Solid Propellant Composition

This invention relates generally to chemical compositions and more specifically to chemical compositions that can be used as rocket propellants.

For certain specialized applications, it is necessary to have a rocket propellant which has good thermal cycling ability so that it will not appreciably deteriorate when exposed to temperature extremes in the range of from about -65.degree. F. to +160.degree. F. Additionally it is important that the rocket propellant be relatively safe, have good storage stability, good ballistic properties, cure rapidly, and be easily processed. Furthermore it is desirable that it be prepared from relatively inexpensive starting materials and that it be readily duplicated.

Over the years research has continually gone on to find rocket propellants which have all the hereinbefore noted properties.

Accordingly, one object of this invention is to provide a rocket propellant.

Another object of this invention is to provide a rocket propellant which can undergo thermal cycling between about -65.degree. F. and +160.degree. F. without substantial deterioration.

A further object of this invention is to provide a rocket propellant which is relatively safe.

A still further object of this invention is to provide a rocket propellant which has relatively good storage stability.

Another object of this invention is to provide a rocket propellant which has relatively good ballistic properties.

Another object of this invention is to provide a rocket propellant which is rapidly cured.

Still another object of this invention is to provide a rocket propellant which can be easily processed.

A still further object of this invention is to provide a rocket propellant which can readily be duplicated.

Yet another object of this invention is to provide a rocket propellant which is prepared from relatively inexpensive starting materials.

These and other objects of this invention are accomplished by providing a rocket propellant comprising (1) ammonium perchlorate, (2) aluminum, (3) poly(1,2-butylene) glycol, (4) the reaction product of propylene oxide and either trimethylolpropane, hexanetriol or mixtures thereof, (5) 2,3-dihydroxypropyl-bis (2-cyanoethyl) amine, (6) hexamethylene diisocyanate, (7) copper chromite, (8) a carboxylic acid ester of either a diol and a monocarboxylic acid or a dicarboxylic acid and a monofunctional alcohol, and (9) sulfur and optionally containing (10) a metal acetylacetonate, (11) 2,4-pentanedione and (12) liquid silicon oil.

In order to obtain a propellant composition which possesses the desirable properties hereinbefore enumerated, it is necessary to blend the various constituents in a particular ratio. Thus, the ammonium perchlorate, which is the oxidizer of the instant composition, should constitute between about 60-85 weight percent of the total composition. Preferably the ammonium perchlorate is 60/40 mixture of ground rotary dried/unground material but this is not essential.

The aluminum, which is the fuel of the instant composition, should constitute between about 2-26 weight percent. Preferably the particle size is in the range of 40-60 microns but this is not essential.

The organic binder is actually a mixture of four different materials. Thus poly(1,2-butylene) glycol constitutes about 2.5-7.5 weight percent of the composition. Although polymers with a molecular weight range of between about 1600 and 2400 work well, the preferred molecular weight range is about 1900-2100. The binder also includes about 1-4 weight percent of a polyoxypropylene derivative of a triol which is the reaction product of propylene oxide with trimethylolpropane, hexane triol or mixtures thereof. Since the propylene oxide adds to the triol the bulk of the polymer weight actually comprises propoxy units so that the product is completely defined by its molecular weight which is between about 3500 and 4700 with a range of 4000-4210 being preferred. The binder also contains about 0.25-0.35 weight percent of 2,3-dihydroxypropyl-bis(2-cyanoethyl) amine as well as about 0.70-1.00 weight percent hexamethylene diisocyanate. The binder is in fact a polyether urethane composed of the polymer diol, the polyether triol crosslinker and the aliphatic diisocyanate curative. Also included is 2,3-dihydroxy-bis(2-cyanoethyl) amine, an oxidizer bonding agent which becomes part of the binder matrix. This material strengthens the bond between filler (NH.sub.4 ClO.sub.4) and binder thereby inhibiting the propagation of tears in the binder. This material also reduces dewetting of the binder from filler thereby increasing both tensile strength and elongation of the propellant.

Copper chromite should constitute about 1.5-3.0 weight percent of the composition and serves as a burning rate accelerator.

The plasticizer of the instant composition should constitute about 2.5-4.5 weight percent and may be (a) an ester of a diol and monocarboxylic acid such as represented by the formula ##STR1## where m and n vary independently and are intergers from 5-9 inclusive and R is alkylene of 6-12 carbon atoms, (b) an ester of a dicarboxylic acid and a monofunctional alcohol such as represented by the formula ##STR2## where X is an interger between 1 and 6 inclusive and R' and R" vary independently and are alkyl of 6-12 carbon atoms or (c) mixtures thereof.

The cure catalyst constitutes 0-0.015 weight percent of the composition and is a metal acetylacetonate. Such acetylacetonates are standard cure catalysts for polyether-urethane propellants but the preferred catalyst is ferric acetylacetonate.

The sole antioxidant of this composition is sulfur, which constitutes about 0.05-0.2 weight percent. When any type of iron is present in the composition, the sulfur not only serves as an antioxidant but serves the purpose of scavenging the excess iron salts through the formation of iron sulfide thereby preventing the iron catalyzed degradation of the urethane linkage in the polymer matrix. The preferred forms of sulfur are flowers of sulfur and colloidal sulfur.

Processing aids, 2,4-pentanedione which constitute 0-0.015 weight percent of the instant composition and liquid silicon oil, such as polydimethyl siloxane, and which constitutes about 0-0.01 weight percent of the instant composition, are also desirable but not essential. The liquid silicon oil acts as a defoaming agent and assists in the casting of the propellant by reducing the "drop" or decrease in propellant height which occurs in rocket chambers filled by the vacuum casting technique. The 2,4-pentanedione acts as a temporary cure retarding agent to extend potlife when used in conjunction with metal acetylacetonates and should be used only when a metal acetylacetonate is used.

The general nature of the invention having been set forth, the following examples are presented as specific illustrations thereof. It will be understood that the invention is not limited to these specific examples but is susceptible to various modifications that will be recognized by one of ordinary skill in the art.

Some typical examples of propellant compositions are as follows:

The propellant compositions of this invention are mixed as follows:

A submix is prepared by blending polydimethyl siloxane, poly (1,2-butylene) glycol, polyoxypropylene derivative of trimethylolpropane and a portion of the isodecylpelargonate in a Cowles dissolver or other high speed mixer. A premix is then made by adding the solid ingredients, sulfur, copper chromite and aluminum, to the prepared submix and blending thoroughly. This premix is then charged into the propellant mixer bowl and the 2,3-dihydroxypropyl-bis-(2-cyanoethyl) amine is added. The oxidizer, ammonium perchlorate, is then added and the mix is thoroughly blended for a period of one half hour at 100.degree. F. At this time a solution of ferric acetylacetonate and hexamethylene dissocyanate is added to the mixed ingredients, which are in the state of a slightly moistened powder at this point of the mix cycle. Further mixing of about 10 minutes is sufficient to fluidize the material. At this point 2,4-pentanedione and the remaining isodecylpelargonate are added, and the mixing proceeds for 20-30 more minutes. At this point the uncured propellant is quite fluid and ready for casting into the rocket chamber. The propellant normally cures in 3-4 days at 110.degree. F. to a shore A hardness of 50-55 but cure time can be decreased to 1-2 days at 135.degree. F.

Obviously, numerous modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described herein.