Note: Descriptions are shown in the official language in which they were submitted.
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CAST EXPLOSIVE COMPOSITION
This invention relates to cast explosive compositions, their preparation
and use. In particular, the invention relates to polymer-bonded explosive
compositions.
Explosives compositions are generally shaped, the shape required
depending upon the purpose intended. Shaping can be by casting, pressing,
extruding or moulding; casting and pressing being the most common shaping
techniques. However, it is generally desirable to cast explosives compositions
as casting offers a greater design flexibility than pressing.
Polymer-bonded explosives (also known as plastic-bonded explosives
and PBX) are typically explosive powders bound into a polymer matrix. The
presence of the matrix modifies the physical and chemical properties of the
explosive and often facilitates the casting and curing of high melting point
explosives. Such explosives could otherwise only be cast using melt-casting
techniques. Melt casting techniques can require high processing temperatures
as they generally include a meltable binder. The higher the melting point of
this
binder, the greater the potential hazard. In addition, the matrix can be used
to
prepare polymer-bonded explosives which are less sensitive to friction, impact
and heat; for instance, an elastomeric matrix could provide these properties.
The matrix also facilitates the fabrication of explosive charges which are
less
vulnerable in terms of their response to impact, shock, thermal and other
hazardous stimuli. Alternatively, a rigid polymer matrix could allow the
resulting
polymer-bonded explosive to be shaped by machining, for instance using a
lathe, allowing the production of explosive materials with complex
configurations
where necessary.
US 6,893,516 describes an explosive mixture in which the crystalline
explosive is coated with polysiloxanes to produce a granular product. The
application of this coating to each crystal smoothes the surface of the
crystals
eliminating fine pores which could otherwise trigger unwanted reaction of the
explosive. As such, the polysiloxane coating reduces the sensitivity of the
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granular explosive, improving safety in handling and during any subsequent
shaping
steps.
Conventional casting techniques often result in a solidified composition which
retains air bubbles introduced during mixing of the material and by the
placing of the
composition into the mould. Typically such placing of the composition into the
mould
will be by pouring of the composition. These voids can reduce the performance
of the
composition as less explosive is present per unit volume. In addition,
porosity or
voids, where present in sufficient quantity, can affect the shock sensitivity
of the
composition, making the composition less stable to impact or ignition from a
shock
wave.
The invention seeks to provide a cast explosive composition in which the
stability of the composition is improved, this may be through the reduction of
the
number and/or total volume of voids, or through other means, such as a
reduction in
the number of volatile components present. Such a composition would not only
offer
improved stability, but also a reduced sensitivity to factors such as
friction, impact
and heat. Thus, the risk of inadvertent initiation of the explosive is
diminished.
In one aspect of the invention there is provided a cast explosive composition
comprising a polymer-bonded explosive and a defoaming agent. Another aspect
relates to a cast explosive composition, comprising a polymer-bonded explosive
and 0.1-2 wt% of a defoaming agent which is silicone-free, and wherein the
polymer-bonded explosive comprises an explosive and a polymer binder.
The presence of the defoaming agent may reduce or substantially eliminate
the voids which would often remain in the composition. Accordingly, where used
herein the term "defoaming agent" is intended to mean an additive with surface
active
properties which acts to eliminate voids from within the polymeric binder of
the cast
explosive composition. Any additive which does not perform this function is
not
regarded as constituting a defoaming agent within the meaning of the
invention. In
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the art, such additives are also known as "anti-foaming agents", "deaerating
agents"
and "air release agents".
The voids are typically found within the body of the binder component of the
polymer-bonded explosive, rather than at the interface between the binder and
the
explosive component. Removal of these voids is particularly desirable where
the
intended use of the explosive will result in exposure to high g-forces, such
as would
be the case in an artillery shell, mortar bomb or missile. It is believed that
under such
conditions, adiabatic compression of the voids occurs making the region around
the
void more prone to premature ignition. Another application where the removal
of
voids is of particular importance is where the intended use of the explosive
will result
in rapid deceleration on impact with a target but where penetration of the
target is
required before the munition is detonated. This would be the case with bombs
and
missiles. Where voids are present, adiabatic compression of these may result
in
ignition on impact, before penetration of the target has occurred. In
addition, the
defoaming agent reduces the viscosity of the composition, allowing the casting
process to be carried out more rapidly than in the absence of this additive.
Further,
compositions containing the defoaming agent have been seen in some instances
to
have a higher density in terms of cY0TMD achieved than when this additive is
absent.
This increase in density has also been linked to an improved stability and
reduction in
sensitivity of the explosive. In many cases, the reduction of voids will
correlate with
an increase in density; however as the compositions of the invention are
complex, an
increase in density can only be taken as an indication that the number of
voids has
been reduced. In many instances other methods, such as X-radiography are used
to
directly visualise the voids and to determine the effect of the defoaming
agent.
In an additional aspect of the invention there is provided a process for
reducing the number and/or total volume of voids in a cast explosive
composition
comprising the steps of:
combining a polymer-bonded explosive and a defoaming agent;
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and
casting the explosive composition.
Another aspect relates to a process for reducing the number or total volume of
voids in a cast explosive composition, comprising the steps of: combining a
polymer-
bonded explosive and 0.1-2 wt% of a defoaming agent which is silicone-free;
and
casting the explosive composition, and wherein the polymer-bonded explosive
comprises an explosive and a polymer binder.
Another aspect of the invention relates to the use of a cast explosive
composition as described herein in an explosive product, and a further aspect
of the
invention relates to an explosive product comprising a cast explosive
composition as
described herein.
Another aspect relates to use of 0.1-2 wt% of a defoaming agent which is
silicone-free for reducing the number or total volume of voids in a cast
explosive
composition also comprising a polymer-bonded explosive, and wherein the
polymer-bonded explosive comprises an explosive and a polymer binder.
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Polymer-bonded explosives include a polymeric binder which forms a
matrix bonding explosive particles within. The binder thus may be selected
from a wide range of polymers, depending upon the application in which the
explosive will be used. However, in general at least a portion of the binder
will
be selected from polyurethane, cellulosic materials such as cellulose acetate,
polyesters, polybutadienes, polyethylenes, polyisobutylenes, PVA, chlorinated
rubber, epoxy resins, two-pack polyurethane systems, alkyd/melanine, vinyl
resins, alkyds, self-crosslinking acrylates, thermoplastic elastomers such as
butadiene-styrene block copolymers, and blends, copolymers and/or
combinations thereof. Energetic polymers may also be used either alone or in
combination, these include polyNIMMO (poly(3-nitratomethy1-3-methyloxetane),
polyGLYN (poly glycidyl nitrate) and GAP (glycidyl azide polymer). It is
preferred that the binder component be entirely selected from the list of
binders
above either alone or in combination. In some embodiments the binder will
comprise at least partly polyurethane, often the binder will comprise 50 - 100
wt% polyurethane, in some instances, 80 - 100 wt%. In some embodiments the
binder will consist of polyurethane. Polyurethanes derived from MDI (methylene
diphenyl diisocyanate) and TDI (toluene diisocyanate) and IPDI (isophorone
diisocyanate) may be used. IPDI is generally preferred as it is a liquid and
hence easy to dispense; it is relatively slow to react, providing a long pot-
life
and slower temperature changes during reaction; and it has a relatively low
toxicity compared to most other isocyanates. It is also preferred that, where
the
binder comprises polyurethane, the polyurethane binder includes a
hydroxyterminated polybutadiene.
The explosive component of the polymer-bonded explosive may, in
certain embodiments, comprise one or more heteroalicyclic nitramine
compounds. Nitramine compounds are those containing at least one N-NO2
group. Heteroalicyclic nitramines bear a ring containing N-NO2 groups. Such
ring or rings may contain for example from two to ten carbon atoms and from
two to ten ring nitrogen atoms. Examples of preferred heteroalicyclic
nitramines
are RDX (cyclo-1,2,3-trimethylene-2,4,6-trinitramine, Hexogen), HMX (cyclo-
1,3,5,7-tetramethylene-2,4,6,8-tetranitramine, Octogen), and mixtures thereof.
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The explosive component may additionally or alternatively be selected from
TATND (tetranitro-tetraminodecalin), HNS (hexanitrostilbene), TATB
(triaminotrinitrobenzene), NTO (3-nitro-1,2,4-triazol-5-one),
HNIW
(2,4,6,8,10,12-hexanitrohexaazaisowurtzitane), GUDN (guanyldylurea dinitride),
FOX-7 (1,1-diamino-2, 2-dinitroethene), and combinations thereof.
Other highly energetic materials may be used in place of or in addition to
the compounds specified above. Examples of other suitable known highly
energetic materials include picrite (nitroguanidine), aromatic nitramines such
as
tetryl, ethylene dinitramine, and nitrate esters such as nitroglycerine
(glycerol
trinitrate), butane triol trinitrate or pentaerythritol tetranitrate, DNAN
(dinitroanisole), trinitrotoluene (TNT), inorganic oxidisers such as ammonium
salts, for instance, ammonium nitrate, ammonium dinitramide (ADN) or
ammonium perchlorate, and energetic alkali metal and alkaline earth metal
salts.
The explosive component of the polymer-bonded explosive may be in
admixture with a metal powder which may function as a fuel or which may be
included to achieve a specific terminal effect. The metal powder may be
selected from a wide range of metals including aluminium, magnesium,
tungsten, alloys of these metals and combinations thereof. Often the fuel will
be
aluminium or an alloy thereof; often the fuel will be aluminium powder.
In some embodiments, the polymer-bonded explosive comprises RDX.
The polymer-bonded explosive may comprise RDX as the only explosive
component, or in combination with a secondary explosive component, such as
HMX. Preferably, RDX comprises 50 - 100 wt% of the explosive component.
In many cases the binder will be present in the range about 5 - 20 wt% of
the polymer-bonded explosive, often about 5 - 15 wt%, or about 8 - 12 wt%.
The polymer-bonded explosive may comprise about 88 wt% RDX and about 12
wt% polyurethane binder. However, the relative levels of RDX to polyurethane
binder may be in the range about 75 - 95 wt% RDX and 5 - 25 wt%
polyurethane binder. Polymer-bonded explosives of this composition are
commercially available, for example, Rowanex 11001-m.
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Many defoaming agents are known and in general any defoaming agent
or combination thereof which does not chemically react with the explosive may
be used. However, often the defoaming agent will be a polysiloxane. In many
embodiments, the polysiloxane is selected from polyalkyl siloxanes,
polyalkylaryl siloxanes, polyether siloxane co-polyrners; and combinations
thereof. It is often preferred that the polysiloxane be a polyalkylsiloxane;
polydimethylsiloxane may typically be used. Alternatively, the defoaming agent
may be a combination of silicone-free surface active polymers, or a
combination
of these with a polysiloxane. Such silicone-free polymers include alkoxylated
= 10 alcohols, triisobutyl phosphate, and fumed silica. Commercially
available
products which may be used include, BYK 088, BYK A500, BYK 066N and BYK
= A535 each available from BYK Additives and Instruments, a subdivision of
Altana; TEGO MR2132 available from Evonik; and BASF SD23 and SD40, both
available from BASF. Of these, BYK A535 and TEGO MR2132 are often used
as they are solventless products with good void reduction properties.
= The defoaming agent may be added to the composition in a solvent
carrier. However, it is generally preferred that solvents be absent. It has
been
found that the use of defoaming agents which are not carried in a solvent, or
even the use of entirely solventless systems, is advantageous as there are
fewer (or substantially no) volatile components =present during processing of
the
s = .
composition, reducing the safety precautions and/or plant modifications
needed.
Further, the exclusion of solvents eliminates the risk of residual volatiles
separating (for instance by evaporation or leaking) from the composition
during
storage resulting in unpredictable modifications of the properties of the
compositions such as the creation of voids as a result of volatile
evaporation.
Often the defoaming agent is present in the range about 0.01 ¨ 2 wt%, e.g. 0.1
--
2 wt% in some instances about 0.03 ¨ 1.5 wt%, often about 0.05 ¨ 1 wt%, in
many cases
= about 0.25 or 0.5 - 1 wt%. At levels below this (i.e. below 0.01 wt%)
there is
= often insufficient defoaming agent in the composition to significantly
alter the
properties of the polymer-bonded explosive, whereas above this level (i.e.
above 2 wt%) the viscosity of the cast solution may be so low that the
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composition becomes inhomogeneous as a result of sedimentation and
segregation processes occurring within the mixture.
Without being bound by theory, it is believed that the defoaming agent
not only acts to reduce viscosity, facilitating the casting process and the
egress
of voids from the composition during casting, but that the defoaming agents
are
surface active at the void-composition interfaces, causing the void bubbles to
coalesce and hence be expelled from the composition as a result of the greater
buoyancy of the larger bubbles produced. This results in compositions with
fewer visible voids, which are more stable than known explosive compositions.
The explosive composition may include a solvent, any solvent in which at
least one of the components is soluble and which does not adversely affect the
safety of the final product may be used, as would be understood by the person
skilled in the art. However, it is preferred, for the reasons described above,
that
in some embodiments that solvent be absent.
Where present, the solvent may be added as a carrier for the defoaming
agent or another component of the composition. The solvent will typically be
removed from the explosive composition during the casting process, however
some solvent residue may remain due to imperfections in the processing
techniques or where it becomes uneconomical to remove the remaining solvent
from the composition. Accordingly, in some embodiments the polymer-bonded
explosive and the defoaming agent are combined in the presence of a solvent.
Often the solvent will be selected from diisobutylketone, polypropylene
glycol,
isoparaffins, propylene glycol, cyclohexanone, butyl glycol, ethylhexanol,
white
spirit, isoparaffins, xylene, methoxypropylacetate, butylacetate, naphthenes,
glycolic acid butyl ester, alkyl benzenes and combinations thereof. In some
instances, the solvent is selected from diisobutylketone, polypropylene
glycol,
isoparaffins, propylene glycol, isoparaffins, and combinations thereof.
Although melt casting processes are compatible with the invention,
typically the inventive composition will be cast using "cast and curing"
techniques. Accordingly, where the components of the cast explosive
composition are not inherently curable (for instance, where all polymer
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components are thermoplastic polymers) a curative may optionally be present.
In many embodiments the casting technique used is vacuum casting as the
resulting product is generally of greater density and no visible voids
compared
with the equivalent air-cast product. In general, the curing step will take
place
after the casting step has occurred.
The composition may also contain minor amounts of other additives
commonly used in explosives compositions. Examples of these include
microcrystalline wax, energetic plasticisers, non-energetic plasticisers, anti-
oxidants, catalysts, curing agents, metallic fuels, coupling agents,
surfactants,
dyes and combinations thereof. Energetic plasticisers may be selected from
eutectic mixtures of alkylnitrobenzenes (such as dinitro- and trinitro-ethyl
benzene), alkyl derivatives of linear nitramines (such as an N-alkyl
nitratoethyl-
nitramine, for instance butyl-NENA), and glycidyl azide digomers.
Casting the explosive composition offers a greater flexibility of process
design than can be obtained with pressing techniques. This is because the
casting of different shapes can be facilitated through the simple substitution
of
one casting mould for another. In other words, the casting process is
backwards-compatible with earlier processing apparatus. Conversely, where a
change of product shape is required using pressing techniques, it is typically
necessary to redesign a substantial portion of the production apparatus for
compatibility with the mould, or the munition to be filled, leading to time
and
costs penalties. Further, casting techniques are less limited by size than
pressing techniques which depend upon the transmission of pressure through
the moulding powder to cause compaction. This pressure falls off rapidly with
distance, making homogeneous charges with large length to diameter ratios
(such as many shell fillings) more difficult to manufacture.
In addition, the casting process of the invention offers a moulded product
(the cast explosive compositions described) with a reliably uniform fill
regardless of the shape required by the casting. This may be partly attributed
to
the use of a casting technique, and partly to the presence of the defoaming
agent. The defoaming agent substantially reduces the number of voids within
the binder and hence the cast explosive composition. In some instances, the
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voids are substantially eliminated. Casting can occur in situ with the housing
(such as a munition) to be filled acting as the mould; or the composition can
be
moulded and transferred into a housing in a separate step. Often casting will
occur in situ.
Further, compositions including polymer-bonded explosives and
hydroxyterminated polybutadiene binders in particular, are more elastomeric
when cast than when pressed. This makes them less prone to undergoing a
deflagration-to-detonation transition when exposed to accidental stimuli.
Instead, such systems burn without detonating, making them safer to use than
1 o pressed systems.
Additionally, the shapes that pressing processes can be reliably applied
to are more limited. For instance, it is often a problem achieving a complete
fill
of a conical shape using pressing techniques as air is often trapped at or
towards the tip of the cone. Casting processes, being intrinsically "fluid"
processes, are not limited in this way.
The process of the invention may be a continuous or batch process as
appropriate. Many known casting processes will be compatible for use with the
invention as modification of these processes to allow for the addition of the
defoaming agent to the polymer-bonded explosive and to allow the defoaming
agent to perform its defoaming function during casting, is within the
capabilities
of the person skilled in the art. Where a continuous process is used this may
make use of static mixing technology such as the technology described in EP
1485669.
The process may utilise a premix or precure as a starting material,
although these are not essential. A premix will typically be a mixture of an
explosive component and a binder component, usually a plasticiser. In some
instances the explosive component is desensitized with water prior to
formation
of the premix, a process known as wetting or phlegmatization. However, as
retention of water within the premix is generally undesirable it will
typically be
removed from the premix prior to further processing, for instance by heating
during the mixing of the explosive component and the plasticiser.
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In some cases the plasticiser will be absent; however the plasticiser will
typically be present in the range 0 - 10 wt% of the plasticiser and explosive
premix, often in the range 0.01 - 8 wt%, on occasion 0.5 - 7 wt% or 4 - 6 wt%.
The plasticiser will often be a non-energetic plasticiser, many are known in
the
art; however energetic plasticisers may also be used in some instances. A
precure will typically be a combination of the premix and the other components
of the composition with the exception of the catalyst and the curing agent. In
some instances the defoaming agent will also be absent from the precure.
The cast explosive composition of the invention has utility both as a main
charge or a booster charge in an explosive product. Often the composition will
be the main charge. The composition of the invention may be used in any
"energetic" application where the presence of voids causes safety or
functional
problems. Such uses include mortar bombs and artillery shells as discussed
above. Additionally, the inventive composition may be used to prepare
explosives for gun-launch applications, explosive filings for bombs and
warheads, propellants, including composite propellants, base bleed
compositions, gun propellants and gas generators.
Except in the examples, or where otherwise explicitly indicated, all
numbers in this description indicating amounts of material or conditions of
reaction, physical properties of materials and/or use are to be understood as
modified by the word "about." All amounts are by weight of the final
composition, unless otherwise specified.
Further, the cast explosive
composition may comprise, consist essentially of, or consist of any of the
possible combinations of components described above and in the claims except
for where otherwise specifically indicated. The process for reducing the voids
in
the composition may comprise, consist essentially of, or consist of the steps
specified above and in the claims.
The following non-limiting examples illustrate the invention.
Examples
Example 1
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A series of commercially available defoaming agents were cast and
cured with Rowanex 1100 (88 wt% RDX and 12 wt% polyurethane agent).
Curing occurred over 5 days at 65 C. 105mm and 155mm shells prepared
using the resulting composition were found to have no detectable voids, and no
adverse effect on the chemical or mechanical properties of the polymer-bonded
explosive were observed. Table 1 below illustrates the effect of binder type
and
level on the viscosity and density of the composition.
TABLE 1
1. Defoaming Agent* Dosage Viscosity Density -
Density - % TMEP
(wt%) (cps)# Vacuum Air Cast
(air cast)
Cast (g/cm3)
(g/cm3)
No Additive 0.12 1.608 1.608 99.3
Solution of foam-destroying 1.0 0.035 1.608 1.602 99.6
polymers and polysiloxanes
in isoparaffin solvent (BYK
088)
Solution of silicone-free 1.0 0.033 1.612 1.606 99.9
foam-destroying polymers in
Alkylbenzene/
methoxypropylacetate 12/1
(BYK A500)
Solution of foam-destroying 0.1 0.12 1.614 1.619 99.6
polysiloxanes in
diisobutylketone (BYK
066N)
Solution of foam-destroying 0.5 0.063 1.618 1.608 99.6
polysiloxanes in
diisobutylketone (BYK
066N)
Solution of foam-destroying 1.0 0.04 1.620 1.605 99.8
polysiloxanes in
diisobutylketone (BYK
066N)
Solvent free mixture of 0.1 0.076 1.6 1.6 98.9
foam-destroying polymers
silicone free (BYK A535)
Solvent free mixture of 0.5 0.07 1.612 1.608 99.6
foam-destroying polymers
silicone free (BYK A535)
Solvent free mixture of 1.0 0.034 1.59 1.597 99.3
foam-destroying polymers
silicone free (BYK A535)
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Concentrate based on 0.1 0.12 1.605 1.622
100
organosiloxanes plus fumed
silica (TEGO MR2132)
Concentrate based on 0.5 0.073 1.613 1.609
99.7
organosiloxanes plus fumed
silica (TEGO MR2132)
Concentrate based on 1.0 0.047 1.594 1.561
97.1
organosiloxanes plus fumed
silica (TEGO MR2132)
Solvent free, silicone free 0.1 0.133 1.611 1.612
99.6
alkoxylated alcohol (BASF
SD23)
Solvent free, silicone free 0.5 0.09 1.597 1.597
98.9
alkoxylated alcohol (BASF
SD23)
Solvent free, silicone free 1.0 0.28 1.623 1.623
100
alkoxylated alcohol (BASF
SD23)
Solvent free, silicone free 0.1 0.08 1.609 1.610
99.5
triisobutyl phosphate (BASF
SD40)
Solvent free, silicone free 0.5 0.06 1.598 1.603
99.3
triisobutyl phosphate (BASF
SD40)
Solvent free, silicone free 1.0 0.07 1.596 1.598
99.4
triisobutyl phosphate (BASF
SD40)
Dibutylketone only 1.0 1.599 1.598
99.4
Dibutylketone only 0.5 1.597 1.602
99.2
defoaming agents were procured from BYK Additives and Instruments, a
subdivision of
Altana; Evonik or BASF
Viscosity determined at 60 C
TMD is the Theoretical Maximum Density of the composition calculated to allow
for the
intrinsic density lowering effect arising when additives are added. The TMD is
the sum
of the relative volume of each component as determined from their relative
mass within
the composition and known density. As a result, the TMD gives a true
indication of the
density modification arising as a result of a change in the number of voids.
As can be seen, the presence of each of the defoaming agents at levels
above 0.1 wt% reduces the viscosity of the composition making it easier to
cast.
Further, as the level of defoaming agent is increased to 1.0 wt%, the
viscosity of
the composition is further reduced.
The presence of defoaming agent also increases the density, providing
an indicator that the number of voids has been reduced. Calculation of the
TMD provides a further indicator, as an increase in the TMD relative to that
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obtained where no additive is present shows that the number of voids in the
sample has been reduced relative to the additive free composition.
It is clear that it is the defoaming agent having a density increasing effect
as the addition of dibutylketone only (i.e. solvent only), reduces the density
of
the composition whether prepared by a vacuum or an air casting technique.
The data above shows that vacuum casting generally produces
compositions of a higher relative density than air casting techniques where
defoaming agents are present. Further, vacuum casting techniques generally
have a more marked effect upon the density of compositions containing
defoaming agents when compared to additive free or solvent only compositions.
However, even where air casting techniques are used, it is clear that the
defoaming agents are acting to reduce the number of voids in the compositions
tested as each defoaming agent provides a composition which is either of
higher density, or has a higher TMD, than the control compositions including
either no additive, or solvent only.
Example 2
The compatibility of the defoaming agents with the Rowanex 1100 was
also tested, and the results set out in Table 2 below.
TABLE 2
1. Defoaming Agent Compatibility
BYK 066N- Pass
Solution of foam-destroying polysilones in Pass
propylene glycol (BYK 088A)
BYK 088- Pass
BYK A500- Pass
BYK A535- Pass
TEGO MR21324 Pass
BASF SD23 Pass
BASF SD40 Pass
* Procured from BYK Additives and Instruments, a subdivision of Altana
# Procured from Evonik
Procured from BASF
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Compatibility was measured following STANAG 4147 Test 1: Procedure
B, at a temperature of 100 C for 40 hours. All of the defoaming agents tested
were found to meet the requirements of this test, and hence to be compatible
with the Rowanex 1100 PBX product, as illustrated by the results in the table
above which indicate that each of the materials tested evolved less than 1
ml/g
of gas for a 5g sample. No adverse reaction was observed with any of the
defoaming agents, although a particularly good compatibility was observed
between Rowanex 1100 and BYK A535. Indeed, the use of BYK A535, a
solventless defoaming agent, has been found to provide a particularly stable
product with acceptable activity in terms of void removal.
Example 3
The sensitivity of the Rowanex 1100 and defoaming agent mixtures was
tested for sensitivity to mechanical impact (Rotter Impact) to determine the
relative hazard associated with using the mixture as opposed to the pure PBX
product. The results are set out in Table 3.
TABLE 3
1. Additive Concentration (wt%) F of I
None 100
BYK 088 1 130
BYK A500 1 130
BYK 066N 1 130
BYK A535 0.5 102
TEGO MR2132 1 109
BASF SD23 1 112
BASF SD40 1 121
The test determines the 50% drop height for the test sample. This
examines the whole probability of ignition versus stimulus-level relationship.
Seven test heights equally spaced on a logarithmic scale are chosen and caps
are tested to see if ignitions take place. Results are expressed in terms of
Figures of Insensitiveness (F of l) relative to standard RDX. All tests are
carried
out on samples of ground up material. The Rotter Impact Test method was
used to determine the F of I using an LSM Rotter machine.
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The F of l value for all of the Rowanex 1100/defoaming agent samples
was found to be greater than or equal to the F of l value for Rowanex 1100
alone. This indicated that the presence of the defoaming agent has no adverse
effect on the sensitivity of the PBX to mechanical impact and that as a result
the
combination products are no more hazardous, and in some cases less
hazardous, to use than Rowanex 1100 alone. Without being bound by theory,
this may be due to the marginal increase in binder, and resultant reduction in
nitramine content because of the presence of the defoaming agent. It is
further
indicated that the Rowanex 1100/defoaming agent samples are likely to be no
more sensitive to ignition than untreated Rowanex 1100.
Example 4
A series of compositions including RDX were prepared, three of these
compositions included defoaming agents.
TABLE 4: Examples of Polymer-bonded Explosive (PBX) Compositions
containing Defoaming Agents
Abbreviation Full name Function PBX
with PBX with PBX with
0.1% BYK- 0.5% BYK- 1% BYK-
PBX
A500 A535 066N
(wt /o) Defoamer Defoamer Defoamer
(wt (wt%) (wt%
DOA Dioctyl Adipate Plasticiser 7.00
6.99 6.96 6.93
Hydroxyterminated Pre-
HTPB Polybutadiene polymer 4.28 4.28 4.26 4.24
Lecithin Surfactant
0.30 0.30 0.30 0.30
2,2'-methylenebis- Anti-
(4-methyl-6- oxidant
A02246 tertiary- 0.10 0.10 0.10
0.10
butylphenol)
lsophorone Curing
IPDI Diisocyanate
Agent 0.42 0.42 0.42 0.42
DBTDL dibutyltin dilaurate Catalyst
0.05 0.05 0.05 0.05
Additive
0.00 0.10 0.50 1.00
RDX* Hexogen Explosive Qs
QS QS QS
Filler
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I l l I I I I I
. May be present as pure RDX or combined with a plasticiser, for
instance in the ratio
94:6 RDX:plasticiser.
The compositions were prepared using cast and curing processes as
described in Example 1 and no voids were detected. No adverse effect on
chemical and mechanical properties was observed relative to the defoaming
agent free RDX composition.
Example 5
The following example illustrates a method of preparing PBX
compositions of the invention, such as the compositions of Example 4, using a
premix. The techniques used would be well known to the person skilled in the
art.
A water-jacketed, vertical mixer fitted with a rotating stirrer blade was
used for the preparation of the composition. All mixing was carried out under
vacuum at a pressure of less than 10 mm Hg. The compositions of this
example were prepared on a 5 Kg scale using the relative proportions of
components set out in Example 4 above.
The premix was prepared from RDX desensitised with water. The water
was then driven off using techniques common in the art. The desensitised RDX
(94 wt%) was then mixed with DOA plasticiser (6 wt%) to form the premix.
The mixer was preheated to 60 2 C and the following ingredients
weighed into the mixer in sequential order in relative amounts as described in
Example 2 above:
1. HTPB
2. DOA
3. Lecithin
4. A02246
5. Premix (first quarter portion, i.e. 25 wt% of total premix to be
added)
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The composition was mixed for 15 minutes. The second, third and final
quarter portions of premix were then added with 10 minutes of mixing between
each addition and after the final addition. The mixer blades and bowl were
scraped down to ensure that any unmixed material was transferred to the
mixing zone of the bowl and the composition mixed for a further 60 minutes.
Defoaming agent was then added and the composition mixed until the
maximum reduction in viscosity upon addition of the defoaming agent to the
composition was observed. In this case mixing was for 25 minutes and
viscosity reduction was measured using a torque meter fixed to the mixer, when
the torque required to complete the mixing stabilised at a lower level than
before the addition of the defoaming agent, the maximum reduction in viscosity
is regarded as having been observed.
The DBTL was added and the composition mixed for 15 minutes, then
the IPDI added and the composition mixed for a further 15 minutes. After
mixing the viscosity of the composition was recorded using a Brookfield
viscometer (60 C).
The composition was cast and any excess mixture removed from the
shell housings. The shells were placed onto a vibrating table and allowed to
vibrate for 5 minutes. The charges were cured for 5 days at 65 2 C.
Example 6
The following example illustrates a method of preparing PBX
compositions of the invention, such as the compositions of Example 4, from a
precure. The techniques used would be well known to the person skilled in the
art.
Mixing conditions were as for Example 5. The precure was prepared
from the premix described in Example 5 above. To this premix was added all of
the components of the composition of Example 5 except for the defoaming
agent, catalyst and curing agent.
The mixer was preheated to 60 2 C and the components of the precure
added and heated for 15 minutes. The precure was then mixed for 30 minutes
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and the mixer blades and bowl scraped to ensure that any unmixed material
was transferred to the mixing zone of the bowl. Defoaming agent was added
and the composition mixed until the viscosity reducing effect of the defoaming
agent is observed, this was measured as described in Example 5 and in this
example required stirring for 25 minutes. The DBTL was added and the
composition mixed for 15 minutes, then the IPDI added and the composition
mixed for a further 15 minutes. The mixer blades and bowl were scraped to
ensure that any unmixed material was transferred to the mixing zone of the
bowl. After mixing the viscosity of the composition was recorded using a
Brookfield viscometer (60 C).
The composition was cast and any excess mixture removed from the
shell housings. The charges were cured for 5 days at 65 2 C.
It should be appreciated that the compositions of the invention are
capable of being incorporated in the form of a variety of embodiments, only a
few of which have been illustrated and described above.
