US3629019A

US3629019A - Solid propellant composition containing polyesters and an inorganic oxide burning rate catalyst

Info

Publication number: US3629019A
Application number: US388944A
Authority: US
Inventors: Ralph W Lawrence
Original assignee: Aerojet General Corp
Current assignee: Aerojet Rocketdyne Inc
Priority date: 1964-08-11
Filing date: 1964-08-11
Publication date: 1971-12-21
Anticipated expiration: 1988-12-21

Abstract

2. A solid propellant composition comprising a cured intimate mixture of a solid inorganic oxidizing salt, said inorganic oxidizing salt being present in an amount of from about 45 percent to about 90 percent by weight of the total propellant composition; an unsaturated polyester resin consisting of the condensation product of a saturated polyhydric alcohol and polycarboxylic acid, said polyester resin being the condensation product of an alkylene glycol, maleic anhydride and sebacic acid heteropolymerized with an unsaturated compound selected from the group consisting of lower alkenes, lower alkynes, phenyl substituted lower alkenes, lower alkyl dienes, lower alkenyl esters of lower alkanoic acids, lower alkyl esters of lower alkanoic acids, lower alkenyl esters of lower alkanoic acids, allyl diglycol carbonate, diallyl diglycollate, and mixtures thereof; and a burning rate catalyst comprising an inorganic oxide selected from the group consisting of the oxides of vanadium, cobalt, iron, chromium, manganese, copper, silver, and mixtures thereof.

Description

United States Patent [72] Inventor Ralph W. Lawrence Glendora, Calif.

[21 Appl. No. 388,944

[22] Filed Aug. 11, I964 [45] Patented Dec. 21, 1971 17 3 Assignee Aerojet-General Corporation Azusa, Calif.

[54] SOLID PROPELLANT COMPOSITION CONTAINING POLYESTERS AND AN INORGANIC OXIDE BURNING RATE CATALYST 3,031,289 4/1962 Philipson 3,058,858 10/1962 Batchelderetal ABSTRACT: 2. A solid propellant composition comprising a cured intimate mixture of a solid inorganic oxidizing salt, said inorganic oxidizing salt being present in an amount of from about 45 percent to about 90 percent by weight of the total propellant composition; an unsaturated polyester resin consisting of the condensation product of a saturated polyhydric alcohol and polycarboxylic acid, said polyester resin being the condensation product of an alkylene glycol, maleic anhydride and sebacic acid heteropolymerized with an unsaturated compound selected from the group consisting of lower alkenes, lower alkynes, phenyl substituted lower alkenes, lower alkyl dienes, lower alkenyl esters of lower alkanoic acids, lower alkyl esters of lower alkanoic acids, lower alkenyl esters of lower alkanoic acids, allyl diglycol carbonate, diallyl diglycollate, and mixtures thereof; and a burning rate catalyst comprising an inorganic oxide selected from the group consisting of the oxides of vanadium, cobalt, iron, chromium, manganese, copper, silver, and mixtures thereof.

SOLID PROPELLANT COMPOSITION CONTAINING POLYESTERS AND AN INORGANIC OXIDE BURNING RATE CATALYST This invention relates to jet propulsion and provides improved solid propellant charges capable of good performance after or during exposure over a wide range of weather and temperature conditions.

In the operation of certain types of rocket motors, it is customary to burn a solid charge in a motor chamber to produce a large volume of gas under pressure, which escapes at high velocity as a gas jet through the exhaust nozzle leading from the chamber producing a resultant high thrust. Typical solid charges have heretofore commonly comprised a thermoplastic fuel such as asphalt having mixed with it a finely divided oxidizing substance in sufficient quantity to burn the fuel. This mixture is ordinarily formed into a solid mass within the chamber, presenting a surface at which the burning occurs.

Rocket motors are commonly exposed to a large variety of weather conditions and a wide range of temperature, between the time of their manufacture and the time of use. Solid propellant charges of the type above described often tend to sag under tropical conditions or become brittle and develop cracks at very low temperatures, thus producing large and irregular burning surfaces. The formation of enlarged exposed surfaces or cracks is undesirable as it increases the area for burning, thus accelerating combustion with an attendant pressure rise in the motor chamber which may produce an explosion. There are known solid propellant charges which do not become unduly brittle or crack in low temperatures and are resistant to sagging in tropical environments. These propellants of the so-called solid type are substantially homogeneous in composition and relatively free from cavities and air bubbles. In addition, they may be composited at room temperature, relieving the necessity of heating any of the ingredients at the time that the oxidizer is incorporated into the resin. These propellant compositions may be cured at temperatures which do not materially exceed 200 F., providing no additional hazard during curing operations.

However, these propellants suffer in having a burning rate which is often too low for effective operation.

It is an object of this invention to provide burning rate additives for solid propellants, so that the burning rate of said solid propellants is increased.

The novel solid propellant charge of this invention comprises an intimate mixture of a finely divided oxidizer together with a burning rate catalyst uniformly distributed in a resinous binder which acts as a fuel. The resin comprises a polyester component; that is, the reaction product of a polycarboxylic acid with a polyhydric alcohol with which there is incorporated a polymerizable unsaturated component such as a vinyl, allyl or olefinic compound compatible with the liquid resin.

The polyester component, sometimes known as an alkyd component or alkyd resin, must possess some degree of unsaturation in the molecule in order to permit it to heteropolymerize with the unsaturated component, which may be, for example, phenyl substituted lower alkenes such as styrene, lower alkenyl esters of lower alkanoic acids such as vinyl acetate, lower alkyl esters of lower alkenoic acids such as esters of acrylic or methacrylic acid; allyl compounds such as allyl diglycol carbonate, lower alkenyl esters of lower alkenoic acids such as diallyl maleate; diallyl diglycollate; other compounds including lower alkyl dienes such as butadiene, lower alkynes such as acetylene, etc.; and derivatives of any of the above substances which will polymerize -with the resin. in general, any unsaturated compound compatible with the resin and which will polymerize with it is suitable. This includes essentially all unsubstituted olefins, and in addition, many substituted olefins. The reason for having unsaturation present in the polyester is to permit the resulting unsaturated polyester to copolymerize with the double bond in the vinyl or allyl compounds or other unsaturated additives. When a sufiicient amount of cross-linkage occurs, the resin becomes thermosetting. With a lesser degree of cross-linkage the resin may be thermoplastic; and in some cases the resin may possess some of the properties of both thermoplastic and thermosetting resins. All these types of resins are within the scope of the present invention.

The polyester components can be made in general as follows: The hydroxy groups of dihydric or polyhydric alcohols are permitted to react in the presence of the monomeric vinyl, allyl or other unsaturated component with the polycarboxylic groups of, for example, a dicarboxylic acid or a mixture of dicarboxylic acids, thereby producing a saturated polyester. The unsaturation to permit the polyester to heteropolymerize with the monomeric vinyl, allyl or other unsaturated component may be supplied by employing either an unsaturated polyhydric alcohol or an unsaturated dicarboxylic acid. The usual and preferred manner is to employ mixtures of an unsaturated polycarboxylic acid or anhydride with a saturated or aromatic polycarboxylic acid, or anhydride and treating this mixture with a polyhydric alcohol. The percentage of the unsaturated acid or anhydride should be sufficient to permit the necessary amount of copolymerization between the vinyl, allyl or other unsaturated additive in the polyester. The polyester may be present in amounts varying between about 10 percent and about percent by weight, based on the weight of the polyester-unsaturated additive mixture, however, in general, about 50 percent by weight of polyester to about 50 percent by weight of the unsaturated additive produces a satisfactory polyester resin type of matrix for the propellant.

The alcohols which can be used, are not limited, however, to the dihydric alcohols, as other polyhydric alcohols such as the trihydric and higher polyhydric alcohols may be used. These afford additional possibilities for cross-linking and, as a consequence, the toughness and brittleness of the final resin may be controlled as desired.

For the polyhydric alcohol component, any of the following alcohols may be used: dihydric alcohols, such as ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol; a trihydric alcohol such as glycerol; tetrahydric alcohols such as the erythritols and pentaerythritol; pentitols which include arabitol, adonitol, xylitol; hexitols including mannitol, sorbitol, dulcitol; and heptitols, for example persitol and volamitol. Mixtures of any of the above alcohols may also be employed, if desired.

Saturated polycarboxylic acids useful in compounding the polyester resins are, for example the aliphatic dibasic acids, including: oxalic, malonic, succinic, glutaric, adipic, pimelic, sebacic, and azelaic, and the saturated anhydrides such as succinic anhydride. Examples of the unsaturated carboxylic acids useful as the acidic components in forming polyester resins are: maleic acid, fumaric acid, citraconic acid, mesaconic acid, and itaconic acid. Examples of aromatic dibasic acids, which are useful in compounding polyester resins, are: phthallic acid and its isomers and naphthalic acid. The anhydrides, such as maleic anhydride, citraconic anhydride, itaconic anhydride and phthallic anhydride, may likewise be used for supplying the desired unsaturation.

Regardless of which of the saturated acids are used, the degree of unsaturation necessary to provide cross-linkage with the vinyl or allyl compounds or other unsaturated component may be had by the addition of any of the above-named unsaturated acids or their anhydrides.

In some cases it may be possible to dispense with the use of the foregoing unsaturated polycarboxylic substances; and instead to fonn a polyester resin by modifying the polyester by incorporating into it, a modifying oil which has some degree of unsaturation and is compatible with the polyester. From a trace to 1 mole of the modifying oil may be added to 1 mole of the polyester. Examples of such oils are: castor oil, mustard seed oil, rape oil, haddock liver oil, linseed oil, hemp oil, poppy seed oil, Chinese and Japanese wood oil, tung oil, and olive oil. The unmodified or modified resin may then be blended with the allyl, vinyl compounds or other monomer described above, to produce mixtures which are capable of being polymerized into the cross-linked type of thermosetting resin or the modified resin may be employed without further additives.

This solid propellant comprises a uniform dispersion of the finely divided inorganic oxidizer and a polyester resin matrix of the type described above. The resin acts as a binder, and regardless of substituents in the molecule will serve as a fuel if the propellant contains a sufficient amount of the oxidizer to insure the necessary oxidation of the organic material; usually all of the carbon is oxidized to CO and one-third of the hydrogen is oxidized to water. As stated above, the preferred condensation product is obtained by reacting the polyhydric alcohol with the polycarboxylic acid having a predetermined degree of unsaturation in the molecule. An especially useful form of this condensation product is the reaction product of sebacic acid and a polyhydric alcohol such as propylene glycol, to which there has been added a small amount of unsaturated anhydride such as maleic anhydride. This product is commonly called a modified alkyd resin.

The percentage of unsaturation in the polyhydric alcohol polycarboxylic acid mixture to form the polyester should be between about 2 and 100 percent by weight, based on the weight of the total polycarboxylic acid or polycarboxylic acid mixture. The preferred percentage of unsaturation is between about and about percent by weight, based on the weight of the acidic component. Although the polyhydric alcohol and polycarboxylic acid will react in stoichoimetric proportions, nevertheless it is a better practice to use an excess of the polyhydric alcohol beyond the stoichoimetric amount; and then remove the excess alcohol from the finished polyester, in order to make the resulting product substantially free from unnecessary matter or impurities.

For the oxidizer, it is preferable to use any stable, solid, inorganic oxidizer The oxidizer is a substance which may be incorporated in the polyester resin unsaturated polycarboxylic unsaturated monomer mixture by stirring and mixing, and preferably the oxidizer is added to the mixture while the resin is in its liquid state. Examples of suitable oxidizers are the inorganic substances including the chromates, dichromates, permanganates, nitrates, chlorates, and perchlorates, such as the alkali metal salts of these radicals including sodium, potassium, lithium, rubidium and cesium; and also the nonmetallic salts, for instance, ammonium or hydrazine of the same radicals. The selection of the oxidizing material depends upon the type of propellant and the specific burning properties desired. The preferred oxidizers are the perchlorates, especially the perchlorates of potassium and ammonium. The amount of oxidizer added to the resinous mixture lies between about 45 and about 90 percent by weight of the total propellant composition and the weight of the unsaturated polyester resin, monomer mixture lies between about 55 and about 10 percent of the same propellant composition.

Catalytic substances are particularly useful for speeding up the rate of polymerization of the polyester resin monomer mixtures with the oxidizer added. Such catalytic substances are the organic peroxides and the organic peresters. The temperature used for curing is dependent somewhat upon the nature of the catalyst and the time during which it is desired to accomplish complete polymerization. Some catalysts such as l-hydroxy cyclohexylhydro peroxide or cumene hydroperoxide, are capable of polymerizing certain resins at room temperature if the charge is permitted to cure for a sufficiently long period of time.

The organic peroxides or peresters should be preferably soluble or compatible with the polyester resin. However, in some instances, even an insoluble organic peroxide or perester functions as a catalyst as long as it can be made to decompose and liberate a free oxygen radical. Specific example of compounds which are suitable catalysts for this polymerization reaction are: tertiarybutyl hydroperoxide, cumene hydroperoxide, benzol peroxide, lauryl peroxide, acetobenzoyl peroxide, ditertiary butyl peroxide, methyl ethyl ketone peroxide, l-hydroxy cyclohexyl hydroperoxide, and other hydroperoxides which are not too volatile at the curing temperature. Specific examples of suitable peresters are: tertiary butyl perbenzoate, and ditertiary butyl diperphthalate.

Such catalysts should be present in the unsaturated polyester resin unsaturated monomer mixture during the time it is subjected to the curing process. In general the weight of the catalyst employed to bring about this result is approximately 0.5 percent by weight based on the weight of the combined unsaturated polyester resin unsaturated mixture. If desired, larger amounts of the catalyst may be employed than those indicated.

In order to increase the burning rate of the solid propellants discussed above a burning rate catalyst is added to the propellant composition at the time the oxidizer is added. Catalysts which may be employed to increase the burning rate of the solid propellant include the oxides of vanadium, cobalt iron, chromium, manganese, copper, silver and mixtures thereof. Compounds containing more than one of these oxides may also be used. The oxide need not be used directly, but organic compounds which will decompose to form the oxide in situ, such as chromic acetylacetonate may also be employed. The weight of catalyst employed based upon the weight of the total propellant composition is about 0.02 percent to about 1.0 by weight. Amounts greater than about 1.0 percent may be employed but little improvement is obtained when greater amounts of catalyst are used.

The following examples in which parts and percentages are by weight unless otherwise indicated, are not intended to limit the scope of the invention.

EXAMPLE 1.

A propellant having the following composition was formulated:

NH,ClO, 75.00% Resin A I235; Styrene l LBSZ Cumene hydroperoxide 0.25% Lecithin 10% solution In styrene) 0.50% Cobalt octoate 1% Co" in styrene) 0.05%

Resin A is prepared y reacting moles adipic acid, 20 moles maleic anhydride and L05 moles diethylene glycol.

The propellant formulation was divided into five batches, and to four of the batches was added a catalyst composed of copper oxide and chromium oxide. The analysis was 17 weight percent CuO, 83% Cr O Varied amounts of the catalyst were added in four batches and the propellant was cured for two days at 70 F. and an additional three days at 185 F. The burning rates of the propellant with a propellant temperature it can be seen from the above results that only a few tenths of a percent of the indicated catalyst produces a great increase in the burning rate of the propellant.

EXAMPLE 2.

A propellant was prepared and cured for 1 day at ll0 F. and then for 2 days at F., using two different varieties of a copper chromite catalyst; a mixture of manganese oxide,

copper oxide, silver oxide and cobalt oxide; and chromic acetylacetonate. The compositions and burning rates are as follows:

Batch 1 2 3 4 NH4ClO4.. 76.00 76.00 76.00 75. 36

Resin B 14.11 14.11 14.11 13.99

Styrene... Cumene hydroperoxide t-Butyl catechol (10% in sty Dioctyl sodium sulfosuccinate (10% styrene) 17% 01103837 CF10; 42% C1101 58% c1103-- 50% M1102, 30% CuO, 0010s, 6%

AgzO Chromic acetylacetonate (21.8% CuO,) Burning rates in secf at 1,000 p.s.i.a.,

l Resin B is prepared by reacting 80 moles adipic acid, moles maleic anhydride and 1.20 moles diethylene glycol.

mate mixture of a solid inorganic oxidizing salt, a cross-linked polymerized polyester resin styrene mixture, the polyester resin being the condensation product of propylene glycol, maleic anhydride and sebacic acid, said inorganic oxidizing salt being present in an amount between about 45 and about percent by weight of the total propellant composition, and a burning rate catalyst comprising an inorganic oxide selected from the group consisting of the oxides of vanadium, cobalt, iron, chromium, manganese, copper, silver, and mixtures thereof.

2. A solid propellant composition comprising a cured intimate mixture of a solid inorganic oxidizing salt, said inorganic oxidizing salt being present in an amount of from about 45 to about 90 percent by weight of the total propellant composition; an unsaturated polyester resin consisting of the condensation product of a saturated polyhydric alcohol and polycarboxylic acid, said polyester resin being the condensation product of an alkylene glycol, maleic anhydride and sebacic acid heteropolymerized with an unsaturated compound selected from the group consisting of lower alkenes, lower alkynes, phenyl substituted lower alkenes, lower alkyl dienes, lower alkenyl esters of lower alkanoic acids, lower alkyl esters of lower alkanoic acids, lower alkenyl esters of lower alkanoic acids, allyl diglycol carbonate, diallyl diglycollate, and mixtures thereof; and a burning rate catalyst comprising an inorganic oxide selected from the group consisting of the oxides of vanadium, cobalt, iron, chromium, manganese, copper, silver, and mixtures thereof.

Claims

2. A SOLID PROPELLANT COMPOSITION COMPRISING A CURED INTIMATE MIXTURE OF A SOLID INORGANIC OXIDIZING SALT, SAID INORGANIC OXIDIZING SALT BEING PRESENT IN AN AMOUNT OF FROM ABOUT 45 PERCENT TO ABOUT 90 PERCENT BY WEIGHT OF THE TOTAL PROPELLANT COMPOSITION; AN UNSATURATED POLYESTER RESIN CONSISTING OF THE CONDENSATION PRODUCT OF A SATURATED POLYHYDRIC ALCOHOL AND POLYCARBOXYLIC ACID, SAID POLYESTER RESIN BEING THE CONDENSATION PRODCUT OF AN ALKYLENE GLYCOL, MALEIC ANHYDRIDE AND SEBACIC ACID HETEROPOLYMERIZED WITH AN UNSATURATED COMPOUND SELECTED FROM THE GROUP CONSISTING OF LOWER ALKENES, LOWER ALKYNES, PHENYL SUBSTITUTED LOWER ALKENES, LOWER ALKYL DIENES, LOWER ALKENYL ESTERS OF LOWER ALKANOIC AICDS, LOWER ALKYL ESTERS OF LOWER ALKANOIC ACIDS, LOWER ALKENYL ESTERS OF LOWER ALKANOIC ACIDS, ALLYL DIGLYCOL CARBONATE, DIALLYL DIGLYCOLLATE, AND MIXTURES THEREOF; AND A BURING RATE CATALYST COMPRISING AN INORGANIC OXIDE SELECTED FROM THE GROUP CONSISTING OF THE OXIDES OF VANADIUM, COBALT, IRION, CHROMIUM, MANAGANESE, COPPER, SILVER, AND MIXTURES THEREOF.
2. A solid propellant composition comprising a cured intimate mixture of a solid inorganic oxidizing salt, said inorganic oxidizing salt being present in an amount of from about 45 to about 90 percent by weight of the total propellant composition; an unsaturated polyester resin consisting of the condensation product of a saturated polyhydric alcohol and polycarboxylic acid, said polyester resin being the condensation product of an alkylene glycol, maleic anhydride and sebacic acid heteropolymerized with an unsaturated compound selected from the group consisting of loweR alkenes, lower alkynes, phenyl substituted lower alkenes, lower alkyl dienes, lower alkenyl esters of lower alkanoic acids, lower alkyl esters of lower alkanoic acids, lower alkenyl esters of lower alkanoic acids, allyl diglycol carbonate, diallyl diglycollate, and mixtures thereof; and a burning rate catalyst comprising an inorganic oxide selected from the group consisting of the oxides of vanadium, cobalt, iron, chromium, manganese, copper, silver, and mixtures thereof.