Title of Invention

"A PROCESS FOR THE PREPARATION OF AN INHIBITOR COMPOSITION FOR ROCKET PROPELLANTS"

Abstract This invention relates to a process for the preparation of an inhibitor composition for rocket propellants comprising the steps of heating the mixture of 75 to 85% hydroxyl poly butadiene binder, 5 to 15% of Polyphosphate ester prepolymer and 2 to 10% of dioctyl adipate, dissolving 0.4 to 0.6% by wt. of pyrogallol and 0.05 to 0.15% of ferric acetyl acetonate in the mixture of step (a), adding 15-25% carbon-black with continuous stirring and deaerating the mixture under vacuum, mixing 6 to 10% curative isophorone di-isocynate to the mixture of step (c) and deaerating again, casting the mixture into sheets and curing.
Full Text FIELD OF THE INVENTION
This invention relates to a process for the preparation of an inhibitor composition for rocket propellants, wherein the composition incorporates a reactive dual purpose additive which is flame retardant as well as adhesive, and has improved mechanical properties.
PRIOR ART
Inhibition of rocket propellants is required to control the burning patterns. For this purpose, the inhibitor material is required to be made non-combustible and to be possessing good adhesion to various surfaces like that of the propellant or insulator on the rocket motor. In big motors a liner material is applied between the insulator of the rocket motor and the inhibitor, for better bonding between the two. To achieve flame retardancy and adhesion, flame retardants and adhesives are added as disparate additive in the inhibitor/liner mix before curing it into an elastomeric matrix.
The inhibitor formulations known in the art use solid additives like Sb2O3 , asbestos or tricresyl phosphate (flame retardant).
The disadvantage of inhibitor formulations using above solid additives is that they are heterogeneous with the binder material of the inhibitor/liner as they are insoluble and unreactive solids.

Another disadvantage of the inhibitor formulation based
on above additives is that these formulations have poor bonding
leading to debonding at interfaces.
Yet another disadvantage of inhibitor formulations
ufcing above solid additives is that in these formulations, after
ageing, boundary separation and settling of solids take place
making the formulation as non-uniform.
Still another disadvantage of inhibitor formulations
using above solid additives is that they have poor mechanical
praparti es.
Further advantage of inhibitor formulations using above
solid additives is that non-uniformity of these formulations,
particularly after ageing, leads to inferior performances and
even catastrophes due to failure of inhibition resulting from
uncontrolled burning of the propellant.
Other inhibition formulations known in the art are
cellulose acetate/ethyl cellulose and Polyester resin for
nitramine based propel 1 ants.
The disadvantage of these inhibition formulation is
that they are very stiff as their strength is very high as
compared to nitramine based propellant and as a result of this
the inhibitor propellant interface bonding is adversely affected
during thermal cycling or storage of the propellant.
Another inhibition formulation for nitramine
propellents known in the art is styrene butadiene.
The disadvantage of using styrene batadiene as
inhibition formulation is that it utilises asbestor which is
highly toxic and as banned in many countries.
Another disadvantage of using styrene butadiene as
inhibition formulation is that it is very stif
OBJECTS OF THE INVENTION
The primary object of the present invention is to
propose an inhibition composition for rocket propellants and a
process for preparation thereof.
Another object of the present invention is to propose
an inhibition composition which is homogeneous with the HTPB
matrix of inhibitor/liner.
Yet another- object of the present invention is to
propose an inhibition composition which uses a reactive dual
purpose additive which acts both as a flame retardant as well as
aclhesi ve.
Still another object of the present invention is to
propose an inhibition composition which remains unaffected during
ageing of the propellant.
4 -
Further object of the present invention is to propose
an inhibition composition which possesses high bond-strength of
:i. nhita i tor-prope 11 ant interface .
Yet further object of the present invention is to
propose an inhibition composition whose mechanical properties are
higher as compared to that of the propellent.
Still further object of the present invention is to
propose an inhibition compositon which results in minimum
migration of plasticiser (nitroglycerine) towards the interface
over a period of time, thereby maintaining the performance of the
props 11 an t,
Other object of the present invention is to propose an
inhibition composition which has higher pot life thereby
improving the processabi1ity and facilitating the application of
inhibitor formulation to the propellant.
Yet other object of the present invention is to propose
sn inhibition composition of which the inhibi tor-prope 1.1. ant bond
is not adversely affected during thermal cycling over a wide
oo
range of temperature from 30 to 55 C.
Further other object of the present invention is to
propose an inhibition composition possessing a glass transition
temperature (T ) lower than the lower limit of propellant
9
operation temperature.
__ K~
ABSTRACT OF INVENTION
The present invention provides an inhibitor composition
containing a dual purpose additive which can act both as a flame
retardant and adhesive for hydroxyl terminated polybutacli ene
(HTPB) based inhibitor/liner for rocket propellant. The additive
also is hydroxyl terminated and, therefore, on curing with a
diisocynate gets cross-linked with the HTPB matrix of the
inhibitor/ 1iner , thereby eliminating the disadvantages of using
heterogeneous additives like Sb0 . The new cured formulation
: 2 3
shows significantly better mechanical properties and flame
retardancy as compared to the formulations known in the art
containing Sta0 . The new cured formulation also shows adequate
2 3
adhesive properties. Both the properties are achieved by the use
of the dual purpose additive, which is polyphosphate ester
ip repo 1 yme r (PEP ) .
STATEMENT OF INVENTION
According to this invention there is provided to a process for the preparation of an inhibitor composition for rocket propellants comprising the steps of:
(a) heating the mixture of 75 to 85% hydroxyl poly butadiene binder, 5 to 15% of Polyphosphate ester prepolymer and 2 to 10% of dioctyl adipate,
(b) dissolving 0.4 to 0.6% by wt. of pyrogallol and 0.05 to 0.15% of ferric acetyl acetonate in the mixture of step (a),
(c) adding 15-25% carbon-black with continuous stirring and deaerating the mixture under vacuum,
(d) mixing 6 to 10% curative isophorone di-isocynate to the mixture of step (c) and deaerating again,
(e) casting the mixture into sheets and curing.
The present invention provides an inhibitor composition containing a dual purpose additive which can act both as a flame retardant and adhesive for hydroxyl terminated polybutadiene (HTPB) based inhibitor/liner for rocket propellant. The additive also is hydroxyl terminated and, therefore, on curing with a di-isocynate gets cross-linked with the HTPB matrix of the inhibitor/liner, thereby eliminating the disadvantages of using heterogeneous additives like Sb2O3. The new cured formulation shows significantly better mechanical properties and flame retardancy as compared to the formulations known in the art containing Sb2O3. The new cured formulation also shows adequate adhesive properties. Both the properties are achieved by the use of the dual purpose additive, which is polyphosphate ester prepolymer (PEP).

DESCRIPTION OF THE INVENTION
In accordance with this invention a mixture is prepared containing hydroxyl terminated poly butadiene (HTPB) binder is taken in 75 to 85% preferably 78 to 82% by weight, with 5 to 15% preferably 8 to 10% by weight of polyphosphate ester prepolymer (PEP) and 2 to 10% preferably 4 to 6% of dioctyl adipate. The mixture prepared is mixed using a mechanical stirrer and heating to around 60°C in an oven for around 30 minute till PEP is dissolved completely. To such a mixture is added 0.2 to 1.2% preferably 0.4 to 0.6% by weight of pyroggallol, 0.05 to 0.15% preferably 0.075 to 0.125% of ferric acetyl acetonate, which is mixed till pyrogallol and FeAA dissolved completely. Upon pyrogallol and FeAA being dissolved, 15 to 25% preferably 18 to 22% of C black is added in small increments with continuous stirring for about 5 minute to ensure uniform mixing. The mixture is deaerated for about 30 minutes in vacuum (
to the numerical values is only by way of an
advantageous example.
This invention will now be illustrated with a working
example which is intended to be a typical example to illustrate
the working of the present invention and is not intended to be
taken restrictedly to imply any limitation to the scope of the
press n t i n v e n t i on .
:WQRKI.NG EXAMPLJE
To 58 g of HTPB, taken in a 1 litre glass beaker, was
added 10 g of PEP and 5g of dioctyl adipate and mixed well using
o
a mechanical stirrer. The mixture was heated to 60 C in an oven
till PEP dissolved completely (~30 minute). 0.5 g of pyrogallol
and 0.08g of FeFF were added to the HPTB matrix and mixed well
ensuring completely dissolution of pyrogallol and FeAA. Further
18g of C-black was added in small increments with continuous
stirring (^5 minute) to ensure uniform mixing. The mixgture was
deaerated for 30 minutes in vacuum «5 mm of Hg). Finally 9 g of
1'PDI was added, mixed well and again deaerated for 10 minutes.
The mix was cast into sheets of uniform thickness (2.5 to 3.0
o
mm). The sheets were cured at 45 C for 8 days and evaluated for
mechanical, thermal and ainterface properties.
The same formulation was used for inhibition of
propellent by bottom casting technique using requisite moulds.
The inhibitor was cured, extracted and statically evaluated.
8 -
OF RESULTS:....
The result® of the evaluation of the PEP containing
formulation is summarised in the table below, along with
comparative data of the control formulation and that coritianing
Sb 0 .
'•• 2 3
FORMULATION TENSILE STRENGTH ELONGATION L01
2
(KG/CM ) Control 8.2 100 16
CHTPB+C black)
Control + Sb 0 13 70 IS
Control +• PEP 33 103 19
As the above table shows that the inhibitor formulation
of present invention incorporating PEP, has significantly highertensile
strength as compared to the control as well as the Sb 0
2 3
containing formulation thus making the cured composition tougher
and matching in tensile strength with the propellent. This makes
the bond between the propellent and inhibitor better and there is
less chance of debonding under conditions of stress. The */.
Elongation of the cured sheet is more or less the same as that of
the control but better than the Sb 0 containing formulation.
/™ -T. 2 &
This means that on PEP incorporation, tougher but flexible sheets
are obtained. The I...OI which is a measure of flame retardancy is
the highest in the case of the PEP containing sheet.
Characteristics of new formulations-
1. Tensile Strength, kg /cm ; 30 •- 35
f
2. P e re en t ag e e 1 ong a t i on : 90 ••- 110
3. Shore hardness, A 5 58 - 60
4. Plasticizer migration V, : 2 - 3
2
5. Bond strength, kg/cm : 8 - 10
o
6. Glass transition temp. C : - 75
o
7. Thermal conductivity/m/. C : 0.0743
8. Rate of erosion, mm/s s 0.02
StatLLc Eyaluat ion; Inhibited propellant using the new
formulation was subjected to static evaluation at ambient
o
temperature as well as —20 C in end burning mode from the point of
view of establishing practical value of inhibition system over a
wide range of temperature. A smooth and neutral P-t profile was
obtained during the combustion of propellant grains, establishing
effective bonding between propellant and inhibitor and proving
the efficacy of the inhibition system.
It is to be understood that the process of the present
invention is susceptible to modifications, changes and
adaptations by those skilled in the art. Such modifications,
changes, adaptations are intended to be within the scope of the
present invention which is further set forth under the following
c1aims
I CLAIM:
1. A process for the preparation of an inhibitor composition for rocket
propellants comprising the steps of:
(a) heating the mixture of 75 to 85% hydroxyl poly butadiene binder, 5 to 15% of Polyphosphate ester prepolymer and 2 to 10% of dioctyl adipate,
(b) dissolving 0.4 to 0.6% by wt. of pyrogallol and 0.05 to 0.15% of ferric acetyl acetonate in the mixture of step (a),
(c) adding 15-25% carbon-black with continuous stirring and deaerating the mixture under vacuum,
(d) mixing 6 to 10% curative isophorone di-isocynate to the mixture of step (c) and deaerating again,
(e) casting the mixture into sheets and curing.

2. A process as claimed in claim 1, wherein hydroxyl terminated poly butadiene binder is preferably 78 to 82% by weight.
3. A process as claimed in claim 1, wherein Polyphosphate ester prepolymer is preferably 8 to 10% by weight.
4. A process as claimed in claim 1, wherein dioctyl adipate is preferably 4 to 6% by weight.
5. A process as claimed in claim 1, wherein Ferric acetyl acetonate is preferably 0.075 to 0.125% by weight.
6. A process as claimed in claim 1, wherein preferably 18 to 22% of carbon-black is added with continuous stirring for about 5 minutes.

7. A process as claimed in claim 1, wherein curative isophorone di-isocynate 6 to 10%, preferably 7 to 8% by weight is added to the mixture.
8. A process as claimed in claim 1, wherein the said curing is preferably carried at 45+2°C for about 8 days.
9. A process for the preparation of an inhibitor composition for rocket propellants substantially described and illustrated in the example.

Documents:

193-DEL-2002-Abstract-(08-07-2008).pdf

193-del-2002-abstract.pdf

193-DEL-2002-Claims-(08-07-2008).pdf

193-del-2002-claims.pdf

193-DEL-2002-Correspondence-Others-(08-07-2008).pdf

193-DEL-2002-Correspondence-Others-(22-02-2010).pdf

193-del-2002-correspondence-others.pdf

193-del-2002-correspondence-po.pdf

193-DEL-2002-Description (Complete)-(08-07-2008).pdf

193-del-2002-description (complete).pdf

193-DEL-2002-Form-1-(08-07-2008).pdf

193-del-2002-form-1.pdf

193-DEL-2002-Form-15-(22-02-2010).pdf

193-del-2002-form-18.pdf

193-DEL-2002-Form-2-(08-07-2008).pdf

193-del-2002-form-2.pdf

193-DEL-2002-Form-26-(08-07-2008).pdf


Patent Number 222017
Indian Patent Application Number 193/DEL/2002
PG Journal Number 32/2008
Publication Date 08-Aug-2008
Grant Date 15-Jul-2008
Date of Filing 04-Mar-2002
Name of Patentee THE ADDITIONAL DIRECTOR (IPR)
Applicant Address DEFENCE RESEARCH & DEVELOPMENT ORGANISATION, MINISTRY OF DEFENCE, GOVT OF INDIA, B-341, SENA BHAWAN, DHQ P.O., NEW DELHI-110 011, INDIA.
Inventors:
# Inventor's Name Inventor's Address
1 SEEMA DILIP KAKADE HIGH ENERGY MATERIALS RESEARCH LABORATORY, ARMAMENT POST, SUTRWADI, PUNE 411 021
2 HARIDWAR SINGH HIGH ENERGY MATERIALS RESEARCH LABORATORY, ARMAMENT POST, SUTRWADI, PUNE 411 021
3 THEKKEKARA MUKUNDAN HIGH ENERGY MATERIALS RESEARCH LABORATORY, ARMAMENT POST, SUTARWADI, PUNE 411 021
4 RAVINDRA SHAMKANT SATPUTE HIGH ENERGY MATERIALS RESEARCH LABORATORY, ARMAMENT POST, SUTRWADI, PUNE 411 021
5 JAYA KAMALESH NAIR HIGH ENERGY MATERIALS RESEARCH LABORATORY, ARMAMENT POST, SUTRWADI, PUNE 411 021
6 PANDHARINATH KRUSHNAJI DIVEKAR HIGH ENERGY MATERIALS RESEARCH LABORATORY, ARMAMENT POST, SUTRWADI, PUNE 411 021
7 SHRI NANDAN ASTHANA HIGH ENERGY MATERIALS RESEARCH LABORATORY, ARMAMENT POST, SUTRWADI, PUNE 411 021
PCT International Classification Number F42B 1/00
PCT International Application Number N/A
PCT International Filing date
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 NA