The study carried out so far on the application of ethylene-propylene diene rubber (EPDM) in the field of insulation of case bonded solid rocket motors has been reviewed. The various studies by the authors (unpublished work) have also been reported. All these findings bring out the excellent potential of EPDM as insulator in view of its ageing resistance, low-temperature flexibility, low erosion rate, and low specific gravity.Keywords: Solid rocket motors, insulation, ethylene-propylene diene rubber, ablation resistance, EPDM, case-bonded solid rocket motors . INTRODUCTIONCertain elastomers find use as thermal insulators for case-bonded solid rocket motors (SRMs) 1 . Insulators, by forming the inner lining of rocket motors, prevent their exposure to the extremely high temperature gases of the propellant during combustion and help the integrity of motor without failure during operation. Selection of an insulation system for solid propellant motor applications involves considerations such as design function, material bonding, compounding and fabrication costs, fabrication techniques, storage, handling, environmental exposures, etc 2 .Apart from general requirements like superior thermal resistance etc, the insulator should be lightweight with low thermal conductivity and good mechanical properties. The insulation must remain intact and fully functional throughout propellant combustion and there should be no migration of its components to or from adjacent interfacial surfaces. It should also retain its elastomeric characteristics to avoid brittleness over operational temperature range for required duration of time to avoid catastrophic failure of the entire mission 3 .Nitrile rubbers, PDMS (polydimethyl siloxane), polyisoprene are few of the various elastomers used as insulators in solid rocket motors 4 . Nitrile/ rubber 5 -based insulation system is being currently used in Indian space programme. Skolnik 6 , et al. have reported the efforts made for replacement of nitrile-rubber based insulation by ethylene-propylene diene rubber (EPDM)-based non-asbestos insulation for Tomahawk booster motor.The technology for the manufacture of casebonded motors 7-8 and insulation laying of nitrile rubber has been well established. But nitrile rubberbased insulation suffers from the disadvantages such as limited shelf life, higher density, inferior low temperature properties etc. The evaluation of elastomers like EPDM 9-14 to replace nitrile rubber in Indian space and missile programme is in progress. REVIEW PAPER309 310 DEF SCI J, VOL. 56, NO. 3, JULY 2006 The use of EPDM as an insulator for case-bonded solid rocket motors was evaluated more than a decade ago 15 and found feasible. Being a material with a low specific gravity 16,17 , EPDM has emerged as a novel material for manifold applications including insulation for solid rocket motors.The main attributes of EPDM rubber are its outstanding resistance to oxidation, ozonisation, and weathering effects. The most important properties from defence application point of...

Ethylene-propylene diene terpolymer (EPDM)-based insulation system is being globally used for case-bonded solid rocket motors. A study was undertaken using EPDM as base polymer, blended with hypalon and liquid EPDM and filled with fibrous and non-fibrous fillers. These formulations were evaluated as rocket motor insulation system. The basic objective of the study was to develop an insulation system based on EPDM for case-bonded applications. A series of rocket motor insulator compositions based on EPDM, filled with particulate and fibrous fillers like precipitated silica, fumed silica, aramid, and carbon fibres have been studied for mechanical, rheological, thermal, and interface properties. Compositions based on particulate fillers were optimised for the filler content. Comparatively, fumed silica was found to be superior as filler in terms of mechanical and interface properties. Addition of fibrous filler (5 parts) improved the peel strength, and reduced the thermal conductivity and erosion rate. All the compositions were evaluated for sulphur and peroxide curing. Superior mechanical properties were achieved for sulphur-cured products, whereas peroxide-cured products exhibited an excellent ageing resistance. Rocket motors were insulated with optimised composition and propellant cast, and the motors were evaluated by conducting static test in end-burning mode.

Elastomeric blends based on ethylene propylene diene (EPDM) rubber as a primary polymer have been investigated for the thermal insulation of case‐bonded solid rocket motors (SRMs) cast with composite propellant containing hydroxy terminated polybutadiene (HTPB) as a polymeric binder. EPDM rubber found as an attractive candidate for the thermal insulation of case‐bonded SRM due to the advantages such as low specific gravity, improved ageing properties, and longer shelf life. In spite of these advantages, EPDM, a non‐polar rubber, lacks sufficient bonding with the propellant matrix. Bonding properties are found to improve when EPDM is blended with other polar rubbers like polychloroprene, chlorosulphonated polyethylene (CSE), etc. This type of polar polymer when blended with EPDM rubber enhances the insulator‐to‐propellant interface bonding. In the present work, an attempt has been made to study the properties of EPDM–CSE based insulator by incorporating HTPB, a polar polymer as well as a polymeric binder, as an additive to the EPDM–CSE blend by varying the HTPB concentration. Blends prepared were cured and characterized for rheological, mechanical, interface, and thermal properties to study the effect of HTPB addition. This paper reports the preliminary investigation of the properties of EPDM–CSE blend containing HTPB, as a novel and futuristic elastomeric insulation for case‐bonded SRM containing HTPB as propellant binder. Copyright © 2007 John Wiley & Sons, Ltd.

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A thin layer of liner is applied to ensure a good bond between the insulator and the propellant in case-bonded rocket motors. It also acts as a protective shield for the insulator by providing a limited fire protection effect. Liner compositions should preferably be based on the same binder system used in the propellant formulations. As the liner has to hold the propellant and the insulator without debond under all the environmental conditions, it plays a key role in predicted performance of a rocket motor. Hence, studies were carried out to improve the liner properties using various hydroxyl compounds, such as butanediol, cardanol, trimethylol propane, pyrogallol, etc as additives. Butanediol and phloroglucinol combination gave the best results in terms of mechanical properties and interface properties for the liner compositions. The effect of filler content on the liner properties was also studied. The results showed that higher filler content does not affect interface properties. Considering the fire retardancy effect and reinforcement of antimony trioxide (S£ 2 0 3 ), the formulation containing higher Sb 2 O 3 was selected. The studies on pot life/castable life of liner showed that propellant could be cast up to 6 days after liner coating, without adversely affecting the bonding and the bond strength.

A series of polyurethane compositions have been formulated using hydroxy-terminated polybutadiene as polymeric binder and carbon black as a major filler. Various binder-to-filler ratios of the formulations were evaluated to get calendered sheets. The formulations have been characterised for pot-life and rollahility and the calendered sheets for mechanical and thennal properties, bum rate, glass transition temperature, shore hardness and density. The different fillers tried were varieties of carbon black as a major filler; metal oxides, silicates and organic compounds; and fue retardants, such as zinc borate, sodium metaborate, ammonium dihydrogen phosphate and antimonv trioxide. The structure and momholoev of the fillers have been correlated w~th the . , -,properties. The optimisedcomposition has been evaluated in an end-burning motor, as an insulator for case-bonded application, using a typical composite propellant. The results of interface bondingbetween the propellant and the~insulitor have also been presented.

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