Title of Invention	"A PROCESS FOR PREPARING AN INHIBITION FORMULATION FOR NITRAMINE PROPELLANTS"
Abstract	A process for preparation of inhibitor formulation for nitramine based composite modified double based (CMDB) propellants comprising in the steps of: a) preparing a binder solution by mixing binder material and plasticiser b) dissolving additives in the binder solution c) adding filler materials with mixing d) adding isocyanate with stirring e) curing of inhibitor formulation

Full Text

FIELD OF INVENTION This invention relates to a process for preparation of inhibitor formulation for nitramine based composite modified double based (CMDB) propellants. PRIOR ART Inhibitor materials are utilised to control the burning of the solid propellants in a desired fashion so as to achieve specific performance of the rocket motors in terms of range and trajectory profile. These inhibitor materials are applied to the surface of the solid propellants. A large number of inhibitor materials are known in the art for application in case of double base and composite propellants. However, very few inhibition materials are known in the art application in case of nitramine based composite modified double base propellants. Nitramine based propellants basically comprise of nitroglycerin or nitrocellulose as binder materials and RDX or aluminium as energetic materials in addition to other additives which are added to impart desirable mechanical properties to the propellants. Nitramine composite modified double based propellants, herein after referred as only nitramine propellants, are comparatively softer than other CMDB solid propellants. This leads to development of stresses at inhibitor propellant interface during thermal cycling of the propellant as inhibitors are generally more rigid. One of the inhibition formulations for nitramine propellants, known in the art, is based on Cellulose Acetate or Ethyl cellulose. The disadvantage associated with such a formulation is that it cannot restrict the combustion of nitramine propellants due to very high flame temperature of such propellants and low softening point of the inhibitors. Another drawback is that these inhibitors have a high affinity for nitroglycerine resulting in a faster rate of NG migration from the propellant to inhibitor leading to the weakening of bound between the inhibitor and the propellant. Another inhibition formulation for nitramine propellants, known in the art, is styrene-butadiene and acrylomtrile. However, it also suffers from the disadvantage that it utilises asbestos which is highly toxic and banned in many countries. Polyester resin is another inhibition formulation for nitramine propellants which is known in the art. However, it also suffers from the disadvantage that it is very stiff as a result of which the inhibitor-propellant interface does not remain stable and debonds during thermal cycling or storage of the propellant. OBJECTS OF THE INVENTION Primary object of the invention is to provide a process for preparation of an inhibition formulation for nitramine propellants which results in high bonding strength of inhibitor-propellant interface when applied to the surface of the propellant. Yet another object of the invention is to provide a process for preparation of an inhibition formulation for nitramine propellants whose tensile strength matches with that of nitramine propellants. Still another object of the invention is to provide a process for preparation of an inhibition formulation for nitraminc propellants which results in minimum migration of plasticizer (nitroglycerin) in the nitramine propellant to the propellant surface over a period of time thereby improving the performance of the propellant. Still further object of the invention is to provide a process for preparation of an inhibition formulation for nitramine propellants which has a higher pot life thereby improving its processibility and facilitating the application of inhibition formulation to the nitramine propellant. — Yet another object of the invention is to provide a process for preparation of an inhibition formulation for nitramine propellants in which the inhibitor- propellant bond is not adversely affected during thermal cycling over a wide range of temperature i.e. from (-30 to (+55°C). Still another object of the invention is to provide a process for preparation of an inhibition formulation having improved compatibility with nitramine propellants which results in higher shelf life of the propellant. Still further object of the invention is to provide an inhibition formulation for nitramine propellant whose glass transition temperature matches with that of the nitramine propellants thereby making it compatible with the nitramine propellant formulation. STATEMENT OF INVENTION According to this invention there is provided a process for preparation of inhibitor formulation for nitramine based composite modified double based (CMDB) propellants comprising in the steps of : a) preparing a binder solution by mixing binder material and plasticiser b) dissolving additives in the binder solution c) adding filler materials with mixing d) adding isocyanate with stirring e) curing of inhibitor formulation In accordance with the present invention, there is provided a process for preparation of an inhibition formulation for nitramine based composite modified double based propellant which results in high bond strength of inhibitor-nitramine propellant interface. The tensile strength of the inhibitor formulation and that of nitramine propellant matches with each other. In case of proposed inhibitor formulation, the inhibitor-propellant interface remains stable during thermal cycling of the propellant over a wide range of temperature from -30 to (+) 55 C and the shelf life of the inhibited propellant is also very high. The inhibitor formulation does not utilise any banned material and it has a higher pot life thereby facilitating the application of inhibitor slurry over the nitramine propellant. The glass transition temperature of the inhibition formulation matches with that of the nitramine. propellant thereby making it compatible with the nitramine propellant. The proposed inhibitor formulation, when applied to the propellant surface, does not result in the significant migration of plasticizer to the propellant surface over a period of time thus improving the performance of the propellant. DESCRIPTION OF THE PROCESS According to present invention, the process for preparing inhibitor formulation for nitramine propellants comprises of following steps. (a) Preparation of binder The binder material viz, hydroxyl terminated polybutadieneJHTPB) and plasticizer material viz, isodecyl pelargonate~(IDP) are taken ma mixer bowl after weighing them individually. The mixture is deaerated under vacuum (at (b)Addition of additives Next, antj oxidant cum cross linking agent (pytogallol) and curing catalyst ferric acetyl acetonate (FeAA) are dissolved in the above prepared binder solution The solution is cooled to the room temperature. (c) Addition of filler materials Carbon black (type N-774) is added to the above solution with continuous stirring, and mixing is carried out for 10 minutes followed by addition of antimony trioxide (Sb2O3) and mixing for 10 minutes. (d) Addition of isocvnate ' The contents from the mixer bowl are transferred in a vacuum dessicator and is dearated for 30 minutes at vacuum( (e) Curing of inhibitor formulation Finally, the slurry is degassed under vacuum and poured in tray to obtain 2.5 - 3.0 mm thick sheets. These sheets are cured at room temperature for one day and post cured at 45 ° C for five days. At the end of the processing, these sheets are characterised for tensile strength and percent elongation using Instron Universal Testing Machine while the decomposition pattern of the inhibitor formulation is studied by carrying differential thermal analysis in air. The glass transition temperature of the formulation is determined by using Differential Scanning Calorimeter Similarly, plasticizer migration and bond strength of the inhibitor-propellant interface are also determined. The inhibitor isslurry cast over the nitramine propellant with bottom feeding technique. WORKING EXAMPLE 500 gm of binder material hydroxyl terminated polybutadiene (HTPB) and 50 gm plasticizer material isodecyl pelargonate (IDP) are taken in a mixer bowl after weighing them individually. The mixture is deaerated under vacuum (at Finally, at the end of the processing, the mechanical and other performance characteristics of the these sheets are studied with the help of standard evaluation techniques. The characteristics of the present inhibitor formulation, determined in above manner, has been summarised in the following table. S No PROPERTY VALUE 1 Tensile Strength (kgf/cm2 ) 18 2 Elongation (%) 120 3. Shore Hardness (A) 55-60 4 Plasticizer migration (%) 3-4 5 Bond Strength (kgf/cm2 >15 6 Viscosity (at 27° C) (cps) 70,000 7 Pot Life (minutes) 50-60 8 Glass Transition Temperature (° C) -75 9 Decomposition (° C) 515 It is to be understood that the process of present invention is susceptible to adaptations, changes, 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 inhibitor formulation for nitramine based composite modified double based (CMDB) propellants comprising in the steps of: a) preparing a binder solution by mixing binder material and plasticiser b) dissolving additives in the binder solution c) adding filler materials with mixing d) adding isocyanate with stirring e) curing of inhibitor formulation 2. A process as claimed in claim 1 wherein said binder material is preferably hydroxyl terminated polybutadiene (HTPB). 3. A process as claimed in claim 1 wherein said plasticiser is Isodecyl Pelargonate (IDP). 4. A process as claimed in claim 1 wherein said additives used are preferably pyrogallol as an anti-oxidant cum cross-linking agent and Ferric acetyl acetonate as curing agent. 5. A process as claimed in claim 1 wherein said filler materials are carbon black and antimony trioxide. 6. A process for preparation of inhibitor formulation for nitramine based composite modified double based (CMDB) propellants as prepared by the process substantially described and illustrated herein.

Documents:

403-del-2000-abstract.pdf

403-del-2000-claims.pdf

403-del-2000-correspondence-others.pdf

403-del-2000-correspondence-po.pdf

403-del-2000-description (complete).pdf

403-del-2000-form-1.pdf

403-del-2000-form-19.pdf

403-del-2000-form-2.pdf

403-del-2000-form-3.pdf

403-del-2000-gpa.pdf