Styrene-ethylene/butylene-styrene (SEBS) block copolymer binder for solid propellants

Currently solid composite propellants are manufactured using bespoke, specially manufactured binders. This adds significant cost and obsolescence risks to their development and manufacture. This paper reports on the production of two composite propellants made from a commercially-available-off-the-self polymer as binder by means of a resonant acoustic mixer (RAM) slurry process. The binder consisted of thermoplastic elastomer styrene-ethylene/butylene-styrene (SEBS) block copolymer and the solid filler, either ammonium perchlorate (AP) or 1,3,5-Trinitro-1,3,5-triazinane (RDX). Thermodynamic code demonstrated that SEBS-based propellants exhibited similar theoretical ballistic performance to conventional HTPB-based propellants. Chemical compatibility between SEBS and the solid fillers was shown by the differential scanning calorimetry (DSC) and vacuum stability methods. The novel combination of RAM and slurry coating process produced a propellant moulding powder that was then consolidated by remote hot pressing to simulate an industrial extrusion or rolling process. The propellants exhibited as expected explosive hazard properties and their thermal analysis by DSC-TGA showed typical oxidizer behaviour between AP and SEBS, characterised by two decomposition exotherms (also reported in AP/HTPB compositions), and little or no interaction between RDX and SEBS. The apparent activation energy for decomposition for AP/SEBS (84/16 % w/w) propellant was similar to that for AP/HTPB propellants. This work demonstrates the viability of using SEBS polymer as a binder for solid propellants. The development of propellants using commercially off the shelf, thermoplastic elastomeric binders could add significant benefits in waste reduction through recycling, security of supply, and manufacturing costs.