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3 Central European Journal of Energetic Materials

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Simulation of Stress Relaxation Behaviour of Composite Propellants with Varying Solid Loading Using the Generalized Maxwell Model

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Bihari B. K. , Kumaraswamy A. , Jain M. , Kurva R. , Vipin L.

Central European Journal of Energetic Materials

2023

tom Vol. 20, no. 2

221--235

Hydroxyl-terminated polybutadiene (HTPB) based composite propellants possess viscoelastic behaviour and hence time and temperature dependent mechanical properties. The mathematical analysis of viscoelastic behaviour of composite propellants becomes complex due to the non-linearity involved under various loading conditions. In the present study, a linear viscoelasticity assumption was considered to simulate stresses related to storage conditions. In this paper, a study of stress relaxation behaviour of composite propellants was carried out using the Generalized Maxwell model to obtain the material viscoelastic characteristics. The relaxation behaviour of composite propellants having solid loading varying from 85% to 89% were studied at different temperatures, from -27 to +32 °C, using a Dynamic Mechanical Analyser (DMA). The generated relaxation curves were curve fitted using MATLAB (R2022a) with the Generalized Maxwell model. The simulation demonstrated that a maximum of four elemental parameters of the Generalized Maxwell model are sufficient and can represent a best fit of the relaxation behaviour of the studied composite propellants. The equilibrium modulus was also evaluated at different temperatures, along with other material constants that are essential parameters for performing the structure integrity analysis of a solid propellant rocket motor. It was observed that the equilibrium modulus decreases with an increase in temperature, but increases with an increase in solid loading in the propellant composition formulations.

Thermal Hazards Studies for the Azidation Process in the Preparation of Tetra Functional Glycidylazide Polymer (t-GAP) Using a Thermal Screening Unit (TSU)

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Adak P. K. , Ghosh M. , Meena A. K. , Jain M. , Banerjee S.

Central European Journal of Energetic Materials

2024

tom Vol. 21, no. 3

282--297

Glycidylazide polymer (GAP) tetraol or tetra functional GAP (t-GAP) is a potential energetic binder, capable of exhibiting superior mechanical properties and better curing behaviour for application in high energy propellants. t-GAP is conventionally prepared through azidation of tetra functional poly-epichlorohydrin (t-PECH). Azidation reactions using a metal azide are known to be sensitive to temperature. The present study was aimed at a systematic evaluation of the safe temperature limit for the preparation of t-GAP and to derive optimized reaction conditions using a thermal screening unit (TSU), through both dynamic and isothermal heating experiments. The thermal hazard studies suggested that the azidation reaction is fairly stable at temperatures above 100 °C as it did not exhibit any abrupt rise in reaction temperature or pressure. The process was validated using laboratory scale batches and completion of the reaction was verified using FTIR spectroscopy.

Study of the Progress of Reaction in the Preparation of tetra-Functional GAP using FTIR Spectroscopy

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Adak P. K. , Meena A. K. , Ghosh M. , Sutar V. , Jain M. , Banerjee S.

Central European Journal of Energetic Materials

2024

tom Vol. 21, no. 2

138--152

Glycidyl azide polymer (GAP) with tetra hydroxyl functional groups or t-GAP is a potential energetic polymeric binder for application in both high energy propellants and high explosives. t-GAP is synthesized via azidation of the precursor tetrafunctional poly-epichlorohydrine (t-PECH) with sodium azide in DMSO solvent medium. In this article, process optimization and progress of chemical reaction for preparation of t-GAP is studied using FTIR spectroscopy and an attempt is made to predict the reaction kinetics with concentration profiling. The characteristic vibrational features corresponding to C‒N3 of t-GAP and C‒Cl of t-PECH have been used to monitor the progress of reaction.