Age resistant low density peroxide cured EPDM rubber based insulation without liquid EPDM and its use thereof in composite rocket motor casing

Abstract

The present invention relates to a low density peroxide cured EPDM rubber based insulation suitable for use in large composite rocket motor casing (CRMC), which uses only conventional filler and without using liquid EPDM. The said insulation can be used in large CRMC cast with all types of propellants viz., Composite based Solid Propellant, double base solid propellant, NEPE based new generation propellant etc. meeting insulation requirements of large CRMCs, improved thermal properties while retaining the required mechanical properties, having longer shelf life, higher thermal stability and excellent interfacial bonding strength with various interfaces. It also relates to a process for preparing peroxide cured EPDM rubber based insulation.

Description

[0001] AGE RESISTANT LOW DENSITY PEROXIDE CURED EPDM RUBBER BASED INSULATION WITHOUT LIQUID EPDM AND ITS USE THEREOF IN COMPOSITE ROCKET MOTOR CASING

[0002] FIELD OF INVENTION

[0003] The present invention relates to a low density peroxide cured EPDM rubber based insulation without liquid EPDM and a process of preparation thereof. Particularly, it relates to EPDM insulation compositions for use in large Composite Rocket Motor Casing (CRMC).

[0004] BACKGROUND OF INVENTION

[0005] The combustion of solid rocket propellant generates extreme conditions within the rocket motor casing. If the hot combustion gases penetrates through the insulation and liner, the casing may melt, causing the rocket motor to fail. Thus, it is crucial that insulation withstands the extreme conditions experienced during propellant combustion and protects the casing from the burning propellant. Also, requirement of low-density insulator is mandatory to reduce the inert weight of the propulsion system.

[0006] Indian patent application 3103 / DEL / 2005 discloses 3 formulation based on EPDM rubber blended with Hypalon, Neoprene and hypalon Neoprene blend as insulation materials for case bonded solid rocket motors. The claimed formulation consists of 50-130 PHR of EPDM, 10-50 PHR of Hypalon, Neoprene and their blend, 30-50 PHR of fumed silica, 1-2 PHR of sulphur as vulcanizing agent. The said composition exhibits tensile strength of 100-400 kgf / cm2, % elongation of 425 -1000, density 1-3.5 g / cm3, shore A hardness 70-80, thermal conductivity 0.110- 0.330 W / mK, erosion rate 0.01- 0.09 mm / sec and peel strength 0.10-3.7 kg / cm. The claimed formulation comprises of Hypalon (which is nothing but chlorosulphonated polyethylene) and sulphur, which will limit its end application only to composite solid propellant and will preclude the end use of insulation for double base propellant and new generation propellant having energetic nitro groups. Further, use of Hypalon increases the density and reduces the flexibility of elastomeric compound, thereby it is less desirable for large CRMC. Indian patent application 3467 / DEL / 2005 discloses a formulation for case bonded solid rocket motors consisting of 50-130 PHR of EPDM rubber, 10-70 PHR of liquid EPDM rubber, 30-50 PHR of fumed silica, 5-20 PHR of fibrous filler and 1-2 PHR of sulphur as vulcanizing agent. The said composition exhibits tensile strength of 100-400 kgf / cm2, % elongation of 425 -1000, density 0.5-3.5 g / cm3, shore A hardness 70-90, thermal conductivity O.11O-O.33O W / mK, erosion rate 0.01- 0.09 mm / sec and peel strength 0.10-3.7 kg / cm. The formulation is sulphur cured and has fibrous fillers.

[0007] Indian Patent application 974 / KOL / 2013 describes a formulation of low density EPDM-BIIR blend for light weight rocket motor insulation compound. The formulation consists of 50-100 parts EPDM elastomer, 5-10 parts polyimide, 5-50 parts Bromobutyl rubber, 5-25 parts nanosilica and 0.3-2.0 parts crystex sulphur. The formulation exhibits tensile strength of 60 kg / cm2, % Elongation of 743, density 0.99-1.02 g / cm3, hardness 55-60, specific heat 0.5 cal / gm / °c, thermal conductivity 0.21 W / mk, erosion rate 0.17mm / sec and peel strength 0.6-0.65 kgf / cm. The tensile strength achieved of the claimed formulation is lower than the requirement of insulation materials for large CRMC. Moreover, this formulation comprises nanosilica which is expensive.

[0008] US Patent 4501841 describes 5 different elastomers including EPDM based elastomer, used as a low smoke insulation for rocket motors. The claimed EPDM rubber based formulation comprises of 100 parts EPDM rubber, 15-75 parts polyaramid pulp, 10-30 parts of hydrated silica and 1-5 parts of peroxide as curing agent. The claimed formulation exhibits tensile strength of 16-39 MPa, % elongation at break of 10-30 and shore A hardness of 85-95. However, % elongation claimed of this formulation makes it unacceptable for large CRMC. Further, presence of Polyaramid pulp might impart appreciable hygroscopicity and scatter in mechanical properties and appreciable difference between mechanical properties of warp and weft directions, which are not desirable for large CRMC. Formulations without Liquid EPDM as claimed in US Patent No: 4501841, are not suitable for large Rocket Motor as % elongation claimed of this formulation makes them unacceptable for large CRMC. US Patent 5985970 describes a formulation of silicone modified EPDM elastomer cured with organic peroxide and the process for production of tack free elastomeric surface. The claimed formulation exhibits tensile strength of 13 MPa, % elongation of 520 and hardness duro A-47. The composition is used for rubber products like hoses, rubber sheets, roofing sheets, canvas sheets, weather strips, sealing sponge, protector tubes, protector sponges, etc. However, this patent reveals no information on thermal properties & and interface properties. Silicone, in general will exhibit poor bonding. Therefore, it raises skepticism over the bond strength of insulation with the various interfaces encountered during insulation lining of large CRMCs.

[0009] US Patent 6071996 describes a formulation, which consists of 100 parts of EPDM rubber, 60-700 parts of carbon black as reinforcing filler, 40-175 parts of processing materials and 2-10 parts of sulphur as curing system. The claimed formulation exhibits tensile strength of 4.5-9 MPa and % Elongation of 290-484. The said formulation is used as walkway pad for excellent weather resistance and low temperature flexibility. This patent too does not reveal any information on thermal properties. Further mechanical properties claimed do not meet the insulation requirement of large CRMC. Moreover, the presence of Carbon black as reinforcing filler is unacceptable for insulator of large CRMC as thermal conductivity has to be as low as possible. Similarly formulation without liquid EPDM as claimed in US Patent 6071996, is also not suitable for large CRMC and used as walkway pad for excellent weather resistance and low temperature flexibility.

[0010] US2018265686A1 relates to a precursor composition for rocket insulation, comprising, before curing: EPDM, precipitated silica, magnesium hydroxide, polymerized l,2-dihydro-2,2,4-trimethylquinoline, a solid chlorinated paraffin, stearic acid, a five carbon petroleum hydrocarbon, a co-agent, and a peroxide. However, this composition involves the use of additional fillers (zinc oxide or magnesium hydroxide or both zinc oxide and magnesium hydroxide) and components like flame retardant, antioxidant. Density claimed by this patent is quite high i.e. 1.05-1.08 g / cm3. It does not disclose on the achieved thermal properties. Further, none of the compositions of this patent meets both tensile strength and % elongation as required by CRMC insulation (Composition which meets tensile strength does not meet % Elongation and vice-versa).

[0011] Indian Patent application No. 202211014898 dated March 17, 2022 provides an elastomeric rubber insulation composition for composite rocket motor casing (CRMC) comprising: (i) Solid ethylene propylene diene terpolymer (EPDM) rubber ranging from 80 to 95 phr; (ii) Liquid EPDM ranging from 5 to 20 phr; (iii) Precipitated silica filler ranging from 20 to 50 phr; (iv) Peroxide curing agent ranging from 1 to 10 phr and; (v) Additives.

[0012] Despite availability of EPDM based insulations for Rocket motors, there is a requirement for development of peroxide cured EPDM insulation having a low curing temperature and which is compatible with new generation NEPE (nitrate ester plasticized polyether) based, conventional composite based and double based propellant, having low density and required mechanical properties, long shelf life, thermal stability while using proven and indigenously available raw-materials and does not use fibrous fillers. The present inventors have surprisingly developed an efficient peroxide cured EPDM insulation composition which ameliorates the aforesaid shortcomings of the prior art.

[0013] OBJECTS OF THE INVENTION

[0014] It is an object of the present invention to overcome the shortcomings of the prior art.

[0015] It is an object of the present invention to overcome the shortcomings of low density peroxide cured EPDM based insulation with respect to cure temperature.

[0016] It is another object of the present invention to demonstrate the ageing resistance of such a low density peroxide cured EPDM insulation through accelerated ageing.

[0017] It is another object of the present invention to demonstrate the thermal stability / heat resistance of the low density peroxide cured insulation without liquid EPDM upon repeated exposure to additional heating cycle as warranted by the Rocket Motor before & during propellant casting. It is another object of the present invention to demonstrate the attainment of required thermal properties especially erosion rate while ensuring just optimum cure at temperature as low as 120°C.

[0018] It is an object of the present invention to provide an elastomeric insulation for large CRMC, which is solely based on EPDM rubber, without having any need to blend with secondary polymers like hypalon and does not require the addition of fibrous filler (Kevlar pulp).

[0019] It is yet another object of the present invention to provide a process of preparation of such elastomeric composition.

[0020] SUMMARY OF THE INVENTION

[0021] According to an aspect of the present invention there is provided a low density peroxide cured EPDM rubber based insulation composition.

[0022] According to another aspect of present invention there is provided a process for preparing a low density peroxide cured EPDM rubber based insulation composition.

[0023] According to yet another aspect of present invention there is provided a composite rocket motor casing (CRMC) composed of an elastomeric rubber insulation composition.

[0024] DETAILED DESCRIPTION OF THE INVENTION

[0025] The following description is provided to assist in a comprehensive understanding of exemplary embodiments of the invention. It includes various specific details to assist in that understanding but these are to be regarded as merely exemplary.

[0026] Accordingly, those of ordinary skill in the art will recognize that various changes and modifications of the embodiments described herein can be made without departing from the scope of the invention. In addition, descriptions of well-known functions and constructions are omitted for clarity and conciseness.

[0027] The terms and words used in the following description and claims are not limited to the bibliographical meanings, but, are merely used by the inventor to enable a clear and consistent understanding of the invention. Accordingly, it should be apparent to those skilled in the art that the following description of exemplary embodiments of the present invention are provided for illustration purpose only and not for the purpose of limiting the scope of the invention as defined by the appended claims and their equivalents.

[0028] It is to be understood that the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise.

[0029] Features that are described and / or illustrated with respect to one embodiment may be used in the same way or in a similar way in one or more other embodiments and / or in combination with or instead of the features of the other embodiments.

[0030] It should be emphasized that the term “comprises / comprising” when used in this specification is taken to specify the presence of stated features, steps or components but does not preclude the presence or addition of one or more other features, steps, components or groups thereof.

[0031] The term “phr” as used herein means parts per hundred rubber.

[0032] The term “CRMC” as used herein means composite rocket motor casing.

[0033] The term “EPDM” as used herein means ethylene propylene diene terpolymer (M refers to polymers having saturated backbone and does not stand for Monomer). “Liquid EPDM” means EPDM terpolymer that is flowable at room temperature.

[0034] The term “vulcanization / compounding” as used herein means a chemical process in which rubber is heated with curative, activator and accelerator. The process involves the formation of cross-links between rubber molecules so as to achieve improved elasticity, resilience, tensile strength, viscosity, hardness and weather resistance.

[0035] The present invention relates to a low density peroxide cured EPDM rubber based insulation and a process of preparation thereof. The present invention pertains to a low density insulation composition for large CRMC, which consists of solid EPDM terpolymer, precipitated silica as reinforcing filler and peroxide as curing agent. The present invention also covers the process for production of rubber compound towards insulation lining of CRMC.

[0036] The present invention shows improvement over the conventional EPDM formulations. Patent application no. 202211014898 relates to a composition comprising 5 to 20 PHR liquid EPDM Rubber. Such an EPDM composition warrants complete curing which occurs at 140°C / 4 hours in order to achieve the required properties especially, the required erosion rate at 300 W / cm2heat flux of 0.2 mm maximum. However, lower temperature curing is required for Composite Rocket Motor Casings because of constraints posed by glass transition temperature (Tg).

[0037] The present invention provides the insulation without liquid EPDM which despite meeting all requirements of large Rocket Motor insulation, also offers flexibility to cure insulation at temperature as low as 120°C. Further, such an insulation exhibits extremely good ageing resistance by retaining Ageing coefficient of 0.77 even after 28 days of ageing at 90°C.

[0038] Liquid EPDM in conventional formulations aids mixing and enhances the uniform distribution of silica filler and peroxide curative & catalyst also. Nonaddition of liquid EPDM leads to appreciable increase in the rigidity of the base EPDM rubber. Therefore, ensuring the homogeneous dispersion of filler & curative, while overcoming the rigidity constraint is the major challenge.

[0039] The present invention gives flexibility of using only solid EPDM (zero PHR of liquid EPDM). The present inventors have innovated the mixing process such that processing difficulties in the absence of liquid EPDM are overcome completely. The composition is solely based on solid EPDM rubber, without having any need to blend with secondary polymers like hypalon and does not require the addition of fibrous filler (Kevlar pulp).

[0040] The present formulation meets the below requirements of Large Rocket Motor: i. The tensile strength in both warp and weft direction should be 100 kg / cm2(minimum) and % Elongation in both warp and weft direction should be 600 (minimum). ii. Thermal conductivity at 80°C should be 0.27 W / m°K (maximum), Specific heat at 80°C should be 1.46 KJ / Kg (minimum) and Co-efficient of linear thermal expansion should be 3.0X10’4 / °C (maximum). iii.The erosion rate at 300 W / cm2heat flux should be as low as possible, preferably less than 0.20 mm / sec. Heat of ablation should be at least 16 MJ / Kg (16-18 MJ / Kg). iv. Insulation should exhibit good interfacial bonding strength as measured in terms of peel strength. Peel strength between composite to Rubber should be 5 kg-f / cm (minimum), Rubber to Rubber should be 2 kg-f / cm (minimum) and Rubber to Propellant should be 0.6 kg-f / cm (minimum). v. Insulation should be less hygroscopic. vi. Insulation should have higher thermal stability, higher ageing resistance & longer shelf life.

[0041] The present invention also provides a process for production of rubber compound towards lining of large CRMC.

[0042] The present invention provides an elastomeric rubber insulation composition for composite rocket motor casing (CRMC) comprising:

[0043] (i) Solid ethylene propylene diene terpolymer (EPDM) rubber of 100 phr;

[0044] (ii) Precipitated silica filler ranging from 20 to 26 phr;

[0045] (iii) Peroxide curing agent ranging from 1 to 10 phr and;

[0046] (iv) Additives;

[0047] Wherein the said composition does not comprise liquid EPDM.

[0048] In an embodiment, the peroxide curing agent is selected from Dicumyl Peroxide (DCP), di-tert-butyl-peroxide (DTBP), l,l-di-(t- butylperoxy)-3 ,3 ,5-trimethylcyclohexane, 1 , 1 -di-(t-butylperoxy)-3 ,3 ,5 - trimethylcyclohexane.

[0049] In an embodiment, the additives are selected from 5 to 25 phr process oil, 5 to 25 phr Aromatic polyether based tackifier, 1 to 5 phr plasticizer and process aids, 0.5 to 5 phr pigment and 2 to 6 phr curing coagents.

[0050] In an embodiment, the process oil is selected from Naphthenic Oil.

[0051] In an embodiment, the tackifier is selected from Aromatic polyether, wingtack-95, Vulkanol FH, aliphatic resin, and the like. In an embodiment, the Plasticizer and Process aids are selected from Polyethylene glycol (PEG), Di-octyl Phthalate (DOP), Diethylene Glycol (DEG), Stearic Acid, and the like

[0052] In an embodiment, the pigment is selected from titanium dioxide (TiO2).

[0053] In an embodiment, the curing co-agents are selected from Zinc Dimethacrylate (ZDMA), trimethylolpropane trimethacrylate, high vinyl poly (butadiene) and the like.

[0054] In an embodiment, density of the EPDM insulation ranges from 0.9932 to 1.0001 g / cm3.

[0055] In an embodiment, said composition is free of fibrous fillers and non- EPDM polymers.

[0056] The present invention also provides a process for preparing an elastomeric rubber insulation composition comprising the steps of:

[0057] I. Pre-mixing the components of solid EPDM, precipitated silica filler, process oil, a portion of Aromatic polyether based tackifier, Plasticizer and Process aids, and pigment;

[0058] II. Warm-up mixing of the rubber mass formed at Step (I);

[0059] III. Adding remaining portion of tackifier after warming up at Step (II);

[0060] IV. Final mixing of the rubber mass of Step (III) with a dissolved solution of peroxide curing agent followed by curing co-agent;

[0061] V. Curing the rubber mixture of step (IV) at 120°C for 4 hours or 140°C for 2.5 hours to obtain the elastomeric rubber insulation composition;

[0062] Wherein the precipitated silica, tackifier, process oil, plasticizer and process aids are added in multiple stages at Step (I) for uniform dispersion of silica; Wherein the ratio of tackifier added at step (I) premixing to Step (III) mixing is 70:30 by weight.

[0063] Advantages of present invention:

[0064] • The present invention provides the insulation without liquid EPDM which despite meeting all requirements of large Rocket Motor insulation, also offers flexibility to cure insulation at temperature as low as 120°C and also for much shorter durations at temperatures such as 140°C (just 2.5 hours). Further, such an insulation exhibits extremely good ageing resistance by retaining Ageing co-efficient of 0.77 even after 28 days of ageing at 90°C.

[0065] • Present Invention does not use fibrous fillers (Kevlar / Poly- aramid pulp) and polar polymers viz. Hypalon (Chloro sulphonated polyethylene).

[0066] • Capable of achieving low density in range of 0.9932 to 1.0001 g / cm3.

[0067] • Provides versatile insulation for large CRMC to be cast with propellant of all types viz., Composite based Solid Propellant, double base solid propellant, NEPE based new generation propellant etc.

[0068] EXAMPLES:

[0069] The following examples are meant to illustrate the present invention. The examples are presented to exemplify the invention and are not to be considered as limiting the scope of the invention.

[0070] EXAMPLE -1

[0071] Preparation of EPDM composition according to present invention

[0072] Solid EPDM terpolymer as base rubber, Ultrasil VN-3 based precipitated silica as reinforcing filler, Rubber oil, plasticizer, aromatic polyether based tackifier, TiCh and suitable peroxide and co-agent. The formulations is given in Table- 1. Table-1: Composition

[0073] Mixing / Compounding Process Details:

[0074] Compounding of rubber using composition of Table 1 was carried out using counter rotating two roll mill of capacity 15 kg. During the entire mixing process, the gap between the rolls was adjusted within 0.1 - 2 mm in order to ensure proper squeezing, band formation, blending and mixing. Chilled water (temperature 15- 20°C) circulation was kept on during the entire mixing process in order to ascertain that the surface temperature of rubber mass being mixed, did not exceed 60-65°C in any point of time during mixing.

[0075] Mixing was carried out in two phases viz. premixing and final mixing. During premixing, all ingredients except peroxide and co-agent were added and mixed together. During final mixing, peroxide and co-agent were added.

[0076] During premixing, solid EPDM was masticated in the two roll mill in order to obtain band of rubber. This was followed by incorporation of precipitated silica in number of small stages and the given quantities of tackifier (70% by weight), naphthenic oil, plasticizer and process aid were also added in number of instances such that mixing difficulty due to friction is overcome and uniform dispersion of silica is ensured despite the absence of liquid EPDM; Thereafter, TiCh is added and mixing is continued with gradually decreasing the gap between the rollers so that best possible homogeneity is achieved during premixing. Adequate time gap is given between premixing and final mixing. Time gap recommended is at least 3-4 hours and preferably 12-16 hours. Humidity control of the mixing facility must be ensured. % Relative humidity must be within 50-60 %.

[0077] During final mixing, the rubber mass is squeezed between the rolls, till the plasticity and smoothness set in. Entire final mixing is carried out under chilled water circulation through the rolls such that at no point of time, temperature of the rubber mass exceeds 65°C.

[0078] Balance quantity of tackifier about 30% of weight is added just after warm up mixing of the EPDM sheet. Thereafter, Peroxide is dissolved in part quantity of one of the liquid ingredients and added as a solution into the rubber mass. After incorporation of peroxide, co-agent is added and mixing is continued. Thereafter, sheet of required thickness is drawn by feeding the rubber into the extruder.

[0079] Whereas, in IN202211014898, entire silica could be added quite fast with simultaneous incorporation of naphthenic oil, part quantity of tackifier 70% by weight, plasticizer and process aid, as liquid EPDM too probably aided the mixing. Furthermore, balance quantity of tackifier was added after addition of co-agent in IN202211014898.

[0080] EXAMPLE-2: Characterization of EPDM composition

[0081] Properties achieved by low density insulation without liquid EPDM cured at 140°C / 4 hours are given in Table-2.

[0082] Table-2: Physical, Mechanical, Thermal & Interface properties of low density insulation without liquid EPDM cured at 140°C / 4 hours

[0083] Properties achieved by low density insulation without liquid EPDM cured at 140°C / 2.5 hours are given in Table-3.

[0084] Table-3: Physical, Mechanical, Thermal & Interface properties of low density insulation without liquid EPDM cured at 140°C / 2.5 hours

[0085] Properties achieved by low density insulation without liquid EPDM cured at 120°C / 4 hours are given in Table-4.

[0086] Table-4: Physical, Mechanical, Thermal & Interface properties of low density insulation without liquid EPDM cured at 120°C / 4 hours

[0087] Table-5: Interface properties Evaluation after 3 Vi months

[0088] Effect of Preheating on Interface Properties: Specimens were prepared after 3 * months of compound manufacturing & subjected to preheating at 105°C for 8 hours & tested for peel strength.

[0089] Table-6: Interface properties Evaluation after 3 Vi months (subjected to 105°C at 8 hours preheating)

[0090] Table-7: Hot air oven Accelerated ageing at 90° C

[0091] Properties achieved of low density insulation without liquid EPDM are given in Table-2, 3 & 4. Such formulation gives flexibility of choosing cure temperature as low as 120°C for 4 hours, as cured properties at 120°C / 4 hours also meet the requirement of Large Rocket Motor (Table-4). Further, such a formulation retains the properties including interface properties up to 3.5 months (Table-5) and undergoes no degradation in interface properties (Table-6) even upon prolonged exposure at 105°C as warranted by the preheating before propellant casting of large Rocket Motors and additional curing in case of insulation repair. Cured insulation has been confirmed to have extremely good ageing resistance by accelerated ageing study (Table-7). EXAMPLE 3:

[0092] Comparative Example:

[0093] Low density peroxide cured EPDM insulation without liquid EPDM is an embodiment of complete perfection in the arena of peroxide cured EPDM insulation of large rocket motors, as it gives the following benefits over the low density peroxide cured EPDM insulation with liquid EPDM (Patent application No. 202211014898 dated March 17, 2022).

[0094] It is to be understood that 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.

Claims

CLAIMS:

1. An elastomeric rubber insulation composition for composite rocket motor casing (CRMC) comprising:(i) Solid ethylene propylene diene terpolymer (EPDM) rubber of 100 phr;(ii) Precipitated silica filler ranging from 20 to 26 phr;(iii) Peroxide curing agent ranging from 1 to 10 phr and;(iv) Additives;Wherein the said composition does not comprise liquid EPDM.

2. The composition as claimed in claim 1, wherein the peroxide curing agent is selected from Dicumyl Peroxide (DCP), di-tert-butyl-peroxide (DTBP), l,l-di-(t-butylperoxy)-3,3,5-trimethylcyclohexane and 1 , l-di-(t- butylperoxy)-3,3,5-trimethylcyclohexane.

3. The composition as claimed in claim 1, wherein the additives are selected from 5 to 25 phr process oil, 5 to 25 phr Aromatic polyether based tackifier, 1 to 5 phr plasticizer and process aids, 0.5 to 5 phr pigment and 2 to 6 phr curing co-agents.

4. The composition as claimed in claim 3, wherein the process oil is selected from Naphthenic Oil.

5. The composition as claimed in claim 3, wherein the tackifier is selected from Aromatic polyether, wingtack-95, Vulcanol FH, aliphatic resin and the like.

6. The composition as claimed in claim 3, wherein the Plasticizer and Process aids are selected from Polyethylene glycol (PEG), Di-octyl Phthalate (DOP), Diethylene Glycol (DEG), Stearic Acid and the like.

7. The composition as claimed in claim 3, wherein the pigment is selected from titanium dioxide (TiCh).

8. The composition as claimed in claim 3, wherein the curing co-agents are selected from Zinc Dimethacrylate (ZDMA) trimethylolpropane trimethacrylate, high vinyl poly (butadiene).

9. The composition as claimed in any one of the claims 1 to 8, wherein density ranges from 0.9932 to 1.0001 g / cm3.

10. The composition as claimed in any one of the claims 1 to 9, wherein said composition is free of fibrous fillers and non- EPDM polymers.

11. A composite rocket motor casing (CRMC) composed of an elastomeric rubber insulation composition as claimed in any one of claims 1 to 10.

12. A process for preparing an elastomeric rubber insulation composition comprising the steps of:I. Pre-mixing the components of solid EPDM, precipitated silica filler, process oil, a portion of Aromatic polyether based tackifier, Plasticizer & Process aids, and pigment;II. Warm-up mixing of the rubber mass formed at Step (I);III. Adding remaining portion of tackifier after warming up at Step (II);IV. Final mixing of the rubber mass obtained at Step (III) with a dissolved solution of peroxide curing agent followed by curing co- agent;V. Curing the rubber mixture of Step (IV) at 120°C for 4 hours or 140°C for 2.5 hours to obtain the elastomeric rubber insulation composition;Wherein the precipitated silica, tackifier, process oil, plasticizer and process aids are added in multiple stages at Step (I) for uniform dispersion of silica;Wherein the ratio of tackifier added at step (I) premixing to Step (III) mixing is 70:30 by weight.

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