MISCIBILITY STUDIES ON POLYMER-PLASTICIZER SYSTEMS FOR COMPOSITE PROPELLANTS:A COMBINED EXPERIMENTAL AND MOLECULAR SIMULATION APPROACH

Abstract

Recent developments in rocket propellants demand composite propellants to have high energy, sufficient structural integrity and low temperature capability to qualify for application in propulsion system. Polymer-plasticizer contributes to all the above three important characteristic of propellants. Polymers and plasticizers need to be screened rigorously to achieve most suitable combination. In the present investigation, experimental and simulation studies have been performed to predict the miscibility of polymer and plasticizer. Solubility parameter is the measure of miscibility or compatibility of any two material of interest, which is evaluated by Gee’s equilibrium swelling experiments for cross-linked polymers and intrinsic viscosity measurements for linear polymers. Molecular dynamic simulations using COMPASS force-field have been used to evaluate solubility parameter of polymers, HTPB, SPG-255, NBR, HTPB-b-polycaprolactone block copolymer and plasticizers, NG, DEGDN, TEGDN, DOA, BuNENA, TMETN, and BTTN. Flory-Huggins interaction parameter χ is also calculated for identifying right combination. Simulated and experimental data proved that energetic plasticizers are not compatible with HTPB. Similarly most suitable plasticizers for SPG-255 and NBR are BuNENA and TMETN where as BuNENA and DOA can be suitable plasticizers for HTPB-b-CP copolymer. Overall, thesis work finds its usefulness in identifying the most suitable plasticizer for a given polymer, which is an initial step for achieving successful propellant formulations.