CA2210438A1 - Thermoplastic polymer structures for rockets and thermoplastic polymer propellants - Google Patents
Thermoplastic polymer structures for rockets and thermoplastic polymer propellantsInfo
- Publication number
- CA2210438A1 CA2210438A1 CA 2210438 CA2210438A CA2210438A1 CA 2210438 A1 CA2210438 A1 CA 2210438A1 CA 2210438 CA2210438 CA 2210438 CA 2210438 A CA2210438 A CA 2210438A CA 2210438 A1 CA2210438 A1 CA 2210438A1
- Authority
- CA
- Canada
- Prior art keywords
- thermoplastic polymer
- fibre
- high temperature
- matrix
- propellant
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Abandoned
Links
Classifications
-
- C—CHEMISTRY; METALLURGY
- C06—EXPLOSIVES; MATCHES
- C06B—EXPLOSIVES OR THERMIC COMPOSITIONS; MANUFACTURE THEREOF; USE OF SINGLE SUBSTANCES AS EXPLOSIVES
- C06B45/00—Compositions or products which are defined by structure or arrangement of component of product
- C06B45/04—Compositions or products which are defined by structure or arrangement of component of product comprising solid particles dispersed in solid solution or matrix not used for explosives where the matrix consists essentially of nitrated carbohydrates or a low molecular organic explosive
- C06B45/06—Compositions or products which are defined by structure or arrangement of component of product comprising solid particles dispersed in solid solution or matrix not used for explosives where the matrix consists essentially of nitrated carbohydrates or a low molecular organic explosive the solid solution or matrix containing an organic component
- C06B45/10—Compositions or products which are defined by structure or arrangement of component of product comprising solid particles dispersed in solid solution or matrix not used for explosives where the matrix consists essentially of nitrated carbohydrates or a low molecular organic explosive the solid solution or matrix containing an organic component the organic component containing a resin
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- Chemical & Material Sciences (AREA)
- Health & Medical Sciences (AREA)
- Life Sciences & Earth Sciences (AREA)
- Dispersion Chemistry (AREA)
- Molecular Biology (AREA)
- Crystallography & Structural Chemistry (AREA)
- Organic Chemistry (AREA)
- Compositions Of Macromolecular Compounds (AREA)
- Processes Of Treating Macromolecular Substances (AREA)
Abstract
A propellant is disclosed, comprising, as binder, a moisture curable ethylene copolymer especially a silane-grafted ethylene/vinyl acetate copolymer. The propellant is particularly useful as a rocket propellant.
A rocket structure is disclosed for use under high temperature stress. The structure comprises thermoplastic polymer in a matrix of fibre having high temperature resistance, the thermoplastic polymer being selected from high temperature-resistant engineering thermoplastic polymers and moisture-curable thermoplastic polymers. The thermoplastic polymer ablates during said high temperature stress to provide a matrix of said fibre having structural integrity. A method of manufacture, especially compression moulding, is disclosed.
A rocket structure is disclosed for use under high temperature stress. The structure comprises thermoplastic polymer in a matrix of fibre having high temperature resistance, the thermoplastic polymer being selected from high temperature-resistant engineering thermoplastic polymers and moisture-curable thermoplastic polymers. The thermoplastic polymer ablates during said high temperature stress to provide a matrix of said fibre having structural integrity. A method of manufacture, especially compression moulding, is disclosed.
Description
TITLE
ihrIOPLASTIC
POLYMER ~-lK~ n~S FOR ROCKETS
AND I~IOPLASTIC POLYMER PROPELLANTS
FIELD OF THE lNV~L~llON
The present application relates to rocket propellants that are based on thermoplastic ethylene co-polymers, especially crosslinkable ethylene vinyl/acetate (EVA), and other related polyolefins, in rocket propellants. An example of such polymer is silane-grafted EVA.
The present invention also relates to rocket structures that are subject to high temperature stress e.g casings, bulkheads and nozzles, and especially to rocket structures formed from thermoplastic polymers and fibre matrices, and to the processes for the manufacture of such structures.
R~cKr,~OUND TO THE INVENTION
The original black powder rocket propellants were replaced in the early l900's with propellants based on nitrocellulose and nitroglycerine. Subsequently propellants were developed that were based on a fuel oil, a binder e.g. asphalt, and an oxidizer e.g. potassium perchlorate. Polysulphide fuel binders that could be cast on cured rubber at cool temperatures and mixtures of ammonium perchlorate, polyester and styrene cured by cumene hydroperoxide were also developed. A number of polybutadiene materials, including in particular polybutadiene acrylonitrile, carboxy terminated polybutadiene and hydroxy-terminated polybutadiene have also been developed and undergone commercial use.
In most cases, propellant formulations require the use of toxic chemicals e.g. di-isocyanates, epoxies or aziridines as curing agents. Ethyl hexyl acrylate or di-- CA 02210438 1997-07-1~
octyl adipate may be used as plasticizers. In addition to safety considerations in the manufacture and use of the propellants, the costs of these materials are relatively high.
A variety of filament wound composite structures are used in rockets and missiles, in particular to provide a favourable combination of strength versus weight of the structure. For instance, replacing a carbon steel rocket casing with a corresponding casing of the same physical dimensions but made from a carbon fibre structure can result in a reduction in weight of about 75%.
In the manufacture of composite structures, filaments of glass or carbon are wound onto a mandrel. A
thermal set resin e.g. an epoxy, is applied over the wound structure and then a combination of heat and pressure are applied. When the structure has cured, the structure is hydraulically removed from the mandrel and post-curing machining operations for nozzle and bulkhead installation are performed. This is a very time consuming and labour intensive process that can last from several hours to days, depending on size of the structure involved. The process is very energy intensive due to the large quantities of heat that are needed to properly cure the composite structure. In many instances, hazardous materials are involved in the process, which necessitates special handling and disposal techniques.
The shelf or pot-life of some constituents, especially epoxides, tend to be very short. This requires that the epoxy resin be mixed in batches, which leads to waste because the mixed compounds can only be used over a short period of time, and cannot be stored for future production runs.
The net result of current processing techniques is that long lead times are required in order to accommodate the large quantity of tooling required and the long processing times required in the process. This imposes severe limits on the changes that may be made in rocket and missile structures, imposing limitations on the CA 02210438 1997-07-1~
flexibility to adapt to new conditions that may be required in the use of rockets and missiles.
Propellant composition and rocket structures offering greater flexibility and less lead time in fabrication would be useful.
SUMM~RY OF THE INVENTION
Propellants and structures formed from thermoplastic polymers, and methods for the manufacture thereof, have now been found.
Accordingly, an aspect of the present invention provides a propellant comprising, as binder, a moisture curable thermoplastic ethylene co-polymer, especially moisture curable ethylene/vinyl acetate copolymer, e.g. a silane-grafted ethylene/vinyl acetate copolymer.
Another aspect of the invention provides a propellant comprising silane-grafted ethylene/vinyl acetate copolymer and at least 60% by weight of an oxidizer.
In preferred embodiments of the propellant of the present invention, the propellant is a rocket propellant.
In another embodiment the propellant additionally contains at least one of an energetic and a ballistic modifier.
A further aspect of the present invention provides a rocket structure for use under high temperature stress, said structure comprising thermoplastic polymer in a matrix of fibre having high temperature resistance, said thermoplastic polymer being selected from high temperature-resistant engineering thermoplastic polymers and moisture-curable thermoplastic copolymers, said thermoplastic polymer ablating during said high temperature stress to provide a matrix of said fibre having structural integrity.
Yet aspect of the present invention provides a method for the manufacture of a rocket structure, comprising forming a structure of a thermoplastic polymer CA 02210438 1997-07-1~
in a matrix of fibre having high temperature resistance, said thermoplastic polymer being selected from high temperature-resistant engineering thermoplastic polymers and moisture-curable thermoplastic co-polymers, said thermoplastic polymer ablating during said high temperature stress to provide a matrix of said fibre having structural integrity, said structure being formed on a pre-form mould and being heated to effect flow of said thermoplastic polymer to impregnate said matrix of fibre.
In a preferred embodiment of the method of the present invention, the structure is formed by forming alternating layers of thermoplastic polymer and fibre matrix on said pre-form mould, especially alternating layers of sheet of thermoplastic polymer and fibre matrix.
In another preferred embodiment, the structure is formed by moulding e.g. compression moulding, of a moisture-curable thermoplastic polymer and the matrix of fibre, especially using fuel grain as pre-form mould.
In a further embodiment of the present invention, the fibre is selected from glass fibre, carbon fibre and aramid fibre.
In another embodiment, the thermoplastic polymer is polyphenylene sulphide, high temperature nylon or silane-grafted cross-linkable ethylene copolymer.
DET~TT-T~'n DESCRIPTION OF THE INVENTION
The propellants of the present invention are particularly for use in rockets, missiles or similar propelled devices. The propellant comprises, as a binder, a moisture-curable ethylene co-polymer, especially a silane-grafted ethylene/vinylacetate co-polymer.
The polymers that are used in the present invention are derived from ethylene co-polymers. Such polymers include co-polymers of ethylene and a vinyl alkanoate, - CA 02210438 1997-07-1~
especially ethylene/vinyl acetate co-polymers.
Alternatively, the polymer may be a co-polymer of ethylene and an acrylate ester, examples of which are ethylene/ethyl acrylate co-polymers, ethylene/methyl acrylate co-polymers and ethylene/butyl acrylate co-polymers. The polymer may also be a co-polymer of ethylene with acrylic acid or methylacrylic acid and the related ionomers viz. co-polymers having the acid groups thereof partially neutralized by metals especially sodium, zinc or aluminium. The polymers may have other copolymerized monomers e.g. carbon monoxide.
The polymer has a moisture-crosslinkable monomer copolymerized into the polymer or grafted onto the polymer. Examples of moisture-crosslinkable monomers are vinyl silanes, particularly vinyl trialkoxysilanes, examples of which are vinyl trimethoxysilane and vinyl triethoxysilane. Such silanes are available commercially. In addition, compositions containing vinyl silane, grafting catalyst and crosslinking catalyst are also available commercially.
Polymers containing vinyl silanes must be maintained in a moisture-free environment at all times prior to the desired time of crosslinking. Crosslinking may be effecting by exposure to moisture, especially by merely exposing the article to atmospheric conditions. Curing by contacting with water, especially steam, is not preferred in view of effects of water on the propellants.
Crosslinking may over a period of a few days in the presence of atmospheric moisture, it being understood that the shape and thickness of the fuel grain is a factor in the cross-linking rate, as the crosslinking reaction is believed to be controlled by the rate of diffusion of water into the fuel grain. Crosslinking catalysts are normally incorporated into the composition.
Techniques for the manufacture of moisture-crosslinkable polymers, and for the curing of such polymers are known.
The propellant will be comprised of the binder i.e.
moisture-curable ethylene copolymer, and at least 60% by - CA 02210438 1997-07-1~
weight of an oxidizer. The propellant may also contain an energetic, a ballistic modifier and other compounds.
A variety of oxidizers may be used, including ammonium perchlorate, ammonium nitrate and potassium perchlorate of which ammonium perchlorate is preferred.
Nonetheless, it is understood that other oxidizers could be used. In particular, the propellant contains at least 60% by weight of oxidizer, and especially at least 70% by weight of oxidizer. In preferred embodiments, the propellant contains 75-80% by weight of oxidizer.
Ammonium perchlorate is the preferred oxidizer because it is non-hygroscopic and stable during normal fabrication procedures.
The propellant may contain an energetic, examples of which are aluminium, magnesium and aluminium/magnesium alloys. The propellant may also contain ballistic modifiers, to increase the burn rate e.g. oxides of iron, copper, chromium and magnesium or to suppress the burn rate e.g. calcium carbonate and other inorganic or organic materials known to suppress the burn rate.
The preferred binder is silane-grafted ethylene-vinyl acetate co-polymer. It has good mechanical properties and temperature resistance when crosslinked.
In addition, it is a strong adhesive, which eliminates the need for epoxy or other adhesive materials in order to obtain mechanical bonding to the oxidizer. The ethylene-vinyl co-polymer may have a melt index as measured by the procedures of ASTM D1238, of less than 100 dg/min, which is a high viscosity ethylene-vinyl co-polymer or melt indices of up to at least 2500 dg/min.
In embodiments the melt index is in the range of 400-2500 dg/min. Small amounts of plasticizers e.g.
polybutene, may be added to the binder in order to improve the processing of the binder.
In order to obtain the propellants, the co-polymer in the form of pellets may be mixed in a dry state with an oxidizer e.g. ammonium perchlorate. Energetic materials, ballistic materials could also be added at CA 02210438 1997-07-1~
this stage. The dry mixture is then heated e.g. to about 85~C, to form a mixture that is flowable. The resultant mixture may then be transferred to a mould and subjected to moderate pressure in order to form a fuel grain.
Vacuum de-gassing procedures are believed to be not required. Crosslinking of the propellant composition can be achieved by either exposure to atmospheric moisture or to water or steam.
Advantages of ethylene/vinyl acetate thermoplastic copolymer-based solid propellant binders over existing technologies include less critical limits on mix ratios of the component, easy processing of the pre-processing, low to non-toxic properties of the binder constituents, the absence of shelf or pot-life problems, the absence of vacuum degassing requirements, and rapid cure times if required. However, the most significant advantage is likely that the lead time required for the production of propellants for rocket motors, because either the pre-mixed propellant or the individual ingredients can be stored indefinitely. Thus rocket motors, or other propellant-using systems could be produced on a just-in-time basis for rapid deployment in the field of use.
An advantage of the use of silane-grafted ethylene/vinyl acetate copolymers as the binder in propellants is the increased safety that may be achieved during the manufacturing process. Energetic materials such as aluminium powder must be handled carefully during traditionally fuel-grain manufacturing processes, as air-borne metallic powders can be extremely volatile under certain conditions. According the present invention, the energetic materials could be compounded simultaneously with the thermoplastic polymer in compounding extruders. In such a method the energetic materials would be completely inhibited and would no longer pose a hazard during the manufacture of fuel-grains. It is understood that such powders are frequently compounded with thermoplastic polymers as colorants or dyes for such polymers.
The present invention also relates to the use of reinforced thermoplastic structures in rocket motor cases, bulkheads and nozzles, especially nozzles, where the article is subjected to temperature stresses such that the thermoplastic polymer is ablated during use.
The structure is formed from a matrix of a fibre that is capable of withstanding the temperature stresses to which the structure would be subjected during use, or which are converted into a fibrous form under such conditions and which in such form are able to withstand the temperature stress. The invention particularly relates to the use of thermoplastic polymers in the formation of such structures. The thermoplastic polymer must be capable of retaining its integrity during use at relatively low temperatures, to permit the structure to be heated to and used at high temperatures.
Examples of fibres that are typically used in the manufacture of composite materials used in rockets include glass, carbon fibre and aramid fibres, which may be either in a pre-woven or in a non-woven form.
The thermoplastic polymer is an engineering high temperature resistant polymer or moisture-curable ethylene copolymer. Examples of such polymers include polyphenylene sulphide, high temperature nylons and moisture-crosslinkable ethylene copolymers e.g.
silane-grafted ethylene copolymers as described above.
Techniques for the formation of composite structures in a desired shape are known. For instance, alternating layers of fibres and film of the thermoplastic polymer may be formed, in a sandwich construction. The fibre materials may be treated with a primer to promote adhesion, or may be in an untreated state. Heat and pressure are briefly applied to melt the binder i.e.
thermoplastic polymer, and force the flow of the molten polymer into the matrix of the fibre to form the reinforced structure. Subsequently, the part is cooled.
If the polymer is a moisture-crosslinkable polymer, the CA 02210438 1997-07-1~
structure of the moisture-crosslinkable polymer and fibre matrix may be compression moulded e.g. directly onto a fuel grain. Such compression moulding may be achieved at temperatures of less than about 90~C. The moisture-curable co-polymer could then be permitted to crosslink by exposure to moisture. An important advantage of using moisture-curable co-polymers is that the fibre/thermoplastic polymer structure may be formed directly on the fuel grain, thereby directly forming a rocket motor casing with its fuel grain already in place.
Such a process eliminates the need to subsequently add fuel grain to the rocket motor casing.
ihrIOPLASTIC
POLYMER ~-lK~ n~S FOR ROCKETS
AND I~IOPLASTIC POLYMER PROPELLANTS
FIELD OF THE lNV~L~llON
The present application relates to rocket propellants that are based on thermoplastic ethylene co-polymers, especially crosslinkable ethylene vinyl/acetate (EVA), and other related polyolefins, in rocket propellants. An example of such polymer is silane-grafted EVA.
The present invention also relates to rocket structures that are subject to high temperature stress e.g casings, bulkheads and nozzles, and especially to rocket structures formed from thermoplastic polymers and fibre matrices, and to the processes for the manufacture of such structures.
R~cKr,~OUND TO THE INVENTION
The original black powder rocket propellants were replaced in the early l900's with propellants based on nitrocellulose and nitroglycerine. Subsequently propellants were developed that were based on a fuel oil, a binder e.g. asphalt, and an oxidizer e.g. potassium perchlorate. Polysulphide fuel binders that could be cast on cured rubber at cool temperatures and mixtures of ammonium perchlorate, polyester and styrene cured by cumene hydroperoxide were also developed. A number of polybutadiene materials, including in particular polybutadiene acrylonitrile, carboxy terminated polybutadiene and hydroxy-terminated polybutadiene have also been developed and undergone commercial use.
In most cases, propellant formulations require the use of toxic chemicals e.g. di-isocyanates, epoxies or aziridines as curing agents. Ethyl hexyl acrylate or di-- CA 02210438 1997-07-1~
octyl adipate may be used as plasticizers. In addition to safety considerations in the manufacture and use of the propellants, the costs of these materials are relatively high.
A variety of filament wound composite structures are used in rockets and missiles, in particular to provide a favourable combination of strength versus weight of the structure. For instance, replacing a carbon steel rocket casing with a corresponding casing of the same physical dimensions but made from a carbon fibre structure can result in a reduction in weight of about 75%.
In the manufacture of composite structures, filaments of glass or carbon are wound onto a mandrel. A
thermal set resin e.g. an epoxy, is applied over the wound structure and then a combination of heat and pressure are applied. When the structure has cured, the structure is hydraulically removed from the mandrel and post-curing machining operations for nozzle and bulkhead installation are performed. This is a very time consuming and labour intensive process that can last from several hours to days, depending on size of the structure involved. The process is very energy intensive due to the large quantities of heat that are needed to properly cure the composite structure. In many instances, hazardous materials are involved in the process, which necessitates special handling and disposal techniques.
The shelf or pot-life of some constituents, especially epoxides, tend to be very short. This requires that the epoxy resin be mixed in batches, which leads to waste because the mixed compounds can only be used over a short period of time, and cannot be stored for future production runs.
The net result of current processing techniques is that long lead times are required in order to accommodate the large quantity of tooling required and the long processing times required in the process. This imposes severe limits on the changes that may be made in rocket and missile structures, imposing limitations on the CA 02210438 1997-07-1~
flexibility to adapt to new conditions that may be required in the use of rockets and missiles.
Propellant composition and rocket structures offering greater flexibility and less lead time in fabrication would be useful.
SUMM~RY OF THE INVENTION
Propellants and structures formed from thermoplastic polymers, and methods for the manufacture thereof, have now been found.
Accordingly, an aspect of the present invention provides a propellant comprising, as binder, a moisture curable thermoplastic ethylene co-polymer, especially moisture curable ethylene/vinyl acetate copolymer, e.g. a silane-grafted ethylene/vinyl acetate copolymer.
Another aspect of the invention provides a propellant comprising silane-grafted ethylene/vinyl acetate copolymer and at least 60% by weight of an oxidizer.
In preferred embodiments of the propellant of the present invention, the propellant is a rocket propellant.
In another embodiment the propellant additionally contains at least one of an energetic and a ballistic modifier.
A further aspect of the present invention provides a rocket structure for use under high temperature stress, said structure comprising thermoplastic polymer in a matrix of fibre having high temperature resistance, said thermoplastic polymer being selected from high temperature-resistant engineering thermoplastic polymers and moisture-curable thermoplastic copolymers, said thermoplastic polymer ablating during said high temperature stress to provide a matrix of said fibre having structural integrity.
Yet aspect of the present invention provides a method for the manufacture of a rocket structure, comprising forming a structure of a thermoplastic polymer CA 02210438 1997-07-1~
in a matrix of fibre having high temperature resistance, said thermoplastic polymer being selected from high temperature-resistant engineering thermoplastic polymers and moisture-curable thermoplastic co-polymers, said thermoplastic polymer ablating during said high temperature stress to provide a matrix of said fibre having structural integrity, said structure being formed on a pre-form mould and being heated to effect flow of said thermoplastic polymer to impregnate said matrix of fibre.
In a preferred embodiment of the method of the present invention, the structure is formed by forming alternating layers of thermoplastic polymer and fibre matrix on said pre-form mould, especially alternating layers of sheet of thermoplastic polymer and fibre matrix.
In another preferred embodiment, the structure is formed by moulding e.g. compression moulding, of a moisture-curable thermoplastic polymer and the matrix of fibre, especially using fuel grain as pre-form mould.
In a further embodiment of the present invention, the fibre is selected from glass fibre, carbon fibre and aramid fibre.
In another embodiment, the thermoplastic polymer is polyphenylene sulphide, high temperature nylon or silane-grafted cross-linkable ethylene copolymer.
DET~TT-T~'n DESCRIPTION OF THE INVENTION
The propellants of the present invention are particularly for use in rockets, missiles or similar propelled devices. The propellant comprises, as a binder, a moisture-curable ethylene co-polymer, especially a silane-grafted ethylene/vinylacetate co-polymer.
The polymers that are used in the present invention are derived from ethylene co-polymers. Such polymers include co-polymers of ethylene and a vinyl alkanoate, - CA 02210438 1997-07-1~
especially ethylene/vinyl acetate co-polymers.
Alternatively, the polymer may be a co-polymer of ethylene and an acrylate ester, examples of which are ethylene/ethyl acrylate co-polymers, ethylene/methyl acrylate co-polymers and ethylene/butyl acrylate co-polymers. The polymer may also be a co-polymer of ethylene with acrylic acid or methylacrylic acid and the related ionomers viz. co-polymers having the acid groups thereof partially neutralized by metals especially sodium, zinc or aluminium. The polymers may have other copolymerized monomers e.g. carbon monoxide.
The polymer has a moisture-crosslinkable monomer copolymerized into the polymer or grafted onto the polymer. Examples of moisture-crosslinkable monomers are vinyl silanes, particularly vinyl trialkoxysilanes, examples of which are vinyl trimethoxysilane and vinyl triethoxysilane. Such silanes are available commercially. In addition, compositions containing vinyl silane, grafting catalyst and crosslinking catalyst are also available commercially.
Polymers containing vinyl silanes must be maintained in a moisture-free environment at all times prior to the desired time of crosslinking. Crosslinking may be effecting by exposure to moisture, especially by merely exposing the article to atmospheric conditions. Curing by contacting with water, especially steam, is not preferred in view of effects of water on the propellants.
Crosslinking may over a period of a few days in the presence of atmospheric moisture, it being understood that the shape and thickness of the fuel grain is a factor in the cross-linking rate, as the crosslinking reaction is believed to be controlled by the rate of diffusion of water into the fuel grain. Crosslinking catalysts are normally incorporated into the composition.
Techniques for the manufacture of moisture-crosslinkable polymers, and for the curing of such polymers are known.
The propellant will be comprised of the binder i.e.
moisture-curable ethylene copolymer, and at least 60% by - CA 02210438 1997-07-1~
weight of an oxidizer. The propellant may also contain an energetic, a ballistic modifier and other compounds.
A variety of oxidizers may be used, including ammonium perchlorate, ammonium nitrate and potassium perchlorate of which ammonium perchlorate is preferred.
Nonetheless, it is understood that other oxidizers could be used. In particular, the propellant contains at least 60% by weight of oxidizer, and especially at least 70% by weight of oxidizer. In preferred embodiments, the propellant contains 75-80% by weight of oxidizer.
Ammonium perchlorate is the preferred oxidizer because it is non-hygroscopic and stable during normal fabrication procedures.
The propellant may contain an energetic, examples of which are aluminium, magnesium and aluminium/magnesium alloys. The propellant may also contain ballistic modifiers, to increase the burn rate e.g. oxides of iron, copper, chromium and magnesium or to suppress the burn rate e.g. calcium carbonate and other inorganic or organic materials known to suppress the burn rate.
The preferred binder is silane-grafted ethylene-vinyl acetate co-polymer. It has good mechanical properties and temperature resistance when crosslinked.
In addition, it is a strong adhesive, which eliminates the need for epoxy or other adhesive materials in order to obtain mechanical bonding to the oxidizer. The ethylene-vinyl co-polymer may have a melt index as measured by the procedures of ASTM D1238, of less than 100 dg/min, which is a high viscosity ethylene-vinyl co-polymer or melt indices of up to at least 2500 dg/min.
In embodiments the melt index is in the range of 400-2500 dg/min. Small amounts of plasticizers e.g.
polybutene, may be added to the binder in order to improve the processing of the binder.
In order to obtain the propellants, the co-polymer in the form of pellets may be mixed in a dry state with an oxidizer e.g. ammonium perchlorate. Energetic materials, ballistic materials could also be added at CA 02210438 1997-07-1~
this stage. The dry mixture is then heated e.g. to about 85~C, to form a mixture that is flowable. The resultant mixture may then be transferred to a mould and subjected to moderate pressure in order to form a fuel grain.
Vacuum de-gassing procedures are believed to be not required. Crosslinking of the propellant composition can be achieved by either exposure to atmospheric moisture or to water or steam.
Advantages of ethylene/vinyl acetate thermoplastic copolymer-based solid propellant binders over existing technologies include less critical limits on mix ratios of the component, easy processing of the pre-processing, low to non-toxic properties of the binder constituents, the absence of shelf or pot-life problems, the absence of vacuum degassing requirements, and rapid cure times if required. However, the most significant advantage is likely that the lead time required for the production of propellants for rocket motors, because either the pre-mixed propellant or the individual ingredients can be stored indefinitely. Thus rocket motors, or other propellant-using systems could be produced on a just-in-time basis for rapid deployment in the field of use.
An advantage of the use of silane-grafted ethylene/vinyl acetate copolymers as the binder in propellants is the increased safety that may be achieved during the manufacturing process. Energetic materials such as aluminium powder must be handled carefully during traditionally fuel-grain manufacturing processes, as air-borne metallic powders can be extremely volatile under certain conditions. According the present invention, the energetic materials could be compounded simultaneously with the thermoplastic polymer in compounding extruders. In such a method the energetic materials would be completely inhibited and would no longer pose a hazard during the manufacture of fuel-grains. It is understood that such powders are frequently compounded with thermoplastic polymers as colorants or dyes for such polymers.
The present invention also relates to the use of reinforced thermoplastic structures in rocket motor cases, bulkheads and nozzles, especially nozzles, where the article is subjected to temperature stresses such that the thermoplastic polymer is ablated during use.
The structure is formed from a matrix of a fibre that is capable of withstanding the temperature stresses to which the structure would be subjected during use, or which are converted into a fibrous form under such conditions and which in such form are able to withstand the temperature stress. The invention particularly relates to the use of thermoplastic polymers in the formation of such structures. The thermoplastic polymer must be capable of retaining its integrity during use at relatively low temperatures, to permit the structure to be heated to and used at high temperatures.
Examples of fibres that are typically used in the manufacture of composite materials used in rockets include glass, carbon fibre and aramid fibres, which may be either in a pre-woven or in a non-woven form.
The thermoplastic polymer is an engineering high temperature resistant polymer or moisture-curable ethylene copolymer. Examples of such polymers include polyphenylene sulphide, high temperature nylons and moisture-crosslinkable ethylene copolymers e.g.
silane-grafted ethylene copolymers as described above.
Techniques for the formation of composite structures in a desired shape are known. For instance, alternating layers of fibres and film of the thermoplastic polymer may be formed, in a sandwich construction. The fibre materials may be treated with a primer to promote adhesion, or may be in an untreated state. Heat and pressure are briefly applied to melt the binder i.e.
thermoplastic polymer, and force the flow of the molten polymer into the matrix of the fibre to form the reinforced structure. Subsequently, the part is cooled.
If the polymer is a moisture-crosslinkable polymer, the CA 02210438 1997-07-1~
structure of the moisture-crosslinkable polymer and fibre matrix may be compression moulded e.g. directly onto a fuel grain. Such compression moulding may be achieved at temperatures of less than about 90~C. The moisture-curable co-polymer could then be permitted to crosslink by exposure to moisture. An important advantage of using moisture-curable co-polymers is that the fibre/thermoplastic polymer structure may be formed directly on the fuel grain, thereby directly forming a rocket motor casing with its fuel grain already in place.
Such a process eliminates the need to subsequently add fuel grain to the rocket motor casing.
Claims (9)
1. A propellant comprising, as binder, a moisture curable ethylene copolymer, especially a silane-grafted ethylene/vinyl acetate copolymer.
2. A propellant comprising silane-grafted ethylene/vinyl acetate copolymer and at least 60% by weight of an oxidizer.
3. The propellant of Claim 1 or Claim 2 that is a rocket propellant.
4. The propellant of any one of Claims 1-3 additionally containing at least one of an energetic and a ballistic modifier.
5. A rocket structure for use under high temperature stress, said structure comprising thermoplastic polymer in a matrix of fibre having high temperature resistance, said thermoplastic polymer being selected from high temperature-resistant engineering thermoplastic polymers and moisture-curable thermoplastic polymers, said thermoplastic polymer ablating during said high temperature stress to provide a matrix of said fibre having structural integrity.
6. A method for the manufacture of a rocket structure, comprising forming a structure of a thermoplastic polymer in a matrix of fibre having high temperature resistance, said thermoplastic polymer being selected from high temperature resistant engineering thermoplastic polymers and moisture-curable thermoplastic polymers, said thermoplastic polymer ablating during said high temperature stress to provide a matrix of said fibre having structural integrity, said structure being formed on a pre-form mould and being heated to effect flow of said thermoplastic polymer to impregnate said matrix of fibre.
7. The method of Claim 6 in which the structure is formed by forming alternating layers of thermoplastic polymer and fibre matrix on said pre-form mould, especially alternating layers of sheet of thermoplastic polymer and fibre matrix or tapes of fibre matrix coated with thermoplastic polymer.
8. The method of Claim 6 or Claim 7 in which the fibre is selected from glass fibre, carbon fibre and aramid fibre.
9. The method of any one of Claims 6-8 in which the thermoplastic polymer is polyphenylene sulphide, high temperature nylon or silane-grafted cross-linkable ethylene copolymer.
Priority Applications (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA 2210438 CA2210438A1 (en) | 1997-07-15 | 1997-07-15 | Thermoplastic polymer structures for rockets and thermoplastic polymer propellants |
| CA 2243254 CA2243254A1 (en) | 1997-07-15 | 1998-07-15 | Thermoplastic polymer propellant compositions |
| US09/613,090 US6740180B1 (en) | 1997-07-15 | 2000-07-10 | Thermoplastic polymer propellant compositions |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA 2210438 CA2210438A1 (en) | 1997-07-15 | 1997-07-15 | Thermoplastic polymer structures for rockets and thermoplastic polymer propellants |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2210438A1 true CA2210438A1 (en) | 1999-01-15 |
Family
ID=29274879
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 2210438 Abandoned CA2210438A1 (en) | 1997-07-15 | 1997-07-15 | Thermoplastic polymer structures for rockets and thermoplastic polymer propellants |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA2210438A1 (en) |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN107867962A (en) * | 2017-08-18 | 2018-04-03 | 湖北航天化学技术研究所 | A kind of thermoplastic composite solid propellant and preparation method thereof |
| CN112279742A (en) * | 2020-10-09 | 2021-01-29 | 西安近代化学研究所 | alpha-AlH3-EVOH double-shell structure compound, preparation method and application |
-
1997
- 1997-07-15 CA CA 2210438 patent/CA2210438A1/en not_active Abandoned
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN107867962A (en) * | 2017-08-18 | 2018-04-03 | 湖北航天化学技术研究所 | A kind of thermoplastic composite solid propellant and preparation method thereof |
| CN112279742A (en) * | 2020-10-09 | 2021-01-29 | 西安近代化学研究所 | alpha-AlH3-EVOH double-shell structure compound, preparation method and application |
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