Kineticsfor Thermal Decomposition Of Several Energetic Binders

Energetic binders have been widely applied in plastic-bonded explosives(PBX) and solid rocket propellant,wherein the representativeisgeminal dinitro-based binders and glycidyl azide polymer (GAP)-based polyurethane binders.Therefore,the study on thermal decomposition kinetics ofgeminal dinitro-based energetic binders and GAP-based energetic binders had great theoretical and practical significance.In this paper, the kineticsofgeminal dinitro-based energetic binders,2,2-dinitro-1,3-propanediol which was the intermediate of geminal dinitro-based energetic binders,and GAP-based energetic binders, wasinvestigated by the measurement of differential scanning calorimetry (DSC)under the non-isothermal condition using differential methods (ASTM E698method, Ozawamethod, Kissinger method and Starink method) and integral methods (Flynn-Wall-Ozawa method and Kissinger-Akahira-Sunose method),to be abtained corresponding kinetic factors (Ea、A、 f(α)),reaction rate constant κand thermodynamicparameters(ΔG≠、ΔH≠、ΔS≠). The results can help to obtainfundamental datas and theoretical guidance,and have very important practical significance on storage and transportation of energetic binders.The main results are as follows:(1) The2,2-dinitro-1,3-propanediol was prepared by nitration oxidation method,and its structurewas characterized by XRD, FT-IR and Elemental Analysis.The crystal transitionof DNPDOH was studied byvariable temperatureXRD, and the kineticsof crystal transition and thermal decomposition were determined by DSCunderthe non-isothermalconditionthroughOzawa method and Kissinger method.Corresponding kinetic factors were obtained. The results of XRD showed thatcrystal of DNPDOH istransformedfrom body-centred tetragonal form to face-centered cubicform at69.8℃. DSC heating curves ofDNPDOH show two endothermic peaks and an exothermic peak, which correspond to crystal transition, meltyand decompositionof DNPDOH, respectively. Activation energy and pre-exponential factor of crystal transitionare520.8kJ·mol-1and66.1s-1, respectively.Activation energy and pre-exponential factor of thermal decomposition are170.7kJ·mol-1and16.7s-1, respectively. (2) Thermal decomposition kineticsof poly(2,2-ditropropyl acrylate)(PDNPA), poly(2,2-ditrobutyl acrylate)(PDNBA) and2,2-dinitropropyl acrylate-2,2-dinitrobutyl acrylate copolymer(DNPA-DNBA), were determined by DSCunder non-isothermal condition employing ASTM E698method, Starink method and KAS method. The results showed that decomposition activation energy of three bindersis142.48kJ·mol-147.10kJ-mol-1and151.8kJ-mol-1, respectively. The order of thermal stability was DNPA-DNBA> PDNBA> PDNPA. The mechanism of thermal decomposition reaction of three binders isall random nucleation and growth. The integral anddifferential forms of the most probable mechanism function are all G(α)=[-1n(1-α)]1/2and f(α)=2(1-α)[-ln(1-α)1/2, respectively. Thermal decomposition kinetic equations of the binders are da/dt=1.02×1014×exp(-1.71×104/T)(1-α)[-ln(1-a)]1/2、dα/dt=2.44×1014×exp(-1.77×104/T)(1-α)[-ln(1-a)]1/2and dα/dt=8.40×1014X exp(-1.82×104/T)(1-α)[-1n(1-a)]1/2, respectively.(3) Thethermal decomposition kineticson gem-dinitro valerylatedpolystyrene (GDN-PS) with degree of substitution(DS)11%was invetigated by DSCunder thenon-isothermalcondition using ASTM E698method, Starink method and KAS method. The TG results revealed that the process on thermal decomposition of GDN-PS ocupyed three stages, and the the second stage with lose mass of26.5%during the temperature range of200-300℃was more important corresponding tothe decomposition of gem-dinitro. The DTA curve of GDN-PS is showing a visible exothermic peak at253.8℃.The second stage with the lose mass of26.5%had an obvious Decomposition activation energycalculated by ASTM E698method, Starink method and KAS methodfor GDN-PSis180.57kJ·mol-1、181.11kJ-mol-1and180.96kJ-mol-1, respectively.The mechanism of thermal decomposition reaction of GDN-PS was all random nucleation growth and the integral form.The most probable mechanism function is G(α)=-1n(1-α), the differential form is f(α)=1-α. Its kinetic equation is dα/dt=2.63×1017×exp(-2.18×104/T)(1-α)。(4) Thethermal decomposition kineticson two GAP-basedpolyurethanes(GAP-HDI and GAP-MDI) were studied by DSCundernon-isothermalcondition employingFWO method and KAS method. The TG results showed that the process of thermal decompositionoccupiedtwo stages.The first stage withthe temperatue from200.C to250℃corresponded to the decomposition of azide group and the second stage withthe temperatue after250℃corresponded to the decomposition of soft segment. The decomposition act.ivation enerey for GAP-HDI and GAP-MDIis148.74kJ·mol-1and155.58kJ·mol-1, respectively.The order of thermal stability was GAP-MDI>GAP-HDI.The same mechanisms of thermal decomposition reaction of GAP-HDI and GAP-MDI are random nucleation growth.The integraland differential form of the most probable mechanism functionareG(α）=[-1n(1-α]3/4and f(α)=0.75(1-α)[-1αn(-1α]-1/4.The kinetic equations was dα/dt=5.68×1014×exp(-1.79×104/T)(1-α)[-1n(1-α]-1/4and dα/dt=5.89×10158×exp(-1.92×104/T)(1-α)[-1n(1-α]-1/4.