GB2466236A

GB2466236A - Dual composition plastic bonded explosive

Info

Publication number: GB2466236A
Application number: GB9310404A
Authority: GB
Inventors: Jean-Claude Cabrol; Bernard Dubocage; Jean-Pierre Mazer
Original assignee: Societe Nationale des Poudres et Explosifs
Current assignee: Societe Nationale des Poudres et Explosifs
Priority date: 1992-06-05
Filing date: 1993-05-20
Publication date: 2010-06-23
Anticipated expiration: 2013-05-20
Also published as: GB2466236B; ITTO930395A1; ITTO930395A0; GB9310404D0; DE4318922A1

Abstract

A dual-composition plastic bonded explosive comprises an inner region of a filled polymeric matrix in which the filler contains at least one organic nitro explosive, and an adjacent outer layer which is a filled polymeric matrix in which the filler contains at least one inorganic oxidising agent or an organic nitro explosive, with a rigid plastics layer at the interface between the two regions. The composition is made by providing the plastics layer in a mould, and then curing the two polymeric regions simultaneously.

Description

S

DUAL-COMPOSITION PLASTIC BONDED EXPLOSIVE

The present invention relates to the field of

ammunition, especially military ammunition, of conventional or attenuated hazard, and more particularly to a dual-composition plastic bonded explosive and a process for making it.

Dual-composition plastic bonded explosives in their casings should generally have an axial symmetry so as to give rise to symmetrical effects. This is not easy to achieve.

A considerable advantage of a dual-composition system is that it is possible to reduce the vulnerability of the loading to a detonation wave, for example one produced fortuitously by the nearby detonation of neighbouring ammunition, by coating a sensitive plastic bonded explosive with a plastic bonded explosive or a pyrotechnic composition which is less sensitive.

As is known in the art, a plastic bonded explosive is a pyrotechnic composition which is functionally capable of detonating, and which consists of a filled polyurethane or polyester, solid polymeric matrix generally of the filler being pulverulent and containing an organic nitro explosive charge, for example RDX, }1MX, pentrite, 5-oxo-3-nitro--1,2,4-triazole (ONTA) or a mixture of at least two of these compounds. This composition is obtained by casting followed by polymerisation of the dough of filled polymerisable binder.

Plastic bonded explosives and a manner of obtaining them are described, for example, in US 4,115,167 and US 5,067,996.

A major disadvantage of multicomposition plastic bonded explosives is that the processes employed hitherto to obtain them by overmoulding or machining are long, complex and very costly. They require a number of curing cycles, broach fitting and dismantling operations and numerous sets of tools. Machining operations in particular involve considerable pyrotechnic hazards and require special equipment. Overmoulding requires as many cure cycles as there are layers to be produced. According to this technique for example, a mould is provided, generally the casing of the explosive filling, containing a removable broach, and a first pasty pyrotechnic composition consisting of a filled uripolymerised binder in which the filler contains at least one organic nitro explosive is cured in the mould. Then the broach is removed and a second pasty pyrotechnic composition is supplied into the space in the mould vacated by the broach, and this second composition is then cured.

In practice, the abovementioned difficulties in procedure have limited the industrial development and the line production of multicomposition fillings, especially dual-composition plastic bonded explosives.

We have now devised a simple and relatively inexpensive process for obtaining multicomposition plastic bonded explosives whereby the abovementioned disadvantages are reduced or overcome and which does not make the filling any less effective and/or more vulnerable.

We have found that, unexpectedly, it is possible to position in the mould, before polymerisation of the pasty pyrotechnic compositions, a rigid film made of plastics material in the place intended as interface between the two regions, without the required fragmentation effect and blast effect being impaired by the presence of this material.

This is surprising because it would be expected that the provision of such an insert would result in the detonation behaviour being greatly perturbed, or even that the peripheral composition would not detonate when the latter is highly insensitive, for example in the case of detonability values of less than 20-25 cards in the Card Gap Test. The presence of this insert material makes it possible to eliminate the broach fitting and dismantling operations, to reduce the number of sets of tools and to decrease the cure cycles, since all the compositions can be polymerised simultaneously by curing. This insert material, which advantageously takes the form of a cup or of a sock made of rigid plastics material, can be very easily and inexpensively obtained, for example by the blow moulding technology, which is well known and widely employed for the manufacture of plastics bottles, or else by extrusion.

According to one aspect of the present invention, there is provided a process for obtaining a dual-composition plastic bonded explosive comprising an inner region and a peripheral adjacent outer region, wherein the inner region is a filled polymeric matrix in which the filler contains at least one organic nitro explosive, and the outer region is a filled polymeric matrix in which the filler contains at least one inorganic oxidising agent or an organic nitro explosive, which process comprises supplying to a mould two different pyrotechnic moulding compositions, that for the inner region comprising a filled unpolymerised binder in which the filler contains at least one organic nitro explosive, and that for the outer region comprising a filled unpolymerised binder in which the filler contains at least one inorganic oxidising agent or an organic nitro explosive, arid then polymerising the compositions to cure them, and wherein, before the polymerisation, a rigid plastics film (as herein defined) is positioned in the mould at the S -4-interface between the two regions, and the compositions are then simultaneously cured.

The invention also provides a dual composition plastic bonded explosive consisting of an inner region and an outer peripheral region, in which the inner region is a filled polymeric matrix in which the filler contains at least one organic nitro explosive, and the outer region is a filled polymeric matrix in which the filler contains at least one inorganic oxidising agent or an organic nitro explosive, the explosive comprising a rigid plastics film (as herein defined) at the interface between the two regions.

In the process, the fillers are generally pulverulent. The mould opening through which the compositions are supplied is generally situated in the upper part of the mould.

By "rigid" film as used herein we mean a film (or other thin layer) capable of withstanding the pressure of the pyrotechnic moulding compositions when the latter are introduced into the mould, and/or when the film defines an enclosure and is introduced into the mould with a pyrotechnic moulding composition already in the enclosure.

The film (or other thin layer) will preferably retain its shape under these conditions.

The mould generally and preferably forms the casing of the dual-composition filling of plastic bonded explosive.

According to the present invention, the term "dual-composition" is not intended in a narrow and restrictive sense to limit the invention to explosives containing only two regions. The technical effect found, and the advantageous results which stem therefrom, remain when the inner region and/or the peripheral region itself is of dual -or multicomposition. A number of insert materials, of different pattern, may be placed in the mould at one, or more, or all of the interfaces between the regions, without this presenting any specific problem.

The inner region is preferably solid, but it may alternatively have one or more cavities, for example an axial cavity extends for part or for the whole length of the region. Such a cavity can., for example, be used to house an initiating system.

Since aliphatic nitro derivatives are not generally used for any major industrial application as an explosive, an "organic nitro explosive" is generally intended to mean an aromatic explosive chosen from nitro explosives (containing at least one C-NO2 group, the carbon atom forming part of an aromatic ring) , nitric ester explosives (containing at least one C-O-N02 group) and nitramine explosives (containing at least one C-N-NO2 group) According to one preferred form of the invention, the inner and outer regions are coaxial and preferably cylindrical -According to another preferred alternative form, the inner region/peripheral region mass ratio is between 0.1 and 2.

The plastics material of which the film (which is preferably rigid) may be made may be thermoplastic or heat-curable, for example an elastomer of the polyurethane or silicone type. It may include reinforcements and/or fillers, such as graphite, carbon or glass, in powder or fibre form.

In one particularly preferred arrangement, the plastics material is a polyalkylene, preferably a low-or high-pressure polyethylene.

According to another preferred feature of the invention, the interface between the two regions has a circular or star-shaped cross-section. In such cases, the rigid plastic film will then advantageously also have a circular or star-shaped cross-section. The star will generally have 6 to 24 arms. The ends of the arms may be of any shape, for example flat, pointed or rounded. The star may be strictly polygonal or may have connecting fillets between the arms. The arms are preferably identical and have an axis of symmetry passing through the centre of the star.

Furthermore, the plastics film very advantageously is in the shape of an enclosure provided with a single opening, for example in the shape of a case, bottle, ogive, cupor sock. When the film is placed in the mould, the opening is positioned facing the opening of the mould, which is generally situated in the upper part of the mould, so as to make the interior of the enclosure accessible through the opening of the mould.

When the film has an enclosure shape provided with a single opening, it is then possible to run the pasty composition for the peripheral layer into the mould before the film is placed in position. When the rigid film is introduced into the mould the film pushes the paste back between the film and the walls of the mould. It is then subsequently possible to run the pasty composition for the inner layer into the enclosure bounded by the film. It is also possible to fill the enclosure of the film before it is introduced into the mould.

In general, whatever the shape of the insert material, the supply to the mould of the two moulding compositions may be carried out, simultaneously or successively, at atmospheric pressure or by injection under pressure, after the rigid plastic film has been placed in position in the mould.

According to another feature, the diameter (or size) of the mould opening is smaller than the corresponding dimension of the rigid plastic film. In this case the plastic, which must be sufficiently rigid for the abovementioned reasons, must also exhibit sufficient flexibility and elasticity for the film to be capable of being compressed without damage for introduction into the mould opening. Once in the mould, the film recovers its shape. For example, polyethylene films can be made which exhibit such properties and they are completely suitable in such a situation.

As a general rule and preferably, the thickness of the rigid plastics film is between approximately 1 mm and approximately 5 mm. This thickness need not be uniform.

In the present invention, the polymeric matrices of the inner and peripheral layers, which may be the same or different, are preferably polyurethanes or polyesters which may be either inert or reactive, that is to say they may contain energetic groups such as fluoro, nitro and/or azide groups.

The polyurethane matrices are generally obtained by reaction of a polymer containing hydroxyl ends with a polyisocyanate.

As examples of prepolymers containing hydroxyl ends there may be mentioned those in which the backbone is a polyisobutylene, a polybutadiene, a polyether, a polyester or a polysiloxane. A polybutadiene containing hydroxyl ends is preferably employed.

As examples of polyisocyanates there may be mentioned isophorone diisocyanate (IPDI) , toluene diisocyanate (TDI), dicyclohexylmethylene diisocyanate (Hylene W) , hexamethylene diisocyanate (HMDI) , biueret trihexane isocyanate (BTHI) and mixtures thereof.

When the polymeric matrix is a polyester matrix, it is generally obtained by reaction of a prepolymer containing carboxyl ends, preferably a polybutadiene containing carboxyl ends (CEPB) or a polyester containing carboxyl ends, with a polyepoxide, for example a condensate of epichlorohydrin and glycerol, or a polyaziridine, for example trimethylaziridinylphosphine oxide (MAPO) -The polymeric matrices may optionally include an inert or active plasticizer, such as those usually employed in the processing of plastic bonded explosives and of composite solid propellants.

According to a preferred feature of the invention, the inner region or layer is a plastic bonded explosive consisting of a filled polyurethane or polyester matrix in which the filler contains at least 15 % by weight, optionally at least 40 % by weight, at least 60 % by weight or at least 80 % by weight, of organic nitro explosive preferably chosen from the group consisting of RDX, HMX, 5-oxo-3--nitro-1,2,4-trizole and mixtures thereof, the percentages being expressed relative to the plastic bonded explosive. The filler may also include, for example, an inorganic oxidising agent such as arnmoniurn perchiorate and/or a reducing metal such as aluminium.

In another arrangement, the peripheral region is a pyrotechnic composition chosen from the group consisting of plastic bonded explosives and pyrotechnic compositions consisting of a filled polymeric matrix in which the filler, which is pulverulent, contains an inorganic oxidising agent.

When the peripheral region or layer is a plastic bonded explosive, it preferably consists of a filled polyurethene or polyester matrix in which the filler contains at least 15 % by weight, optionally at least 40 % by weight, at least 60 % by weight or at least 80 % by weight, of organic nitro explosive preferably chosen from the group consisting of RDX, HMX, 5-oxo-3-nitro-1,2,4-triazole, pentrite, triaminotrinitrobenzene, nitroguanidine and mixtures thereof, the percentages being expressed relative to the plastic bonded explosive.

The charge may also include, for example, an inorganic oxidising agent such as ammoniurn perchiorate and/or a reducing metal such as aluminium.

When the peripheral region is a pyrotechnic composition consisting of a filled polymeric matrix in which the filler, which is pulverulent, contains an inorganic oxidising agent, the polymeric matrix is preferably a polyurethane or polyester matrix. In addition, the filler is then preferably devoid of organic nitro explosive. It may consist, for example, solely of the inorganic oxidising agent or of a mixture of inorganic oxidising agent and a reducing metal such as aluminium, zirconium, magnesium, boron and mixtures thereof. However, it may also include other fillers such as non-explosive organic fillers, for

example oxamide.

As examples of inorganic oxidising agent employed for the outer layer there may be mentioned ammonium perchlorate, potassium perchiorate, ammonium nitrate, sodium nitrate and mixtures thereof.

In another preferred arrangement of the invention, the peripheral region is less sensitive to a detonation wave than the inner layer. This alternative form is used especially during the production of ammunition of attenuated hazard.

The expression "less sensitive to a detonation wave" means in practice that the detonability value (DV) according to the detonability test behind a barrier (Card Gap Test) is lower. This test, standardised either at 40-mm diameter or 75-mm diameter, is well known to a person skilled in the art.

In order that the invention may be more fully understood, the following Examples are given by way of illustration only.

Example 1 Dua1-coposition plastic bonded explosive with polyethylene insert material in the form of cylindrical enclosure of circular cross-section.

A rigid cylindrical case of circular cross-section, provided with a flat bottom, made of low-pressure polyethylene, 2 mm in thickness, of 128-mm internal diameter and 450 mm in length is introduced into a cylindrical structure of circular cross-section, provided with a flat bottom on which it rests, made of steel, 462 mm in length, of 273-mm external diameter and 12.5 mm in thickness, through the completely open face at the other end from the bottom. The case is positioned coaxially in the structure, the bottom of the case_________________________________________ -10 -resting on the bottom of the structure. The face of the case at the other end from the bottom is completely open.

Into the polyethylene case are introduced 9.96 kg of a pasty pyrotechnic composition at a temperature of 60°C and which is a filled unpolymerised binder of the following composition: -12 % by weight of a binder based on a polybutadiene containing hydroxyl ends with a mass of approximately 2000 and on isophorone diisocyanate (IPDI), -88 % by weight of pulverulent fillers: -20 % by weight of RDX, -43 % by weight of ainmonium perchiorate, -25 % by weight of aluminium.

Into the space included between the polyethylene case and the structure are then introduced 29.0 kg of a pasty pyrotechnic composition at a temperature of 60°C and which is a filled unpolymerised binder of the follow-ing composition: -12 % by weight of the same binder as that employed to fill the polyethylene case, -88 % by weight of pulverulent fillers: -51 % by weight of anunonium perchiorate, -5 % by weight of oxamide, -32 % by weight of aluminium.

The two pasty components are then polymerised simultaneously by heating at 60°C for 7 days.

The inner layer has a DV of 80 cards according to the Card Gap Test and the peripheral layer, still less sensitive, a DV < 1 card.

A Comparative Example 1 which does not form part of the invention and which represents the most closely related state of the art is produced in parallel so as tO demonstrate clearly the technical effect offered by the invention and the advantages which stem therefrom.

The same pasty compositions as for Example 1 and a strictly identical metal structure are employed for It this Comparative Example 1.

A cylindrical solid broach of circular cross-section, 128 mm in diameter and 450 mm in length, is positioned coaxially in the structure. The broach rests on the bottom of the structure. The peripheral pasty composition (29.5 kg) at a temperature of 60°C is then run into the space situated between the broach and the structure. This composition is then polymerised at 60°C for 7 days.

The broach is then dismantled and the internal pasty composition (9.96 kg) at a temperature of 60°C is then run into the corresponding space released. This composition' is then polymerised at 60°C for 7 day8.

The performance of the two fillings (Example 1 according to the invention and Comparative Example 1) is then determined, detonation being initiated by a planar-wave generator 76 mm in diameter consisting of a cylindroconical rounded cap made of plastic bonded explosive consisting of 14 % by weight of a polyurethane binder obtained by reaction of a polyetherdiol with IPDI and 86 % by weight of KMX. The cavity of the rounded cap is filled with a plasticbonded explosive consisting of 11.5%by weight of the same binder as that employed for the spherical cap, 17 % by weight of pentrite and 71.5 % by weight of red lead. The cylindroconical rounded cap is extended by a booster of the same 76-mm diameter, 45 mm in thickness, consisting of the same plastic bonded explosive as that of the rounded cap. The booster is in contact with the inner layer and the planar-wave generator is situated coaxially with the filling. This generator itself is initiated by a hexowax tablet used in com-bination with a conventional detonator.

The measured performance characteristics are, on the one hand, the rate of rise and the fragment velocity and, on the other hand, the blast effect.

* -12- The rate of rise of the metal casing as a func-tion of the radial expansion and the velocity of the fragments formed following the rupture of the casing are recorded with the aid of a slit camera, according to the cylindrical rise experiment, which is conventional for a person skilled in the art.

The results obtained are collated in Table 1 which follows: Radial expansion Rate of rise (mis) (nmi) Example 1 Comparative

Example 1

10 388 439 684 694 857 826 1250 1250 Fragmentation 1500 1570

Table 1

The velocity measured during the fragmentation corresponds to the velocity of the fragments formed.

All these results show that there is no signifi-cant difference between Example 1 and Comparative Example 1 and therefore that the presence of the insert material does not significantly alter the required fragmentation effect.

The blast effect is measured by virtue of piezo-resistive sensors placed between 10 and 35 m from the * 35 filling, approximately 1.25 m from the ground, which record the pressure as a function of time. Analysis of 13 -these curves makes it subsequently possible, for example, to trace the maximum pressure curve as a function of the distance from the filling.

At an equal distance from the filling the curves recorded by the sensors in Example 1 and in the Compara-tive Example 1 do not exhibit any significant difference and the curves of maximum pressure as a function of the distance which are derived from these are virtually superposable. At a distance of 15 m from the filling the maximum pressure is 410�10 mbar and the time of arrival of the aerial shock wave is 24.5�0.5 ms. At 23 m from the filling the measured maximum pressure is 215 inbar in Example 1 akd 190 mbar in Comparative Example 1 and the times of arrival of the aerial shock wave are 43 ms in Example 1 and 45 ms in Comparative Example 1.

These blast effect performance characteristics are of the same magnitude as those obtained with a 60/40 hexolite single-composition filling. The presence of the insert material does not significantly alter the required blast effect.

Example 2 ual-composition plastic bonded explosive with polyethylene insert material in the form of cylindrical enclosure of star-shaped cross-section.

A rigid cylindrical case of star-shaped cross- section, provided with a flat bottom, made of low-pressure polyethylene, 2 mm in thickness, of 128-nun internal diameter and 300 mm in length is introduced into a cylindrical structure of circular cross-section, provided with a flat bottom on which it rests, made of steel, 312.5 mm in length, of 115-mm external diameter and 12.5 nun in thickness, through the completely open face at the opposite end to the bottom. The star has 10 identical arms and has an axis of symmetry passing through the centre of the star. Each arm is therefore separated from the neighbouring arms by an angle of iriS.

The inscribed circle of the star has a diameter of 34 mm and its circumscribed circle a diameter of 54 mm.

The case is positioned coaxially in the struc-ture, the bottom of the case resting on the bottom of the structure. The face of the case at the opposite end to the bottom is completely open.

The polyethylene case is then filled with a pasty pyrotechnic composition at a temperature of 60°C and which is a filled unpolymerised binder of the following composition: -14 % by weight of a polyurethane binder obtained by reaction of a polyether containing hydroxyl ends with IPDI, -86 % by weight of pulverulent HEX.

The space included between the polyethylene case and the structure is then filled with a pasty pyrotechnic composition at a temperature of 60°C and which is a filled unpolymerised binder of the following composition: -16 % by weight of a polyurethane binder obtained by reaction of a polybutadiene containing hydroxyl ends with IPDI, -84 % by weight of pulverulent fillers: -72 % by weight of 5-oxo-3--nitro-1,2,4-triazole (ONTA) -12 % by weight of Mlix.

The two pasty compositions are then polymerised simultaneously by heating at 60°C for 7 days.

The inner layer has a DV of 150 cards according to the Card Gap Test and the peripheral layer, much less sensitive, has a DV of 25 cards.

A Comparative Example 2 which does not form part of the invention is carried out in parallel so as to demonstrate clearly the technical effect offered by the invention and the advantages which stem therefrom.

The same pasty compositions as in Example 2 and a strictly identical metal structure are employed for & this Comparative Example 2.

A cylindrical solid broach of star-shaped cross-section, 300 mm in length, is placed coaxially in the structure. The star is identical with that of Example 2 (10 identical arms, inscribed circle diameter 34 mm, circumscribed circle diameter 54 mm). The broach rests on the bottom of the structure. The peripheral pasty com-position is then run at a temperature of 60°C into the space situated between the broach and the structure. This composition is then polymerised at 60°C for 7 days.

The broach is then disassembled and the internal pasty composition at a temperature of 60°C is then run into the corresponding space released. This composition is then polymerised at 60°C for 7 days.

The rate of rise of the metal ca8ing as a func-tion of the radial expansion and the velocity of the fragments formed are then measured for the 2 fillings (Example 2 according to the invention and Comparative Example 2), using the same technique as in Example 1, detonation being initiated by a planar-wave generator mm in diameter consisting of a cylindroconica]. rounded cap consisting of the same plastic bonded explosive as that of the inner layer of the filling, the cavity of the rounded cap being filled with a plastic bonded explosive of composition 22.5 % by weight of a polyurethane binder obtained by reaction of a polyetherdiol with IPDI, 29.5 % by weight of pentrite and 48 % by weight of red lead. The cylindro-conical rounded cap is extended by a booster of the same 90-mm diameter, 30 mm in thickness, consisting of the same plastic bonded explosive as that of the rounded cap. The booster is in contact with the inner layer of the filling and the planar-wave generator is situated coaxially with the filling. This generator itself is initiated by a hexowax tablet used in combination with a conventional detonator. 16 -

The results obtained are collated in Table 2 which follows: Radial expansion Rate of rise (mis)

_________________

(mm) Example 2 Comparative

Example 2

795 750

_________________ ___________________

970 910 1060 1020 40 1150 1100 1210 1170 Fragmentation 1220 1190

________________ ___________________

Table 2

The slightly superior performance characteristics found according to the invention are at the limit of sig- nificance, bearing in mind the accuracy of the measure-ments. These results clearly show that the presence of the insert material does not result in a drop in performance.

Furthermore, using a conventional rig well known to a person skilled in the art, we have observed the shape of the detonation wave at the sample end, with the aid of a slit camera. Unexpectedly, we have found that the presence of the insert material practically does not alter the detonation behaviour.

Claims

CLAIMS1. A process for obtaining a dual-composition plastic bonded explosive comprising an inner region and a peripheral adjacent outer region, wherein the inner region is a filled polymeric matrix in which the filler contains at least one organic nitro explosive, and the outer region is a filled polymeric matrix in which the filler contains at least one inorganic oxidising agent or an organic nitro explosive, which process comprises supplying to a mould two different pyrotechnic moulding compositions, that for the inner region comprising a filled unpolymerised binder in which the filler contains at least one organic nitro explosive, and that for the outer region comprising a filled unpolymerised binder in which the filler contains at least one inorganic oxidising agent or an organic nitro explosive, and then polymerising the compositions to cure them and wherein, before the polyznerisation a rigid plastics film (as herein defined) is positioned in the mould at the interface between the two regions, and the compositions are then simultaneously cured.
2. A process according to claim 1, wherein the two regions are coaxial.
3. A process according to claim 2, wherein the two regions are cylindrical.
4. A process according to claims 1,2 or 3 wherein the rigid plastics film is a polyalkylene.
5. A process according to claim 4, wherein the polyalkylene is polyethylene.
6. A process according to any of the preceding claims, wherein the thickness of the rigid plastics film is between approximately 1 mm and approximately 5 mm.
7. A process according to any of claims 2 to 6 wherein the rigid plastics film has a circular or star shape cross-section.
8. A process according to any preceding claim, wherein the rigid plastics film defines an enclosure provided with a single opening, the opening being positioned so as to make the interior of the enclosure accessible through the opening of the mould.
9. A process according to claim 8, wherein the pasty composition for the outer region is supplied to the mould before the rigid plastics film is placed in position.
10. A process according to claim 9, wherein before or after the rigid plastics film is placed in position in the mould, the pasty composition for the inner region is supplied to the enclosure defined by the film.
11. A process according to any of claims 1 to 8, wherein the two pasty compositions are supplied simultaneously or successively after the plastics film has been placed in the mould.
12. A process according to any preceding claim, wherein the size of the mould opening is smaller than the cross-sectional size of the rigid plastics film.
13. A process according to any preceding claim, wherein the inner region is a plastic bonded explosive consisting of a filled polyurethane or polyester matrix in which the filler contains at least 15 % by weight (relative to the plastic bonded explosive) of organic nitro explosive.
14. A process according to claim 13, wherein the organic nitro explosive is chosen from RDX, HMX, 5-oxo-3-nitro-1,2,4-triazole and any mixture of two or more thereof.
15. A process according to any preceding claim, wherein the outer region is either a plastic bonded explosive consisting of a filled polyurethane or polyester matrix in which the filler contains at least 15 % by weight (relative to the plastic bonded explosive) of organic nitro explosive, or a pyrotechnic composition consisting of a filled polyurethane or polyester polymeric matrix in which the filler contains an inorganic oxidising agent and is devoid of organic nitro explosive.
16. A process according to claim 15, wherein the organic nitro explosive is chosen from RDX, HMX, pentrite, triaminotrinitrobenzene, nitroguanidine, 5-oxo-3-nitro- 1,2,4-triazole, or any mixture of two or more thereof.
17. A process for obtaining a dual-composition plastic bonded explosive substantially as herein described in any ofthe Examples.
18. A dual-composition plastic bonded explosive consisting of an inner region and an outer peripheral region, in which the inner region is a filled polymeric matrix in which the filler contains at least one organic nitro explosive, and the outer region is a filled polymeric matrix in which the filler contains at least one inorganic oxidising agent or an organic nitro explosive, the explosive comprising a rigid plastics film (as herein defined) at the interface between the two regions.
19. A dual-composition plastic bonded explosive according to claim 18, wherein the peripheral region is less sensitive to a detonation wave than the inner region.
20. A dual-composition plastic bonded explosive substantially as herein described in any of the Examples.