invention but the invention should not be unduly limited thereby:

Example I A butadiene/Z-niethyl-S-vinylpyridine copolymer was prepared by emulsion polymerization at 41 F. using a recipe of the following type 1,3-butadiene Potassium pyrophosphate 0.253 Para-menthane hydroperoxide 0.1

A series ofruns was made to an average conversion of 85.9 percent, the products blended, the resulting rubher having a Mooney viscosity (ML-4) of 22.4. As a shortstop, 0.1 part of potassium dimethyldithiocarbamatewas used and 1.76 percent by weight, based uponthe rubber, of phenol-beta-naphthylamine was added as an antioxidant.

The latex was master batched with 22.5 parts by weight of carbon black (Philblack A) per parts of rubber.

Portions of this master batch were incorporated in a. variety of recipes as set forth in the following table. Itwill be noted that the, first two recipes serve as controls,

I a sulfur cure being used in each. The last two recipes. disclose propellants prepared using the chlorinated paraffins of the present invention. w

Sulfur Cure I Sulfur Cure II Chlorowax-70 Cure Chlorowax-40 Cure Phr Wt. Phr Wt. Phr Wt. Phr Wt.

Percent Percent Percent Percent 100. 10. 75 100. 0 10. 49 100. 0 9. 06 100. 0 9. 06 22. 2. 42 22. 5 2. 36 22. 5 2. 04 22. 5 2. 04 10. 0 1. 03 10. 0 1. 05 10. 0 0. 91 10. 0 0. 91 3. 0 0. 32 3.0 0. 31, 3.0 0. 27 3.0 0. 27 3.0 0. 32 Ur. 2. 5 0. 26 Methyl Tuads 1.0 0.10 Santueure 5 1.0 0. 11 Stearic Acid 1. 0 0. Zinc Oxide 3.0 0. 31 Chlorowax-70 30. 0 2. 72 Chlorowax-40 30. 0 2. 72 Binder Total 139. 5 15. 148. 0 15.00 165. 5 15.00 165. 5 15.00 Ammonium Perchlorate- 70. 00 70.00 70.00 70. 00 Ammonium Nitrate"--- 15. 15.00 15. 00 15. 00 Propellant TotaL.-. 100. 00 100. 00 100.00 100. 00

1 An aromatic oil used as rubber extender.

Morpholine disulfide. 4 Tetremethyl thluramdisulfide. N -cyolol1exyl-2-benzothiazylsulfenamide.

Each of these compositions was made by a particular procedure. At the start, 600 grams of the butadiene/Z- methyl-S-vinylpyridine polymer containing the carbon black was milled for 3 minutes with the water on the rolls set at 120 F. After this milling, the polymer was dissolved in normal hexane using a Model l-VG Cowles Dissolver, a variable speed churn utilizing a combination cutter-impeller to facilitate solution. One-half gallon of normal hexane was used for the binder which was cut into small pieces in order to facilitate solution. During the dissolving, the copolymer was cleaned from the sides of the container and the impeller every fifteen minutes and additional normal hexane was added to maintain a solution of approximately 30 percent by weight rubber solids. The operating speed of the dissolver was maintained in the range of 2900 to 3000 rpm. approximately 2% hours being required to obtain a smooth solution. The solids content of the mixture at this point circulating through-the bowl at approximately F. All of the ingredients were added except for the am monium perchlorate and ammonium nitrate and the resulting mixture was mixed for two minutes. Thereafter the oxidants were added and mixing was continued for sixty minutes. At this point, while continuing mixing, the temperature was raised and all of the solvent removed. This was accomplished by raising the temperature of the water supplied to the mixer to about 140 F., the temperature of the mixer rising to the boiling point of the solvent. tem to accelerate solvent removal which took approximately 35 minutes. Infrared analysis of the off-gas from the mixer indicates degree of removal of the solvent.

Test specimens were prepared in order to determine elongation, tensile, modulus, and ignition and ballistic properties on each of the compositions. The results of these tests are set for-thin Table II:

Sulfur Cure I Sulfur Cure II Ohloaowax-7O Chlorowax-40 ure Cure Physical Properties St E 6 St E Cure at 190 F.:

72 hours Oven age at 190 F.:

1 week 2 weeks 4 weeks 5 sec. @[5 min. Impact Sensitivity. Density #/in.

e04 F/480 F. 52 lnJlb. 0.0607.

1 Sample Overcnred.

was determined by oven drying a 4-6 gram portion for one hour at F. and additional solvent was added as needed to maintain the 30 percent solution. The mixture was then transferred to a Baker-Perkins mixer equipped with dispersion blades and the additional ingredients were added while maintaining cooling water Examination of the data of this table shows that excellent properties can be obtained using the compositions of the present invention. The run using Chlorowax 70 is particularly outstanding because of the excellent tensile values obtained and the modulus in the desired range. Another outstanding feature is the small change in these A vacuum was applied to the sys-,

7 physical properties regardless of the time of cure. The composition using the Chlorowax 40 is also very good, although longer curing times are required. Both compositions are superior to the control compositions using ,the sulfur cure. The ignition and ballistic properties of both compositions containing Chlorowax are good. The compositions are not pressure sensitive, and provide :propellants of higher density, this being an improvement.

invention without departing from the scope thereof, it is to be understood that all matter herein set .forth is to be interpreted as illustrative and -not'as unduly the invention.

I claim:

1. A rocket propellant composition consisting essentially of a rubbery binder, said :binder being a rubbery copolymer of 1,3-butadiene and 2-methyl-5-vinylpyridine and, based upon 100 parts by weight of said rubbery binder, to 60 parts of a filler, 0 to 20 parts of a plasticizer, 0 to 3 parts of an antioxidant, 100 to 900 parts of a solid inorganic oxidizing salt, and to '50 parts 'of'a chlorinated parafiin, said chlorinated paraffin being a liquid to resinous material containing 25 to 70 weight percent of chlorine and having a specific gravity in the range of 1.15 to 1.7.

2. A rocket propellant composition consisting essentially of a rubbery binder, said binder being a rubbery polymer of a conjugated diene of 4 .to 6 carbon atoms and a compound of the pyridine and quinoline series containing a substituent where R is selected from the group consisting of hydrogen and methyl and, based upon 100 parts by weight of said rubbery binder, 0 to 60 parts of .a filler, 0 to parts of a plasticizer, 0 to 3 parts of an anti-oxidant, 100 .to 900 parts of a solid inorganic oxidizing salt, and 10 to 50 parts of a chlorinated parafiin, said chlorinated paraffin being a liquid to resinous material containing to 70 weight percent of chlorine and having a specific gravity in the range of 1.15 to 1.7.

3. The composition of claim 2 wherein said polymer is a polymer of 1,3-butadiene and 2,5-vinylpyridine.

4. The composition of claim 2 wherein said polymer is a polymer of 1,3-butadiene and 2-vinylpyridine.

5. A rocket propellant composition consisting essentially of the following ingredients:

Parts by weight Butadiene/2-methyl-5-vinylpyridine copolymer 9.06 Carbon black 2.04 Plasticizer 0.91 Antioxidant 0.27 Chlorinated parafiin 2.72 Ammonium perchlorate 70.00 Ammonium nitrate 15.00

having a specific gravity in the range of 1.15 to 1.7.

6. The method of preparing arocket propellant com- I prising milling a rubbety binder, said binder comprising a rubbery copolymer of 1,3-butadiene and Z-methyl-S- vinylpyridine, dissolving said binder in normal hexane,

the :amount of said normal :hexane being sufiicient to As many possible embodiments can be. made of this elem provide a rubber content of approximately 30 percent,

adding with agitation 'the rest of the propellant com-j 'ponents, said components including 10 to 50 parts by -weight of a chlorinated paraffin per 100 parts of said rubbery binder, said chlorinated paralfin being a liquid to resinous material containing 25 to weight percent of chlorine and having a specific gravity in the range of 1.15 to 1.7, and raising the temperature of the mixture to remove the normal hexane.

7. 'The method of preparing a rocket propellant comprising milling a rubbery binder, said binder comprising a rubbery polymer of a conjugated diene of 4 to 6 carbon atoms and a compound of the pyridine and quinoline series containing a substituent where R is selected from the group consisting of hydrogen and methyl, dissolving the binder in an or ganic solvent, said solvent being capable ofdissolving the binder but non-reactive with said binder, the amount of said solvent being sufficient to provide a rubber content of approximately 30 percent, adding the rest of the propellant components, said components including, based upon parts by weight of binder, 10 to 50 parts ofa chlorinated paraflin, said chlorinated paraffin being a liquid to resinous material containing 25 to 70 weight percent of chlorine and having a specific gravity in the range of 1.15 to 1.7.

References Cited in the file of this patent UNITED STATES PATENTS OTHER REFERENCES Chem. and Eng. News, Oct. 7, 1957, pages 62-63.

Claims

1. A ROCKET PROPELLANT COMPOSITION CONSISTING ESSENTIALLY OF A RUBBER BINDER, SAID BINDER BEING A RUBBER COPOLYMER OF 1,3-BUTADIENE AND 2-METHYL-5-VINYLPYRIDINE AND, BASED UPON 100 PARTS BY WEIGHT OF SAID RUBBERY BINDER, 0 TO 60 PARTS OF A FILLER, 0 TO 20 PARTS OF A PLASTICIZER, 0 TO 3 PARTS OF AN ANTIOXIDANT, 100 TO 900 PARTS OF A SOLID INORGANIC OXIDIZING SALT, AND 10 TO 50 PARTS OF A CHLORINATED PARAFFIN, SAID CHLORINATED PARAFFIN BEING A LIQUID TO RESINOUS MATERIAL CONTAINING 25 TO 70 WEIGHT PERCENT OF CHLORINE AND HAVING A SPECIFIC GRAVITY IN THE RANGE OF 1.15 TO 1.7.