Nontoxic Obscurant Compositions and Method of Using Same

Info

Publication number: 20120267016
Type: Application
Filed: Jun 13, 2011
Publication Date: Oct 25, 2012
Inventor: John L. Lombardi (Tucson, AZ)
Application Number: 13/159,324

Abstract

A composition of matter capable of producing a nontoxic smoke upon combustion comprising a smoke formulation. The composition of matter further comprises an oxidizer selected from the group consisting of potassium chlorate and sodium chlorate. The smoke formulation further comprises a fuel.

Description

Description

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

The U.S. Government has a paid-up license in this invention and the right in limited circumstances to require the patent owner to license others on reasonable terms as provided by the terms of “Replacement of Red Phosphorus in Smoke Producing Munitions” US Marine Corps Phase I SBIR Contract # M67854-07-C-6521.

TECHNICAL FIELD

The present invention relates to compositions that produce an obscurant cloud upon combustion and a method of making obscurant devices based on said composition.

BACKGROUND ART

Obscurants are compounds that are capable of blocking, scattering, and/or absorbing light and are often leveraged in military operations. Obscurants can aid with friendly operations by, for example, providing cover for troop movement, concealing the location and size of friendly forces, concealing valuable facilities from enemy forces, and marking targets. Obscurants can also obstruct and disrupt enemy operations by, for example, interfering with enemy communications and coordination.

Naturally occurring obscurants, such as fog, snow, or rain are unpredictable, and in many geographic locations, infrequent. As such, artificial obscurants are common in military operations. Artificial obscurants may be selected to block electromagnetic radiation in the visible spectrum (approximately 0.38 μm to approximately 0.78 μm), the near infrared spectrum (NIR) (approximately 0.78 μm to approximately 3 μm), the mid infrared spectrum (MIR) (approximately 3 μm to approximately 50 μm), the far infrared spectrum (FIR) (approximately 50 μm to approximately 1000 μm), or a combination thereof.

Modified versions of traditional weapon delivery systems are used to deploy obscurants in the field. The explosive payload of various munitions, including grenades, rockets, and other artillery, are removed and replaced with a payload comprising an obscurant composition. The use of a particular munition type depends on the particular use. For example, obscurant grenades may be employed in small scale tactical combat operations. Rockets, mortars, or large scale artillery carrying obscurant composition payloads may be used to conceal or protect large areas, such as air fields or large scale troop movements. Upon ignition or detonation, the obscurant composition burns to produce a cloud of smoke that blocks a given spectrum of light.

Obscurant compositions currently used by the military include white phosphorous (WP), red phosphorous (RP), hexachloroethane (HC), and terephthalic acid (TA). These obscurants exhibit a number of undesirable properties, including high toxicity, poor shelf life, and high burn temperatures.

When white phosphorous burns in air, it produces a hydroscopic compound, diphosphorus pentoxide. As the diphosphorus pentoxide absorbs moisture from the atmosphere, small airborne droplets of phosphoric acid are formed. White phosphorous, however, is pyrophoric at relatively low temperatures. It will ignite in air at about 30° C., making it hazardous to handle, store, and transport.

Red phosphorous (RP) has largely replaced white phosphorous for obscurant purposes. Over time red phosphorous slowly degrades to highly toxic phosphine gas, a pyrophoric gas that can self ignite when mixed with air.

All phosphorous-based obscurants (both red and white) have a number of other drawbacks. First, because they burn at high temperatures (>500° C.) and have a high flame front, they pose the risk of burning nearby personnel or noncombatants, damaging nearby buildings or equipment, and igniting secondary fires. Second, the resulting obscurant cloud is composed of acidic water vapor, which is a respiratory irritant. Inhalation of this vapor can pose a health threat to nearby personnel and civilians.

Hexachloroethane-based obscurant compositions (HC) are produced by combining hexachloroethane, aluminum powder, and zinc oxide. Upon combustion, the mixture produces zinc chloride, which in turn absorbs moisture from the air to form an obscurant cloud. The zinc chloride in the resulting cloud is lethal if inhaled, capable of causing gross pathological pulmonary injuries and death due to pulmonary edema. Hexachloroethane-based obscurants, like the phosphorous-based variations, also have a high combustion temperature.

Terephthalic acid-based obscurants (TA), unlike phosphorous-based and hexachloroethane-based obscurants, produce a nontoxic smoke. However, terephthalic acid-based obscurants have limited obscuring properties as compared to WP, RP, or HC.

The rate or production of obscuring smoke produced by conventional obscurants is largely dependent on the packing density of the components. Obscurant devices with higher packing densities produce obscurant smoke at a higher rate. Packing densities, however, are difficult to control in practice and generally result in inconsistent results. Moreover, obscurant devices with varying rates of smoke production (i.e., a initial high production rate followed by a slower sustaining rate) are likewise difficult to produce with any reliability by varying packing densities.

Accordingly, it would be an advance in the state of the art to provide an obscurant composition for use in traditional applications that (i) burns at a lower temperature than existing compositions, (ii) produces a non-toxic obscurant cloud, (iii) equals or outperforms existing compositions in obscuring performance, (iv) remains stable during long term storage, (v) is capable of producing variable smoke production rates without relying on packing density, (vi) is produced from nontoxic components, (vii) is environmentally friendly, and (viii) is cost competitive with existing obscurants.

SUMMARY OF THE INVENTION

An embodiment of the present invention provides a composition of matter capable of producing a nontoxic smoke upon combustion. The composition of matter comprises a smoke formulation. In certain embodiments, Applicant's smoke formulation comprises melamine and methyl gallate. The composition of matter further comprises an oxidizer selected from the group consisting of potassium chlorate and sodium chlorate. The smoke formulation further comprises a fuel. The fuel comprises sucrose.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be more fully understood by referring to the following Detailed Description of Specific Embodiments in conjunction with the Drawings, of which:

FIG. 1 is a graph comparing % transmittance over time for one embodiment of Applicant's obscurant formulation against conventional obscurants;

FIG. 2 is a graph comparing the minimum % transmittance for one embodiment of Applicant's obscurant formulation against conventional obscurants;

FIG. 3 is a graph comparing recovery time to 10% transmittance for one embodiment of Applicant's obscurant formulation against conventional obscurants;

FIG. 4 is a graph comparing minimum % transmittance for one embodiment of Applicant's obscurant formulation against various obscurant formulations, including those based on the individual components of Applicant's smoke formulation;

FIG. 5 is a graph of mass extinction coefficient across the visible and near infrared spectrum for various embodiments of Applicant's obscurant formulation compared to terephthalic acid, a conventional obscurant composition;

FIG. 6 is a graph of mass extinction coefficient across the visible and near infrared spectrum for multiple tests of red phosphorous, a conventional obscurant composition;

FIG. 7 is a graph showing thermal aging results of Applicant's obscurant formulation;

FIGS. 8(a) and 8(b) are ternary plots showing various burn rates of Applicant's obscurant formulation achieved by varying the relative amounts of oxidizer, fuel, and coolant components;

FIG. 9 shows the molecular structure of example melamine derivatives used in various embodiments of Applicant's obscurant formulation;

FIG. 10 shows a polymerization reaction between melamine and a melamine derivative that occurs in one embodiment of Applicant's obscurant formulation;

FIG. 11 shows amine-containing melamine derivatives for use in various embodiments of Applicant's smoke formulation;

FIG. 12 is a flowchart showing an exemplary method for producing a dual-burn rate obscurant device capable of producing an initial heavy smoke screen followed by a lower sustaining smoke screen;

FIG. 13 is a graph comparing the minimum % transmittance for various embodiments of Applicant's obscurant formulation, including embodiments containing 1% and 5% of various dicarboxylic acids;

FIG. 14 is a graph comparing recovery time to 10% transmittance for various embodiments of Applicant's obscurant formulation, including embodiments containing 1% and 5% of various dicarboxylic acids;

FIG. 15 is a graph comparing the minimum % transmittance for various embodiments of Applicant's obscurant formulation, including embodiments containing dimethylsulfone;

FIG. 16 is a graph comparing recovery time to 10% transmittance for various embodiments of Applicant's obscurant formulation, including embodiments containing dimethylsulfone;

FIG. 17 is a graph comparing the minimum % transmittance for various embodiments of Applicant's obscurant formulation, including embodiments containing Bisphenol S;

FIG. 18 is a graph comparing recovery time to 10% transmittance for various embodiments of Applicant's obscurant formulation, including embodiments containing Bisphenol S;

FIG. 19 is a graph comparing the minimum % transmittance for various embodiments of Applicant's obscurant formulation, including embodiments containing diphenylsulfone;

FIG. 20 is a graph comparing recovery time to 10% transmittance for various embodiments of Applicant's obscurant formulation, including embodiments containing diphenylsulfone;

FIG. 21 is a graph comparing the minimum % transmittance for various embodiments of Applicant's obscurant formulation, including embodiments containing Bisphenol A;

FIG. 22 is a graph comparing recovery time to 10% transmittance for various embodiments of Applicant's obscurant formulation, including embodiments containing Bisphenol A;

FIG. 23 is a graph comparing the minimum % transmittance for various embodiments of Applicant's obscurant formulation, including embodiments containing 5-Methoxy MeGallate or THEIC; and

FIG. 24 is a graph comparing recovery time to 10% transmittance for various embodiments of Applicant's obscurant formulation, including embodiments containing 5-Methoxy MeGallate or THEIC.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

This invention is described in preferred embodiments in the following description with reference to the Figures, in which like numbers represent the same or similar elements. Reference throughout this specification to “one embodiment,” “an embodiment,” or similar language means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrases “in one embodiment,” “in an embodiment,” and similar language throughout this specification may, but do not necessarily, all refer to the same embodiment.

The described features, structures, or characteristics of the invention may be combined in any suitable manner in one or more embodiments. In the following description, numerous specific details are recited to provide a thorough understanding of embodiments of the invention. One skilled in the relevant art will recognize, however, that the invention may be practiced without one or more of the specific details, or with other methods, components, materials, and so forth. In other instances, well-known structures, materials, or operations are not shown or described in detail to avoid obscuring aspects of the invention.

Applicant has developed an obscurant formulation based on nontoxic components that is capable of producing a nontoxic cloud with excellent obscuring properties. In one embodiment, Applicant's formulation comprises a powdered melamine/methyl gallate obscurant additive combined with a sucrose/chlorate fuel-oxidizer system. Upon ignition, the heat produced by the combustion of the fuel causes the melamine/methyl gallate to sublime, producing an obscurant smoke. The melamine/methyl gallate mixture sublimes at a relatively low temperature, therefore the burn temperature of Applicant's formulation is lower than conventional obscurants and produces a minimal flame front.

The following Example is presented to further illustrate to persons skilled in the art how to make and use the invention. This Example is not intended as a limitation, however, upon the scope of Applicant's invention.

Example 1

In one embodiment, a 70/30 weight percentage ratio melamine/methyl gallate formulation is prepared using the components in Table 1.

TABLE 1 70%/30% Melamine/Methyl Gallate Formulation Component Type Component Wt. % Quantity (g) Combustion Sucrose 39.20 3.92 Component Sodium Chlorate 35.40 3.54 Smoke Melamine 15.70 1.57 Formulation Methyl Gallate 6.70 0.67 Binder Ethyl Cellulose 3.00 0.30 Intermediate Isopropanol — 10.8 Solvent Toluene — 3.54

Preparing the Smoke Formulation

The sucrose, sodium chlorate, melamine, and methyl gallate are pre-ground to a fine powder and passed through a #70 (212 μm) mesh sieve. The powdered sucrose, sodium chlorate, melamine (1), and methyl gallate (2) are added to a mortar and pestle and gently mixed for approximately 5-10 minutes. In one embodiment, potassium chlorate is used as the oxidizer in the combustion component. In one embodiment, a mixture of potassium chlorate and sodium chlorate is used as the oxidizer in the combustion component.

The sucrose is confectionary sugar sold in commerce by Sysco Food Services. Sodium chlorate is sold in commerce by Gallade Chemical. Melamine is sold in commerce by US Chemical. Methyl gallate is sold in commerce by Dudley Chemical.

The formulation in Table 1 contains a weight percentage ratio of combustion component to smoke formulation of 77/23. In various embodiments, the weight percentage ratio of combustion component to smoke formulation ranges from at or between 80/20 to 60/40. A shift in the ratio toward increased combustion component will result in a faster burn rate, increased burn temperature, and an increased flame front. In one embodiment, the weight percentage ratio of combustion component to smoke formulation is about 80/20. In one embodiment, the weight percentage ratio of combustion component to smoke formulation is about 75/25. In one embodiment, the weight percentage ratio of combustion component to smoke formulation is about 70/30. In one embodiment, the weight percentage ratio of combustion component to smoke formulation is about 65/35. In one embodiment, the weight percentage ratio of combustion component to smoke formulation is about 60/40.

The formulation in Table 1 contains a weight percentage ratio of melamine to methyl gallate or 70/30. In various embodiments, the weight percentage ratio of melamine to methyl gallate ranges from at or between 50/50 to 80/20. A shift in the ratio toward increased melamine increases the rate of production of smoke during combustion. As such, layers of varying ratios could be arranged to create an obscurant device capable of producing varying amounts of smoke over time. In one embodiment, the weight percentage ratio of melamine to methyl gallate is about 50/50. In one embodiment, the weight percentage ratio of melamine to methyl gallate is about 55/45. In one embodiment, the weight percentage ratio of melamine to methyl gallate is about 60/40. In one embodiment, the weight percentage ratio of melamine to methyl gallate is about 65/35. In one embodiment, the weight percentage ratio of melamine to methyl gallate is about 75/25. In one embodiment, the weight percentage ratio of melamine to methyl gallate is about 80/20.

Adding the Binder:

In one embodiment, Applicant's obscurant formulation includes a binder. The addition of a binder allows for the formation of highly densely packed pellets for use in obscurant devices. In another embodiment, Applicant's obscurant formulation does not include a binder.

The binder is prepared by combining isopropanol and toluene in a flask. The resultant solution is heated and maintained at 60° C. under stirring. The ethyl cellulose is added to the solution and stirred until the solution returns to 60° C. The powdered smoke formulation/combustion component is slowly added to the solution. The resulting mixture is mixed for approximately 10 to 15 minutes, removed from the heat, poured into a dish, and allowed to air dry. The dry mixture is added to a mortar and pestle and ground back into a fine powder.

Pressing the Pellets:

A small amount, 0.5 grams, of the powdered smoke formulation/combustion component/binder mixture is added to a 1 inch diameter pellet dye and compressed using a Carver Press at a pressure of 8,000 pounds for about 10 seconds. The compressed pellet is removed from the pellet press. In different embodiments, the pressure to form the pellets is between 1,000 pounds to 35,000 pounds. In different embodiments, the pellets are made from between 0.5 grams to 20 grams of the mixture. In different embodiments, the pellets are made from greater than 20 grams of the mixture.

The obscurant smoke produced by the pellets upon combustion is nontoxic. Also, all components in Table 1 are biodegradable as is the resulting obscurant smoke. Finally, the pellets burned at a temperature below 350° C., significantly less than red phosphorous, which burns at temperatures greater than 500° C.

Referring to FIG. 1, a transmittance graph 100 comparing the light obscuring performance of various obscurant formulations is depicted. The graph was generated from data collected by combusting various obscurant formulations in a 243 cubic inch box with a 7.5 inch width. Light from a fluorescent light source was directed across the width of the box to a light detector. The percentage transmittance is represented by the y-axis 102. A 100% transmittance value indicates that the light from the source to the detector is not being hindered. A 0% transmittance value indicates that no light from the source is reaching the detector. Time is represented by the x-axis 104.

Lines 110 and 106 represent two different terephthalic acid obscurant formulations. Line 108 represents an embodiment of Applicant's obscurant formulation. Applicant's formulation used in this test comprises a 70/30 weight percentage ratio of combustion component to smoke formulation. The smoke formulation comprises a 70/30 ratio of melamine to methyl gallate. The 100% transmission value for each line 106, 108, and 110 establishes a baseline before each test. As indicated by line 108, this embodiment of Applicant's melamine/methyl gallate obscurant formulation exhibits superior initial obscuring performance and equivalent obscuring performance over time.

Referring to FIG. 2, a bar graph 200 of the minimum percent transmittance (min % T) value for various obscurant formulations is depicted. The min % T, represented by the y-axis 202, is the lowest transmittance value recorded in the tests described with respect to FIG. 1. Bars 206 and 208 represent the min % T for two different terephthalic acid obscurant formulations. Bar 204 represents the min % T for Application's melamine/methyl gallate obscurant formulation. As indicated by bar graph 200, Applicant's formulation exhibits a lower min % T than either terephthalic acid formulations.

Referring to FIG. 3, a bar graph 300 of the values of recovery time to 10 percent transmittance (10% T) for various obscurant formulations is depicted. The 10% T, represented by the y-axis 302, is the time elapsed to reach 10% transmittance in the tests described with respect to FIG. 1. Bars 306 and 308 represent the recovery time to 10% T for two different terephthalic acid obscurant formulations. Bar 304 represents the recovery time to 10% T for Application's melamine/methyl gallate obscurant formulation. Graph 300 shows that the obscurant smoke produced by Applicant's formulation requires more recovery time to reach 10% T than either terephthalic acid formulations.

Referring to FIG. 4, a bar graph of the minimum percentage transmittance (min % T) value for various obscurant formulations, including the individual components of Applicant's formulation, is depicted. The min % T, represented by the y-axis 402, is the lowest transmittance value recorded for each obscurant test. Bar 404 represents the min % T for a terephthalic acid obscurant formulation.

Bar 406 represents the min % T for Application's melamine/methyl gallate obscurant formulation. The embodiment of Applicant's obscurant formulation used in this test comprises a 70/30 wt % ratio of melamine/methyl gallate, a potassium chlorate (KClO₃) oxidizer component, and a 70/30 wt % ratio of smoke formulation/combustion component. The min % T for Applicant's obscurant formulation is substantially lower than that of the terephthalic acid obscurant formulation in bar 404, thereby showing that Applicant's formulation produces a more effective obscurant cloud.

Bar 408 represents the min % T for a melamine obscurant formulation with the smoke formulation consisting only of melamine. Bar 410 represents the min % T for a methyl gallate obscurant formulation with the smoke formulation consisting of methyl gallate only. When used alone, the individual components of one embodiment of Applicant's melamine/methyl gallate obscurant formulation, as shown in bars 408 and 410 respectively, have a substantially higher min % T value than the combined melamine/methyl gallate formulation in bar 406.

Bar 412 represents the min % T for a gallic acid (3) obscurant formulation, with the smoke formulation consisting of a mixture of melamine and gallic acid. Gallic acid is formed by replacing the methyl group on methyl gallate with a hydroxyl group.

The min % T of the melamine/methyl gallate obscurant formulation represented by bar 406 was substantially lower than that of the gallic acid formulation represented by bar 412.

Bar 414 represents the min % T for a melamine/trimethyl methyl gallate (4) obscurant formulation.

Trimethyl methyl gallate (methyl-3,4,5-trimethoxybenzoate) can be synthesized by dissolving methyl gallate (5.00 g, 27 mmol, 1 equiv.) in 150 mL acetone with stirring. Dimethyl sulfate (9.0 mL, 95 mmol, 3.5 equiv.) and potassium carbonate (13.70 g, 109 mmol, 4 equiv.) are added to the reaction, and refluxed for 6 hours. The reaction is filtered, and the filtrate dried using rotary evaporation. The solid product is mixed with 100 mL ice water, and then extracted 3 times with 100 mL ethyl acetate. The pooled ethyl acetate extract is washed once with 100 mL saturated NaHCO₃and once with 100 mL 2 M NH₄OH. The ethyl acetate extract is dried over anhydrous MgSO₄, dried using rotary evaporation, and stored under vacuum overnight.

The min % T of the melamine/methyl gallate obscurant formulation represented by bar 406 was substantially lower than that of the gallic acid formulation represented by bar 414.

Referring to FIG. 5, an extinction coefficient graph for obscuring smoke produced by pyrophoric grenades loaded with various obscurant compositions is depicted. The tests were conducted by Edgewood Chemical Biological Center in Edgewood, Md. The x-axis 504 represents wavelength in μm and the y-axis 502 represents the extinction coefficient in m²/grams.

Line 514 is data from a standard M83 terephthalic acid smoke grenade. The terephthalic acid formulation has a relatively flat extinction coefficient profile across the visible spectrum (˜0.38 to ˜0.78 μm) and into the near infrared spectrum (˜>0.78 μm).

Line 516 is data from one embodiment of Applicant's obscurant formulation prepared according to the components in Table 2.

TABLE 2 Component Type Component Wt. % Combustion Sucrose 12 Component Potassium Chlorate (KClO₃) 42 Coolant Magnesium Carbonate (MgCO₃) 6 Smoke Melamine 28 Formulation Methyl Gallate 12

The formulation was loaded into a pyrophoric grenade configured to burn from one end (end-burn configuration).

Line 512 is data from one embodiment of Applicant's obscurant formulation prepared according to the components in Table 2 loaded into a pyrophoric grenade configured to burn from the center (core-burn configuration).

Line 506 is data from one embodiment of Applicant's obscurant formulation prepared according to the components in Table 3.

TABLE 3 Component Type Component Wt. % Combustion Sucrose 12 Component Potassium Chlorate (KClO₃) 30 Coolant Magnesium Carbonate (MgCO₃) 18 Smoke Melamine 28 Formulation Methyl Gallate 12

The formulation was loaded into a pyrophoric grenade configured to burn from one end (end-burn configuration).

Line 510 is data from one embodiment of Applicant's obscurant formulation prepared according to the components in Table 3 loaded into a pyrophoric grenade configured to burn from the center (core-burn configuration).

Line 508 is data from one embodiment of Applicant's obscurant formulation prepared according to the components in Table 4.

TABLE 4 Component Type Component Wt. % Combustion Sucrose 10 Component Potassium Chlorate (KClO₃) 25 Coolant Magnesium Carbonate (MgCO₃) 15 Smoke Melamine 35 Formulation Methyl Gallate 15

The formulation was loaded into a pyrophoric grenade configured to burn from one end (end-burn configuration).

Line 518 is data from one embodiment of Applicant's obscurant formulation prepared according to the components in Table 4 loaded into a pyrophoric grenade configured to burn from the center (core-burn configuration).

Referring to FIG. 6, an extinction coefficient graph for obscuring smoke produced by pyrophoric grenades loaded with red phosphorous is depicted. Comparing the red phosphorous lines in FIG. 5 with the lines representing Applicant's formulations in FIG. 4 shows that Applicant's formulations have superior extinction coefficient values across the tested spectrum in most instances.

Considering the data from FIGS. 5 and 6, the performance of Applicant's obscurant formulation can be derived. The comparison of Applicant's formulation against the terephthalic acid (TA) and red phosphorous (RP) formulations are set forth below at 0.55 μm and 0.50 μm, two wavelengths in the visible spectrum that are of particular interest. The photopic cone cells of the human eye have a maximum sensitivity at 0.55 μm. The scotopic rod cells of the human eye have a maximum sensitivity at 0.50 μm.

TABLE 5 Extinction Coefficient at 0.55 μm extracted from FIGS. 5&6 0.55 μm (550 nm) Smoke Extinction Coefficient Formulation (m²/g) Terephthalic Acid 4.85 Red Phosphorus 4.00 Applicant's Formulation 5.11 (Line 508 in FIG. 4)

The extinction coefficient, also known as the mass attenuation coefficient, is based on the Beer-Lambert Law. The extinction coefficient is calculated by:

I=I₀e^−(μ/p)pl

Where: I₀is the original intensity of the beam, I is the intensity of the beam at distance l into the substance, e is Euler's number, about 2.718, μ is the absorption coefficient, p is the density, (μ/p) is the mass attenuation coefficient and pl is the area density, also known as mass thickness.

Using this formula and the data from Table 5, Applicant's melamine/methyl gallate obscurant formulation at 550 μm exhibits a 1.8 fold higher extinction coefficient as compared to the terephthalic acid smoke and a 12.9 fold higher extinction coefficient as compared to the red phosphorous smoke.

TABLE 6 Extinction Coefficient at 0.50 μm extracted from FIGS. 5&6 0.50 μm (500 nm) Smoke Extinction Coefficient Formulation (m²/g) Terephthalic Acid 4.71 Red Phosphorus 4.35 Applicant's Formulation 5.25 (Line 508 in FIG. 4)

Using the extinction coefficient formula above and the data from Table 6, Applicant's melamine/methyl gallate obscurant formulation at 0.50 μm exhibits a 3.5 fold higher extinction coefficient as compared to the terephthalic acid smoke and a 7.9 fold higher extinction coefficient as compared to the red phosphorous smoke.

Referring to FIG. 7, a plot 700 of the thermal aging effect on 0.5 g pellets of Applicant's melamine/methyl gallate obscurant formulation is depicted. The pellets were stored at 70° C. for up to 10 weeks to simulate long-term thermal aging. The x-axis 704 represents the equivalent thermal aging time. The y-axis 702 represents the minimum % transmittance for a tested sample. As is shown in the plot 700, no statistical significant changes in obscurant power were observed due to thermal aging.

Referring to FIGS. 8(a) and 8(b), a ternary plot showing the effect on burn rate of various embodiments of Applicant's obscurant formulation with varying oxidizer, fuel, and coolant components is depicted. In each of FIGS. 8(a) and 8(b), axis 802 represents the amount of coolant in each formulation, axis 804 represents the amount of oxidizer in each formulation, and axis 810 represents the amount of fuel in each formulation. The amount of smoke formulation for each test in FIG. 8(a) was held constant while the relative amounts of oxidizer, fuel, and coolant were varied. Likewise, the amount of smoke formulation for each test in FIG. 8(b) was held constant while the relative amounts of oxidizer, fuel, and coolant were varied, but the ratio of smoke formulation/combustion component was higher in the FIG. 8(b) tests as compared to the FIG. 8(a) tests.

The burn rate values 806 in seconds/inch are indicated on the plots. Eight burn rate values are shown for FIG. 8(a) and six burn rate values are shown for FIG. 8(b). A burn rate of 0 sec/in indicates that the formulation did not ignite. As shown in FIGS. 8(a) and 8(b), a desired burn rate can be selected by varying the relative amounts of oxidizer, fuel, and coolant. The tests in FIG. 8(a) show burn rates ranging from 0-136 sec/in. The tests in FIG. 8(b), where the formulations contain a higher amount of smoke formulation, show burn rates ranging from 56-110 sec/in.

High temperatures will cause the components of the smoke formulation to burn, resulting in undesirable darkening of the produced smoke and a decrease in smoke production. For each of Applicant's tested formulations represented in FIGS. 8(a) and 8(b) that ignited, only white smoke was produced, indicating that burn rates can be successfully varied without resulting in undesirable discoloration or decreased production of the obscuring smoke.

In various embodiments, Applicant's two-part smoke formulation comprises melamine or a melamine derivative. Referring to FIG. 9, various melamine derivatives for use in various embodiments of Applicant's smoke formulation are depicted. N-imidization of melamine 902 yields derivative 904. N-alkylation of melamine 902 yields derivative 906. N-acetylation of melamine 902 yields derivative 908.

Referring to FIG. 10, a polymerization reaction between N-imidization 904 and melamine 1002 is depicted. The product 1004 shows the formation of a bond that would result in polymerization if the two reactants are available in large quantities. Smoke formulations relying on polymerization reactions form high molecular weight smoke particulates.

Referring to FIG. 11, various amine-containing melamine derivatives for use in various embodiments of Applicant's smoke formulation are depicted. Cyanuric chloride 1102 is reacted with various amine-containing compounds to introduce functional group substitutes (e.g. aromatic, non-aromatic, and heterocyclic) (see 1104), alcohols (see 1106), carboxylic acids (see 1108), esters, and ethers (see 1110) onto melamine's heterocyclic triazine ring.

In various embodiments, Applicant's smoke formulation comprises melamine derivatives provided in Table 7.

TABLE 7

In various embodiments, Applicant's smoke formulation comprises melamine derivatives formed by a reaction between melamine and an acid anhydride. Acid anhydrides readily acylate melamine. The acid anhydrides include, but are not limited to acetic achydride, trifluoroacetic anhydride, phthalic anhydride, chlorophthalic anhydride, glutaric anhydride, maleic anhydride, fumaric anhydride, chloromaleic anhydride, succinic anhydride, alkyl succinic anhydride, aryl succinic anhydride, benzoic anhydride, mellitic anhydride, pyromellitic dianhydride, oxydiphtalic dianhydride, benzophenone tetracarboxylic dianhydride, hexafluoroisopropylidene anhydride, benzoquinone tetracarboxylic dianhydride, and ethylene tetracarboxylic dianhydride.

In various embodiments, Applicant's smoke formulation comprises amino substituted derivatives of melamine. In various embodiments, Applicant's smoke formulation comprises amino substituted C—N derivatives of melamine, including but not limited to cyanamide, dicyandiamine, ammeline, Ammelide, melem, melon, cyameluric acid, cyanuric acid, and heptazine. In certain embodiments, Applicant's smoke formulation comprises one or more of the melamine derivatives described in B. Bann & S A Miller “Melamine & Derivatives of Melamine” Chemical Reviews vol 58 pp 131-72 (1958), which is incorporated by reference herein.

In various embodiments, Applicant's smoke formulation comprises urea and substituted ureas, including but not limited to ethylene urea, methyl urea, phenyl urea, diphenyl urea, polysubstituted alkyl, and aryl substituted ureas.

In various embodiments, Applicant's smoke formulation comprises a substituted gallate. In various embodiments, the substituted gallates include, but are not limited to, those which have been O-alkylated (aromatic ring hydroxyls have been converted to corresponding ether linkages) using haloacetic acid and haloacetic acid esters (e.g. chloroacetic, methyl chloroacetate, ethyl chloroacetate, bromoacetic, and methyl bromoacetate). In various embodiments, the substituted gallates include those which have been O-alkylated using dimethyl sulfate, diethyl sulfate, benzyl chloride, or benzyl bromide.

In various embodiments, Applicant's smoke formulation comprises gallic acid derivatives including but not limited to gallic acid and its salts, methyl gallate, ethyl gallate, propyl gallate, octyl gallate, dodecyl gallate, gallocatechin gallate, epicatechin gallate, gallamide, alkyl and aryl substituted gallamide derivatives, and mono, di and tri-substituted hydroxybenzoic acid derivatives.

In one embodiment, Applicant's smoke formulation comprises a mixture of melamine, methyl gallate, and terephthalic acid.

In one embodiment, Applicant's smoke formulation comprises an imide, including but not limited to succinimide, maleimide, adipimide, phthalimide, diphenyl imide, naphthalimide, glutarimide and a gallate ester. In one embodiment, Applicant's smoke formulation comprises an imide and melamine. In one embodiment, Applicant's smoke formulation comprises an imide, melamine, and a gallate ester.

In various embodiments, Applicant's smoke formulation comprises a bisphenol derivative. In different embodiments, the bisphenol derivative is, without limitation, Bisphenol A (BPA), Bisphenol F, Bisphenol S (BPS), Bisphenol E, Bisphenol B, Bisphenol P, Bisphenol PH, Bisphenol BP, Bisphenol AF, Bisphenol AP, Bisphenol C, Bisphenol E, Bisphenol G, Bisphenol M, Bisphenol TMC, Bisphenol Z, hydroxybenzophenone, dihydroxybenzophenone, hydroxyacetophenone or a combination thereof. In some embodiments, Applicant's smoke formulation comprises a bisphenol derivative and melamine. In some embodiments, Applicant's smoke formulation comprises a bisphenol derivative and methyl gallate. In some embodiments, Applicant's smoke formulation comprises a bisphenol derivative, melamine, and methyl gallate.

In various embodiments, Applicant's smoke formulation comprises polyphenolic derivatives including but not limited to ellagic acid, triphenol, trishydroxyphenyl ethane, phL dihydroxyphenyl acetic acid and its salts, dihydroxyphenyl propionic acid and its salts, phloroglucinol, gallocatechin or epigallocatechin, or a combination thereof. In some embodiments, Applicant's smoke formulation comprises a polyphenolic derivative and melamine. In some embodiments, Applicant's smoke formulation comprises a polyphenolic derivative and methyl gallate. In some embodiments, Applicant's smoke formulation comprises a polyphenolic derivative, melamine, and methyl gallate.

Provided below are examples of compounds included in various embodiments of Applicant's smoke formulation:

In various embodiments, Applicant's smoke formulation comprises one of more of the bisphenol derivatives and dicarboxylic acids presented in Table 8.

TABLE 8

The following Examples are presented to further illustrate to persons skilled in the art how to make and use the invention. The Examples are not intended as a limitation, however, upon the scope of Applicant's invention.

Example 2

In one embodiment, an obscurant formulation having a smoke component consisting of melamine, methyl gallate, and 1 weight % sebacic acid is prepared according to Table 9.

TABLE 9 1% Sebacic Acid Formulation Component Type Component Wt. % Quantity (g) Combustion Sucrose 38.1 3.81 Component Potassium Chlorate 38.1 3.81 Smoke Melamine 15.2 1.52 Formulation Methyl Gallate 6.5 0.65 Sebacic Acid 1.00 0.10 Binder Ethyl Cellulose 1.00 0.10

Example 3

In one embodiment, an obscurant formulation having a smoke component consisting of melamine, methyl gallate, and 5 weight % sebacic acid is prepared according to Table 10.

TABLE 10 5% Sebacic Acid Formulation Component Type Component Wt. % Quantity (g) Combustion Sucrose 38.1 3.81 Component Potassium Chlorate 38.1 3.81 Smoke Melamine 12.4 1.24 Formulation Methyl Gallate 5.3 0.53 Sebacic Acid 5.00 0.50 Binder Ethyl Cellulose 1.00 0.10

Example 4

In one embodiment, an obscurant formulation having a smoke component consisting of melamine, methyl gallate, and 1 weight % adipic acid is prepared according to Table 11.

TABLE 11 1% Adipic Acid Formulation Component Type Component Wt. % Quantity (g) Combustion Sucrose 37.7 3.77 Component Potassium Chlorate 37.7 3.77 Smoke Melamine 15.8 1.58 Formulation Methyl Gallate 6.8 0.68 Adipic Acid 1.00 0.10 Binder Ethyl Cellulose 1.00 0.10

Example 5

In one embodiment, an obscurant formulation having a smoke component consisting of melamine, methyl gallate, and 5 weight % adipic acid is prepared according to Table 12.

TABLE 12 5% Adipic Acid Formulation Component Type Component Wt. % Quantity (g) Combustion Sucrose 38.1 3.81 Component Potassium Chlorate 38.1 3.81 Smoke Melamine 12.4 1.24 Formulation Methyl Gallate 5.3 0.53 Adipic Acid 5.00 0.50 Binder Ethyl Cellulose 1.00 0.10

Example 6

In one embodiment, an obscurant formulation having a smoke component consisting of melamine, methyl gallate, and 1 weight % azelaic acid is prepared according to Table 13.

TABLE 13 1% Azelaic Acid Formulation Component Type Component Wt. % Quantity (g) Combustion Sucrose 38.1 3.81 Component Potassium Chlorate 38.1 3.81 Smoke Melamine 15.2 1.52 Formulation Methyl Gallate 6.5 0.65 Azelaic Acid 1.00 0.10 Binder Ethyl Cellulose 1.00 0.10

Example 7

In one embodiment, an obscurant formulation having a smoke component consisting of melamine, methyl gallate, and 5 weight % azelaic acid is prepared according to Table 14.

TABLE 14 5% Azelaic Acid Formulation Component Type Component Wt. % Quantity (g) Combustion Sucrose 38.1 3.81 Component Potassium Chlorate 38.1 3.81 Smoke Melamine 12.4 1.24 Formulation Methyl Gallate 5.3 0.53 Azelaic Acid 5.00 0.50 Binder Ethyl Cellulose 1.00 0.10

Example 8

In one embodiment, an obscurant formulation having a smoke component consisting of melamine, methyl gallate, and 1 weight % dimethylsulfone is prepared according to Table 15.

TABLE 15 1% Dimethylsulfone Formulation Component Type Component Wt. % Quantity (g) Combustion Sucrose 38.1 3.81 Component Potassium Chlorate 38.1 3.81 Smoke Melamine 15.2 1.52 Formulation Methyl Gallate 6.5 0.65 Dimethylsulfone 1.00 0.10 Binder Ethyl Cellulose 1.00 0.10

Example 9

In one embodiment, an obscurant formulation having a smoke component consisting of melamine, methyl gallate, and 5 weight % azelaic acid is prepared according to Table 16.

TABLE 16 5% Dimethylsulfone Formulation Component Type Component Wt. % Quantity (g) Combustion Sucrose 38.1 3.81 Component Potassium Chlorate 38.1 3.81 Smoke Melamine 12.4 1.24 Formulation Methyl Gallate 5.3 0.53 Dimethylsulfone 5.00 0.50 Binder Ethyl Cellulose 1.00 0.10

Example 10

In one embodiment, an obscurant formulation having a smoke component consisting of melamine, methyl gallate, and 1 weight % Bisphenol S is prepared according to Table 17.

TABLE 17 1% Bisphenol S Formulation Component Type Component Wt. % Quantity (g) Combustion Sucrose 38.1 3.81 Component Potassium Chlorate 38.1 3.81 Smoke Melamine 15.2 1.52 Formulation Methyl Gallate 6.5 0.65 Bisphenol S 1.00 0.10 Binder Ethyl Cellulose 1.00 0.10

Example 11

In one embodiment, an obscurant formulation having a smoke component consisting of melamine, methyl gallate, and 5 weight % Bisphenol S is prepared according to Table 18.

TABLE 18 5% Bisphenol S Formulation Component Type Component Wt. % Quantity (g) Combustion Sucrose 38.1 3.81 Component Potassium Chlorate 38.1 3.81 Smoke Melamine 12.4 1.24 Formulation Methyl Gallate 5.3 0.53 Bisphenol S 5.00 0.50 Binder Ethyl Cellulose 1.00 0.10

Example 12

In one embodiment, an obscurant formulation having a smoke component consisting of melamine, methyl gallate, and 1 weight % Bisphenol A is prepared according to Table 19.

TABLE 19 1% Bisphenol A Formulation Component Type Component Wt. % Quantity (g) Combustion Sucrose 38.1 3.81 Component Potassium Chlorate 38.1 3.81 Smoke Melamine 15.2 1.52 Formulation Methyl Gallate 6.5 0.65 Bisphenol A 1.00 0.10 Binder Ethyl Cellulose 1.00 0.10

Example 13

In one embodiment, an obscurant formulation having a smoke component consisting of melamine, methyl gallate, and 5 weight % Bisphenol A is prepared according to Table 20.

TABLE 20 5% Bisphenol A Formulation Component Type Component Wt. % Quantity (g) Combustion Sucrose 38.1 3.81 Component Potassium Chlorate 38.1 3.81 Smoke Melamine 12.4 1.24 Formulation Methyl Gallate 5.3 0.53 Bisphenol A 5.00 0.50 Binder Ethyl Cellulose 1.00 0.10

Example 14

In one embodiment, an obscurant formulation having a smoke component consisting of melamine and THEIC is prepared according to Table 21.

TABLE 21 THEIC Formulation Component Type Component Wt. % Quantity (g) Combustion Sucrose 38.1 3.81 Component Potassium Chlorate 38.1 3.81 Smoke Melamine 15.9 1.59 Formulation THEIC 6.80 0.68 Binder Ethyl Cellulose 1.00 0.10

Example 15

In one embodiment, an obscurant formulation having a smoke component consisting of melamine and 5-methoxy methyl gallate is prepared according to Table 22.

TABLE 22 5-Methoxy Methyl Gallate Formulation Component Type Component Wt. % Quantity (g) Combustion Sucrose 38.1 3.81 Component Potassium Chlorate 38.1 3.81 Smoke Melamine 15.9 1.59 Formulation 5-Methoxy Methyl Gallate 6.80 0.68 Binder Ethyl Cellulose 1.00 0.10

Example 16

In one embodiment, an obscurant formulation having a smoke component consisting of melamine and dimethylsulfone is prepared according to Table 23.

TABLE 23 Melamine/Dimethylsulfone Formulation Component Type Component Wt. % Quantity (g) Combustion Sucrose 38.1 3.81 Component Potassium Chlorate 38.1 3.81 Smoke Melamine 15.9 1.59 Formulation Dimethylsulfone 6.80 0.68 Binder Ethyl Cellulose 1.00 0.10

Example 17

In one embodiment, an obscurant formulation having a smoke component consisting of methyl gallate and dimethylsulfone is prepared according to Table 24.

TABLE 24 Methyl Gallate/Dimethylsulfone Formulation Component Type Component Wt. % Quantity (g) Combustion Sucrose 38.1 3.81 Component Potassium Chlorate 38.1 3.81 Smoke Methyl Gallate 6.80 0.68 Formulation Dimethylsulfone 15.9 1.59 Binder Ethyl Cellulose 1.00 0.10

Example 18

In one embodiment, an obscurant formulation having a smoke component consisting of melamine and Bisphenol A is prepared according to Table 25.

TABLE 25 Melamine/Bisphenol A Formulation Component Type Component Wt. % Quantity (g) Combustion Sucrose 38.1 3.81 Component Potassium Chlorate 38.1 3.81 Smoke Melamine 15.9 1.59 Formulation Bisphenol A 6.80 0.68 Binder Ethyl Cellulose 1.00 0.10

Example 19

In one embodiment, an obscurant formulation having a smoke component consisting of methyl gallate and Bisphenol A is prepared according to Table 26.

TABLE 26 Methyl Gallate/Bisphenol A Formulation Component Type Component Wt. % Quantity (g) Combustion Sucrose 38.1 3.81 Component Potassium Chlorate 38.1 3.81 Smoke Methyl Gallate 6.9 0.69 Formulation Bisphenol A 15.9 1.59 Binder Ethyl Cellulose 1.00 0.10

Example 20

In one embodiment, an obscurant formulation having a smoke component consisting of melamine and Bisphenol A is prepared according to Table 27.

TABLE 27 Melamine/Bisphenol S Formulation Component Type Component Wt. % Quantity (g) Combustion Sucrose 38.1 3.81 Component Potassium Chlorate 38.1 3.81 Smoke Melamine 15.9 1.59 Formulation Bisphenol S 6.80 0.68 Binder Ethyl Cellulose 1.00 0.10

Example 21

In one embodiment, an obscurant formulation having a smoke component consisting of methyl gallate and Bisphenol A is prepared according to Table 28.

TABLE 28 Methyl Gallate/Bisphenol S Formulation Component Type Component Wt. % Quantity (g) Combustion Sucrose 38.1 3.81 Component Potassium Chlorate 38.1 3.81 Smoke Methyl Gallate 6.8 0.68 Formulation Bisphenol S 15.9 1.59 Binder Ethyl Cellulose 1.00 0.10

Referring to FIG. 13, a bar graph 1300 of the minimum percent transmittance (min % T) values for the obscurant formulations presented in Examples 2-7 is depicted. The min % T, represented by the y-axis 1302, is the lowest transmittance value recorded in testing for each obscurant formulation. The obscurant formulation for each bar is identified on the x-axis 1304. Bar 1306 represents the min % T for the obscurant formulation with a 70/30 weight percentage ratio of melamine/methyl gallate and a 77/23 weight percentage of propellant and binder/smoke formulation. Bar 1308 represents the min % T for the obscurant formulation containing melamine, methyl gallate, and 1% adipic acid according to Example 4. Bar 1310 represents the min % T for the obscurant formulation containing melamine, methyl gallate, and 5% adipic acid according to Example 5. Bar 1312 represents the min % T for the obscurant formulation containing melamine, methyl gallate, and 1% azelaic acid according to Example 6. Bar 1314 represents the min % T for the obscurant formulation containing melamine, methyl gallate, and 5% azelaic acid according to Example 7. Bar 1316 represents the min % T for the obscurant formulation containing melamine, methyl gallate, and 1% sebacic acid according to Example 2. Bar 1318 represents the min % T for the obscurant formulation containing melamine, methyl gallate, and 5% sebacic acid according to Example 3.

Referring to FIG. 14, a bar graph 1400 of the values of recovery time to 10 percent transmittance (10% T) for the obscurant formulations presented in Examples 2-7 is depicted. The 10% T values, represented by the y-axis 1402, is the time elapsed to reach 10% in testing for each obscurant formulation. The obscurant formulation for each bar is identified on the x-axis 1404. Bar 1406 represents the 10% T for the obscurant formulation with a 70/30 weight percentage ratio of melamine/methyl gallate and a 77/23 weight percentage of propellant and binder/smoke formulation. Bar 1408 represents the 10% T for the obscurant formulation containing melamine, methyl gallate, and 1% adipic acid according to Example 4. Bar 1410 represents the 10% T for the obscurant formulation containing melamine, methyl gallate, and 5% adipic acid according to Example 5. Bar 1412 represents the 10% T for the obscurant formulation containing melamine, methyl gallate, and 1% azelaic acid according to Example 6. Bar 1414 represents the 10% T for the obscurant formulation containing melamine, methyl gallate, and 5% azelaic acid according to Example 7. Bar 1416 represents the 10% T for the obscurant formulation containing melamine, methyl gallate, and 1% sebacic acid according to Example 2. Bar 1418 represents the 10% T for the obscurant formulation containing melamine, methyl gallate, and 5% sebacic acid according to Example 3.

The data from the tests depicted in FIGS. 13 and 14 is summarized in Table 26:

TABLE 26 Comparison of Melamine/Methyl Gallate Obscurant to the Formulations in Examples 2-7. 1% Melamine/ Adipic 5% Adipic 1% Azelaic 5% Azelaic 1% Sebacic 5% Sebacic MeGallate Acid Acid Acid Acid Acid Acid Min % T 1.6 1.7 2.4 1.2 2.3 5.8 3.1 Std Dev 0.5 0.5 0.5 0.5 0.8 2.7 0.4 P-value N/A 0.618 0.045 0.157 0.158 0.052 0.001 Time <10% T 192.7 176.4 115.5 153.8 137.5 73.5 120.5 Std Dev 26.8 35.2 11.8 18.6 11.3 53.2 15.9 P-value N/A 0.441 0.000 0.009 0.000 0.016 0.000

Referring to FIG. 15, a bar graph 1500 of the minimum percent transmittance (min % T) values for the obscurant formulations presented in Examples 8, 9, 16, and 17 is depicted. The min % T, represented by the y-axis 1502, is the lowest transmittance value recorded in testing for each obscurant formulation. The obscurant formulation for each bar is identified on the x-axis 1504. Bar 1506 represents the min % T for the obscurant formulation with a 70/30 weight percentage ratio of melamine/methyl gallate and a 77/23 weight percentage of propellant and binder/smoke formulation. Bar 1508 represents the min % T for the obscurant formulation containing melamine and dimethylsulfone according to Example 16. Bar 1510 represents the min % T for the obscurant formulation containing methyl gallate and dimethylsulfone according to Example 17. Bar 1512 represents the min % T for the obscurant formulation containing melamine, methyl gallate, and 1% dimethylsulfone according to Example 8. Bar 1514 represents the min % T for the obscurant formulation containing melamine, methyl gallate, and 5% dimethylsulfone according to Example 9.

Referring to FIG. 16, a bar graph 1600 of the values of recovery time to 10 percent transmittance (10% T) for the obscurant formulations presented in Examples 8, 9, 16, and 17 is depicted. The 10% T values, represented by the y-axis 1602, is the time elapsed to reach 10% in testing for each obscurant formulation. The obscurant formulation for each bar is identified on the x-axis 1604. Bar 1606 represents the 10% T for the obscurant formulation with a 70/30 weight percentage ratio of melamine/methyl gallate and a 77/23 weight percentage of propellant and binder/smoke formulation. Bar 1608 represents the 10% T for the obscurant formulation containing melamine and dimethylsulfone according to Example 16. Bar 1610 represents the 10% T for the obscurant formulation containing methyl gallate and dimethylsulfone according to Example 17. Bar 1612 represents the 10% T for the obscurant formulation containing melamine, methyl gallate, and 1% dimethylsulfone according to Example 8. Bar 1614 represents the 10% T for the obscurant formulation containing melamine, methyl gallate, and 5% dimethylsulfone according to Example 9.

The data from the tests depicted in FIGS. 15 and 16 is summarized in Table 27:

TABLE 27 Comparison of Melamine/Methyl Gallate Obscurant to the Formulations in Examples 8, 9, 16 and 17. Melamine/ Dimethyl- 1% 5% Melamine/ Dimethyl- sulfone/ Dimethyl- Dimethyl- MeGallate sulfone MeGallate sulfone sulfone Min % T 1.6 10.5 24.1 2.6 3.2 Std Dev 0.5 1.4 6.5 0.5 1.3 P-value N/A 0.001 0.006 0.008 0.092 Time <10% 192.7 0.0 5.8 150.8 134.0 T Std Dev 26.8 0.0 11.5 20.8 39.8 P-value N/A 0.000 0.000 0.008 0.051

Referring to FIG. 17, a bar graph 1700 of the minimum percent transmittance (min % T) values for the obscurant formulations presented in Examples 10, 11, 20, and 21 is depicted. The min % T, represented by the y-axis 1702, is the lowest transmittance value recorded in testing for each obscurant formulation. The obscurant formulation for each bar is identified on the x-axis 1704. Bar 1706 represents the min % T for the obscurant formulation with a 70/30 weight percentage ratio of melamine/methyl gallate and a 77/23 weight percentage of propellant and binder/smoke formulation. Bar 1508 represents the min % T for the obscurant formulation containing melamine and Bisphenol S according to Example 20. Bar 1510 represents the min % T for the obscurant formulation containing methyl gallate and Bisphenol S according to Example 21. Bar 1512 represents the min % T for the obscurant formulation containing melamine, methyl gallate, and 1% Bisphenol S according to Example 10. Bar 1514 represents the min % T for the obscurant formulation containing melamine, methyl gallate, and 5% Bisphenol S according to Example 11.

Referring to FIG. 18, a bar graph 1800 of the values of recovery time to 10 percent transmittance (10% T) for the obscurant formulations presented in Examples 10, 11, 20, and 21 is depicted. The 10% T values, represented by the y-axis 1802, is the time elapsed to reach 10% in testing for each obscurant formulation. The obscurant formulation for each bar is identified on the x-axis 1804. Bar 1806 represents the 10% T for the obscurant formulation with a 70/30 weight percentage ratio of melamine/methyl gallate and a 77/23 weight percentage of propellant and binder/smoke formulation. Bar 1808 represents the 10% T for the obscurant formulation containing melamine and Bisphenol S according to Example 20. Bar 1810 represents the 10% T for the obscurant formulation containing methyl gallate and Bisphenol S according to Example 21. Bar 1812 represents the 10% T for the obscurant formulation containing melamine, methyl gallate, and 1% Bisphenol S according to Example 10. Bar 1814 represents the 10% T for the obscurant formulation containing melamine, methyl gallate, and 5% Bisphenol S according to Example 11.

The data from the tests depicted in FIGS. 17 and 18 is summarized in Table 28:

TABLE 28 Comparison of Melamine/Methyl Gallate Obscurant to the Formulations in Examples 10, 11, 21 and 22. Melamine/ Melamine/ BPS/ 1% Bis- 5% Bis- MeGallate BPS MeGallate phenol S phenol S Min % T 1.6 3.3 0.8 2.5 1.1 Std Dev 0.5 1.0 0.1 0.9 0.3 P-value N/A 0.016 0.001 0.093 0.058 Time <10% 192.7 131.4 505.8 187.0 232.6 T Std Dev 26.8 26.4 6.4 23.5 17.2 P-value N/A 0.003 0.000 0.713 0.006

Referring to FIG. 19, a bar graph 1900 of the minimum percent transmittance (min % T) values for the obscurant formulations presented in Examples 8, 9, 16, and 17 is depicted. The min % T, represented by the y-axis 1902, is the lowest transmittance value recorded in testing for each obscurant formulation. The obscurant formulation for each bar is identified on the x-axis 1904. Bar 1906 represents the min % T for the obscurant formulation with a 70/30 weight percentage ratio of melamine/methyl gallate and a 77/23 weight percentage of propellant and binder/smoke formulation. Bar 1908 represents the min % T for the obscurant formulation containing melamine and dimethylsulfone according to Example 8. Bar 1910 represents the min % T for the obscurant formulation containing methyl gallate and dimethylsulfone according to Example 9. Bar 1912 represents the min % T for the obscurant formulation containing melamine, methyl gallate, and 1% dimethylsulfone according to Example 16. Bar 1914 represents the min % T for the obscurant formulation containing melamine, methyl gallate, and 5% dimethylsulfone according to Example 17.

Referring to FIG. 20, a bar graph 2000 of the values of recovery time to 10 percent transmittance (10% T) for the obscurant formulations presented in Examples 8, 9, 16, and 17 is depicted. The 10% T values, represented by the y-axis 2002, is the time elapsed to reach 10% in testing for each obscurant formulation. The obscurant formulation for each bar is identified on the x-axis 2004. Bar 2006 represents the 10% T for the obscurant formulation with a 70/30 weight percentage ratio of melamine/methyl gallate and a 77/23 weight percentage of propellant and binder/smoke formulation. Bar 2008 represents the 10% T for the obscurant formulation containing melamine and dimethylsulfone according to Example 8. Bar 2010 represents the 10% T for the obscurant formulation containing methyl gallate and dimethylsulfone according to Example 9. Bar 2012 represents the 10% T for the obscurant formulation containing melamine, methyl gallate, and 1% dimethylsulfone according to Example 16. Bar 2014 represents the 10% T for the obscurant formulation containing melamine, methyl gallate, and 5% dimethylsulfone according to Example 17.

The data from the tests depicted in FIGS. 19 and 20 is summarized in Table 29:

TABLE 29 Comparison of Melamine/Methyl Gallate Obscurant to the Formulations in Examples 8, 9, 16, and 17. Melamine/ Diphenyl- 1% 5% Melamine/ Diphenyl- sulfone/ Diphenyl- Diphenyl- MeGallate sulfone MeGallate sulfone sulfone Min % T 1.6 20.1 13.1 1.1 1.2 Std Dev 0.5 4.2 3.7 1.0 0.4 P-value N/A 0.003 0.008 0.362 0.140 Time <10% 192.7 0.0 5.3 197.4 146.5 T Std Dev 26.8 0.0 10.5 38.3 11.4 P-value N/A 0.000 0.000 0.814 0.001

Referring to FIG. 21, a bar graph 2100 of the minimum percent transmittance (min % T) values for the obscurant formulations presented in Examples 12, 13, 18, and 19 is depicted. The min % T, represented by the y-axis 2102, is the lowest transmittance value recorded in testing for each obscurant formulation. The obscurant formulation for each bar is identified on the x-axis 2104. Bar 2106 represents the min % T for the obscurant formulation with a 70/30 weight percentage ratio of melamine/methyl gallate and a 77/23 weight percentage of propellant and binder/smoke formulation. Bar 2108 represents the min % T for the obscurant formulation containing melamine and Bisphenol A according to Example 18. Bar 2110 represents the min % T for the obscurant formulation containing methyl gallate and Bisphenol A according to Example 19. Bar 2112 represents the min % T for the obscurant formulation containing melamine, methyl gallate, and 1% Bisphenol A according to Example 12. Bar 2114 represents the min % T for the obscurant formulation containing melamine, methyl gallate, and 5% Bisphenol A according to Example 13.

Referring to FIG. 22, a bar graph 2200 of the values of recovery time to 10 percent transmittance (10% T) for the obscurant formulations presented in Examples 12, 13, 18, and 19 is depicted. The 10% T values, represented by the y-axis 2202, is the time elapsed to reach 10% in testing for each obscurant formulation. The obscurant formulation for each bar is identified on the x-axis 2204. Bar 2206 represents the 10% T for the obscurant formulation with a 70/30 weight percentage ratio of melamine/methyl gallate and a 77/23 weight percentage of propellant and binder/smoke formulation. Bar 2208 represents the 10% T for the obscurant formulation containing melamine and Bisphenol A according to Example 18. Bar 2210 represents the 10% T for the obscurant formulation containing methyl gallate and Bisphenol A according to Example 19. Bar 2212 represents the 10% T for the obscurant formulation containing melamine, methyl gallate, and 1% Bisphenol A according to Example 12. Bar 2214 represents the 10% T for the obscurant formulation containing melamine, methyl gallate, and 5% Bisphenol A according to Example 13.

The data from the tests depicted in FIGS. 19 and 20 is summarized in Table 30:

TABLE 30 Comparison of Melamine/Methyl Gallate Obscurant to the Formulations in Examples 12, 13, 18, and 19. Melamine/ Melamine/ BPA/ 1% Bis- 5% Bis- MeGallate BPA MeGallate phenol A phenol A Min % T 1.6 6.6 0.8 0.6 Std Dev 0.5 0.8 0.3 0.6 P-value N/A 0.000 0.003 0.011 Time <10% 192.7 45.8 410.0 203.0 T Std Dev 26.8 13.4 35.9 28.7 P-value N/A 0.000 0.000 0.527

Referring to FIG. 23, a bar graph 2300 of the minimum percent transmittance (min % T) values for the obscurant formulations presented in Examples 14 and 15 is depicted. The min % T, represented by the y-axis 2302, is the lowest transmittance value recorded in testing for each obscurant formulation. The obscurant formulation for each bar is identified on the x-axis 2304. Bar 2306 represents the min % T for the obscurant formulation with a 70/30 weight percentage ratio of melamine/methyl gallate and a 77/23 weight percentage of propellant and binder/smoke formulation. Bar 2108 represents the min % T for the obscurant formulation containing melamine and 5-methoxy methyl gallate according to Example 15. Bar 2110 represents the min % T for the obscurant formulation containing melamine and THEIC according to Example 14.

Referring to FIG. 24, a bar graph 2400 of the values of recovery time to 10 percent transmittance (10% T) for the obscurant formulations presented in Examples 14 and 15 is depicted. The 10% T values, represented by the y-axis 2402, is the time elapsed to reach 10% in testing for each obscurant formulation. The obscurant formulation for each bar is identified on the x-axis 2404. Bar 2406 represents the 10% T for the obscurant formulation with a 70/30 weight percentage ratio of melamine/methyl gallate and a 77/23 weight percentage of propellant and binder/smoke formulation. Bar 2408 represents the 10% T for the obscurant formulation containing melamine and 5-methoxy methyl gallate according to Example 15. Bar 2410 represents the 10% T for the obscurant formulation containing melamine and THEIC according to Example 14.

The data from the tests depicted in FIGS. 23 and 24 is summarized in Table 31:

TABLE 31 Comparison of Melamine/Methyl Gallate Obscurant to the Formulations in Examples 14 and 15. Melamine/ 5-Methoxy MeGallate MeGallate THEIC Min % T 1.6 4.9 7.9 Std Dev 0.5 2.3 1.3 P-value N/A 0.065 0.002 Time <10% T 192.7 73.8 28.5 Std Dev 26.8 36.3 13.4 P-value N/A 0.003 0.000

In some embodiments, Applicant's obscurant formulation comprises oxamide or a oximide derivative. In some embodiment, Applicant's obscurant formulation comprises a 1:1 molar condensation product between diethyl oxalate and ethylene diamine. In one embodiment, the condensation product comprises a mixture of ethylene oxamide cyclics and polyethylene oxamide oligomers as shown in (I).

In one embodiment, Applicant's smoke formulation comprises the condensation product from (I) and methyl gallate. In one embodiment, Applicant's obscurant formulation comprises the condensation product from (I) and a sucrose/alkali chlorate propellant.

In one embodiment, a polyethylene oxamide oligomer is prepared by adding diethyl oxalate dropwise with stirring to a solution of ethylene diamine in a toluene solvent at room temperature. The solution is stirred for 30 minutes followed by filtering off the white polyethylene oxamide precipitate. The precipitate is vacuum dried to remove residual solvent and is then blended with methyl gallate. In one embodiment, the ratio of ethylene oxamide to methyl gallate is determined by the melamine/methyl gallate mixtures descried herein, except that an equimolar amount of ethylene oxamide is substituted for the melamine.

In various embodiments, Applicant's smoke formulation comprises boron, boron carbide, boron nitride, titanium hydride powder, or a combination thereof. In various embodiments, Applicant's smoke formulation comprises methyl gallate combined with boron, boron carbide, boron nitride, titanium hydride powder, or a combination thereof.

In one embodiment, Applicant's smoke formulation comprises alkylene oxamide and methyl gallate. In one embodiment, Applicant's obscurant formulation comprises alkylene oxamide and a sucrose/alkali chlorate propellant.

In various embodiments, the propellant of Applicant's obscurant formulation comprises sucrose, lactose, glucose, fructose, sorbitol, threose, erythritol, pentaerythritol, or a combination thereof. In other embodiments, Applicant's obscurant formulation comprises any compound known to be capable of readily oxidizing and, in the presence of a strong oxidizer, capable of generating sufficient heat to vaporize the smoke formulation.

In one embodiment, Applicant's obscurant formulation comprises a coolant. In one embodiment, Applicant's obscurant formulation does not include a coolant. In one embodiment, the coolant comprises MgCO₃. In one embodiment, the coolant comprises NaHCO₃.

In one embodiment, Applicant's formulation does not include a binder. In one embodiment, Applicant's formulation includes a binder. In one embodiment, the binder includes Citroflex, a plasticizer sold in commerce by Vertellus Specialties, Inc., which results in pellets that are generally easier to press than non-plasticized formulations. In one embodiment, the binder comprises nitrocellulose. In one embodiment, the binder comprises ethylcellulose.

Referring to FIG. 12, an exemplary method of preparing an obscurant device capable of producing obscurant smoke at various rates is depicted. The method begins at step 1202. An obscurant formulation with a burn rate of 136 sec/in is prepared at step 1204. An obscurant formulation with a burn rate of 24 sec/in is prepared at step 1206. The 136 sec/in formulation is pressed into the form of a cylinder to form a core at step 1208. The 24 sec/in formulation is pressed into a cylinder around the 136 sec/in core to form a concentric cylinder at step 1210. A fuse is inserted into the concentric cylinder at step 1212. The concentric cylinder is loaded into an obscurant device housing at step 1214. In various embodiments, the obscurant device housing is a smoke grenade, an obscurant rocket, or other type of obscurant artillery. The method ends at step 1216.

When the obscurant device is triggered and the fuse ignited, the inner portion of the concentric cylinder, containing the 136 sec/in obscurant formulation burns, producing a dense obscurant smoke (i.e., the high burn rate results in higher smoke production). Once the inner portion of the concentric cylinder fully combusts, the outer portion of the concentric cylinder burns, producing a lower density obscurant smoke (i.e., the lower burn rate results in a lower rate of smoke production). This dual-burn rate configuration can produce a heavy initial smoke screen followed by a sustaining smoke screen to maintain the obscurant effect for a longer period of time as compared to single-burn rate configurations. In different embodiments, the device contains 3 or more layers of obscurant formulations, each with a different burn rate. While the exemplary method described in FIG. 12 includes obscurant formulations with 136 and 24 sec/in burn rates, different formulations and combinations of formulations of Applicant's obscurant (with different burn rates) may be used as necessary for different purposes.

In addition to military applications, a formulation capable of producing nontoxic smoke at a low burn temperature has application in the civilian realm. For example, smoke precursors may be used for detecting leaks within heating ventilation and air conditioning (HVAC) systems. A ductwork test is typically performed after the initial installation of each new HVAC system. Periodic testing after installation is also desirable. In various embodiments, the smoke produced by Applicant's nontoxic melamine-based, low burn temperature formulations described herein is directed into the ductwork of a HVAC system. The high density smoke flows through the ductwork and out any openings, thereby identifying any leaks in the system.

While specific values have been recited for the various embodiments recited herein, it is to be understood that, within the scope of the invention, the values of all parameters, including amounts and ratios, may vary over wide ranges to suit different applications.

While the invention is described through the above-described exemplary embodiments, it will be understood by those of ordinary skill in the art that modifications to, and variations of, the illustrated embodiments may be made without departing from the inventive concepts disclosed herein. For example, although some aspects have been described with reference to a flowchart, those skilled in the art should readily appreciate that functions, operations, decisions, etc. of all or a portion of each block, or a combination of blocks, of the flowchart may be combined, separated into separate operations or performed in other orders. In addition, although a obscurant has been described, the disclosed methods and formulations may be used for other purposes, including location marking, special effects, and included in pyrotechnic displays. Furthermore, disclosed aspects, or portions of these aspects, may be combined in ways not listed above. Accordingly, the invention should not be viewed as being limited to the disclosed embodiment(s).

Claims

1. A composition to produce smoke upon combustion, comprising:

a combustion component; and

a smoke formulation.

2. The composition of claim 1, wherein said smoke formulation comprises a gallate ester.

3. The composition of claim 2, wherein said smoke formulation further comprises melamine.

4. The composition of claim 3, wherein said smoke formulation further comprises a polyphenolic derivative.

5. The composition of claim 3, wherein said smoke formulation further comprises a dicarboxylic acid.

6. The composition of claim 3, wherein said smoke formulation further comprises an imide.

7. The composition of claim 2, wherein said smoke formulation comprises bisphenol S.

8. The composition of claim 7, wherein said smoke formulation further comprises melamine.

9. The composition of claim 2, wherein said smoke formulation comprises bisphenol A.

10. The composition of claim 9, wherein said smoke formulation further comprises melamine.

11. The composition of claim 2, wherein said smoke formulation comprises diemthylsulfone.

12. The composition of claim 11, wherein said smoke formulation further comprises melamine.

13. The composition of claim 1, wherein said smoke formulation comprises melamine.

14. The composition of claim 13, wherein said smoke formulation further comprises THEIC.

15. The composition of claim 13, wherein said smoke formulation further comprises an oxamide.

16. The composition of claim 13, wherein said smoke formulation further comprises an imide.

17. The composition of claim 13, wherein said smoke formulation further comprises a boron-containing compound.

18. The composition of claim 1, further comprising a combustion component.

19. The composition of claim 18, wherein said combustion component comprises sucrose, lactose, glucose, fructose, sorbitol, threose, erythritol, pentaerythritol, or a combination thereof.

20. The composition of claim 19, wherein said combustion component further comprises an chlorate oxidizer.