Title of Invention

"A process for preparing of a propellant with ultra high burn rate"

Abstract

This invention is related to a composite propellent having ultra high burn.The composite p ropellant has an i norganic oxidiser, a po1ymeric binder, plasticissr, a curative agent, processing aid, bonding agent and at least two modifiers of which at least one modifier is a liquid and is a plasticizer The invention is also related to a process for the preparation of the above composite propel1ant. The process comprises in reacting a polymeric binder at a temperature of 45 to 550C„ A modifier is added to said reaction mixture,, Inorganic oxidiser is then added and allowed to react with said mixture under stirring for 4 to S minutes,,

Full Text

This invention relates to a process for preparation of a propellant with ultra high burn rate. In .particular, this invention relates to a propellant based on hydroxy terminated polybutadiene (HTPB). The composite propellants as reported in prior art comprises of inorganic oxidisers like ammonium perchlorate, metallic fuel like aluminium powder polymeric fuel binder like hydroxy terminated polybutadiene herein after to be named as HTPB. The HTPB used is cured with a di-isocyanate. At times the composite propellants without aluminium fuel are used for specific applications having a requirement of gaseous exhaust free from condensed particles. Certain additives like burn-rate modifiers, curing agents, processing aids, bonding agents etc have also been proposed to be incorporated in the propellant formulation for the said purpose. Ammonium perchlorate, herein after to be named as AP, of varied particles sizes from 10 microns to 400 microns have been reported in composite propellants to achieve required burn rates, improved processability and maximum possible loading density. Composite propellants of prior art in general comprises of coarse AP, hereinafter to be named as C-AP, of about 220 microns particle size and of fine AP, hereinafter to be named as F-AP, the particle size generally above 10 microns and upto above 40 microns. The coarse to fine ratio generally varies form-50/50 to 70/30 which in turn is selected to achieve required burn rate of the composite propellants. The disadvantage of this composition with this particle size is that this does not result in ultra high burn rate properties of the composite propellants. Another disadvantage of this composition is that as content of F-AP is increased for achieving higher burn rates, it will require more binder for surface wetting which may cause increase in viscosity of the resulted slurry. this in turn looses its, flow properties and finally results in processing problems and casting becomes difficult. The metal based bum rate modifiers already known in the prior art, like ferric oxide, cupric oxide, copper chromite, etc suffer from the drawback that the increase in concentration of these modifiers to further increase the burn rates of composite propellants results in very fast viscosity build-up of the propellant by accelerating propellant curing reactions, again causing processing problems! Certain liquid bum rate modifiers reported in the prior art like ferrocene derivatives are also reported to be used in composite propellants even in high concentrations. The disadvantage of such modifiers of the prior art is that the high concentration of such inert liquid bum rate modifiers alone in the propellant compositions adversely affects the energetics of the propellant. The composite propellants based on nitrocellulose, nitro poly alcohols or oxygen carriers with certain organic or inorganic metal compounds such as lead salts of higher fatty acids or specific organic compounds of copper, manganese or lead have direct effect on burning properties not to the extent of desired ultra high burning properties. Furthermore, the generally known composite propellants of prior art requires high percentage of modifiers for high bum rate which in turn results in processing and curing problems. An object of the present invention is to propose a process for preparation of a propellant with desired ultra high bum rates and a process for the preparation thereof. Another object of the present invention is to propose a process for preparation of a propellant having ultra high bum rates comprising at least two bum rate modifiers which are in turn used in low concentration. Yet another object of the present invention is to propose a process for preparation of a propellant comprising atleast one solid burn rate modifier and one liquid burn rate modifier. Still another object of the present invention is to propose a process for preparation of a propellant formulation having good flow properties in addition to the presence of high loading of very F-AP. Yet another object of the present invention is to propose a process for preparation of a propellant with no propellant processability and energetic disadvantages. A further object of this invention is to propose a process for preparation of a propellant with atleast two burn rate modifiers, one of which acts as plasticizer and processing aid also. According to this invention there is provided a process for preparation of a propellant with ultra high burn rate comprising the steps of reacting a binder, plasticiser, a processing aid and a bonding agent in reaction vessel with stirring under vacuum of less than 10mm of mercury for 30 to 35 minutes with continuous circulation of water at temperature of 62 to 65°C in the outer jacket of reaction vessel so as to achieve temperature of 45°C to 55°C inside the reaction vessel, wherein binder is hydroxy terminated polybutadiene (HTPB) in amount 55 to 65% by weight, plasticiser is di-octyl adipate (DOA) in amount 35 to 45% by weight, processing aid is lecithin in amount 0.3 to 0.5% and bonding agent is adduct of methyl aziridine phosphine oxide, tartaric acid, each taken in amount 0.3 to 0.5% by weight; releasing the vacuum and adding to the reaction mixture obtained by step (a) solid and liquid burn rate modifier wherein solid burn rate modifier is copper chromite in amount 0.5 to 2.5% by weight and liquid burn rate modifier is n-butyl ferrocene in amount 0.5 to 2.5% by weight; adding inorganic oxider in 2 to 4 in statements with iritermediate mixing for 4 to 8 minutes on each addition followed by stirring for 60 to 130 minutes without vacuum which is then followed with stirring for 30 to 60 minutes with vacuum of less than 10mm of mercury obtaining propellant in slurry form wherein inorganic oxider is a mixture of coarse particles of ammonium per chlorate of 220 to 230 microns and fine particles upto 5 microns of ammonium per chlorate wherein fine particles of ammonium per chlorate and coarse particles of ammonium per chlorate are in the ratio of 90:10; adding toluene di-isocyanate (DOA) as curative agent in amount 1.5 to 6% by weight, after lowering down the temperature of outer jacket of reaction vessel to a temperature of 30 to 35°C by circulation of cold water, followed by mixing for 30 to 50 minutes without vacuum and for 15 to 25 minutes with vacuum; casting the slurry thus obtained by step (d) and curing in water jacketed oven at temperature of 60 to 80°C for 6 to 7 days into the desired shapes to obtain the propellant. According to the preferred method of manufacture of proposed solid composite propellant of the present invention, the HTPB based binder system is stirred under vacuum less than 10mm of mercury for 30 to 35 minutes preferably in the vertical planetary mixer with provision of continuous circulation of tap water preferably at the temperature of 62 to 65°C, in the outer jacket of the reaction vessel to achieve 45 to 55°C temperature inside the reaction vessel. The burn rate modifier comprising of solid and liquid modifiers are added to the-reacting mixers in the reaction vessel after releasing the vacuum. Subsequently, the AP is added in the ratio of 90:10 of very fine and coarse AP in preferably 2 to 4 installments to achieve the complete wetting process preferably by intermediate mixing each of 4 to 8 minutes on each additions. The stirring of the reacted mixer is continued for 60 to 130 minutes preferably 80 to 100 minutes, atleast for 30 to 60 rninutes without vacuum and 30 to 60 minutes with vacuum preferably less than 10mm of mercury; better results are achieved by mixing preferably 50 to 60 minutes under vacuum and also 50 to 60 minutes without vacuum and the resulted propellant is in slurry form to which the said curative agent is added after lowering down the temperature of the outer jacket of about -30 to 35° C by circulation of cold water. On complete addition of said curative agent, the mixing is further carried out 30 to 50 minutes• preferably 40; to 65 minutes for atleast 20 to 40 minutes without vacuum and 15 to 25 minutes with vacuum. The resulted composite propellant in slurry form is cast into'pre-assembled casting fixtures and which are in turn kept for curing in water jacketted 'oven at selected temperatures of 60 to 80° preferably 67 to 72°C for about six to eight days for better results. Cured composite propellant grains are taken out from casting fixtures in the shape of tubular cylinder form or any other internal configuration as per required applications. The present invention is illustrated': by the following working examples which are self explanatory. The object of the present disclosures are not intended to limit the scope of the invention, any such modifications are within the scope of the proposed invention. The composite propellants manufactured according to the method described here in above having follwing formulations according to the preferred embodiments of the present invention are Example 1 : A solid composite propellant prepared according to the described method comprises of AP 80%(C-AP/F-AP= 10/90); HTPB based binder system 20%, binder system consists of HTPB=58%, DOA =39%, di-isocyanate = 3%, lecithin=0.3 parts per 100 parts, said bonding agent =' 3 parts per 100 parts and modifier=nil. Propellant viscosity ( Kpa, 30° C) : 7.2, burning rate at 70 Kg/cm2 (mm/ sec): 13.7. Example 2: A solid composite propellant prepared according to the der.cr.ibed method comprises of AP 80%(C-AP/F-AP= 10/90), HTPB bared binder system 20%,' binder system consists of HTPB= 58%, DO A- 39%, di-isocyanate = 3%, lecithin= 0.3 parts per 100 parts, said bonding agent =3 parts per ; 100 parts and modifier = copper chromite — 2 parts per 1.00 parts, Propellant. viscosit (KPa, 3 00C ) : 16. 1 and burning rate at 70 Kg/cm2 (mm/sec) : 20.9. Example 3 : A solid composite propellant prepared according to the described method comprises of AP 80%(C-AP/F-AP= 10/90),- HTPB based binder system 20%, binder system consists of HTPB =58%, DOA- 39%, di-isocyanate =3%, processing aid=0.3 part per 100 parts, bonding agents" =3 parts per .100 parts and modifier=copper chromite =1.75 per part per ,100 parts and n-bntyl ferrocene =1.75 per part for 100 parts. Propellant viscosity (Kpa, 30°C) : 7.9, burning rate at 7 0 Kg/cm2 (mm/sec) : 3 1.3.. Example 4: A solid composite propellant prepared "according to the described method comprises of AP 80%(C-AP/E-AP= 10/90), HTPB based binder system 20%, binder system consists of HTPB = 5fU , DOA =3 9%, di-isocyanate= 3%, lecithin=0.3 parts per 100 parts, said bonding agents= 3 parts per 1.00 parts and modifier= copper chromite =2 parts per 100 parts, n-butyl ferrocene=2 parts per 100 parts. Propellant viscosity (KPa, 30 G) : 7.4 , burning rate at 7 0 Kg/cm2 (mm/ sec) : 3 7.5 I CLAIM: 1. A process for preparation of a propellant with ultra high bum rate comprising the steps of:- (a) reacting a binder, plasticiser, a processiilg aid and a bonding agent in reaction vessel with stirring under vacuum of less than 10mm of mercury for 30 to 35 minutes with continuous circulation of water at temperature of 62 to 65°C in the outer jacket of reaction vessel so as to achieve temperature of 45°C to 55°C inside the reaction vessel, wherein binder is hydroxy terminated polybutadiene (HTPB) in amount 55 to 65% by weight, plasticiser is di-octyl adipate (DOA) in amount 35 to 45% by weight, processing aid is lecithin in amount 0.3 to 0.5% and bonding agent is adduct of methyl aziridine phosphine oxide, tartaric acid, each taken in amount 0.3 to 0.5% by weight; (b) releasing the vacuum and adding to the reaction mixture obtained by step (a) solid and liquid burn rate modifier wherein solid burn rate modifier is copper chromite in amount 0.5 to 2.5% by weight and liquid bum rate modifier is n-butyl ferrocene in amount 0.5 to 2.5% by weight; (c) adding inorganic oxider in 2 to 4 in statements with intermediate mixing for 4 to 8 minutes on each addition followed by stirring for 60 to 130 minutes without vacuum which is then followed with stirring for 30 to 60 minutes with vacuum of less than 10mm of mercury obtaining propellant in slurry form wherein inorganic oxider is a mixture of coarse particles of ammonium per chlorate of 220 to 230 microns and fine particles upto 5 microns of ammonium per chlorate wherein fine particles of ammonium per chlorate and coarse particles of ammonium per chlorate are in the ratio of 90:10; (d) adding toluene di-isocyanate (DOA) as curative agent in amount 1.5 to 6% by weight, after lowering down the temperature of outer jacket of reaction vessel to a temperature of 30 to 35°C by circulation of cold water, followed by mixing for 30 to 50 minutes without vacuum and for 15 to 25 minutes with vacuum; (e) casting the slurry thus obtained by step (d) and curing in water jacketed oven at temperature of 60 to 80°C for 6 to 7 days into the desired shapes to obtain the propellant; 2. A process as claimed in claim 1 wherein said stirring without vacuum after addition of inorganic oxidizer ammonium per chlorate is carried out preferably for 50 to 60 minutes. A process as claimed in claim 1 wherein said stirring with vacuum of less than 10mm Hg is carried out preferably for 50 to 60 minutes. A process as claimed in claim 1 wherein said stirring without vacuum after addition of curative agent is carried out preferably for 40 to 45 minutes. A process as claimed in claim 1 wherein said curing after casting is carried out preferably between 67 to 72°C. A process for preparation of a propellant with ultra high burn rate as substantially described and herein illustrated.

Documents:

2338-del-1995-abstract.pdf

2338-del-1995-claims.pdf

2338-del-1995-complete cpecification (granted).pdf

2338-del-1995-correspondence-others.pdf

2338-del-1995-correspondence-po.pdf

2338-del-1995-description (complete).pdf

2338-del-1995-form-1.pdf

2338-del-1995-form-2.pdf

2338-del-1995-form-3.pdf

2338-del-1995-form-4.pdf

2338-del-1995-gpa.pdf