US Government As Represented by the Secretary of the Army

Henry C Allen

Marjorie T Cucksee

Marjorie E Ducote

Frederick W Clarke

Everette M Pierce

Marjorie T Cuksee

A process is disclosed for improving the mechanical properties and procesility of thermoplastic composite propellants achieved by incorporation in the propellant of from about 0.1% to 1.0% of an organic titanate of the general formula Ti(OR).sub.4, where R represents a common alkyl group. The process comprises dissolving in an excess amount of a volatile organic solvent a thermoplastic elastomer which consists of hard segments having substantially crystalline properties and soft segments having substantially amorphous properties. The hard segments impart rigid properties to a solid propellant composition with which it is combined, and the soft segments imparting rubbery properties to a solid propellant composition with which it is combined. The Ti(OR).sub.4 functions as a medium between the surface of the ammonium perchlorate (AP) oxidizer and the thermoplastic elastomer to improve processability and to provide a bonding substrate to enhance the adhesive bond between the AP and the thermoplastic elastomer. After solvent removal, the propellant pellets are heat formed in a mold, the mold is cooled, and the molded product is released in the form of a solid propellant grain.

Tetra-alkyl titanates as bonding agents for thermoplastic propellants

Disclosed is a thixotropic flame inhibitor for a rocket propellant grain luding an organic thixotrope in amounts from about 5 parts to about 30 parts into HTPB liquid polymer in amounts from about 70 parts to about 95 parts by stirring at elevated temperatures. After cooling the mixture to room temperature, appropriate quantities of di- or polyfunctional isocyanates and cure catalysts are added to promote cure at room temperature. Fine particulate matter may also be added to increase viscosity. The resulting formulation is a room-temperature curable, thixotropic mixture which will not flow under its own weight when applied to wettable non-horizontal surfaces in appreciable thicknesses, and which, when cured, is suitable as an inhibitor for composite solid rocket propellants. Thixotropy may be controlled by the level of organic thixotrope in the formulation while viscosity may be adjusted by the level of particulate filler; these parameters determine the allowable thicknesses from one-coat applications.

Thixotropic flame inhibitors for rocket propellant grains

The polyamine compound, TEPAN, a partially cyanoethylated tetraethylene pamine, is reacted with a selected ammonium salt to form an adduct of TEPAN and the selected ammonium salt. The ammonium salt is selected from ammonium perchlorate (AP), ammonium nitrate (AN), ammonium sulfate (AS), and ammonium formate (AF). The process for preparation of the adduct comprises reacting a water solution of the selected ammonium salt with TEPAN while stirring at room temperature. A TEPAN-glycidol derivative product is also reacted with the selected oxidizer salt to form an adduct of the TEPAN-glycidol derivative product. The disclosed adducts (having adduct ratios of 1.0 to 1.8 equivalents of ammonium salt per mole of TEPAN or TEPAN-glycidol derivative product, TEPANOL) improve mechanical properties and processiblity of composite propellant composition containing about 88 weight percent solids (ammonium perchlorate, aluminum, and Fe.sub.2 O.sub.3 catalyst), a binder of hydroxy-terminated polybutadiene and dioctyladipate cured with a mixture of isophorone diisocyanate and a trifunctional isocyanate. Mechanical properties, especially strain at maximum stress at -40.degree. C. are substantially improved. The processing time, particularly the mix cycle time, is shortened because of the amine salt bonding agent eliminating or minimizing in situ ammonia generation during the incorporation and mixing of ammonium perchorate into the propellant mix.

Amine salts as bonding agents

Water-soluble protein is coated onto particles of nitramines by making a rry of nitramine powder in a water solution of the protein and removing the water by evaporation or by filtration after previously precipitating the protein by addition of ethanol. The protein coating acts as a bonding agent to enhance the bond strength between propellant binders and the nitramine particles, resulting in substantial enhancement of desirable propellant properties.

Bonding agent for nitramines in rocket propellants

A process is disclosed by which thermoplastic elastomers may be utilized to repare melt-formable composite rocket propellants. The thermoplastic elastomer is dissolved in a volatile organic solvent, the other propellant ingredients are mixed in, and the volatile organic solvent is evaporated. The dried propellant is melt-formed to final shape by molding or extruding above the melting point of the elastomer. An example of a usable thermoplastic elastomer is a block copolymer comprised of about 5 to about 20 weight percent styrene and of about 80 to 95 weight percent diene. The formed grain can be reclaimed by melting or dissolution in an organic solvent for reuse of the propellant ingredients.

Thermoplastic composite rocket propellant

A liner composition is employed as a liner/inhibitor for a solid propellant rain while functioning as a liner-binder between the propellant grain and insulation or the motor case. The liner and inhibitor composition is prepared from the conventional binder systems (e.g., hydroxy terminated polybutadiene (HTPB), polysulfide, polyurethane, and polyester). The composition employs a cool burning oxidizer selected from oxamide and nitroguanidine. The type of solid propellant grain, particularly the crosslinking or reaction mechanism to form a chemical bond between the binder of the liner composition and the binder of the propellant, dictates the type formulation of the liner/inhibitor composition. A representative liner/inhibitor for a HTPB propellant grain contains from about 10 to about 70 weight percent oxidizer, from about 0.1 to about 1.0 weight percent cure catalyst selected from ferric acetyl acetonate and triphenyl bismuth, an isocyanate curing agent selected from toluene diisocyanate, hexamethylene diisocyanate, and isophorone diisocyanate from about 1 to about 10 weight percent, and the balance of formulation hydroxy terminated polybutadiene. The use of the proper cure catalyst will produce a cured system at ambient (70.degree. F. or higher) in 24 hours. A chemical bond is formed between the liner and inhibitor binder and the propellant binder by the crosslinking action of the isocyanate curing agent and the hydroxyl groups of the binder systems. The chemical bond withstands the stresses of gas flow as well as the effects of spinning the rocket motor. Thus, the cool burning oxidizer in combination with the bonds between the binder systems which withstands the flow of gases will result in extinguishment of the liner/inhibitors at sudden pressure drop encountered at end of propellant grain burning and thereby result in elimination of smoke from the liner/inhibitor which is extinguished prior to bond failure.

Ambient cured smokeless liner/inhibitor for propellants

A method of mixing poly(neopentylglycol)azelate (NPGA) is disclosed which hances its solubility in polyurethane binders for composite solid propellants. The method comprises withholding the addition of NPGA from the propellant submix and from the total propellant formulation mixing procedure until after the addition of the curing agent has taken place and reaction has taken place for a predetermined period of time with the bonding agent until a 'break' in viscosity occurs. The 'break' in viscosity has taken place when the other binder ingredients have reacted with the curing agent HDI (hexamethylenediisocyanate) so that immiscibility between the binder ingredients is reduced. The late NPGA addition method resulted not only in apparently complete solubilization of the NPGA but also yielded a propellant with dramatically lower end of mix viscosity (reduced by a factor of 10), superior flow characteristics, and better physical properties. Propellants made by the disclosed method of mixing have desirable lower modulus and higher tensile strength. Thus, the propellant mixed in accordance with the late NPGA addition method yields a propellant with a high tensile strength to modulus ratio. The high tensile strength to modulus ratio at low temperature is an indicator of a good propellant.

Solubility of NPGA in a polyurethane binder

A new combination of bonding agents when employed in hydroxy-terminated pbutadiene propellant compositions yields greatly improved high temperature aging characteristics and greatly improved low temperature physical properties for the compositions. The combination or bonding agent system consists of MT4 (reaction product of 2.0 moles of tris 1(2 methylaziridinyl)phosphine oxide, 0.7 mole adipic acid, and 0.3 mole tartaric acid); HX752 (bis isophthaloyl 1(2 methyl)aziridine); and BIDE (butyliminodiethanol) in a weight percent range of the propellant composition of 0.10% to 0.20%, 0.10% to 0.20% and 0.02% to 0.05% respectively.

Bonding agent system for improved propellant aging and low temperature

Diols of the general formula, R(OH).sub.2, wherein R is an alkylene radic and iminodiols of the general formula, R'N(R'OH).sub.2, wherein R' is an aryl or alkyl radical and R' is an alkylene radical, with melting points of less than 60.degree. C (140.degree. F) are effective dispersing aids for the bonding agent MT-4. MT-4 which functions as an interfacial bonding agent is prepared by reacting together 2.0 moles of tris 1(2 methylaziridinyl)phosphine oxide, 0.7 mole adipic acid, and 0.3 mole tartaric acid. The specified dispersing aids react to become a part of the binder matrix without causing degradation of physical properties or nullification of the functions of MT-4. The specified dispersing aids for the bonding agent MT-4 were found to be particularly effective to ensure uniform coating of solids in solid propellants employing a hydroxy-terminated polybutadiene binder system while not imparting negative side effects that the dispersing adjuvant of 'added' water causes.

Dispersing aids for MT-4

The reaction products formed from tri-functional aziridinylphosphine oxides r their derivatives reacted with monofunctional carboxylic acids, the tri-aziridinyl derivatives of triazine, the tri-aziridinyl derivatives of benzenetriacyl, the aziridine compound N-phenethylaziridine, and selected alkyl diaziridine compounds are representive of the aziridine compounds which are utilized in isocyanate curable composite propellant compositions to extend usable pot life required for mixing and processing of the specified compositions. The compositions are comprised of a binder of hydroxy terminated liquid polymer systems, (e.g. hydroxy terminated polybutadiene and the like) selected plasticizers, optional metal fuel, and the inorganic oxidizer, ammonium perchlorate, that is substantially of very fine particle size (less than 20 microns).

Pot life extension of isocyanate cured propellants by aziridine compounds

Trioctylphosphine oxide and tributylphosphine oxide are representative of e phosphine oxide compounds which are utilized in isocyanate curable composite propellant compositions to extend usable pot life required for mixing and processing of the specified compositions. The compositions are comprised of a binder of hydroxy terminated liquid polymer systems, (e.g. hydroxy terminated polybutadiene and the like) optional selected plasticizers, optional metal fuel, and the inorganic oxidizer, ammonium perchlorate, that is substantially of very fine particle size (less than 20 microns).

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Decatur, AL, United States of America

Henry C Allen