Note: Descriptions are shown in the official language in which they were submitted.
CA 022432~4 1998-07-1
TITLE
THERMOPLASTIC POLYMER PROPELLANT COMPOSITIONS
Field Of The Invention
The present application relates to propellant
compositions e.g. rocket propellant or gas generator
compositions, that are based on thermoplastic ethylene
co-polymers, especially ethylene/vinyl acetate
copolymers(EVA) and other related polyolefins. In
embodiments, the binder is a cross-linkable
ethylene/vinyl acetate copolymer, or related cross-
linkable copolymer. In particular, such polymers form
the binder of the propellant composition. An example of a
cross-linkable polymer is silane-grafted EVA.
Background To The Invention
The original black powder rocket propellants were
replaced in the early 1900'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 and cured at cool temperatures, mixtures of ammonium
perchlorate, polyester and styrene cured by cumene
hydroperoxide and compositions based on polyvinyl
chloride plastisols 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 particular, propellant compositions
using polybutadiene acrylonitrile (PBAN) as binder have
been developed and are used in a number of rocket
systems, including the solid rocket boosters for the
Space Shuttle. Propellant compositions using hydroxy-
terminated polybutadiene (HTPB) are also known and in
use. It is understood that systems utilizing thermoset
polymers such as PBAN and HTPB exhibit relatively long
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curing times (several days) unless promoted through heat
and/or catalysis, and that pot-life suffers accordingly,
and may be as short as about 20 minutes.
In most cases, propellant compositions using the
above binder systems and related systems require the use
of toxic chemicals such as epoxides, diisocyanates or
aziridines as curing agents. In addition, plasticizers
e.g. ethyl hexyl acrylate or di-octyl adipate may be
used, which are also known to exhibit toxicological
properties. In addition to safety considerations during
manufacture of the propellants, the cost of many of these
constituents is relatively high.
The shelf life of some of these constituents, such
as epoxides and diisocyanates, tends to be short.
Special handling e.g. freezing or refrigeration and/or
inert gas blanketing, is required to extend their useful
life, which further increases the overall cost of the
propellants.
Of greater concern is the potential for allergic
reactions and the consequent need for special handling in
order to protect persons handling the compositions.
Propellant compositions offering greater
flexibility, less stringent handling requirements and
less lead time in fabrication would be useful.
Summary Of The Invention
Propellants formed from thermoplastic polymers, and
methods for the manufacture thereof, have now been found.
Accordingly, an aspect of the present invention
provides a solid propellant composition comprising, as
binder, a thermoplastic ethylene co-polymer, especially
ethylene/vinyl acetate copolymer.
In embodiments of the compositions, the binder is a
silane-grafted ethylene/vinyl acetate copolymer.
Another aspect of the invention provides a
propellant comprising an ethylene co-polymer, especially
ethylene/vinyl acetate copolymer, and at least 40% by
weight of an oxidizer. In particular, the propellant
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contains at least 60% by weight of oxidizer.
In preferred embodiments of the propellant of the
present invention, the propellant is a rocket propellant
or gas generator.
In another embodiment the propellant contains at
least one of the following: fuel additives, energetic
compounds, ballistic modifiers, rheology modifiers,
bonding agents, opacifiers, stabilizers, metal de-
activators, anti-oxidants, and other agents known to the
trade to modify processing, performance, mechanical
properties, storage stability or shelf life.
A further aspect of the present invention provides a
pre-propellant composition comprising ethylene/vinyl
acetate copolymer and at least one of an energetic and a
ballistic modifier.
Brief Description of the Drawings
The present invention is illustrated by the
embodiments shown in the drawings, in which:
Figure 1 is a photograph of a control sample of
propellanti
Figure 2 is a photograph of a second control sample
of propellant; and
Figure 3 is a photograph of a propellant of the
invention.
Detailed Description Of The Invention
The following acronyms are used in this application:
PETN pentaerythritol tetranitrate
TMETN trimethanolethane trinitrate
BTTN butanetriol trinitrate
GAP glycidyl azide polymer
HMX cyclotetramethylenetetranitramine
RDX cyclotrimethylenetrinitramine
PGN propylglycidyl nitrate
BAMO/AMMO bis-azidomethyloxetane/azidomethyl-
methyloxetane copolymer
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BAMO/NMMO bis-azidomethyloxetane/nitramethyl-
methyloxetane copolymer
PBAN polybutadiene acrylonitrile
HTPB hydroxy-terminated polybutadiene
AP ammonium perchlorate
The propellants of the present invention are
particularly intended for use in rockets, missiles, gas
generating devices or similar devices. The propellant
comprises, as a binder, an ethylene co-polymer,
especially an ethylene/vinyl acetate co-polymer.
The polymers that are used in the present invention
are ethylene co-polymers. Such polymers include co-
polymers of ethylene and a vinyl alkanoate, especially
ethylene/vinyl acetate co-polymers (EVA). 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 or the related ionomers viz.
co-polymers having the acid groups thereof partially
neutralized by metals especially sodium, zinc or
aluminum. The polymers may have other copolymerized
monomers e.g. carbon monoxide.
Compositions formed from EVA tend to exhibit
physical properties equivalent to, or superior to for
instance PBAN, and functional at temperatures of up to
about 50~C.
The preferred binder is ethylene/vinyl acetate co-
polymer. It has good overall mechanical properties,
which may be further improved especially at elevated
temperatures, through cross-linking. Propellant
compositions may be manufactured for use at temperatures
in the range of -65~C to 130~C. In addition, it has good
adhesive properties, which has the potential to eliminate
the need for bonding agents as are often required in
other systems to improve mechanical adhesion of the
binder to the oxidizer particles. These same adhesive
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properties also potentially eliminate the need for tie-
coats or other enhancements of the propellant. These
adhesive properties may be enhanced through cross-
linking.
The ethylene/vinyl acetate co-polymer may have a
wide range of melt index. Melt index is measured by the
procedures of ASTM D1238. For example, melt indices of
from about 0.4 dg/min which is a high viscosity
ethylene/vinyl acetate co-polymer, up to at least 2500
dg/min are known, and may be selected according to the
use. 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 either the binder or
formulated propellant system to enhance processability
and/or mechanical properties.
Examples of ethylene/vinyl acetate copolymers
include ElvaxTM 210, Elvax 220 and Elvax 240
ethylene/vinyl acetate copolymers.
The propellant will normally be comprised of the
binder i.e. ethylene copolymer, and at least 40% by
weight of an oxidizer. In particular, the propellant
contains at least 40% by weight of oxidizer, preferably
at least 60% by weight and especially at least 70% by
weight of oxidizer. The propellant may also contain an
energetic, a ballistic modifier and other compounds.
A variety of oxidizers known to the trade may be
used, including but not limited to ammonium perchlorate,
potassium perchlorate, lithium perchlorate, sodium
perchlorate, ammonium nitrate, potassium nitrate, sodium
nitrate, strontium nitrate, guanidine nitrate, ammonium
dinitramide. Nonetheless, it is understood that other
oxidizers could be used.
In preferred embodiments, the propellant contains
75-90% by weight of oxidizer. Ammonium perchlorate (AP)
is the preferred oxidizer for many applications because
it is relatively non-hygroscopic, stable during normal
storage and fabrication procedures and relatively low in
cost, in addition to providing good performance.
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As in other solid propellant systems, oxidizers may
be incorporated in various particle sizes as necessitated
by burn rate requirements, process rheology, solids
loading, and commercial availability. Typically,
propellant system utilize blends of particle sizes to
improve packing density and thus achieve a high solids
loading as is necessary for high performance. Typical
coarse sizes of ammonium perchlorate, for example, would
be 400-600 microns, medium sizes would be 50-200 microns,
and fine AP e.g. ground onsite, commonly would be have a
mean particle size of 5-15 microns. Ultrafine and other
particle sizes may also be present e.g. particle sizes
from submicron to 5 microns. A mixture of more than one
particle size would normally be used.
In addition to the above, the propellant may contain
one or more of the following: fuel additives, e.g. metal
or non-metal powders or metal hydrides; energetic
materials e.g. crystalline high explosives such as HMX or
RDX, liquid high explosives such as TMETN or BTTN;
ballistic modifiers e.g. ferrocene or ferrocene
derivatives, borohydrides, copper chromite, oxamide,
oxides of iron, lead, chromium, copper, magnesium, and
others; thermally-conductive burn rate modifiers such as
silver wire staples or graphite whisker; coupling
agents/rheology modifiers such as titanates, zirconates,
aluminates; bonding agents; opacifiers, stabilizers,
metal de-activators, anti-oxidants, or other agents known
to the trade to modify processing, performance,
mechanical properties, storage stability or shelf life.
Examples of stabilizers include zinc oxide, nickel oxide
and triacetin. Examples of flame colorants include salts
of strontium, barium sodium and lithium.
Examples of energetic materials are solid high
explosives such as HMX, RDX, nitroguanidine,
nitrocellulose, PETN, lead azide, sodium azide; liquid
high explosives such as nitroglycerin, diethylene glycol
dintrate, triethylene glycol dinitrate, TMETN, BTTN,
energetic polymeric binders such as glycidyl azide
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polymer, BGN, BAMO/AMMO and BAMO/NMMO.
In order to obtain the propellant, according to one
embodiment of the invention, the co-polymer in the form
of pellets or powder may be mixed in a dry state with an
oxidizer e.g. ammonium perchlorate.
Fuel additives, energetic materials and other
modifiers may be added at this stage, or in many cases
may be pre-blended into the polymer. As noted herein, a
pre-propellant is an important feature of an aspect of
the invention. The dry mixture is then heated e.g. to
about 85-130~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.
In preferred embodiments of the method of
manufacture of propellant compositions, a pre-propellant
composition is formed. In this method, the polymer is
mixed with some or all of the additives and modifiers
required in the final formulation, excluding oxidizer and
energetic materials and any catalysts. The resultant
composition is then pelletized or powdered in an
extruder. To manufacture a propellant composition from
this material, it is typically first pre-coated with a
plasticizer, e.g. polybutene. The oxidizing and
energetic materials and any other additives are then
added, and the subsequent mixture is mixed at a typical
temperature of about 85-130~C, to form a flowable,
heterogenous propellant composition.
The composition is then formed into propellant
grains. In a typical process, the propellant is pre-
loaded into a ram extruder. The pre-loaded composition
is then transferred to a press, in which the grain is
formed under moderate pressure, conforming to the inner
surface of the liner in the ram extruder, and to the
mandrel in the extruder which defines the profile of the
inner core of the propellant grain (if required). The
mandrel and/or clamping blocks which retain the grains
may be pre-heated to minimize surface freezing, then
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switched to a cold cycle during a pressing operation to
speed the overall cure cycle. Small propellant grains
have been formed by this method with a cycle time of 30-
120 seconds, but it is anticipated that shorter cycle
times may be achieved.
The resultant propellant grains have a uniform
consistency, showing excellent distribution of the
constituents, especially when compared to non de-gassed
pour-cast propellant compositions, with an absence of
significant bubbles. The propellant shows a high tensile
strength and elongation at break. Such properties, in
addition to good adhesive properties, are important for
the finished propellant grain in order to minimize
mechanical problems during storage and handling.
As noted herein, in more preferred embodiments of
the method of manufacture of the propellant compositions,
a pre-propellant composition is formed using EVA. The
EVA is mixed with modifiers e.g. zirconates, aluminates
or titanates, with energetics e.g. aluminum, magnesium,
aluminum/magnesium powders, optionally with zinc powder
or chlorinated hydrocarbons if tracing is required, and
any ballistic modifiers to modify the burn rate e.g. iron
oxide, copper oxide, chromium oxide or magnesium oxide,
or calcium carbonate. The resultant composition is
pelletized in an extruder. To add oxidizer to the
pellets, the pellets may be coated with polybutene and
then oxidizer e.g. ammonium perchlorate added. The
ammonium perchlorate is typically a mixture of particle
sizes which aids in formation of a uniform composition.
The resultant mixture of oxidizer and pellets is mixed to
a dough-like consistency, which may be formed into a
cylindrical preform for the forming of propellant grains.
Propellant grains are then formed in a ram extruder,
under pressure, using a rapid hot/cold cycle. The use of
a ram extruder permits the fabrication of propellant
grains of complicated or sophisticated shapes without the
need for post-forming operations. The requirement for
vacuum de-gassing is believed to be reduced or
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eliminated. However, the process may easily be run under
vacuum to effect removal of trapped and dissolved gases,
traces of volatiles, etc.
It is understood that other fabrication techniques
may be used.
Propellant grains formed in the ram extruder have a
uniform consistency, even when viewed under a microscope
as shown in the Figures herein, especially compared to
PBAN, with an excellent distribution of constituents and
an absence of significant bubbles. The propellant grains
have high tensile strength and elongation. Such
properties are important for the propellant grain in
order to withstand acceleration during firing in a rocket
without cracking. Cracking could have major adverse
effects, on the rocket, including destruction.
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-propellant,
low to non-toxic properties of the binder constituents,
the absence of shelf or pot-life problems, the potential
absence of vacuum degassing requirements, the ability to
recycle components and rapid cure times if required.
However, the most significant advantage is likely 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. In addition, components
may be safely stored near a location where the propellant
is to be used, and manufactured as needed in apparatus
that is easy to operate.
The manufacture of the pre-propellant i.e.
propellant without oxidizer, is a rapid continuous
process utilizing apparatus known in the plastics
industry. Similarly, the mixing of pre-propellant and
oxidizer, and the forming of fuel grains may also be
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operated on a continuous basis. In both instances,
recycle of materials may be used, but the amount of
recycle material should be minimal. Nonetheless, the
ability to recycle components is an important
characteristic of the present invention as it improves
economics of the process and reduces or eliminates the
need to dispose of components of the propellant by, for
example, burning. This is environmentally advantageous.
It is understood that recycling would normally not
be carried out with cross-linked compositions. However,
cross-linkable compositions may be recycled. For
instance, the pre-propellant would normally be prepared
without the cross-linking catalyst, which would permit
recycling for a period of time.
In embodiments of the invention, especially where
higher temperatures are involved in deployment and
service, especially ambient or storage temperatures that
might exceed about 40~C., the propellant compositions may
be formed with a crosslinked copolymer. Cross-linked
polymer may also be used at other temperatures including
low ambient temperatures, but generally is not necessary.
Cross-linking will improve physical properties,
especially at elevated temperatures. It will further
reduce the likelihood of cracking, slumping, de-bonding
or other mechanical problems of the propellant
compositions. In these embodiments, the propellant
compositions is formed using a polymer that 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
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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 take place 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.
An advantage of the use of 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 traditional fuel-grain
manufacturing processes, as air-borne metallic powders
can be extremely volatile under certain conditions.
According to the present invention, the energetic
materials may be compounded with the thermoplastic
polymer in compounding extruders. In such a method, the
energetic materials would be inhibited and would no
longer pose a hazard during shipping or the manufacture
of fuel-grains. It is understood that such powders are
frequently compounded with thermoplastic polymers as
colorants or dyes for such polymers.
Shelf life of the components, including in
particular the compounds of the pre-propellant that is
formed, is generally indefinite. Thus, pot-life is not a
consideration. However, if crosslinked compositions are
prepared, steps must be taken to protect the vinyl
compounds from moisture, as discussed above.
The present invention provides a fuel grain with
uniform properties, and a method of manufacture that is
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versatile and easy to operate. Components may be
recycled.
The propellant compositions may be used in a variety
of end uses, including as rocket propellants or in gas
generators. The latter use a propellant composition to
produce gas for mechanical work such as start a turbine
engine, drive a piston, or inflate an airbag, in contrast
to a rocket motor which exhausts the gas through a nozzle
to generate a reaction force.
One of the most desirable features of the present
invention is that unlike most conventional propellant
systems and processes this invention provides a
propellant system and process which exhibits the
combination of a very long or nearly indefinite pot-life,
with a very short casting and curing time.
The present invention is illustrated by the
following examples.
Example I
A control sample (Sample #1) of a first typical
AP/Al/HTPB propellant composition was prepared. This
composition employed a tri-modal blend of 400, 200 and 90
micron AP, 3 micron spherical aluminum, and HTPB binder,
in addition to HX-878 bonding agent and carbon black
opacifier in minor percentages. This sample was
processed under atmospheric pressure, to show the severe
porosity of propellants processed in this manner.
The total time required for preparation, including
weighing, mixing and cast cycle time was 6 hours. The
cure time was 2 days.
Figure 1 shows a photograph of a cross-section of
the propellant. The dark pockets are voids of
approximately 250-340 micron in diameter. Porosity of
this magnitude would at least result in erratic
performance and low density of the propellant, and likely
result in catastrophic motor failure from pressure
fluctuations or adiabatic compression. In addition, the
AP particles show weak bonding in the binder matrix as
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evidenced by the crescent shaped air pockets created
during sample preparation.
A second propellant composition (Sample #2) nearly
identical to the first sample was prepared, with the
major exception that the process was run under high
vacuum for 1.5 hour mix cycle. In addition, this
composition employed state of the art bonding agents to
enhance adhesion of the binder to the AP particles.
The total time required for preparation, including
weighing, mixing and cast cycle time was 6 hours. The
cure time was 6 days.
Figure 2 shows a photograph of a cross-section of
the propellant. The surface shows clean cleavage of the
AP particles and lack of de-bonding under the shear force
of cutting, in addition to an excellent surface
distribution profile. Some tearing and pocketing is
evident at the perimeter of the sample, as expected
during sample preparation. The measured density of this
sample is 0.0589 pounds per cubic inch (1.630 g/cc).
A sample (Sample #3) of propellant of the invention
was prepared, with identical solids composition to the
second sample except that ethylene/vinyl acetate co-
polymer was used as binder. The propellant was formed
from pre-propellant, using the ram extruder, as
described. The total mix cycle for this batch was 20
minutes, under atmospheric pressure (no vacuum).
The total time required for preparation, including
weighing, mixing and mix cycle time was 1.5 hours. The
time for extrusion, pressing, cooling and curing in non-
continuous prototype equipment was 4 minutes/grain.
Figure 3 shows a photograph of a cross-section of
the propellant. This sample exhibits the same excellent
surface distribution as the second sample above, as well
as aggressive bonding of the AP particles to the binder
matrix. No voids are visible other than at the periphery
of the sample. The measured density of this sample is
0.05962 pounds per cubic inch (1.650 g/cc), an increase
of 1.2% over the second sample.
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14
Example II
Propellant compositions were prepared by the
following procedure. A mixing bowl was heated to 210-
215~F (99-102~C). Fine to medium particulate ammonlum
perchlorate (AP) was fed to the bowl, together with any
burn rate catalysts, and mixed for two minutes. All
remaining AP was added, and dry mixed for 3-5 minutes at
high speed.
A mixture of ethylene/vinyl acetate copolymer,
polybutene or other plasticizer, rheology modifiers (if
present) was prepared. This mixture was added to the
mixer. Mixing was continued until the polymer had
melted, and then for a further 10 minutes. The resultant
mixture was then extruded into propellant grains in the
ram extruder.
Example III
The procedure used for preparing pre-propellant
blends was as follows. Using a Ross LDM-4 double
planetary mixture, the temperature was set at 265~ F
(129~ C), when the ethylene-vinyl acetate copolymer was
ElvaxTX 205 or 210 polymer. All fine dry materials of the
composition were added to the mixing bowl, with any dust
being allowed to settle. The mixing head was then wiped
to remove settled material. The Elvax ethylene-vinyl
acetate copolymer and all other medium to coarse
materials were added, including fluid ingredients if any.
A vacuum was then applied to the mixture.
The dry mixing cycle was commenced, at low speed
mixing. The mixing speed was increased when the
temperature passed the melting point of the composition,
typically about 100~ C, and mixing was continued for 20
minutes. The mixing bowl was scraped down once after
about 10 minutes.
The mixing head was then lifted, leaving the blades
at the surface of the composition for 1-2 minutes to
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allow adhered material to flow into the bowl with minimal
trapped air. The contents of the bowl were then
discharged. A similar procedure may be used with
different types of mixer, including mixes that do not
operate under vacuum.
Example IV
A composition was prepared in a K-5 air mixer. The
mixing bowl temperature was set at 99-102~ C, and all fine
to medium sized particulate ammonium perchlorate and any
burn rate catalyst was added to the mix bowl. The
mixture was then mixed at high speed for 2 minutes. Any
remaining ammonium perchlorate was added and the
resultant mixture was preheated for 3-5 minutes under
high speed mixing. A mixture of Elvax ethylene/vinyl
acetate copolymer with any polybutene or other
plasticizer, rheology modifiers or other ingredients was
then added, and mixed at a moderate mixing speed. After
the mixture had reached the melting point, the mixture
was mixed for a further 10 minutes. The mixture was
subsequently extruded into grains.
Using this procedure a composition was prepared as
follows:
Material: Weight Charged (g)
AP-400* 500.5
AP-200* 115.5
AP-90* 153.5
Pre-blend** 215.5
Polybutene 6 (Soltex) 10
NZ-33 neo-alkoxy 5
zirconate***
Batch total 1000 grams
* Ammonium perchlorate, with 400, 200 or 90
micron particulate size.
** Pre-blend of Example VII, below.
*** Kenrich Petrochemicals, Inc.
Processing was difficult in that the composition
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16
exhibited high initial tack, requiring more frequent
scraping.
The procedure was repeated, using a pre-blend of
binder PB-6 and NZ-33. All ammonium perchlorate was
added at the same time. The mixture dispersed easily as
it heated, and suddenly transitioned into a crumbly,
mobile blend. Extrusion in the ram extruder was good.
Example V
The procedure of Example IV was repeated, using the
following composition:
Material: Weight Charged (g)
AP-400 479.45
AP-200 122.1
AP-90 212.3
Pre-blend* 66.3
ElvaxTM 210 EVA 103.85
Polybutene-6 10
NZ-33 neo-alkoxy zirconate 5
Iron oxide
Batch Total 1000 grams
* Pre-blend of Example VII, below.
This formulation has reduced aluminum content (2%),
an increased amount of 90 micron AP (from 25 to 30~ by
weight), and iron oxide, with a proportional reduction in
ammonium perchlorate of 400 micron size. These changes
were intended to reduce nozzle erosion and increase
ignition response.
CA 022432~4 1998-07-1
Example VI
A pre-blend batch was prepared with the following
composition:
Material:Weight Charged (g)
Elvax 210 EVA 719.28
Polybutene 6 0.00
Carbon Black 2.40
Zinc, (Purity Zinc Metals 1678.32
UP-6)
Batch Total 2400 grams
No problems were experienced in the mixing cycle,
the extrusion cycle or pelletising of the pre-blend.
The pre-blend was then formulated into a propellant
grain using 50.05% by weight of the pre-blend and 49.95%
by weight of 200 micron particulate ammonium perchlorate.
Example VII
A pre-blend was formed of the following composition:
Material:Weight Charged (g)
Elvax 210 EVA 2088.17
Polybutene 6 0.00
Carbon Black 6.96
Aluminum, spherical904.87
Iron oxide 0.00
Batch Total 3000 grams
The pre-blend was blended with ammonium perchlorate,
to form propellant grain, with the resultant composition
containing 21.55% by weight of the pre-blend.
No problems were encountered in the processing of
the composition.
Example VIII
Samples similar to Sample #2 and #3 of Example I
were subjected to Martin-Marietta PEPcode analysis to
determine characteristics of the compositions as
propellants. Sample #2 is a HTPB control sample and
CA 022432~4 l998-07-l~
18
Sample #3 iS an EVA composition of the invention.
The results obtained were as follows:
Sample #2 Sample #3
Density lb/in3O. 05946 0.06017
g/cm3 1. 6457 1.6654
Specific Impulse
Frozen Flow 233.9 233.3
Shifting Flow236.3 236.6
Density Impulse
Fro~en Flow 384.9 388.5
Shifting Flow388.8 394.0
The composition of the invention showed a small
increase in density impulse indicating that the
composition is at least equivalent to a HTPB composition,
and possibly superior for some uses.
