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A number of nanocomposites have been synthesized biomimetically by embedding various transition metal salts in polyvinyl alcohol (PVA) as the preorganised matrix. The metal salts were reduced to metallic form using aqueous sodium borohydride solution. In the present paper, very comprehensive studies on thermal decomposition behavior of these composites have been carried out using thermogravimetric and differential scanning calorimetric studies. The transition metal salts/ metals based composites exhibit increased thermal stability as indicated by shift in the decomposition temperature of pure PVA. The DSC data show increase in glass transition temperature of all composites, except the one containing iron, in comparison with neat PVA.The improvement in the thermal stability is explained in terms of decrease in the segmental mobility of polymer chains due to entrapment of metal salt / metal forming a complex with the hydroxyl group of the polymer chains and thus decreasing heat transfer process for decomposition of polymer composites.

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[a] 1IntroductionComposite propellants are composed of an elastomeric polymeric binder,i nw hich solid particles, such as oxidizer, fuel, and additivesa re incorporated.R ockets and missiles are propelled by composite propellants.T hey basically contain an oxidizer,m ainly ammonium perchlorate (AP), ab inder such as hydroxyl terminated polybutadiene (HTPB), and am etallic fuel like aluminum powder along with certain process aids as well as ballistic modifiers [1]. The burning rate of composite propellants is considered to be one of the most important properties governing the ballistic performance of solid rocket motors,w hich in turn dependsm ostly on particle characteristics of oxidizers, burning rate catalystsa nd metallic fuel [2].T oa chieve the desired burning rate of composite propellant formulations, the amount of oxidizer,p article size of oxidizer,a nd burning rate modifiers are used as variables. AP is used in composite propellantf ormulationsa st he major ingredient (oxidizer) [3] in different size fractions to enhance the burning rate. However,f ine and superfine particle fractions of AP increase the burning rate as well as the propellant slurry viscosity thus casting of slurry becomes difficult [4].Therefore, to cope with suchp roblems, burning rate modifiersa re preferred. The burning rate modifiers are transition metal oxides (TMOs) or their complexes. The burning rate modifiers added in small quantities affect the burning rate by lowering the thermald ecomposition temperature of AP and binder [5].T he effect of transition metal oxides on thermal decomposition of ammonium perchlorate has been studieda nd reviewed in literature [5,6].M any researchersh ave studied in detail the effect of TMOss uch as Fe 2 O 3 ,C uO, Co 2 O 3 ,N iO, and Cr 2 O 3 over ballistic properties of propellant mainly on burning rate behavior and found substantial increase in burning rate [7,8] [16].A lso, the number of nanoscale catalyst, Abstract:D ifferentp ropellant compositions were prepared by incorporatingn ano-sizedc obalt oxide from 0.25 %t o 1% in HTPB/AP/Al-based composite propellant formulations with 86 %s olid loading. The effects on viscosity buildup, thermal, mechanical and ballistic properties were studied. The findings revealed that by increasing the percentage of nano-Co 3 O 4 in the composition,t he end of mix viscosity,t he modulus and the tensile strength increased, whereast he elongation decreased accordingly.T he thermal property data envisaged ar eduction in the decomposition temperature of ammonium perchlorate( AP) as well as formulations based on AP.T he ballistic property data revealed an enhanced burning rate from 6.11mms À1 (reference composition) to 8.99 mm s À1 at 6.86 MPa and am arginal increase in pressure exponent from 0.35 (reference composition) to 0.42 with 1% nano-cobalt oxide.

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