Research Article Noncrystalline Binder Based Composite .

Hindawi Publishing CorporationISRN Aerospace EngineeringVolume 2013, Article ID 679710, 6 pageshttp://dx.doi.org/10.1155/2013/679710Research ArticleNoncrystalline Binder Based Composite PropellantMohamed Abdullah, F. Gholamian, and A. R. ZareiFaculty of Chemistry, Malek Ashtar University, P.O. BOX 16705-3454, Tehran, IranCorrespondence should be addressed to Mohamed Abdullah; mohamedazizam@gmail.comReceived 29 June 2013; Accepted 7 August 2013Academic Editors: C. Meola and R. K. SharmaCopyright 2013 Mohamed Abdullah et al. This is an open access article distributed under the Creative Commons AttributionLicense, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properlycited.This study reports on propellants based on cross-linked HTPE binder plasticized with butyl nitroxyethylnitramine (BuNENA)as energetic material and HP 4000D as noncrystalline prepolymer. This binder was conducted with solid loading in the 85%.The results showed an improvement in processability, mechanical properties and burning rate. In addition, its propellant delivers(about 6 seconds) higher performance (specific impulse) than the best existing composite solid rocket propellant. Thermal analyseshave performed by (DSC, TGA). The thermal curves have showed a low glass transition temperature (𝑇𝑔 ) of propellant samples,and there was no sign of binder polymer crystallization at low temperatures ( 50 C). Due to its high molecular weight andunsymmetrical or random molecule distributions, the polyether (HP 4000D) has been enhanced the mechanical properties ofpropellants binder polymer over a large range of temperatures [ 50, 50 C]. The propellants described in this paper have presentedhigh volumetric specific impulse ( 500 s gr cc 1 ). These factors combined make BuNENA based composite propellant a potentiallyattractive alternative for a number of missions demanding composite solid propellants.1. IntroductionMuch research on composite solid propellants has beenperformed over the past few decades and much progress hasbeen made, yet many of the fundamental processes are stillunknown, and the development of new propellants remainshighly empirical. Ways to enhance the performance of solidpropellants for rocket and other applications continue tobe explored experimentally, including the effects of variousadditives and the impact of fuel and oxidizer particle sizes onburning behavior.In view of higher energy (𝐼sp 264 s), composite propellants have been extensively used for rocket/missile applications and space missions. A higher specific impulse (𝐼sp ) ofcomposite propellants is obtained by incorporating a maximum possible amount of solids (oxidizer/metallic fuel) in thebinder matrix and substituting the inert materials with energetic ones (energetic plasticizers). Present day applicationsdemand propellants of superior mechanical properties inaddition to higher energy content. Due to these contradictoryrequirements hydroxy-terminated polyether (HTPE) basedpropellants are plasticized with energetic plasticizers, suchas BuNENA, bolster performance and mechanical properties[1].HTPE with HP 4000D as Prepolymer is capable oftaking up solids up to 85% and impart superior mechanicalproperties without compromising on high storage life, due toits random molecule distributions that prevent crystallizationat low temperatures in addition, the presence of BuNENA (𝑇𝑔 86 C) [2] eliminates completely this phenomenon (crystallization of polyether) at operational temperature ranges[ 50, 50 C] of solid rocket motors. Lately, much scholarlywork has been done on the hydroxy-terminated polyetherbased (HTPE) propellants instead of hydroxy-terminatedpolybutadiene-based (HTPB) propellants and has introducedBuNENA as energetic plasticizer in high-energy nitroesterpolyether (or polyester) (NEPE) propellants [3]. Plasticizerplays the essential role of complementary element to reducethe viscosity of the slurry and to improve the mechanicalproperties by lowering the 𝑇𝑔 and the modulus of the binder.The use of BuNENA in composite propellants confers excellent properties, due to its characteristics such as, insensitiveenergetic material, low glass transition temperatures, andgood thermal stability, so we are interested to use it in

2ISRN Aerospace EngineeringTable 1: Materials used in composite propellant binder.ReagentNamePrepolymerHP 4000DBASFCuring agentN-100Nitro diphenylamine NAMAR Brand Curative(HX-878)BayerWater whiteliquidPolyisocyanateFlukaOrange crystalDYNO ASA,NorwaySlightly yellowliquidViscous amberliquidStabilizerEnergeticplasticizerBonding agentCompany3MTable 2: Composite propellant compositions.IngredientsAl (22 𝜇m)RDX (5 𝜇m)AP (200 𝜇m)AP (20 𝜇m)HP4000DBuNENAHX 8782-NDPAN100Percentage by 19.033.023.19.905.758.000.200.250.80our formulae to improve composite propellant compositions.A number of studies have been carried out in the past onthe formulation, processing, and improvement of mechanicalproperties and ballistic evaluation of HTPE based compositepropellants, but with inert plasticizers and using conventional polyether that can be crystallized at low temperatures[3]. Other studies on double base and gun propellants havebeen published using BuNENA as energetic plasticizer [4–7].However, detailed information on composite propellants withenergetic plasticizers and new polyether like (HP-4000D)is not reported in the open literature. However, propellantsbased on cross-linked HTPE binders are being used as alternatives to HTPB compositions because they give a less severeresponse in slow cookoff tests for insensitive munitions (IM)compliance [8–10].2. Experimental2.1. Materials. Bimodal blends of AP were used, consisting ofa medium sized (200 𝜇m) fraction and a small sized (20 𝜇m)fraction. This combination was recommended as offering anoptimum AP particle size width distribution to give the bestrheology and to improve propellant slurry processabillity, andalso, RDX 5 microns and Al of 23 micron were used as fillerin the propellant composition. Materials used for binder havebeen described in Table 1.CharacteristicsHydroxyl no.mg KOH/gmMolecularweight .2. Propellant Processing and Characterization. The propellant ingredients were mixed in a 3-liter capacity sigma mixerfor two batches (mix1, mix2) prepared according to Table 2.The processability of the slurry was monitored by measuringthe end-of-mix viscosity (EOM) and viscosity build up fora period of 10 hours. Propellant slurry was cast into Tefloncoated moulds, under vacuum, for evaluation the mechanicalproperties and strand burn rate. The mechanical propertiesof cured propellant samples were evaluated using dumb bellsconforming to ASTM standards D-412-68 (Type-C) at across-head speed of 50 mm/minute at 40, 25, and 50 C.The cured propellant slabs were machined into strands ofdimensions 175 5 5 mm. The strands were inhibited withcoatings of phenolic epoxy resin or polyvinyl acetate paint.They were burned in a nitrogen pressurized Crawford-typebomb over a pressure range from 2 to 18 MPa.3. Results and Discussion3.1. Mechanical and Ballistic Properties. As seen in Table 3,propellant samples, mix1 and mix2, exhibit a high densityimpulse ( 500 g s cc 1 ), good processabillity expressed bylow viscosity of EOM ( 4 K Poise), and reasonable pot life(8 hours). In addition, it has shown excellent mechanicalproperties especially at low temperatures ( 40 C) whenbinder elongation at maximum stress reached to 65–70%.Thus, we have believed that the withstanding properties referto kind of prepolymer used and to the presence of BuNENAin composition. The use of HP 4000D, as prepolymer, whichis Ethylene-Oxide (EO) capped polypropylene glycol (PPG)polyols with low insaturation content, also when plasticizedwith BuNENA, which has low glass transition temperature(𝑇𝑔 86 C), has enhanced the binder elongation at lowtemperatures and prevented binder to crystallize (improvedby thermal behavior next). When more RDX is used (mix2),the burning rate and pressure exponent decreased, respectively; see Table 3. In addition, mix2 showed increase inspecific impulse (about 4 seconds).3.2. DSC and TGA Analyses. In order to analyze the thermal behavior of propellant samples, differential scanningcalorimeter (DSC) analysis was performed to determineglass transition temperature (𝑇𝑔 ) and thermal decomposition(TA). Thermogravimetric analyses (TGA) were also carried

ISRN Aerospace Engineering3Table 3: Mechanical, rheological, and ballistic properties of propellant samples.Composite propellantsDensity, 𝜌Specific impulse (theoretical), 7/0.1 MPaDensity specific impulse (𝜌 I sp )Burning rate at 7 MPaPressure exponent (𝑛), (2–18) MPaProcessabilityEnd of mixing (EOM) viscosityPot life (to 15 K poise)Mechanical Properties 𝑇 C //50 mm min 1Max. tensile strength 𝜎maxElongation at 𝜀maxElongation at breakE-modulusGlass transition DSC8!&n-BuNENAn-BuNENA, 5.8000 mgIntegralNormalizedOnsetPeakUnitg cm 3secg cm 3 secmm s 1—Mix11.882665008.500.45Mix21.832704947.000.40K Poisehour𝑇 CN mm 2%%N mm 2 C4.08250.878862.2 75.034.510250.770762.0 77.47 401.565705.56479.89 mJ1117.22 Jg 1190.36 C210.92 C0.1570.1054320.00500.578811.6! Mix1 Tg 100 30Mix1 Tg 100 30, 9.8000 mgGlass transitionOnsetMidpointInflect. Pt.Inflect. Slp.Midpoint ASTM, IECDelta cp ASTM, IEC 0.051 78.72 C 73.52 C 75.03 C 1.41e 03 Wg 1 C 1 72.31 C0.121 Jg 1 K 1Onset 25.62 C 0.10 40 200204060801001201401601802002202402602800 10.05(Wg 1 )(Wg 1 )6 401.858635.8500.686911.8 90 80 70 60 50 40 30 20 10 0( C)Figure 1: BuNENA DSC curve.Figure 2: DSC 𝑇𝑔 curve of propellant sample (mix1).! Mix2 Tg0.3 Mix2 Tg , 5.4000 mg0.2(Wg 1 )out. The thermal analyses were performed using MettlerTA4000 thermal analyzer equipped with a TA processor TC11 and a DSC 30 measuring cell. An inert environment wasmaintained during all the analyses by using a flow of nitrogenof 40 cm3 per min. Analyses were performed at a heatingrate of 10 C per min in the temperature range from 100 to 30 C for 𝑇𝑔 , 30 to 500 C for TA analysis, and 30 to 550 C forTGA. Figure 2 shows the DSC 𝑇𝑔 curve of propellant samplemix1 (9.8 mg of sample), and Figure 3 is related to samplemix2 (5.4 mg of sample). As we have shown, 𝑇𝑔 is 75.03 Ccorresponding to mix1 and 77.47 C to mix2. Figure 4 showsthe DSC TA curve of (0.9 mg of sample) mix1 and Figure 5shows the DSC TA curve (2.2 mg) of sample mix2. Figure 6shows the thermogravimetric curve (4.3 mg) of sample mix1.As can be seen from Figures 2 and 3, the glass transitiontemperatures for propellant samples mix1 and mix2 are veryclose. The 𝑇𝑔 for these samples was around 76 C. On theother hand, the thermal decomposition observed in Figures4 and 5 and several peaks, either exothermic or endothermic,are present during propellant thermal decomposition. Threeendothermic peaks can be seen after 150 C from samples mix110 20( C)0.10.0 0.1Glass transitionOnsetMidpointInflect. Pt.Inflect. Slp.Midpoint ASTM, IECDelta cp ASTM, IEC 80.84 C 76.73 C 77.47 C 15.26e 03 Wg 1 C 1 76.89 C0.774 Jg 1 K 1Onset 25.87 C 0.2 90 80 70 60 50 40 30 20 10 0( C)10 20Figure 3: DSC 𝑇𝑔 curve of propellant sample (mix2).and mix2 in Figures 4 and 5, respectively. The exothermicpeaks at around 188 and 193 C, with an onset around 160 C,can be assigned to the energetic plasticizer BuNENA. Inpropellant mix1, this peak can be seen at 199 C and it looks