AU641970B2 - Copper chelate ballistic modifiers - Google Patents

Description

641970 Form COMMONWEALTH OF AUSTRALIA PATENTS ACT 1952-62 COMPLETE SPECIFICATION

(ORIGINAL)

FOR OFFICE USE: Application Number: Lodged: Complete Specification Lodged: Accepted: Published: Priority: Related Art: Class Int. Class i Name of Applicant: Address of Applicant: Actual inventor: Address for Service: TO BE COMPLETED BY APPLICANT THE COMMONWEALTH OF AUSTRALIA Anzac Park, Canberra, Australian Capital Territory, Commonwealth of Australia BRIAN LAURENCE HAMSHERE and JUAN FREDERICK HOOPER Care of R.K,,,MADDERN ASSOCIATES, 345 King William Street, Adelaide, State of South Australia, Commonwealth of Australia Complete Specification for the invention entitled: "COPPER CHELATE BALLISTIC MODIFIERS" The following statement is a full description of this invention, including the best method of performing it known to r5. us.

Ji TTAD ARKS -1 I nr- A BACKGROUND OF THE INVENTION This invention relates to a new class of ballistic modifiers which, when incorporated in certain propellant mixtures, enhance the burn rate, promote low burn rate pressure exponency, and improve batch to batch reproducibility, without undue adverse effect on propellant binder cure and propellant aging.

It is well known in the prior art to add various additives to propellants in order to modify their ballistic performance in some way. In general, additives serve to enhance burn rate but some also serve to reduce the dependency of burn rate on pressure given by the empirical relationship: rb =Ap n

S

1 i where rb is the burn rate, A is an empirical- constant, p is se***e b the pressure exerted by the combustion gases and n is the pressure exponent. With certain additives, n can be reduced to zero resulting in a propellant with plateau burning i('pressure independent) characteristics, which is highly desirable in rocket motor applications calling for a continually changing operating pressure, but requiring a constant burning rate. In addition to promoting enhanced burn rate and plateau burning in propellants, it is desirable that the additives do not unduly adversely affect the long term aging properties of the propellant.

Many different types of ballistic modifiers have been suggested in the past (see eg US Patent Nos 3,677,839; 4,000,025; 4,202,714; 4,239/,561; 4,243,444; 4,260,437; 4,263,071 and 4,391,660).

Copper chromite, as a catalytic additive to certain propellant mixtures, produces an acceptable plateau burning effect and enhanced burn rate. However, for some propellant mixtures, notably those containing an unsaturated 2 polybutadiene-type matrix, copper chromite has an adverse effect on the long-term storage properties. The catalyst tends to accelerate oxidative hardening of the polymeric S matrix. This can result in consequent cracking of the surface of the propellant charge upon expansion or contraction caused by temperature fluctuations, and. possible catastrophic destruction of the rocket motor on ignition.

Another problem with copper chromite is that it is highly hygroscopic, which means that great care must be taken to dry it and keep it free from moisture prior to use in propellants, to ensure adequate batch to batch reproducibility It is also an inherent feature of many other coppercontaining burn rate catalysts, that they tend to accelerate the cure reaction between the binder prepolymer and the curing agent. Practical casting methods dictate that the propellant have a sufficiently slow cure reaction to enable successful motor charge filling operations to be conducted (ie the propellant must have a suitable pot life).

0* It has now been found that some or all of the aboverlentioned problems can be overcome or alleviated by incorporating a new class of ballistic modifiers into propellant mixtures.

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SUMMARY OF THE INVENTION SThe ballistic modifiers according to the present invention are copper chelates comprising two or more copper atoms or ions complexed with three or more organic ligand S. 00 molecules, which may be the same or different, the number of ligand molecules being greater than the number of copper atoms or ions. Thus, the copper chelate, which may be polymeric in structure, will comprise two or more copper atoms or ions substantially enclosed within an organic shell.

A propellant mixture, incorporating at least one of these ballistic modifiers, may display one or more of the following desirable characteristics: plateau burning effect (ie zero or very low burn rate pressure exponent) over a wide pressure range; enhanced batch to batch reproducibility and long-term storage properties (compared with conventional coppercontaining ballistic modifiers); little catalytic effect on the cure reaction between the binder prepolymer and the curing agent; and enhanced burn rate.

The high degree of burn rate enhancement afforded by these ballistic 'modifiers is attributable to the relatively high percentage of copper present in the molecular structure when compared with other previously-used organo-copper S* compounds (eg copper phthalocyanine). In addition, the chelate structure of the present ballistic modifiers serves to isolate the copper atoms or ions from the propellant binder, and hence slow down the deleterious surface hardening zw reaction.

The improved batch to batch reproducibility and aging properties of the mixture result in a lower rejection rate and an enhanced service life for rocket motor charges made fom such propellants, with concomitant increase in reliability and cost savings.

So o 6 0-° DESCRIPTION OF THE PREFERRED EMBODIMENTS.

Preferred chelates are of the formula 1: [wherein R ,is a hydrogen or halogen atom, an amino, hydroxy o r thic). group, or a 0111 alkyl, alkenyl, alkynyl, cycloalkyl,.acyl, aryl, heterocyclic, alko'xy, alkenoxy, alkynoxy, cycloalkyloxy, 'acyloxy, aryloxy or heterocyclicoxy radical, each of which may be further substituted by one or more suitable radicals; and n is an integer from 1 to 4].

A paiticularly preferred catralyst is bis Isalicylal-oaminophenol-copper or CuSAP of formula 2: 0 N=Cu.

*fee 0 0 0 The ballistic modifiers of the present invention can be used in conjunction with any conventional propellant mixture.

The propellant can be either a non-aluminised,.hydrocarbontype propellant or a metallised propellant (eg incorporating aluminium).. Preferred propellants are polybutadiene-type composites,,incorporating ammonium perchlorate as oxidant.

Ahy polybutadiene polymer or copolymer can be used as the binder: the essential feature is that there should be unsaturation in the polymer chain. Exemplary binders are hydroxy-terminated polybutadiene (HTPB), having a functionality of about 2.2 (ie there are some additional hydroxyl groups present in the chain); carboxy-terminated polybutadiene (CTPB); polybutadiene acrylonitrile (.PBAN) and polybutadiene acrylic acid (PBAA). Hydroxy-terminated polybutadienes are most preferred. Suitable crosslinking agents and curatives are diisocyanates and epoxides.

The CuSAP (or similar) catalyst may be incorporated into the propellant mixture in amounts up to approximately 3% (or I higher, in some cases) of the propellant mass. Other 7 standard components, as used in the automative and propellant industries, may also be incorporated in the propellant mixtures. Stabilizers, such as antioxidants, may be included V to slow down aging. Examples of suitable antioxidants include phenyl beta-naphthylamine (PBNA) and phenolic antioxidants such as 2,2-methylene-bis[6-tert.butyl-4-methylphenol] (A02246). The phenolic type is preferred, as it promotes a longer pot life than PBNA.

The copper chelates of the present invention, being" improved burn rate catalysts for polybutadiene-based and .similar propellants, are suitable for both rocket and gas generator applications.

The copper chelates used in the propellant mixtures are, in general, known compounds, or may be prepared according to conventional methods. The following examples set forth the method of preparation of the preferred catalyst, CuSAP, and tests carried out on this catalyst.

EXAMPLE I: Preparation of CuSAP N-2-Hydroxyphenylsalicylideneimine (SAP): Salicylaldehyde (48.8g, 0.4 moles) and o-aminophenol (43.6g, 0.4 moles) are dissolved with stirring in warm ethanol (2.0 1, absolute grade). On cooling, the orange crystals are separated by suction filtration, washed with ethanol and then dried in the air. Yield 82g Bis[Salicylal-o-aminophenol-copper (CuSAP): Copper acetate monohydrate (17.33g, 0.087 moles) and sodium acetate (18g, 0.22 moles) were dissolved in ethanol/water (1:1,800ml). To this was then added a suspension of SAP (18.46g, 0.087 moles) in ethanol (700 ml) with the resulting mixture being stirred for 15 mins. A voluminous green solid was filtered by suction (this complex was found to darken in colour on heating or drying), and dissolved in pyridine (700 S* ml, AR grade) with gentle heating and stirring.

Precipitation of the golden-brown pyridinate complex was accomplished batchwise using 150 ml samples of the pyridine solution being poured into 600 ml volumes of water. The 20"* solid accumulated after filtration was then boiled in ethanol

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(200 ml) for one hour, filterd, washed with ethanol and dried in an oven at 100'C. Yield 17g This procedure was then repeated until the desired amount of CuSAP had been obtained.

6 *6 EXAMPLE II': Testing folMo sture Sensitivity Moisture sensitivity of CuSAP was determined and compare. with that of copper chromite by monitoring, over a 20 hour period, moisture uptake in samples of CuSAP and copper chromite dried for 48 hours at 110'C and exposed to 75% relative humidity atmosphere at\'20°C. With measured weight ,increases of approximately 0.2% and 2% respectively, the moisture sensitivity of CuSAP is an order of magnitude less than that of copper chromite.

EXAMPLE III: Testing for Burn Rate and Aging Properties Comparative strand burning tests were performed on hydroxy-terminated polybutadiene-based composite propellants containing CuSAP and copper chromite as burn rate catalysts.

The burning rate-pressure profiles of the CuSAP and copper chromite propellants were very similar and displayed a zero or low (less than 0.1) burning rate pressure exponent over an extended pressure range (typically 7 to 14 MPa). Subsequent accelerated a ing tests demonstrated the superior aging characteristics of the CuSAP propellants over those containing copper chromite. Whereas the copper chromitecontaining propellants crusted after only 10 to 12 weeks aging in air at 60°C, the CuSAP-containing propellants showed no signs of crusting even after 30 weeks at that temperature.

While the present invention has been described in terms of preferred embodiments in order to facilitate better understanding of the invention, it should be appreciated that various modifications can be made without departing from the principle of the invention. Therefore, the invention should be understood to include all such modifications within its scope..

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Claims (18)

1. A ballistic modifier comprising a copper chelate of two or more copper atoms or ions complexed with three of more organic ligand molecules, which may be the same or different, the number of ligand molecules being greater than the number of copper atoms or ions, and the structure of the chelate being such that the copper atoms or ions are substantially enclosed within an organic shell formed from the ligand molecules.

2. A ballistic modifier comprising a copper chelate of the formula 1: R N=CR i- u Cu wherein R is a hydrogen r halogen atom, an amino, hydroxy or thiol group, or a C1-2 alkyl, alkenyl, alkynyl, cycloalkyl, acyl, aryl, alkoxy, alkenoxy, alkynoxy, cycloalkyloxy, acyloxy or aryloxy radical, each of which may be further intege from to 4. a wherein R is a hydrogen or halogen atom, an amino, hydroxy or thiol group, or a C -12 alkyl, alkenyl, alkynyl, cycloalkyl, acyl, aryl, alkoxy, alkenoxy, alkynoxy, cycloalkyloxy, acyloxy or aryloxy radical, each of which may be further substituted by one or more suitable radicals; and n is an integer from 1 to 4. ©9 q

3. A ballistic modifier comprising bis[salicylal-o- aminophenol-copper of formula 2: C=N 0 0

4. A propellant mixture comprising as ballistic modifier, a copper chelate of two or more copper atoms or ions complexed with three or more organic ligand molecules) which may be the same or different, the number of ligand molecules being greater than the number of copper atoms or ions, and the structure of the chelate being such that the copper atoms or ions are substantially enclosed within an organic shell formed from the ligand molecules, a S. propellant and customary additives. 2S

5. A propellant mixture according to claim 4, wherein said copper chelate is of the formula 1: *o C C=N U. S Rn •go t L wherein R is a hydrogen or haloqen atom, an amino, hydroxy or thiol group, or a C 1 1 2 alkyl, alkenyl, alkynyl, cycloalkyl, acyl, aryl, alkoxy, alkenoxy, alkynoxy, cycloalkyloxy, acyloxy or aryloxy radical, each of which may be further substituted by one or more suitable radicals, and n is an integer froi to 4.

6. A propellant mixture according to claim 4 or 5, wherein said copper chelate is bis[salicylal-o-aninophenol-copper of formula 2: is Z O O\ 0 N=C H C0 o0 00 g0 S*

7..A 7. A propellant mixture according to any one of claims 4 to .le 6, comprising either a non-aluminised, hydrocarbon-type 00 Spropellant or,, a metallised propellant.

8. A propellant mixture according to any one of claims 4 to S 7, further domprising a polybutadiene-type binder.

9. A propellant mixture according to claim 8, wherein said binder is hydroxy-termina ted polybutadiene, carboxy- terminated polybutadiene, polybutadiene acrylonitrile or S polybutadiene acrylic acid.

A propellant mixture according to any one of claims 4 to 9, further comprising an oxidant.

11. A propellant mixture according to claim 10, wherein said oxidant is ammonium perchlorate.

12. A propellant mixture according to any one of claims 4 to 9, further comprising an antioxidant.

13. A propellant mixture according to claim 12, wherein said antoxidant is phenyl beta-naphthylamine or a phenolic Santioxidant.

14. A method of enhancing the burn rate of a propellant mixture comprising adding thereto a ballistic modifier acording to any one of claims 1 to 3.

15. A method of enhancing the storage properties of a propellant mixture cpmprising adding thereto a ballistic modifier according to any one of claim'. 1 to 3.

16. A ballistic modifier according to any one of claims 1 to 3, suIstantially as described herein.

17. A propellantslmixture according to any one of claims 4 to 13, substantially as described herein. 1 0

18. A method according to claim 14 of enhancing the burn rate of a propellant mixture, substantially as described herein. S19. A method according to claim 15 of enhancing the storage properties of a propellant mixture, substantially as described herein.- Dated this 3rd day of January 1991. THE COMMONWEALTH OF AUSTRALIA, By its Patent Attorneys, R.K. MADDERN A0SOCIATES 12 3 ii