Single-step production method for nano-sized energetic cocrystals by bead milling and products thereof

Abstract

A safe and simple method for synthesizing insensitive nano-size cocrystals of high explosive materials such as HMX and Cl-20 by suspending the explosive materials in a nonsolvent solution and bead milling the solution.

Claims

1. A process for producing nano-sized cocrystals of high explosives comprising: mixing a suspension comprising crystalline high explosive coformers in a stoichiometric ratio and a nonsolvent, wherein said coformers are insoluble in said nonsolvent; dissolving in said suspension at least one excipient; and bead milling said suspension to obtain cocrystals wherein said cocrystals have an average particle size of less than 1 m and the total weight of the solids in the suspension is between about 0.01% to about 50% by weight.

2. The process of claim 1, wherein the nonsolvent is water.

3. The process of claim 1 wherein the coformers are at least two crystalline high explosives selected from the group comprising RDX, HMX, CL-20, diacetone diperoxide, TNT, tribromotrinitrobenzene, TATB, DNAN, NTO, NQ, DNMT.

4. The process of claim 1, wherein the coformers are CL-20 and HMX.

5. The process of claim 4, wherein the CL-20 and HMX are mixed at a ratio of 2:1 molar ratio.

6. The process of claim 1, wherein the mean particle size of the cocrystals is about 50 nm to about 200 nm.

7. The process of claim 1, wherein the shape of the cocrystals is generally round.

8. The process of claim 1, wherein the total weight of the solids in suspension is about 5% to about 30% by weight.

9. The process of claim 1, wherein the excipient is a surfactant, binder, antifoaming agent, or plasticizer.

10. The process of claim 1, wherein the excipient is an alcohol or a polymer.

11. The process of claim 10, wherein the excipient is polyvinyl alcohol or isobutanol.

12. The process of claim 1, wherein the bead milling is performed for at least 60 minutes.

13. A process for producing nano-sized cocrystal of high explosives comprising: mixing a suspension comprising; water, 2:1 molar ratio of Cl-20 to HMX, wherein said HMX and CL-20 is insoluble in the water, polyvinyl alcohol, isobutanol, and; bead milling said suspension for at least 60 minutes to obtain cocrystals of HMX and CL-20 wherein said cocrystals have an average particle size of about 50 nm to about 300 nm.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Further features and advantages of the present invention may be understood from the drawings.

(2) FIG. 1 is an X-Ray diffractogram of HMX and CL-20 after 6 minutes of milling.

(3) FIG. 2 is an X-Ray diffractogram of HMX and CL-20 after 30 minutes of milling.

(4) FIG. 3 is an X-Ray diffractogram of HMX and CL-20 after 60 minutes of milling.

(5) FIG. 4 is a scanning electron micrograph of the cocrystal after 60 minutes of milling.

DETAILED DESCRIPTION

(6) The single-step production process for making nano-sized energetic cocrystals as described in the present invention starts with the preparation of a suspension, which consists of the high explosive (HE) coformers of the desired energetic cocrystals with a nonsolvent or mixture of nonsolvents. The suspension mixture may also include excipients that function as a binder, plasticizer, surfactant, and anti-foaming agent. It is contemplated that a single excipient may have multiple functions. Acceptable binders include: polyisobutylene, chlorowax, flourowax, cellulose acetate butyrate, and polyvinyl acetate. Possible surfactants include: polyoxypropylene glycol alkyl ethers, glucoside alkyl ethers, dodecyldimethylamine oxide, docusates and dimethyldioctadecylammonium chloride. Possible antifoaming agents include oils, fatty waxes, ester waxes, alkyl polyacrylates and paraffin waxes. Possible plasticizers include dioctyal adipate, BIS 2.2-Dinitropropyl acetate, BIS 2,2-Dinitropropyl formal, adipates, sebacates, maleates, and trimellitates.

(7) The relative amounts of the various ingredients in the mixture should be chosen to reflect the desired composition of the final product. The coformers should be loaded in the correct stochiometric ratio for forming the specific cocrystal. The loading of the solids, including the coformers, can vary between 0.01-50 wt. % of the suspension. The preferred loading of the solids is about 5% to about 30 wt. %. The selection of the suspension liquid or nonsolvent used in the present invention is flexible, and is based on the solubility of the ingredients to be processed as well as parameters such as viscosity. It is contemplated herein that the coformers should be highly insoluble in the suspension liquid or nonsolvent.

(8) The resultant solution is then placed into a bead mill and milled for the required period of time, which will vary based on the targeted type of cocrystals. The time, speed of milling, and bead size are among factors that will directly affect the conversion from the coformers to the energetic cocrystals and the final particle size, which can be as small as 50 nm.

(9) A number of bead mills are commercially available which allow one to create these types of nano-sized energetic cocrystals. The preferred bead mill is Netzsche Bead Mill (Microseries) with yttria-stabilized zirconia beads. Selection of a proper surfactant can achieve quick formation of cocrystals and the desired reduction of particle size. In some cases, the binder can also act as a suitable surfactant. For laboratory work, the fastest milling speed is desirable because it renders the material quickest, however, for industrial applications energy costs will need to be taken into account. Generally, milling time can control particle size fairly effectively. In some cases, an anti-foaming agent may be required. After milling for a required period of time, nano-sized energetic cocrystals can be obtained by removing them from the suspension using a variety of existing processing techniques including spray drying, freeze drying or filtration.

(10) To aid in the understanding of the subject inventive method, the following examples are provided as illustrative of thereofhowever, they are merely examples and should not be construed as limitations on the claims:

Example 1

(11) Nano-sized energetic cocrystals of CL-20/TNT with a molar ratio of 1:1 were prepared by bead milling. The process began by mixing commercially obtained 10.27 g of TNT, 19.73 g of FEM CL-20, 3 g of polyvinyl alcohol (to act as a surfactant/binder), 5 g of isobutanol (to act as antifoaming agent), and 400 g of deionized water. The slurry was milled using a Netzsche Bead Mill (Microseries) with 300 m size yttria-stabilized zirconia beads. The mill was set to a speed of 6800 rpm and the solution was milled for 60 minutes. The cocrystal structure was confirmed by powder XRD analysis. The crystal size appeared in the nano-scale regime by scanning electron microscopy (SEM).

Example 2

(12) Nano-sized energetic cocrystals of CL-20/HMX with a molar ratio of 2:1 was prepared by bead milling. The process began by mixing 7.5 g of commercially available fluid energy milled (FEM) HMX, 22.2 g of FEM CL-20, 3 g of polyvinyl alcohol (to act as a surfactant/binder), 10 g of isobutanol (to act as antifoaming agent), and 400 g of de-ionized water. Both coformers have a mean particle size of about 1 to 2 m. The solution was milled using a Netzsche Bead Mill (Microseries) with 300 m size yttria-stabilized zirconia beads. The mill was set to a speed of 6800 rpm and the solution was milled for 60 minutes.

(13) The formation of cocrystals of CL-20/HMX was confirmed using X-ray diffraction and scanning electron microscopy (SEM) analysis of specimens at various milling times. After 6 minutes of milling, the HMX and CL-20 coformers are in separate crystal phases (FIG. 1). After 30 minutes of milling, the coformers are still in separate crystal phases but are beginning to form cocrystals (FIG. 2). After 60 minutes of milling, the HMX and CL-20 coformers have completely converted to cocrystals (FIG. 3). The size of the energetic cocrystals were observed to be rounded in shape and less than 200 nm using scanning electron microscopy (FIG. 4).

(14) While embodiments have been set forth as illustrated and described above, it is recognized that numerous variations may be made with respect to relative weight percentages of various constituents in the composition. Therefore, while the invention has been disclosed in various forms only, it will be obvious to those skilled in the art that additions, deletions and modifications can be made without departing from the spirit and scope of this invention, and no undue limits should be imposed, except as to those set forth in the following claims.