Insensitive melt cast explosive compositions containing...

Details Insensitive melt cast explosive compositions containing... Insensitive melt cast explosive compositions containing...

2001-06-26

2003-05-13

Carone, Michael J. (Department: 3641)

Explosive and thermic compositions or charges

Structure or arrangement of component or product

Solid particles dispersed in solid solution or matrix

C149S019600, C149S018000, C149S092000, C149S109600, C149S105000

Reexamination Certificate

active

06562159

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to melt cast compositions containing new energetic copolyurethane thermoplastic elastomers. It concerns mainly the use of melted TNT as a solvent to dissolve these energetic thermoplastic elastomers to produce insensitive, recyclable, high-energy melt cast plastic bonded explosives.
BACKGROUND OF THE INVENTION
Conventional melt cast explosives consist of TNT or a dispersion of high-energy crystals in TNT. The most simple and widely used formulation is the mixing of melted trinitrotoluene (“TNT”) with anti-cracking agent and waxes. Other compositions such as: Composition B, a mixture of TNT and hexahydro-1,3,5-trinitro-1,3,5-triazine (“RDX”)(40:60); Octol, a mixture of TNT and octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (“HMX”)(30:70) and some other TNT compositions are mixed in melt-cast systems. These compositions are usually melted and cast into artillery shells, rockets, bombs etc. where they are allowed to cool and solidify. These explosive formulations exhibit poor mechanical properties and show undesirable defects such as cracks, exudation, voids, brittleness, which can affect the ballistic performance and the impact sensitivity. One way to improve the mechanical properties of the formulations is to introduce a rubbery binder which serves as binding agents for energetic products. These formulations will be able to absorb impact, resist heat, etc. Such munitions are considered to be insensitive or less sensitive than regular munitions.
High-energy solid compositions such as propellants and composite explosives are usually prepared by combining a variety of materials including oxidizers, binders, plasticizers and a curing agent. Many energetic binders are available for use in the preparation of these high-energy compositions. Usually, these binders are obtained by mixing the energetic or non-energetic prepolymers with the other ingredients followed by a curing reaction involving the use of polyisocyanates. The rubbery binders give the insensitive character to high-energy compositions (U.S. Pat. Nos. 5,061,330, 4,985,093, 4,012,245 and 4,988,397). For composite explosives, the use of these binders leads to plastic bonded explosives (“PBXs”) which are chemically crosslinked and therefore not recyclable. A disadvantage of this technology resides in the fact that the mixing period is limited by the pot-life due to increased viscosity, and that long curing times at 60-80° C. are needed to crosslink the material leading to an expensive and undesirable process.
In general, formulators dislike doing a chemical reaction in their mixes since this leads to more complex batch processes. Moreover, the existing melt cast facilities are not suitable for these cast-cured PBXs.
A better way to prepare PBXs in melt cast facilities is to use thermoplastic elastomers leading to recyclable PBXs. High concentrations of these inert polymers make these compositions less hazardous, but also less energetic. The use of thermoplastic elastomers that are energetic will result in a loss of less energy. Some researchers identified inert thermoplastic elastomers and introduced them in melt cast formulations (U.S. Pat. Nos. 5,949,016, 4,284,442, 4,445,948, 4,978,482 and 4,325,759). Melting and mixing the thermoplastic elastomers with the other ingredients of the formulation to cast the final products was the ultimate goal of this invention. The limitation of this technology is that there are only a few thermoplastic elastomers that melt in the range of 80-100° C. and those melting at higher temperatures are not suitable for this process. Energetic thermoplastic elastomers of the type ABA and AB
n
melting at 83° C. were synthesized by Manser and Wardle but were very viscous and difficult to process in melt cast facilities (U.S. Pat. Nos. 4,483,978, 4,707,540, 4,806,613 and 4,952,644). In the present invention, energetic copolyurethane thermoplastic elastomers based on glycidyl azide polymer (“GAP”) have been found to be completely dissolved by TNT and were introduced in melt-cast formulations to isolate new insensitive recyclable plastic bonded explosive compositions.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a process using melted TNT as a solvent to dissolve energetic copolyurethane thermoplastic elastomers having melting points higher than 100° C. This was achieved in melt-cast systems and new insensitive melt-cast recyclable plastic bonded explosive compositions were isolated. This process using a melted explosive as a solvent for thermoplastic elastomers having melting points higher than 100° C. is not restricted to TNT and could be extended to other explosives that could eventually replace TNT in melt-cast formulations such as 1,3,3-trinitroazetidine (“TNAZ”). Plasticizers, energetic or not can also be used to dissolve the copolyurethane and introduce it in the formulation.
In accordance with one aspect of the present invention, there is provided a process to use melted TNT to dissolve energetic copolyurethane thermoplastic elastomer comprising linear polyurethanes physically cross-linked to one another by hydrogen bonds of the formula:
HO—P—(D—P)
n
—D—P—OH
wherein D is a group resulting from the reaction of a diisocyanate with hydroxyl groups of two separate prepolymers; P is a dihydroxyl terminated telechelic energetic prepolymer having a functionality of two or less, reacted with the isocyanate groups of two separate diisocyanates and n is 1 to 100. A complete description of the structure and the syntheses of these copolyurethane thermoplastic elastomers can be found in U.S. patent application Ser. No. 09/058,865 (filed April, 1998), which is herein incorporated by reference.
Preferably, the dihydroxyl terminated telechelic energetic polymer has a molecular weight ranging from about 500 to about 10,000 and is selected from the group consisting of glycidyl azide polymer (“GAP”), poly 3-nitratomethyl-3-methyloxetane (“NIMMO”) and poly glycidyl nitrate (“GLYN”), poly 3-azidomethyl-3-methyloxetane (“AMMO”) and poly bis 3,3-azidomethyloxetane (“BAMO”). These energetic copolyurethane thermoplastic elastomers can include a chain extender. Suitable chain extenders are low molecular weight diols such as ethylene glycol or a diol of the formula:
OH—CH
2
—(CH
2
)
n
—CH
2
—OH
wherein n is 1 to 8. The chain extenders can have primary hydroxyl or secondary hydroxyl groups. The preferred chain extenders having secondary hydroxyl groups are 2,4-pentanediol or 2,3-butanediol. The chain extenders can also be low molecular weight diamines. Preferably, the diisocyanate is aromatic such as 4,4′ methylenebis-phenyl isocyanate (“MDI”) and toluene diisocyanate (“TDI”) or aliphatic such as hexamethylene diisocyanate (“HMDI”) and isophorone diisocyanate (“IPDI”). The resulting copolymer can be dissolved by melted TNT and be mixed with other components of a melt-cast formulation. Cooling of the mixture resulted in the re-formation of the physical crosslinking of the energetic thermoplastic elastomers to yield new recyclable plastic bonded explosives. Aluminum, magnesium and other state of the art additives can be added to the formulation to increase the performance and the mechanical properties.
The advantage of the present invention is to provide a simple way of introducing copolyurethane thermoplastic elastomers having melting points higher than 100° C. in melt-cast formulations using the existing facilities. Since melted TNT is used to dissolve the copolyurethane thermoplastic elastomers, the temperature of operation is the same as for the conventional melt cast formulations. Moreover, compared to cast-cure processes, there is no pot-life and no extended curing time to prepare the PBXs. Therefore, this process is an improved way of introducing energetic thermoplastic elastomers having melting points higher than 100° C. in melt-cast formulations, leading to new recyclable insensitive melt cast PBXs.
According to one aspect of the present invention, it provides the use of energetic copolyurethane thermoplastic elastomer (“ETPE

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