Title of Invention

"A TPE BASED NITRAMINE PROPELLANT COMPOSITION AND A PROCESS FOR PREPARATION THEREOF"

Abstract

According to present invention, there is provided a thermoplastic elastomer (TPE) binder based nitramine propellant composition and a process for preparation thereof. The proposed nitramine propellant composition is a universal TPE based propellant composition which can utilise any one of the TPEs such as Kretan, Estane or EVA. The proposed TPE based nitramine propellant composition has higher specific impulse for rocket propellant applications, higher force constant for gun propellant applications and higher velocity of detonation for explosive formulations. The proposed composition is highly insensitive to external impact or friction stimuli. It has better combustion behavior in low pressure region and low pressure exponent value in high pressure region. The propellant composition comprises 60-80% RDX of about 5µm as energetic ingredient, 10-20 oxidiser additive ammonium perchlorate, 12-18% TPE binder and 2-4% plasticiser.

Full Text

FIELD OF INVENTION The present invention relates to a thermoplastic elastomers (TPE) binder based nitramine propellant composition and a process for preparation thereof. PRIOR ART Conventional rocket/gun propellants are based on nitrocellulose(NC) binder and nitroglycerine (NG) plasticizer. Hydroxy terminated polybutadiene (HTPB) binders are used for LOVA gun propellant as well as plastic bonded explosives in view of its clean cross-linking reaction with isocynate curative and superior low temperature strain capability. However, HTBP binders have limited pot life and these can not be recycled and thus need 'to be" disposed. Thermoplastic elastomers (TPE) binder based propellant compositions are improved binder systems, which do not rely on chemical cross-linking during processing of propellant formation. TPE based propellant compositions have low vulnerability, superior structural integrity and offer ease in processing. TPE based propellant compositions can also be processed at elevated temperatures. TPEs are basically co-polymers of type ABA or AB, where A & B are respectively the hard and soft segments. The hard segment is capable of crystallisation and this segment imparts thermoplastic behavior to the co-polymer whereas the soft segment imparts elastomeric characteristics to the co-polymer. The thermoplastic behavior is the result of crystalline domain fomation by chain associations due to reversible interactions such as dipole-dipole intera'ctions, hydrogen bonding etc. Since the physical links are reversible, the TPEs can be remelted or dissolved in a solvent. Components of propellant formulations can be easily incorporated with binder in molten stage as well as in the form of a solution. These TPEs are known to the prior art Examples of thermoplastic elastomers are kraton (Styrene-diene block copolymers such as styrene-butadine, styrene-isoprene, styrene-ethylene/butylene cpolymer), Estane and ethyl vinyl acetate (Eva). Kraton is a widely used TPE, which is particularly used in gun propellants of LOVA class, and it is known to the prior art. However, kraton based propellant compositions suffer from the problem of low energy. Similarly, Estane finds application as binder for extruded rocket propellants. However, these known thermoplastic elastomers are specific purpose in the sense that each of these thermoplastic elastomers are utilised for specific types of propellants only. Thus, there is a need for a propellant composition which does not need any specific TPE and which can utilise any thermoplastic elastomers. OBJECTS OF THE INVENTION Primary object of the invention is to provide a universal thermoplastic elastomers (TPE ) binder based nitramine propellant composition and a process for preparation thereof. Another object of the invention is to provide a TPE binder based nitramine propellant composition and a process for preparation thereof wherein the process provides a composition which has superior mechanical properties. Yet another object of the invention is to provide a TPE binder based nitramine propellant composition and a process for preparation thereof wherein the process provides a composition, which is highly insensitive to external stimuli. Still another object of the invention is to provide a TPE binder based nitramine propellant composition and a process for preparation thereof wherein the process provides a composition, which has high energetics having higher specific impulse for rocket propellants, higher force constant for gun propellants and higher velocity of detonation for explosive formulations. Yet further object of the invention is to provide a TPE binder based nitramine propellant composition and a process for preparation thereof wherein the process provides a composition, which has low pressure exponent value in high pressure region. Still further object of the invention is to provide a TPE binder based nitramine propellant composition and a process for preparation thereof wherein the process provides a composition which has better combustion behavior in low pressure region. (i) Preparation of alcoholated RDX by mixing, fine RDX with ethyl alcohol: 60-80% fine RDX (having approximate particle size 5µm) is mixed with distilled alcohol in a sigma blade mixer for 20-30 minutes to obtain alcoholated fine RDX. The ratio of RDX to alcohol is preferably in the range of 1: 0.3 to 1: 0.5. (ii) Mixing of ammonium perchlorate with alcoholated RDX: • 10-20% ammonium perchlorate and 1-3 parts (over 100 parts of the propellant composition) of ballistic modifier is added to this alcoholated RDX in the sigma blade mixer. The mixing is carried out for 20-30 minutes. (iii) Mixing of plasticiser with RDX-AP mix: 2-4% plasticiser is added to above mix and again mixing is carried out for another 20-30 minutes. The plasticiser used is triacetin (TA) or glycidyl azide prepolymer (GAP) (iv) Preparation of binder solution: Binder solution is prepared separately by dissolving 12-18% of TPE granules in the solvent at 60-80 °C under continuous stirring till a free flowing binder solution is obtained. The solvent is toluene, acetone or chloroform and the ratio of the TPE and solvent should be 2:1 to 2:1.5. The TPE is Hytrel, EVA, Estane or Kraton. (v) mixing of binder solution with plasticiser, RDX and AP mix prepared in step (iii) The binder solution prepared in step (iv) is transferred in another sigma blade mixer and to this solvated binder matrix, the plasticised fine RDX, AP mix prepared in step (iii) is added in 3 installments and mixing is carried out for 2-3 hours. (vi) Drying ofdiix prepared in step (v) The mix obtained in step (v) is unloaded from sigma blade mixer and dried at 40-50 °C for 24-48 hours to remove the solvent. (vii) Preparation of propellant sheet by hot rolling The dried mix is hot rolled at 60-80 °C to obtain extrudable propellant sheets. The sheets can be used as such or extruded through a die of desired dimensions at 60-80° C. The process of the present invention will now be illustrated with working examples which are intended to be typical examples to illustrate the working of the invention and are not intended to be taken restrictively to imply any limitation on the scope of the present invention. According to the invention there is provided a process for preparation of a thermoplastic elastomer (TPE) binder based nitramine propellant composition comprising of: (i) preparation of alcoholated RDX as herein described by mixing fine RDX with ethyl alcohol, (ii) mixing of ammonium perchlorate (AP) with alcoholated RDX, (iii) mixing of plasticiser as herein described with RDX-AP mixture, (iv), mixing of binder solution with plasticiser, RDX and AP mixture prepared in step (iii), (v) drying of mixture obtained in step (iv), (vi) preparation of propellant sheet by hot rolling. WORKING EXAMPLE-1 800 gm of fine RDX (having approximate particle size of 5 um) is taken in a sigma blade mixer and 20 gm of distilled ethyl alcohol is added to it. Mixing is carried out for about 30 minutes to obtain alcoholated fine RDX. To this alcoholated fine RDX, 40 gm of plasticiser TA is added and again mixing is carried out for another 30 minutes. In another mixer, 160 gm of TPE (Hytrel/EVA/Estane/Kraton) is dissolved in 80 gm of toluene by heating the mixture at 60 ± 5 °C for about 30 minutes under continuous stirring till a free flowing binder solution is obtained. Next, this binder solution is transferred to another sigma blade mixer and the plasticised RDX is added to this solvated binder mix in three equal installments (each installment of 250-300 gm) and mixing is carried out-for 2 hours. This mix is unloaded and dried at 45 ± 5 °C in oven for about 25 hours to remove the solvent. The dried mix is hot rolled at 60 ± 5 °C using preheated steel roller with smooth finish to obtain extrudable propellant sheets. The ballistic, mechanical and vulnerability characteristics of the formulations obtained through above working example are given in the following table. Table-1(Table Removed) WORKING EXAMPLE-2 800 gm of fine RDX (particle size 5 µrn) is taken in a sigma blade mixer and 20 gm of distilled ethyl alcohol is added to it. Mixing is carried out for about 30 minutes to obtain alcoholated fine RDX. To this alcoholated fine RDX, 40 gm of plasticiser GAP is added to improve the energetic of the propellant and again mixing is carried out for another 30 minutes. In another mixer 160 gm of any TPE (Hytrel/EVA/Estane/Kraton) is dissolved in 80 gm of toluene by heating the mixture at 60 ± 5 °C for about 30 minutes under continuous stirring till a free flowing binder solution is obtained. Next, this binder solution is transferred to another sigma blade mixer and the plasticised RDX is added to this solvated binder mix in three equal installments (each installment of 250-300 gm) and mixing is carried out for 2 hours. This mix is unloaded and dried at 45 ± 5°C in oven 25 hours to remove the solvent. The dried mix is hot rolled at 60 ± 5 °C using preheated steel roller with smooth finish to obtain extrudable propellant. The ballistic, mechanical and vulnerability characteristics of the formulations are given in the'following table. Table - 2 (Table Removed)It is to be understood that the process of the present invention is susceptible to adaptations, changes, and modifications by those skilled in the art. Such adaptations, changes, modifications are intended to be within the scope of the present invention, which is further set forth by the following claims. WE CLAIM: 1. A process for preparation of a thermoplastic elastomer (TPE) binder based nitramine propellant composition comprising of: (i) preparation of alcoholated RDX as herein described by mixing fine RDX with ethyl alcohol, (ii) mixing of ammonium perchlorate (AP) with alcoholated RDX, (iii) mixing of plasticiser as herein described with RDX-AP mixture, (iv) mixing of binder solution with plasticiser, RDX and AP mixture prepared in step (iii), (v) drying of mixture obtained in step (iv), (vi) preparation of propellant sheet by hot rolling. 2. The process as claimed in claim 1 wherein said RDX constitute about 60-80% by weight of the composition. 3. The process as claimed in claim 1 wherein the ratio of fine RDX and ethyl alcohol is from about 1:0.3 to 1:0.5. 4. The process as claimed in claim 1 wherein said mixing of said fine RDX and alcohol is done for about 20-30 minutes. 5. The process as claimed in claim l\wherein said ammonium perchlorate constitute about 10-20% by weight of the propellant composition. 6. The process as claimed in claim 1 wherein said plasticiser constitute about 2-4% by weight of the propellant composition. 7. The process as claimed in claim 1 wherein said plasticiser is preferably triacetin (TA) or glycidyl azide prepolymer (GAP). 8. The process as claimed in claim 1 wherein said binder solution is prepared at about 60-80°C. 9. The process as claimed in claim 1 wherein said TPE is preferably Hytrel or EVA or Estane or Kraton. 10. The process as claimed in claim 1 wherein said solvent for TPE is preferably toluene or acetone or chloroform. 11. The process as claimed in claim 1 wherein the ratio of said TPE and said solvent is preferably from 2:1 to 2:1.5. 12. The process as claimed in claim 1 wherein said final mix is dried at about 40-50°C. 13. The process as claimed in claim 1 wherein said hot rolling is carried out at about 60-80°C. 14. A TPE binder based nitramine propellant composition comprising 60-80% fine RDX, 10-20% ammonium perchlorate, 2- 4% plasticiser triacetin or glycidyl azide prepolymer and binder selected from Hytrel, EVA, Estane or Kraton 12-18%. 15. A TPE binder based nitramine propellant composition prepared by the process substantially as described and exemplified herein.

Documents:

498-del-2001-abstract.pdf

498-del-2001-claims.pdf

498-del-2001-correspondence-others.pdf

498-del-2001-correspondence-po.pdf

498-del-2001-description (complete).pdf

498-del-2001-form-1.pdf

498-del-2001-form-18.pdf

498-del-2001-form-2.pdf

498-del-2001-form-3.pdf

498-del-2001-gpa.pdf