Title of Invention	A COMPOSITE SOLID PROPELLANT COMPOSITION BASED ON HYDROXYL TERMINATED POLYBUTADIENE AND A PROCESS FOR MAKING THE SAME
Abstract	This invention relates to a composite solid propellant composition with improved burn rate. e(-crystalline ferric oxide is added as ballistic modifier to conventional propellant composition having hydroxyl terminated. polybutadiene, aluminium powder and ammonium perchlorate. Aliphatic and aromatic isocyanates are also added to said composition. This invention also includes a process of making a composite propellant composition.

Title of Invention

A COMPOSITE SOLID PROPELLANT COMPOSITION BASED ON HYDROXYL TERMINATED POLYBUTADIENE AND A PROCESS FOR MAKING THE SAME

Abstract

This invention relates to a composite solid propellant composition with improved burn rate. e(-crystalline ferric oxide is added as ballistic modifier to conventional propellant composition having hydroxyl terminated. polybutadiene, aluminium powder and ammonium perchlorate. Aliphatic and aromatic isocyanates are also added to said composition. This invention also includes a process of making a composite propellant composition.

Full Text	This invention relates to a composite solid propellant composition based on hydroxyl terminated polybutadiene. This invention also includes a process of preparing such compositions. The composite solid propellants of this invention exhibit excellent burn rate modifying property to get the desired burning rate for the propellant formulation. Viscosity build up, pot life and amenability of large scale processing of the composite propellant formulation are regulated by the addition of isocyanates in the mixture. Composite propellant compositions based on hydroxyl terminated polybutadiene as binder, ammonium perchlorate as oxidiser and aluminum powder as metallic fuel are known in the art. As ballistic modifiers, different transition metal oxides or their complexes have been of use. For Instance copper chromite, active copper oxide and n-butyl ferrocene are reported as ballistic modifiers in composite solid propellants. However, these hitherto known ballistic modifiers have certain inherent drawbacks. Some of these compounds are non reproducible in nature thereby affecting quality control and performance of different samples. Storage problems like surface hardening are also observed in certain oases. In the case of liquid burn rate modifier migration to the surface of the composite leads to defects in the cast propellant composites. Copper chromite which is a mixed metal oxide consisting of a predominant oxide ion lattice with Cu2++ and Cr3+ occupying interstitial sites and has a formula CuO.CuCr2O4, This causes a certain degree of non reproducibility in its preparation. Ferrocene derived modifiers are found to be hazardous during propellant processing. They also exhibit migration problems discussed hereinbefore and are not cost effective. Thus an object of this invention is to identify a suitable burn rate modifier which avoids the above referenced drawbacks. We have found that -crystalline ferric oxide exhibits excellent burn rate modifying properties when added to solid propellants. Large surface area and low particle size of -crystalline ferric oxide overcomes many of the drawbacks noticed when other modifiers are used. Low cost of production, reproducibility, good compatibility with other propellant components make it a suitable ballistic modifier. Ageing properties of composites using crystalline ferric oxide are superior to that of other compositions. The propellant composition consists of hydroxyl terminated polybutadiene which may be produced by free radical polymerisation of butadiene. Ammonium perchlorate may have bimodal distribution of coarse and fine grades in the weight ratio varied from 4:1 to 2:1. In addition, the propellant composite may contain conventional fillers, plasticizers and curing agents. Curing agents that show excellent results are toluene diisocyanate, aliphatic isocyanates like isophorone diisocyanate and 4,4 methylene bis (cyclohexoyl) isocyanate. Any known diol-triol mix comprising diols such as ethylene glycol, propylene glycol, 1,3 propane diol, 1,4 butane diol and triols such as glycerol, 1,1,1 trimethylol propane in the ratios ranging from 3:1 to 1:3 may be added to the composition to control the chain extension and cross linking of hydroxyl terminated polybutadiene. The diol-triol mix must have a hydroxyl value of 1200-1225 measured as mgmKOH/gm, refractive index at 25°C of 1.453 - 1.457 and a moisture content of Max 0.10. The composite solid propellant composition according to this invention comprises hydroxyl terminated polybutadiene, ammonium perchlorate and aluminum powder wherein said composite has ©(-crystalline ferric oxide as ballistic modifier and at least one aromatic and/or aliphatic isooyanates as curing agents. This invention also includes a process for preparing a composite solid propellant composition which comprises the steps of mixing hydroxyl terminated poly butadiene, ammonium perchlorate, and aluminium powder and adding -crystalline ferric oxide and atleast one aromatic or aliphatic ieocyanate to form a slurry and subsquently casting said slurry. Propellant mixing operations are carried out in conventional horizontal sigma kneader or vertical change-can kneader. Castability of the resultant slurry is monitored by measuring its viscosity at regular intervals for a period of 5 to 50 hrs. The slurry may then be subjected to deareation and oast into polythene cartons at a residual pressure of 3 to 5 torr. The cast propellants are then evaluated and burn rates are measured. - crystalline ferric oxide is used at a concentration level of 0.01 to 0.75% by weight. -crystalline ferric oxide enhances burn rate by 44% at 0.25%, 52% at 0.5% and 64% at 0.75% wt concentration. Propellant composition may have 86% by wt of solid loading containing 18% by wt of aluminium powder with coarse and fine ammonium perchlorate in the weight ratio of 3:1. Three different types of isocyanates namely toluene di-isocyanate, isophorone di isooyanate and 4,4"methylene bis (cyclohexyl) isooyanate are used either alone or in combination with each other. The viscosity build up of the propellant slurry, mechanical properties and burn rates are determined. It is seen that aromatic toluene di isooyanate is more reactive and as such the resultant propellant has shorter pot life. Primary and secondary isooyanate groups of alicyclic isophorone di isooyanate are slow to cure and gives longer pot life. The secondary nature of both isocyanate groups present in the alyoyclic 4,4" methylene bis(cyclohexyl) isocyanate gives longest pot life. Curing takes place when the composite is kept for a period of time at the cure temperature. Mechanical properties such as tensile strength, elongation modules and hardness may be adjusted by varying NCO/OH ratio of the composition. A process of preparing (-crystalline ferric oxide has been described and claimed in our copending patent specification No.547/MAS/99. For the production of this propellent composition, the -crystalline ferric oxide prepared by that process may be used. Obviously -crystalline ferric oxides obtained by any other process may also be effectively used. In the above referenced patent application -crystalline ferric oxide is prepared by adding an aqueous solution of an alkali to an aqueous solution of ferric salt under ambient conditions to obtain an yellowish brown precipitate, separating, washing, drying and subsequently grinding said precipitate to powder and further drying said powder to obtain ferric oxide having -crystalline structure. However, this invention is not limited to the use of-crystalline ferric oxide prepared by the above described process. The invention and the appended claims include obvious equivalents known to persons skilled in the art. WE CLAIM: 1. A composite solid propellant composition comprising hydroxyl terminated polybutadiene, ammonium perehlorate and aluminium powder wherein said composite has -crystalline ferric oxide and atleast one aromatic/aliphatic isooyanate as curing agent, 2. The composite solid propellant composition as claimed in claim 1, wherein said -crystalline ferrio oxide is in the range of 0.01 to 0.75% by weight. 3. The composition as claimed in claims 1 and 2, wherein said -crystalline ferrio oxide is prepared by adding an aqueous alkali solution to an aqueous ferric salt solution separating washing and drying the precipitate formed, grinding said dried precipitate and further drying the same. 4. The composite solid propellant composition as claimed in claims 1-3, wherein said ammonium perchlorate is a mixture of fine and coarse grades in the weight ratio of 4:1 to 2:1. 5. The composite solid propellant composition as claimed in claims 1-4, wherein said isocyanates are toluene di isooyanate, isophorone di isooyanate, and 4,4"methylene bis (cyclohexyl) isooyanate or a combination thereof. 6. The composite solid propellent composition as claimed in claims 1-5, wherein said composition has conventional fillers plasticizers and curing agents. 7. The composite solid propellant composition as claimed in claims 1-6, wherein said composition optionally has a diol-triol mixture. 8. The composite solid propellant composition as claimed in claims 1-7, wherein said diol-triol mixture has a hydroxyl value of 1200-1225 measured as mgmKOH/g and a refractive index of 1.453 to 1.457 at 25o. 9. A process for preparing a composite solid propellant composition comprising the steps of mixing hydroxyl terminated polybutadiene, ammonium perchlorate and aluminium powder, and adding -crystalline ferric oxide and atleast one aromatic/aliphatic isocyanate to form a slurry and subsequently casting said slurry. 10. The process for preparing a composite solid propellant composition claimed in claim 9 wherein said crystalline ferric oxide is added to the mixture in the range of 0.01 to 0.75% by weight. 11. The process as claimed in claim 9 or 10, wherein said -crystalline ferric oxide is obtained by adding an aqueous alkali solution to an aqeuous ferric salt solution, separating, washing and drying the precipitate formed, grinding said dried precipitate and further drying the same. 12. The process as claimed in claims 9-11, wherein ammonium perchlorate added has fine and coarse grades in the weight range of 4:1 to 2:1. 13. The process for preparing a composite solid propellant composition as claimed in claims 9-12 wherein the isocyanates added are selected from toluene diisocyanate, isophorone disiocynate and 4,4 methylene bis (cyclohexyl) isocyanate or a combination thereof. 14. The process for preparing a composite solid propellant composition as claimed in claims 9-13, wherein conventional fillers, plasticizers and curing agents are added. 15. The process for preparing a composite solid propellant composition as claimed in claims 9-14, wherein diol-triol mixture is added to said composition. 16. The process for preparing a composite solid propellant composition as claimed in claims 9-15, wherein said diol-triol mixture has a hydroxyl value of 1200-1225 measured as mgmKOH/g and a refractive index of 1.453 to 1.457 at 25°C. 17. A composite solid propellant composition substantially as herein described. 18. A process for preparing a composite solid propellant composition substantially as herein described.

Full Text

This invention relates to a composite solid propellant composition based on hydroxyl terminated polybutadiene. This invention also includes a process of preparing such compositions.
The composite solid propellants of this invention exhibit excellent burn rate modifying property to get the desired burning rate for the propellant formulation. Viscosity build up, pot life and amenability of large scale processing of the composite propellant formulation are regulated by the addition of isocyanates in the mixture.
Composite propellant compositions based on hydroxyl terminated polybutadiene as binder, ammonium perchlorate as oxidiser and aluminum powder as metallic fuel are known in the art. As ballistic modifiers, different transition metal oxides or their complexes have been of use. For Instance copper chromite, active copper oxide and n-butyl ferrocene are reported as ballistic modifiers in composite solid propellants. However, these hitherto known ballistic modifiers have certain inherent drawbacks. Some of these compounds are non reproducible in nature thereby affecting quality control and performance of different samples. Storage problems like surface hardening are also observed in certain oases. In the case of liquid burn rate modifier migration to the surface of the composite leads to defects in the cast propellant composites.

Copper chromite which is a mixed metal oxide consisting of a predominant oxide ion lattice with Cu2++ and Cr3+ occupying interstitial sites and has a formula CuO.CuCr2O4, This causes a certain degree of non reproducibility in its preparation. Ferrocene derived modifiers are found to be hazardous during propellant processing. They also exhibit migration problems discussed hereinbefore and are not cost effective.
Thus an object of this invention is to identify a suitable burn rate modifier which avoids the above referenced drawbacks. We have found that -crystalline ferric oxide exhibits excellent burn rate modifying properties when added to solid propellants. Large surface area and low particle size of -crystalline ferric oxide overcomes many of the drawbacks noticed when other modifiers are used. Low cost of production, reproducibility, good compatibility with other propellant components make it a suitable ballistic modifier. Ageing properties of composites using crystalline ferric oxide are superior to that of other compositions.
The propellant composition consists of hydroxyl terminated polybutadiene which may be produced by free radical polymerisation of butadiene. Ammonium perchlorate may have bimodal distribution of coarse and fine grades in the weight ratio varied from 4:1 to 2:1.

In addition, the propellant composite may contain conventional fillers, plasticizers and curing agents. Curing agents that show excellent results are toluene diisocyanate, aliphatic isocyanates like isophorone diisocyanate and 4,4 methylene bis (cyclohexoyl) isocyanate. Any known diol-triol mix comprising diols such as ethylene glycol, propylene glycol, 1,3 propane diol, 1,4 butane diol and triols such as glycerol, 1,1,1 trimethylol propane in the ratios ranging from 3:1 to 1:3 may be added to the composition to control the chain extension and cross linking of hydroxyl terminated polybutadiene. The diol-triol mix must have a hydroxyl value of 1200-1225 measured as mgmKOH/gm, refractive index at 25°C of 1.453 - 1.457 and a moisture content of Max 0.10.
The composite solid propellant composition according to this invention comprises hydroxyl terminated polybutadiene, ammonium perchlorate and aluminum powder wherein said composite has ©(-crystalline ferric oxide as ballistic modifier and at least one aromatic and/or aliphatic isooyanates as curing agents.
This invention also includes a process for preparing a composite solid propellant composition which comprises the steps of mixing hydroxyl terminated poly butadiene, ammonium perchlorate, and aluminium powder and adding -crystalline ferric oxide and atleast one aromatic or aliphatic ieocyanate to form a slurry and subsquently casting said slurry.

Propellant mixing operations are carried out in conventional horizontal sigma kneader or vertical change-can kneader. Castability of the resultant slurry is monitored by measuring its viscosity at regular intervals for a period of 5 to 50 hrs. The slurry may then be subjected to deareation and oast into polythene cartons at a residual pressure of 3 to 5 torr. The cast propellants are then evaluated and burn rates are measured.
- crystalline ferric oxide is used at a concentration level of 0.01 to 0.75% by weight. -crystalline ferric oxide enhances burn rate by 44% at 0.25%, 52% at 0.5% and 64% at 0.75% wt concentration. Propellant composition may have 86% by wt of solid loading containing 18% by wt of aluminium powder with coarse and fine ammonium perchlorate in the weight ratio of 3:1.
Three different types of isocyanates namely toluene di-isocyanate, isophorone di isooyanate and 4,4"methylene bis (cyclohexyl) isooyanate are used either alone or in combination with each other. The viscosity build up of the propellant slurry, mechanical properties and burn rates are determined. It is seen that aromatic toluene di isooyanate is more reactive and as such the resultant propellant has shorter pot life. Primary and secondary isooyanate groups of alicyclic isophorone di isooyanate are slow to cure and gives longer pot life. The

secondary nature of both isocyanate groups present in the alyoyclic 4,4" methylene bis(cyclohexyl) isocyanate gives longest pot life.
Curing takes place when the composite is kept for a period of time at the cure temperature. Mechanical properties such as tensile strength, elongation modules and hardness may be adjusted by varying NCO/OH ratio of the composition.
A process of preparing (-crystalline ferric oxide has been described and claimed in our copending patent specification No.547/MAS/99. For the production of this propellent composition, the -crystalline ferric oxide prepared by that process may be used. Obviously -crystalline ferric oxides obtained by any other process may also be effectively used.
In the above referenced patent application -crystalline ferric oxide is prepared by adding an aqueous solution of an alkali to an aqueous solution of ferric salt under ambient conditions to obtain an yellowish brown precipitate, separating, washing, drying and subsequently grinding said precipitate to powder and further drying said powder to obtain ferric oxide having -crystalline structure.
However, this invention is not limited to the use of-crystalline ferric oxide prepared by the above described process.
The invention and the appended claims include obvious equivalents known to persons skilled in the art.

WE CLAIM:
1. A composite solid propellant composition comprising
hydroxyl terminated polybutadiene, ammonium perehlorate and
aluminium powder wherein said composite has -crystalline ferric
oxide and atleast one aromatic/aliphatic isooyanate as curing
agent,
2. The composite solid propellant composition as claimed in claim 1, wherein said -crystalline ferrio oxide is in the range of 0.01 to 0.75% by weight.
3. The composition as claimed in claims 1 and 2, wherein said -crystalline ferrio oxide is prepared by adding an aqueous alkali solution to an aqueous ferric salt solution separating washing and drying the precipitate formed, grinding said dried precipitate and further drying the same.
4. The composite solid propellant composition as claimed in claims 1-3, wherein said ammonium perchlorate is a mixture of fine and coarse grades in the weight ratio of 4:1 to 2:1.
5. The composite solid propellant composition as claimed in claims 1-4, wherein said isocyanates are toluene di isooyanate, isophorone di isooyanate, and 4,4"methylene bis (cyclohexyl) isooyanate or a combination thereof.

6. The composite solid propellent composition as claimed
in claims 1-5, wherein said composition has conventional fillers
plasticizers and curing agents.
7. The composite solid propellant composition as claimed in claims 1-6, wherein said composition optionally has a diol-triol mixture.
8. The composite solid propellant composition as claimed in claims 1-7, wherein said diol-triol mixture has a hydroxyl value of 1200-1225 measured as mgmKOH/g and a refractive index of 1.453 to 1.457 at 25o.
9. A process for preparing a composite solid propellant composition comprising the steps of mixing hydroxyl terminated polybutadiene, ammonium perchlorate and aluminium powder, and adding -crystalline ferric oxide and atleast one aromatic/aliphatic isocyanate to form a slurry and subsequently casting said slurry.
10. The process for preparing a composite solid propellant
composition claimed in claim 9 wherein said crystalline ferric
oxide is added to the mixture in the range of 0.01 to 0.75% by
weight.

11. The process as claimed in claim 9 or 10, wherein said
-crystalline ferric oxide is obtained by adding an aqueous
alkali solution to an aqeuous ferric salt solution, separating,
washing and drying the precipitate formed, grinding said dried
precipitate and further drying the same.
12. The process as claimed in claims 9-11, wherein ammonium perchlorate added has fine and coarse grades in the weight range of 4:1 to 2:1.
13. The process for preparing a composite solid propellant composition as claimed in claims 9-12 wherein the isocyanates added are selected from toluene diisocyanate, isophorone disiocynate and 4,4 methylene bis (cyclohexyl) isocyanate or a combination thereof.
14. The process for preparing a composite solid propellant composition as claimed in claims 9-13, wherein conventional fillers, plasticizers and curing agents are added.
15. The process for preparing a composite solid propellant composition as claimed in claims 9-14, wherein diol-triol mixture is added to said composition.

16. The process for preparing a composite solid propellant
composition as claimed in claims 9-15, wherein said diol-triol
mixture has a hydroxyl value of 1200-1225 measured as mgmKOH/g
and a refractive index of 1.453 to 1.457 at 25°C.
17. A composite solid propellant composition substantially
as herein described.
18. A process for preparing a composite solid propellant
composition substantially as herein described.

Documents:

1091-mas-1999 abstract duplicate.pdf

1091-mas-1999 abstract.pdf

1091-mas-1999 claims duplicate.pdf

1091-mas-1999 claims.pdf

1091-mas-1999 correspondence-others.pdf

1091-mas-1999 correspondence-po.pdf

1091-mas-1999 description (complete) duplicate.pdf

1091-mas-1999 description(complete).pdf

1091-mas-1999 form-1.pdf

1091-mas-1999 form-19.pdf

1091-mas-1999 form-26.pdf

1091-mas-1999 form-3.pdf

1091-mas-1999 form-8.pdf

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Patent Number

217041

Indian Patent Application Number

1091/MAS/1999

PG Journal Number

21/2008

Publication Date

23-May-2008

Grant Date

24-Mar-2008

Date of Filing

11-Nov-1999

Name of Patentee

INDIAN SPACE RESEARCH ORGANISATION

Applicant Address

DEPARTMENT OF SPACE, ANTARIKSH BHAVAN, NEW BEL ROAD, BANGALORE 560 094,

Inventors:

#	Inventor's Name	Inventor's Address
1	DR. THOPPIL LUKOSE VARGHESE	VIKRAM SARABHAI SPACE CENTRE, TRIVANDRUM - 695 022,
2	DR. SATTIRAJU SOMESWARA RAO	VIKRAM SARABHAI SPACE CENTRE, TRIVANDRUM - 695 022,
3	DR. KOVOOR NINAN NINAN	VIKRAM SARABHAI SPACE CENTRE, TRIVANDRUM - 695 022,

PCT International Classification Number

C06B 45/10

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA