Flexible Explosive Composition Comprising Particulate RDX, HMX or PETN and a Nitrostarch Binder Plasticized With TEGDN or TMETN

Flexible, self-supporting explosive compositions comprising a high explosive, such as RDX (cyclotrimethylenetrinitramine), HMX (cyclotetramethylenetetranitramine), and/or PETN (pentaerythritol tetranitrate), and a plasticized nitrocellulose binder system have been found considerable application in the art. TMETN (trimethylolethane trinitrate) because of its relatively low sensitivity, high explosive power and lack of headache producing properties, is a particularly desirable energetic plasticizer for use in preparing such explosive compositions containing essentially 100% explosively active ingredients. However, its lack of ready colloiding power for nitrocellulose, as noted in U.S. Pat. No. 3,400,025 and my copending U.S. application Ser. No. 454,900, filed Mar. 26, 1974, and now U.S. Pat. No. 3,943,017, has largely discouraged its use as a plasticizer for nitrocellulose. TEGDN (triethyleneglycol dinitrate), which colloids nitrocellulose relatively readily, is also a desirable energetic plasticizer for use in such explosive compositions.

An object of the present invention is to provide a flexible explosive composition of very high power (at least 130% of the explosive power of TNT) and brisance (rate of detonation at least 8000 meters per second) based on a finely divided explosive such as cyclotetramethylenetetranitramine (HMX), cyclotrimethylenetrinitramine (RDX), pentaerythritol tetranitrate (PETN) or mixtures thereof bonded with TMETN- or TEGDN-plasticized nitrostarch.

Another object of the invention is to provide an explosive composition which, in the form of sheets of at least one-quarter inch thickness, possesses sufficient flexibility so that it may be made to conform to the contours of uneven surfaces with a minimum of manipulation, thus aiding in the ease of destruction of the object or device to be demolished.

Another object is to provide flexible sheet explosives which have good cap sensitivity while being sufficiently insensitive to impact and friction as to present no undue hazard to field personnel carrying this material under fire.

A further object of this invention is provision of a flexible explosive cmposition which is not adversely affected by water.

A still further object is the provision of a flexible explosive composition which retains flexibility at temperatures of -40.degree. F. or lower.

Other and further objects of this invention will become apparent as the invention is further described hereinafter.

In accordance with the present invention, the foregoing objects are accomplished by novel explosive compositions, which are composed essentially entirely of explosive ingredients and consist essentially of 60-80% by weight of a finely divided high explosive selected from the group consisting of RDX, HMX and PETN and mixtures thereof and 20-40% by weight of a binder system consisting essentially of nitrostarch and a plasticizer therefor selected from the group consisting of TMETN and TEGDN and mixtures thereof, wherein the weight ratio of the nitrostarch to the plasticizer is about from 0.7/1 to 1.4/1, respectively. Small amounts up to 2-5% of conventional additives, such as stabilizers, pigments, etc. may also be present in the novel explosive compositions.

In view of its lack of ability to colloid nitrocellulose easily, as noted above, it was not obvious that TMETN could readily colloid nitrostarch without the use of a solvent, such as acetone and ethyl acetate, although solvents have been also employed in many cases in the present invention to assure of rapid preparational procedures. Further, it was not obvious that nitrostarch could be employed in place of nitrocellulose according to the present invention in view of the fact that low viscosity nitrocellulose cannot be substituted for high viscosity nitrocellulose in binder systems for flexible explosive compositions containing RDX, HMX and/or PETN, as disclosed in the aforementioned references.

When the high explosive content of the novel explosive compositions is between 60 and 74 weight percent, the aforesaid plasticized nitrostatch binder system content is between 26 and 40 weight percent, and the nitrostarch/plasticizer weight ratio is about from 0.7/1 to 1.2/1, the compositions generally can be rolled into sheets of good flexibility, and are therefore preferred. When the proportions and ratios of these ingredients are outside these preferred parameters, but are within the aforesaid broad parameters for the novel explosive compositions, the compositions generally are not sufficiently plastic to permit rolling into sheets suitable for use as a flexible sheet explosive; however, they can be compression molded and machined and still possess sufficient flexibility or resilience so that the charges can be press loaded to conform to slight contour irregularities of the item casing. When the proportion of the particulate high explosive exceeds about 80%, the composition produced is generally too stiff for compression molding to produce flexible compositions; and when the proportion thereof is less than about 60%, the composition is too soft and sticky. Further, when the weight ratio of nitrostarch to plasticizer is less than about 0.70, the strength of the binder system is generally insufficient for use in the present compositions; while when the weight ratio thereof is greater than about 1.4, the composition tends to harden on storage until at a ratio of about 1.5 or higher, it generally loses flexibility within a few days.

The high explosives employed in the compositions of the present invention possess an average particle size not exceeding about 25 microns, although both larger and smaller particles thereof may be present. Preferably 100% of the particulate explosive must pass through a No. 200 USS sieve and at least 90%, and preferably not less than 95%, should pass through a No. 325 USS sieve. Use of any appreciable amounts of coarser grades of particulate explosive tends to result in increased flexibility, loss of elasticity and a product in which the grains of particulate explosive are readily visible by reflected light.

Commercial nitrostarches, as ordinarily produced by nitration of starch, contain from about 12.6% to about 13.3% nitrogen, and are suitable for use in the present invention. For optimum results, the nitrostarch employed in the explosive compositions of the present invention possesses a nitrogen content within the range of about from 12.9% to 13.1%.

The following examples provide further specific illustrations of the explosive compositions of this invention. In the examples the percentages reported are by weight.

Compositions 1-13 shown in example I-IV were prepared in 50 gram batches by mixing together the dry particulate high explosive, nitrostarch and DPA (diphenylamine) stabilizer, stirring in the plasticizer and solvent, if used, allowing the mixture to stand covered for periods of about 4 to 24 hours, rolling on a roll mill with a 0.002 inch gap setting held at 135.degree.-140.degree. F until all odor of solvent had disappeared. Where no solvent was employed, the composition was rolled for 5 minutes, about the average time taken in rolling when solvent was used, so that there would be no appreciable processing differences between the various compositions. In each case, the thin sheets thus obtained were later consolidated on the roll mill using a gap setting of 0.230 inch and at the indicated temperature. As reported in the examples, the DPA was present as an added percentage above 100%.

These were all rolled into approximately 1/4 inch thick sheets at a roll temperature of 65.degree. C. After cooling to room temperature, the sheets possessed the following properties:

All three compositions, when comminuted, can be compression-molded to produce a charge, the surface of which yields under pressure of the fingers and returns to its original position on release of such pressure.

These were rolled in the same manner as were Compositions 1-3 with the following results:

The sheets thus obtained lost most of their tackiness on storage for a couple of days to become good flexible sheets with that of Composition No. 5 being somewhat more flexible and elastic than that of Composition No. 4.

These were all prepared and rolled in the same way as were Compositions 1-3 and gave the following results:

In both compositions the initial mixing of dry HMX, nitrostarch and DPA was done by hand, this mixture was transferred to a small sigma blade mixer, the TMETN and ethyl acetate added and the mixer run about 3 minutes with the top closed, stirring stopped, material cut down from the walls, the mixer run two minutes longer with the top off, and the mixtures rolled into thin sheets as described earlier. In each case, the thin sheets were then consolidated on the roll mill at a gap setting of 0.240 inch and a roll temperature of 75.degree. C, Reasonable smooth tough elastic sheets were obtained from both compositions. These materials were tested with the following results:

This composition, identical compositionwise with Composition No. 15, was prepared by placing the ethanol-moist HMX and nitrostarch in a five gallon sigma blade mixer and stirring these together about two minutes. The material was cut down off the sides of the mixer and the TMETN and DPA, dissolved in the ethyl acetate added and the whole mixed 30 minutes in three 10-minute periods at the end of each of which the material was cut down off the walls. After standing overnight, the batch was formed into sheets by rolling on a large mill in a manner identical with that used with Composition No. 15. This material was characterized by several tests as follows:

Composition 16 was also pressed into 2.5 inch diameter pellets as follows:

In preliminary work leading to the compositions of the present invention, it was noted that mixtures of nitrostarch and TMETN were essentially clear while corresponding mixtures of nitrocellulose and TMETN wherein colloidation was complete, even when very minor amounts of nitrocellulose were present, exhibited varying degrees of haziness by comparison. It was unexpectedly discovered that nitrostarch/TMETN bonded explosive compositions of the present invention could be compressed to products having densities greater than the calculated theoretical maximum density. In view of the foregoing, it is believed, although not as yet proved, that the nitrostarch at least in part forms a true solution in the plasticizers employed so that conventional TMD calculations of the resulting compositions result in values below those representing the true situation as is normal for solutions.

The foregoing disclosure is merely illustrative of the principles of this invention and is not to be interpreted in a limiting sense. I wish it to be understood that I do not desire to be limited to the exact details of construction shown and described, because obvious modifications will occur to a person skilled in the art.