WO1999063298A1

WO1999063298A1 - Hydrogen absorbing rubber

Info

Publication number: WO1999063298A1
Application number: PCT/US1999/012561
Authority: WO
Inventors: Philip L. Posson
Original assignee: Marconi Aerospace Defense Systems Inc
Current assignee: BAE Systems Integrated Defense Solutions Inc
Priority date: 1998-06-03
Filing date: 1999-06-03
Publication date: 1999-12-09
Anticipated expiration: 2000-12-03
Also published as: AU4420699A

Abstract

Disclosed is a hydrogen absorbing rubber comprising a polyalkylene material such as polybutadiene and a hydrogenation catalyst. The disclosed hydrogen absorbing rubber is useful as packing material in storage and transport of pyrotechnic devices.

Description

DESCRIPTION HYDROGEN ABSORBING RUBBER

Background of the Invention

Pyrotechnic compositions containing magnesium or other active metals can generate hydrogen from reaction with hydroxylitic compounds. These compounds, mainly water, are introduced inadvertently during composition manufacture or packaging. Impermeable hermetic sealing and increased shelf life requirements have made this gas generation more obvious and objectionable. Detrimental consequences include swelling of barrier bags, straining and breakage of packing cases and toppling of case stacks in storage. Preparation of the contained pyrotechnic devices for use becomes slower and more hazardous. The flammability of hydrogen- air mixtures increases the hazard to ground personnel. Inspection of stores must be done with increased frequency. Often the gas pressure deforms hermetically sealed cartridge cases, leading to unusable devices.

Increasing the hydrogen permeability of the exterior packaging is an unacceptable answer to the problem, as inward permeation of atmospheric water also increases. Differential- permeability films such as sputtered palladium are expensive and maintain some package internal hydrogen pressure by their very nature. Gas-relief valves are costly, failure-prone if tightly confined, and reduce the packing density of the devices. In addition, gas-relief valves do not answer the problems of hydrogen generation internal to the devices themselves.

Mixtures of acetylenic unsaturated organic compounds plus hydrogenation catalyst and (inert) binder have been devised to reduce the ill effects of hydrogen generation. Hydrogen getters described by Anderson et al. in US Patent 3,896,042 utilized metal catalysts coated with dimerized acetylene derivatives or polydipropargyl ether of bisphenol-A. This technique arose from research directed to nuclear-weapons programs and is unconcerned with economics, whereas current military and civilian procurement policies stress economic value. The acetylenic absorbers described in the Anderson patent suffer from several disadvantages, for example, they are expensive, produced as fine chemicals, and currently dependent on imported raw materials. Furthermore, the amount of inert binder employed to support these crystalline absorbers reduces the total capacity of the mixtures. Sheppold et al, in U.S. Patent 5,624,598, describe hydrogen absorbers which, like those of Anderson et al. employ acetylenic bonds and which, in addition, withstand storage/operating temperatures in excess of 100° C. Such triple bond containing molecules are difficult and expensive to synthesize. Actual maximum military and civilian pyrotechnic storage conditions range from 74° to 96° C, generally at the lower figure. This makes the special high temperature properties referred to in Sheppold et al. largely unnecessary.

Secco et al., in U.S. Patent 4,714,592, teach hydrogen absorbing compositions intended to protect optical fibers. These compositions utilize polymerized diene monomers of "at least conjugated unsaturation" as hydrogen receptors. The compositions of Secco et al. lack utility in regard to pyrotechnic applications, as their viscosity is greater than desired during manufacture or emplacement in pyrotechnic packaging, and their finished form is that of a viscid semi-fluid paste. Such illustrated physical properties are at variance with the desired low mixing viscosity and temperature-stable, non-migrating elastomeric form in use.

Other attempts at solving the problem of pyrotechnic compound-created hydrogen include oxidizing agents such as copper oxide, silver oxide or Hopcalite, all of which have been proposed for use in destroying unwanted hydrogen. However, the product of such reactions is water, which can recycle to oxidize more active metals, thus regenerating hydrogen. The net effect is transfer of oxygen to the metal and reduction of usable potential unless a water scavenger is incorporated. The exothermicity of the oxidation also raises the possibility of gas ignition under unexpected circumstances.

In view of the above, there is a need for a product that absorbs hydrogen produced by stored pyrotechnic devices, particularly infrared flares and the like, that is effective, economical, and produced from readily available materials.

Summary of the Invention

The present invention involves a hydrogen absorbing rubber ("HAR") comprising, for example, hydroxy-terminated polybutadiene ("HTPB"), cured or crosslinked with polyisocyanates, anhydride adducts of HTPB, dianhydrides or other suitable agents, and a catalytic component. The HAR is useful in applications in which the hydrogen absorbing material is disposed in contact with hydrogen gas and is effective to catalyze the reduction of alkylene double bonds in the polybutadiene backbone of the rubber composition, thus removing unwanted hydrogen from an enclosed space. The invention provides improvements over prior art hydrogen absorption materials in being markedly more economic to manufacture and emplace, having improved absorption capacity, and in using ingredients with a large-volume assured source of supply. This new class of materials is contemplated to be particularly useful as a packing material in pyrotechnics packaging, such as in the packaging of visible-light and infrared flares and other essentially closed systems wherein reaction of an active metal or alloy with hydroxylitic materials may cause unwanted accumulation of hydrogen gas. This new class of materials may also serve in its cured or crosslinked from as a sealant, vibration dampener, coating, structural member, fuel, ablative, binder and potting material. In general, the present invention contemplates a hydrogen absorbing rubber, comprising a cured or crosslinked polyunsaturated alkenic reactive base material and a hydrogenation catalyst. Such an HAR is produceable by a method comprising using a crosslinking agent to cure or crosslink a reaction mixture comprising a combination of a polyunsaturated alkenic reactive base material, a hydrogen catalyst, and any other desired components. In some preferred embodiments, the crosslinking agent is exemplified as comprising at least one of a polyisocyanate or isocyanate prepolymer of HTPB, a polyanhydride, or an anhydride adduct of HTPB, either alone or in combination with other ingredients. Of course, any agent that accomplishes the goal of crosslinking may be used, and the invention is not limited by the specific agents disclosed herein.. In some specific embodiments of the invention, the polyunsaturated alkenic reactive base material is hydroxy-terminated polybutadiene, although any suitable the polyunsaturated alkenic reactive base material may be used. Presently preferred polyunsaturated polymers for use in the invention include, but are not limited to polybutadienes, in particular, polybutadienes of about 1000 to about 3000 number molecular weight. Polybutadiene substituent groups other than hydroxyl, such as carboxyl, epoxide, or vinyl, plus suitable co-reactants may be employed to enable polymerization and use of the HAR composition.

The hydrogenation catalyst may comprises one or more of iron, cobalt, nickel, copper, ruthenium, rhodium, palladium, silver, platinum, or lanthanum, either alone, or supported on a carrier. In some present embodiments, the hydrogenation catalyst is carbon-palladium. In other specific embodiments, the hydrogenation catalyst is a boride compound, for example, amorphous nickel boride and/or cobalt boride. Of course, any hydrogenation catalyst may be used. One important consideration with regard to hydrogenation catalysts is cost. Many of the catalysts comprise expensive components, i.e., silver, palladium, and platinum. In order to reduce the cost of the HAR, one may desire to select a less expensive, less effective catalyst and use it in greater concentration than a more expensive, more efficient one.

The hydrogen absorbing rubber may further comprise a promoter that serves to maintain catalyst action by either increasing the reaction speed of the hydrogenation catalyst or intercept poisons of the catalyst that may be in the feedstocks placed into the reaction mixture, or both. For example, the promoter may be used to intercept such compounds a sulfur, which can severely reduce the catalysis ability of the catalyst. In some embodiments, the promoter comprises one or more of chromium, molybdenum, tungsten, vanadium, or manganese. In a presently preferred embodiment, the HAR comprises hydroxy- terminated polybutadiene and carbon-palladium. In a more specific embodiment, this HAR is crosslinked by using a polyisocyanate compound.

Other aspects of the present invention contemplate a hydrogen absorbing packing material for pyrotechnic devices comprising a hydrogen absorbing rubber as discussed above. Such a packing material may further comprise a suitable moisture absorbent. For example, the moisture absorbent may be a zeolite, silica gel, or other suitable absorbent.

The packing materials of the present invention may be used in the construction of a package for storing or transporting hydrogen producing pyrotechnic devices. In preferred embodiments, the package will define an interior space which will comprise the HAR. The interior will further optionally contain a moisture absorbent material. In some presently contemplated embodiments, the hydrogen producing pyrotechnic will be a flare, al though the present invention is not so limited. The HAR described herein may be employed in methods of preventing hydrogen accumulation in a closed system that includes a pyrotechnic composition. In such case, the pyrotechnic composition may be comprised in an infrared or visible-light flare. In some aspects, the invention contemplates methods of making a hydrogen absorbing rubber comprising: (1) obtaining a polyunsaturated alkenic reactive base material; (2) obtaining a hydrogenation catalyst; (3) obtaining a crosslinking agent; (4) mixing the polyunsaturated alkenic reactive base material, hydrogenation catalyst, and crosslinking agent; and (5) forming a cured or crosslinked hydrogen absorbing rubber. As disclosed above, the crosslinking agent may comprise a polyisocyanate or isocyanate prepolymer of HTPB, a polyanhydride, an anhydride adduct of HTPB, or any other agent. The remaining components employed to make HAR using the contemplated methods may be as defined above. In accordance with long-standing patent law convention, the words "a" and "an," when used in conjunction with the word "comprising" in this patent specification, including the claims, denote "one or more."

Brief Description of the Drawings

FIG. 1 depicts data from a test of an acetylene derivative hydrogen getter and the polybutadiene hydrogen getter or absorber of the present disclosure. Hydrogen is measured as cell pressure over time in days. The solid line represents data from the acetylene derivative hydrogen getter (test 1) and the triangle line represents data from the HTPB-derived hydrogen getter (test 2). The circles represent a no-getter control in test 1 and the vertical lines represent a no-getter control in test 2.

FIG. 2 depicts the amount of hydrogen produced in grams during test 1 (solid line) and test 2 (circles) as described in description of FIG. 1.

Description of Illustrative Embodiments

HAR (Hydrogen Absorbing Rubber) is an elastomeric body composed of hydroxy- terminated polybutadiene (HTPB) or other reactive alkenic unsaturated base polymer plus crosslinking means, a catalytic agency, and other accessory materials for attaining and maintaining its physical and chemical utility as a hydrogen gettering material. HAR may be cast, sprayed, calendered or extruded into usable form and typically is used by being disposed in gaseous contact with hydrogen-evolving bodies. The hydrogen absorbing rubber of the present invention is particularly useful in the packing of pyrotechnic devices such as infrared flares or other magnesium and/or other active-metal containing materials. The HAR may be disposed as a slip of material, a potting material or incorporated into a shock absorbing material in a cartridge for flares or compositions containing magnesium or other active metal powder, or it may be disposed outside a cartridge case or plastic barrier, for example in a barrier bag. Preferred polyunsaturated polymers include, but are not limited to polybutadienes, in particular, polybutadienes of about 1000 to about 3000 number molecular weight. In certain embodiments, the present inventors have demonstrated the successful use of commercially available PolyBd ^® resins marketed by Elf Atochem, including the R-45HT and R-20LM HTPB's. The HTPB base, in preferred embodiments, is present as 25-90 weight % of the finished cured HAR product. Polymers with mole unsaturation < 5%, such as butyl rubber, are considered insufficiently active to be useful as a polyunsaturate base polymer in the practice of the disclosed invention.

Some suitable accessory materials include, but are not limited to, a polymerization reactant and (optional) curing catalyst, a hydrogenation catalyst, stabilizers and antioxidants, free-radical scavengers, plasticizers and extenders with or without usable double bond content, fibrous reinforcing agents, permeability-increasing agents such as chopped minutely-perforate polyolefin or flourocarbon polymer tubes, defoaming/ deairentraining agents, flame retardants, colorants and/or UV-tracers, and the like. Examples of suitable polymerization reactants include toluene diisocyanate, aromatic modified MDI polyisocyanates such as Isonate 2143L (Dow Chemical Company), PAPI (polymethylene polyphenylsiocyanate, and aliphatic polyisocyanates such as Desmodur I (Isophorone diisocyanate, Bayer Corporation), Desmodur N-100 (polymeric hexamethylene diisocyante, Bayer Corporation), DDI-1410 dimeryl diisocyanate, Henkel), and/or prepolymer adducts of such aromatic or aliphatic isocyanates, plus HTPB. Other polymerization reactants include maleic or other polyanhydride anhydride adducts of HTPB such as #131 MA- 10 or #130-MA8 (Ricon Resins, Inc.), plus 1-2% of tertiary amine catalyst like DAMA 1010 (Ethyl Corporation). If unsaturated base polymer reactive substituent groups other than hydroxyl are chosen, suitable polymerization co-reactants may contain epoxide, carboxyl, or amino or hydrosilyl groups as are commonly employed in the curing of such substituted base polymers.

Suitable curing catalysts include, but are not limited to, stannous octoate, dibultyltin dilaurate, Dabco #131 (Air Products), or other organosoluble tin complex salts, triphenyl bismuth, amines such as Dabco (Air Products), acetylacetonates, ethylhexanoates, or napthenates of transition metals such as iron, copper, zinc, cobalt, and manganese, and titanium compounds such as tetraethyl titanate or organo-substituted titanates such as KR55 or KR38S (Kenrich Petrochemicals). Catalyst levels are chosen to control HAR pot life and physical properties after curing. Antioxidants and stabilizers are necessary to preserve the active double bond content of the subject compositions from oxidation and to maintain physical properties over time. Representative antioxidants suitable for use include Irganox 1010 (Ciba-Geigy) and Cyanox 2246 (American Cyanamide). These may be used at a suitable level, for example, about .5 to 10% of the HTPB ingredient weight, and in some preferred examples, about 1% of the HTPB ingredient weight. As a stabilizer aiding the action of the antioxidant can be Pro-Tech 2001 or 3001 (Mach 1, Inc.) at a suitable use level of, for example, 0.1%.

Representative plasticizers can be ditridecyl adipate, diundecyl phthalate, linseed or other unsaturated vegetable oils, monohydroxy terminated polybutadiene, or other suitable plasticizers. These plasticizers are usually used at a level of less than 20% by weight on the basis of HTPB content.

As dispersants may be mentioned Ganex polymers #V220, V216 (ISP Technologies), lecithin, and or Surfynol #104 or 400-series surfactants (Air Products). These additives maximize the heterogenous hydrogenation step. In addition, they reduce viscosity of dispersing finely-divided drying agent. The Surfynol materials also act as defoaming or deairentraining agents and wetting agents.

Other materials from the above list of performance additives will be obvious to anyone skilled in the art.

The hydrogenation catalyst may be a supported or finely-dispersed or organosoluble complex form of precious metal such as palladium or platinum, or alternatively, an amorphous boride of nickel and/or cobalt which may contain promotors such as chromium, tungsten, molybdenum, vanadium or manganese. Such boride catalysts may be formed by the borohydride reduction of soluble cobalt and/or nickel compounds in polar solvent mixtures in the presence of promotor salts, followed by isolation. (Ganem and Osby, Chem, Rev. 1986, 763-780) The hydrogenation catalyst typically is used in the proportion of 0.1-50% by weight of supported active material (5 weight % activity) or .01 to 50% by weight of the unsupported catalytic species. A preparation of 10% by weight is preferred in some embodiments, although any percentage that will accomplish the goals of the invention is within the scope of the invention. Alternate catalyst materials may include, but would not be limited to, iron, cobalt, nickel, copper, ruthenium, rhodium, palladium, silver, osmium, iridium, platinum, gold, lanthanum, and combinations or alloys thereof.

The optional water-absorbing additive may comprise a finely-divided active metal mixed into the polymer and/or silica gel, active carbon, a zeolite, or an organic acid anhydride. The water absorber material may be in separate but associated form. This may be an advantage when devices must be removed from and later replaced in impermeable packaging. If a binder is used in the separable water absorbing body, it may be the same or different from the polyunsaturated binder in the HAR component. The following example is included to demonstrate a preferred embodiment of the invention. It should be appreciated by those of skill in the art that the techniques disclosed in the example which follows represent techniques discovered by the inventor to function well in the practice of the invention, and thus can be considered to constitute preferred modes for its practice. However, those of skill in the art should, in light of the present disclosure, appreciate that many changes can be made in the specific embodiments which are disclosed and still obtain a like or similar result without departing from the spirit and scope of the invention.

Example 1 General Procedures for the Making of HAR

There a many variations in production processes that can be made and still produce a HAR product within the scope of the present invention. Typically, one who how makes such a compound will do so by blending hydrogen-absorbing functionalized polybutadiene with stabilizers, active fillers, and plasticizers if desired. An antioxidant may be added and mixed in to the reaction mixture until dissolved. For example, in typical procedures, 0.5-1.0% of an antioxidant such as, for example, Irganox 1010 or Cyanox 2246 may be employed.

For HAR that is intended to have resilient (compressible) properties one may add a suitable component such as of expanded plastic microballoons, for example #55 IDE or #09 IDE Expancel in a suitable amount, for example 1-25 volume percent.

One will often seek to blend in both a water absorber and hydrogenation catalyst. The water absorber can be in the form of beads, for example Phonosorb 551, Davison, powder (Silosiv A3 powder, Davison, or any other suitable form. For may applications a powder water absorber is preferable as most have higher absorptive power and better suspension flow properties. A three- Angstrom pore diameter Molecular Sieve is preferred for its water selectivity, although this is not required. The water absorber can be milled with a the catalyst, for example, rod or ball milling may be employed.

The catalyst is typically a vacuum-dried, supported catalyst, for example 5%-palladium- on-carbon. The exact nature of the catalyst support is not critical, for example, it may be carbon or any number of finely-divided inorganic or organic solids possessing the requisite inertness and high surface area for economical use of the catalyst. If the catalyst is a soluble noble metal salt or complex, as in palladium acetylacetonate or trifluoroacetate, it may be dissolved in an aliquot of the HTPB prior to being blended with the rest of the reaction mixture.

If a thixotropic finished product is desired, a suitable component 0.5-5% of silica aerogel such as Aerosil 200 (Degussa) at this point. The mass should be thoroughly mixed, for example, under dry gas cover to disperse the (solid) catalyst particles as much as possible. This acts to expose the maximum amount of the hydrogen-absorbing moiety to the action of the solid catalyst. Shear involved in most mixing processes also assists in the development of the full thixotropic properties of any thickener added. Dispersing agents used, such as Ganex V-220 or lecithin, should be dissolved in a small amount of warm polymer before addition to the mixture. After the above steps are taken, the resulting mixture may be allowed sit, tightly sealed, for a sufficient amount of time, for example, about 24 hours, to release suspended and adsorbed air.

When the HAR is to be used, one can stir the base polymer proportion until uniform and weigh out or volume-proportion the ingredients. If a polyisocyanate is used as curing agent, one will add a suitable proportion, for example a 1-1.1 mole ratio of isocyanate/hydroxyl groups. A slight excess of isocyanate lead to a better cured surface as well as improving HAR adhesion to metals and plastics. Different isocyanates have different equivalent weights, which should be factored in to determining the amount of isocyanate to add. The mixture should be thoroughly mixed, preferably under dry gas cover, before use. The two components can also be continuously mixed, as through a motionless mixer, in the process of use. This is advantageous as it overcomes pot life problems and allows variable controllable setting times.

Continuous mixing can be difficult if low-viscosity isocyanates, such as 2143L or IPDI, are employed. In such cases a prepolymer may be prepared from two equivalents of isocyanate per equivalent of hydroxyl, by heating the components at 50-60° C for 1-2 hours under nitrogen. This prepolymer may be stored under nitrogen or another inert gas, then cured with one more equivalent of HTPB, making the viscosities and volumes of the two ingredients more nearly equal and aiding mixing.

The prepared mixture is injected into the cavities, areas or surfaces of ultimate use and cured at room or slightly elevated temperature, up to about 60° C. Relatively dry air is typically used to surround the mixture as it cures so as to avoid the ingress of moisture. The product is stable in ambient storage, having low to negligible toxicity, low flammability and a practically useful hydrogen-absorbing capacity. Example 2 Specific Example of Making HAR

Exemplary hydrogen absorbing rubber (HAR) has been made as follows using compositions shown in Table 1. Hydroxy-terminated polybutadiene, 100 grams of R45HT (Elf Atochem, Channelview, Texas), was mixed with an isocyanate (Isonate 2143L) 12.5 grams, stannous octoate 5 drops, 5% palladium-carbon catalyst 10.0 grams, and Molecular Sieve 3A 1/16" beads 10.0 grams. The black fluid mixture was cast into sheet molds coated with release agent, sealed with aluminum foil, and cured. The resulting resilient sheet was removed from the molds and stored sealed in foil. A strip of the hydrogen absorbing rubber 0.120 inch thick and weighing 5 grams was placed in a sealed aluminum test bomb with a reactive, hydrogen-evolving flare grain of MTV (Magnesium-Teflon- Viton) 1 X 2X 6 inches in size.

Table 1

The bomb, plus an identical control bomb containing only an MTV grain, was placed in a 80°C temperature chamber to increase the rate of gas evolution. Pressure transducers monitored the time and temperature progress of the study. Both test bombs gave evidence of increased pressure within three hours of sealing due to the temperature rise. The internal pressure on the third day of the study (measured as millivolts output from the pressure transducers) was 3.31 and 3.32 MV, control/HAR. Seventeen hours later the bomb pressures were control 4.17 MV, HAR bomb 2.00 MV. At time =10:00 AM of day 2, the pressures were control 4.26, HAR 1.87 MV. At 8:30 AM of day 3, the pressures had become 4.85 and 0.97 MV. After seven days exposure, (10:30 AM), the pressures were control 6.22, HAR 0.48. This data is graphically described in FIG. 1 and FIG. 2.

FIG. 1 shows the results of a test of a acetylene derivative hydrogen getter and the HAR polybutadiene hydrogen getter made according to this example. Hydrogen is measured as cell pressure over time in days. The solid line represents data from the acetylene derivative hydrogen getter (test 1) and the triangle line represents data from the HTPB-derived hydrogen getter (test 2). The circles represent a no-getter control in test 1 and the vertical lines represent a no-getter control in test 2. FIG. 2 depicts the amount of hydrogen produced in grams during test 1 (solid line) and test 2 (circles) as described in description of FIG. 1. The data indicate that pressure in the control bomb continued to increase due to hydrogen evolution from the magnesium-containing MTV composition. The gas pressure in the bomb containing the HAR experimental absorber did not increase. Hydrogen gas appears to have been incorporated into the unsaturated backbone of the polymer. Due to the elevated temperature and an assumed time/temperature exponent of 2.5 X per 10°C, this test was the equivalent of 7.2 years ambient storage. A possible side reaction, catalytic reduction of oxygen, would produce water to be absorbed by the Zeolite and activated carbon present. This would account for the observed subatmospheric pressure condition in the HAR test bomb. Direct adsorption of hydrogen by the palladium catalyst does not account for the gas volume removed. Such direct adsorption is, in addition, an uneconomic use of the precious metal. The hydrogen-absorbing capacity of the HAR compound made in the above method has estimated at 320 cm³ per gram. The estimated capacity of the prior art acetylenic absorber used in "test 1" described in FIG. 1 and FIG. 2. is only 250 cm³ per gram, the difference being largely due to the use of inactive (silicone rubber) matrix in the acetyleneic material.

The improved hydrogen absorber of the present example meets requirements of the aerospace and civilian pyrotechnics industry. The hydrogen absorber is economical to manufacture and use, and withstands - 65 to +165°F temperature extremes. It does not undergo objectionable physical changes during function. HAR is composed of readily-available materials with well-known properties, and can serve mechanical and pyrotechnic as well as a gas absorber functions. Example 3 Specific Process of Making HAR

Exemplary process instructions for a hydrogen absorber mixing and casting according to the present example are as follows:

The mixture used to produce the hydrogen absorbing rubber is HTPB R45HT resin, Isonate #4133L curing agent, tin curing catalyst, palladium-carbon hydrogen catalyst, and Molecular Sieve drying agent beads.

The mix ratio is 100 parts R45HT, 12.5 parts Isonate 2143L, 0.05% dibutyl tin oxide or stannous octoate, and 10 parts 5% palladium on carbon. Ten parts Molecular Sieve 1/16" pellets, #4A or #3A, are added to the product.

1. A flat sheet is prepared with edge guides to cast a 0.120 inch thick sheet. A thin film or spray of release agent (Vaseline) is applied to the casting sheet.

2. The HTPB, tin catalyst, and palladium catalyst are weighed into a plastic beaker and mixed until uniform. The Isonate curing agent is weighed in a fume hood. The curing agent is added to the beaker, and the materials are mixed again until uniform. The Molecular Sieve beads are added followed by more mixing.

3. The batch of hydrogen absorbing rubber is split into two beakers and they are placed into a vacuum oven. A vacuum (25-27 inches) is pulled and maintained until the bubbles have risen and fallen again, at which time air is released into the oven. The two containers are covered with aluminum foil to protect against atmospheric moisture.

4. The contents of one beaker are poured onto the level greased casting sheet. A piece of greased aluminum foil or Saran Wrap is placed on top of the glob of rubber mixture. It is then rolled out towards the edges of the casting sheet with a metal bar. When the sheet fills most or all of the space and is level with the top, rolling is stopped. The edges of the casting sheet and the polyethylene sheet are sealed with tape.

5. The cast rubber sheet(s) are allowed to cure overnight. The finished hydrogen absorbing rubber is pulled out of the casting sheet and put in a sealed container with some Molecular Sieve or silica gel. The sheet must be protected from the environment, as once the sheet has absorbed water from the air it cannot be reconditioned. Example 4 Alternative Example of Making HAR

An alternative manner of preparing HAR is as follows: 250 grams each Sylosieve #3 A molecular sieve powder and Degussa El 99 U/D 5% Pd/C catalyst, vacuum-dried, are placed in a closed mill jar with five .5 x 5 inch PTFE rods. The mixture is milled for 1 hour at 2 revolutions/second, then 2.55 Kg of PolyBd™ R45HT resin (+ %% Irganox 1010 antioxidant) is blended with 0.51 Kg of the powder mixture. The mixture is tightly sealed and left 24 hours for air bubbles to escape. Prior to mixing and extruding the HAR, typically 89% of the HTPB-Pd/C-3A premix is mixed with 11% of Isonate 2143L MDI isocyanate. Typically, there will be no curing catalyst added at this point, so as to maximize the pot life. Thorough stirring is required, as MDI tends to sink to the bottom. The HAR mixture is extruded into plastic assemblies. When assemblies are extruded, they are covered, sealed, and allowed to cure for 24 hours. The assemblies can be stored in a sealed metal can with desiccant until use.

* * *

While the compositions and methods of this invention have been described in terms of preferred embodiments, it will be apparent to those of skill in the art that variations may be applied to the compositions and/or methods and in the steps or in the sequence of steps of the methods described herein, without departing from the concept, spirit and scope of the invention. More specifically, it will be apparent that certain agents which are chemically related may be substituted for the agents described herein, while the same or similar results would be achieved. All such similar substitutes and modifications apparent to those skilled in the art are deemed to be within the spirit, scope and concept of the invention as defined by the appended claims.

Claims

1. A hydrogen absorbing rubber, comprising a cured or crosslinked polyunsaturated alkenic reactive base material and a hydrogenation catalyst.

2. The hydrogen absorbing rubber of claim 1 , produceable by a method comprising using a crosslinking agent selected from the group of a polyisocyanate or isocyanate prepolymer of HTPB, a polyanhydride, or an anhydride adduct of HTPB.

3. The hydrogen absorbing rubber of claim 1, wherein said polyunsaturated alkenic reactive base material is hydroxy-terminated polybutadiene.

4. The hydrogen absorbing rubber of claim 1, wherein said hydrogenation catalyst comprises one or more of iron, cobalt, nickel, copper, ruthenium, rhodium, palladium, silver, platinum, or lanthanum.

5. The hydrogen absorbing rubber of claim 4, wherein said hydrogenation catalyst is carbon- palladium.

6. The hydrogen absorbing rubber of claim 4, wherein said hydrogenation catalyst is amorphous nickel boride and/or cobalt boride.

7. The hydrogen absorbing rubber of claim 1 , further comprising a promotor.

8. The hydrogen absorbing rubber of claim 7, wherein the promoter comprises one or more of chromium, molybdenum, tungsten, vanadium, or manganese.

9. A hydrogen absorbing rubber, comprising hydroxy-terminated polybutadiene and carbon- palladium.

10. The hydrogen absorbing rubber of claim 9, further comprising a polyisocyanate compound.

11. A hydrogen absorbing packing material for pyrotechnic devices comprising a hydrogen absorbing rubber comprising a cured or crosslinked polyunsaturated alkenic reactive base material and a hydrogenation catalyst.

12. The hydrogen absorbing packing material of claim 11, wherein the hydrogen absorbing rubber comprises hydroxy-terminated polybutadiene and carbon-palladium.

13. The hydrogen absorbing packing material of claim 11, further comprising a moisture absorbent.

14. The hydrogen absorbing packing material of claim 13, wherein said moisture absorbent is a zeolite or silica gel.

15. A package for storing or transporting hydrogen producing pyrotechnic devices, wherein said package defines a closed interior space and wherein said closed interior space contains a hydrogen absorbing rubber comprising a cured or crosslinked polyunsaturated alkenic reactive base material and a hydrogenation catalyst and wherein said interior further contains a moisture absorbent material.

16. The package of claim 15, wherein the polyunsaturated alkenic reactive base material comprises hydroxy-terminated polybutadiene and the hydrogenation catalyst comprises carbon- palladium.

17. The package of claim 15, wherein said moisture absorbent material comprises a zeolite or silica gel.

18. The package of claim 15, wherein said hydrogen producing pyrotechnic is a flare.

19. The package of claim 15, wherein said hydrogen catalyst is carbon-palladium or amorphous nickel boride and/or cobalt boride.

20. The package of claim 15, wherein said hydrogen absorbing rubber further comprises a promotor.

21. The package of claim 20, wherein the promoter comprises one or more of chromium, molybdenum, tungsten, vanadium, or manganese.

22. A method of preventing hydrogen accumulation in a closed system that includes a pyrotechnic composition, comprising providing in said closed system a hydrogen absorbing rubber comprising a cured or crosslinked polyunsaturated alkenic reactive base material and a hydrogenation catalyst.

23. The method of claim 22, wherein said pyrotechnic composition comprises an infrared or visible-light flare.

24. A method of making a hydrogen absorbing rubber comprising: a) obtaining a polyunsaturated alkenic reactive base material; b) obtaining a hydrogenation catalyst; c) obtaining a crosslinking agent; d) mixing the polyunsaturated alkenic reactive base material, hydrogenation catalyst, and crosslinking agent; and e) forming a cured or crosslinked hydrogen absorbing rubber.

25. The method of claim 24, wherein the crosslinking agent is selected from the group of a polyisocyanate or isocyanate prepolymer of HTPB, a polyanhydride, or an anhydride adduct of HTPB.

26. The method of claim 24, wherein said polyunsaturated alkenic reactive base material is hydroxy-terminated polybutadiene.

27. The method of claim 24, wherein said hydrogenation catalyst comprises one or more of iron, cobalt, nickel, copper, ruthenium, rhodium, palladium, silver, platinum, or lanthanum.

28. The method of claim 27, wherein said hydrogenation catalyst is carbon-palladium.

29. The method of claim 27, wherein said hydrogenation catalyst is amorphous nickel boride and/or cobalt boride.

30. The method of claim 24, further comprising obtaining a promotor and mixing it with the polyunsaturated alkenic reactive base material, hydrogenation catalyst, and crosslinking agent.

31. The method of claim 24, wherein the promoter comprises one or more of chromium, molybdenum, tungsten, vanadium, or manganese.