GB2166128A - Flexible, self supporting, plastic bonded high explosive compositions - Google Patents

Abstract

A plastic bonded high explosive which is flexible, self supporting and water resistant. This comprises an intimate and uniform mixture of between 60-92% by weight of a particulate high explosive and 8-40% by weight of a thermo-elastomeric binder system. The elastomer referred to in this system is a block copolymer of polyether and polyamide. This may be used alone or in conjunction with polyisobutylene to act as an extender/tackifier and may be up to 50% by weight of the binder system. If desired further plastisizers may be employed. Amongst the explosives that may be used in this invention are PETN, RDX and HMX. The explosive formulations may be made by dissolving the binder in a suitable solvent and then adding the explosive followed by a drying step. Alternatively the formulation may be made "dry" in a suitably heated vessel.

Description

SPECIFICATION Flexible, self supporting, plastic bonded high explosive compositions This invention relates to flexible and self supporting plastic bonded explosive compositions that are water resistant.

More particularly the invention relates to the finding that a relatively novel thermoplastic copolymer (a polyether block amide) either when used alone, or in conjunction with, chemically and physically compatible plasticisers, extenders and tackifiers, serves as an extremely practical binder system, in the form of an elastomeric matrix to envelop extremely high loadings of several very powerful and brisant particulate high explosives. The explosive compositions so produced, can take the form of a tough and rubberlike flexible sheet, tape or cord of explosive, or, may be used to form blocks, slabs or cylinders of explosive, all of which may be physically tailored to specific requirements to form shaped charges.

The present invention comprises an intimate and uniform mixture of from 60-92 per cent by weight of a 'cap sensitive' particulate high explosive, and from 8-40 per cent by weight of the thermoplastic polymer binder system.

The thermoplastic polymeric binder system used in the present invention consists of a block copolymer of a polyether with nylon termed PEBAX 2533SN00 and manufactured in France by ATO Chemie, and available in the U.K. This product may either be used alone, (when incorporated with the highest percentage weight loadings of the chosen particulate high explosive) or in conjunction with 'Vistonex' polyisobutylene, an Esso Chemicals product, or a polyisobutylene of at least a molecular weight of 2000, in the following % by weight ratios of PEBAX 2533SN00 to the chosen polyisobutylene.

A) 90-10, B) 80-20, C) 70-30, D) 60-40, E) 50-50.

The polyisobutylene acting as an additional tackifier/extender. If so desired, the PEBAX 2533SN00 may be further plasticised by the addition of NN Butyl Benzene Sulphonamide.

High explosives suitable for use in the present invention include 'cap sensitive' particulate materials which are chemically compatible with the ingredients of the binder system, and which are stable under the processing conditions employed in the manufacture of the said compositions. These include (i) Pentaerythritol tetranitrate referred to as P.E.T.N., (ii) Cyclotrimethylenetrinitramine referred to as R.D.X. and (iii) Cyclotetramethylene tetranitramine or H.M.X.

One particularly preferred 'cap sensitive' high explosive when the compositions are used in sheet, tape or cord form is P.E.T.N.

The crystal shape of the P.E.T.N. has not been found critical to the success of the invention, but best results have been achieved by using a 'superfine' grade of P.E.T.N. i.e. the average particle size of the P.E.T.N. is less than 50 microns in maximum dimension.

Explosive compositions containing the previously described binder system may be made in the following manner: The PEBAX 2533SN00 either alone or if used together with the Polyisobutylene and additional NN Butyl Benzene Sulphonamide is/are dissolved in N Butanol (normal Butyl alcohol), at a temperature of 90-115"C. When all the components are completely dissolved in the N Butanol a binder 'lacquer' will have been created. Sufficient N Butanol is now allowed to evaporate from the mix (without any solid form of PEBAX mix or PEBAX being allowed to precipitate from the solution), until a fairly viscous 'binder syrup' is obtained. The desired amount of particulate high explosive is now added incrementally to this binder lacquer and thoroughly stirred in, until a completely homogenous explosive paste has been created.This 'explosive paste' is then scooped into teflon coated or PTFE moulds, further solvent allowed to evaporate, and then the 'explosive putty' so formed is rolled with heavy PTFE lined rubber or brass rollers while still pliable to the desired caliper sheet, on a brass or stainless steel plate, and the remaining solvent allowed to fully evaporate.

Alternatively being of a thermoplastic nature the PEBAX (and PEBAX plus extender plus plasticiser) binder system should enable the explosive compositions to be manufactured into the specifically desired physical forms, by a preferably solventless extrusion means on a suitable extrusion machine giving high pressures and heating zone capability up to 120"C and forcing through suitable dies at this temperature. In order to achieve the last suggested method of manufacture, the explosive compositions would require all solvent to be removed from them after the initial 'binder lacquer' compounding stage.

For processing into block, slab or cylinder form, suitable mechanical presses could be used with 'mould heating facility' (again with up to a 1200C heat output capability).

By way of example the following compositions were formulated by the first described 'hand rolling method' and were found to possess excellent flexural strength when rolled out in sheet form to a caliper of 3-4 m.m.

C()MPOSITIO,-T 1. COMPOSITION 2.

% % By Weight By weight PEES1iX 2533SNOO 10 PEEBAX 2533SN300 9.1 P.E.T.N. Gesso B Vi stanex LMMH' ( 50uparticle 90 Polyisobutylene 3.9 size) P.E.T.N. ( 50uparticle ) 87.0 size Both compositions were found to be able to wrap around a 4 inch diameter metal bar in a caliper of 3MM without showing any surface stress cracking.

Claims (6)

1. A plastic bonded high explosive in which the binder consists of a block copolymer of polyether and polyamide.

2. A composition as described in claim 1) in which the binder forms 8-40% by weight of the composition.

3. A composition as described in claim 2) which can be extended by up to 50% by weight of binder using polyisobutylene.

4. A composition as described in claim 1) in which the explosive component comprises PETN, RDX or HMX.

5. An explosive as described in claim 4) in which the explosive component comprises PETN of average particle size less than 50

6. An explosive charge comprising an agent as described in any one of claims 1) to 5).