Ballistic properties of a polybutadiene propellant for rocket application

Abstract

Hydroxy-terminated polybutadiene (HTPB) based propellant is a complex chemical reagent used for rocket propulsion, and changes in the chemical formulation can significantly affect the propellant ballistic performance. However, the archive for commercial solid propellant formulation is found to be limited due to international security and commercial interest. Furthermore, the rocket propellant development in Malaysia is impacted by these constraints. The research investigated the effect of oxidizer particle size on the composite propellant mechanical and ballistic properties. Experimental propellant studied in this research consists of 68% Ammonium Perchlorate (AP), 15% aluminum powder (Al), 17% HTPB- Isophorone diisocyanate (IPDI). Four AP particle sizes ranging from below 90 microns, between 90 and 150 microns, between 150 and 250 microns, and above 250 microns were chosen for this research conducted in UTM, Malaysia. Morphology of the propellant was carefully studied using Nikon Microphat-FXL high resolution microscope, while Fourier Transform Infrared (FTIR) was used to study the changes in hydrogen bond region and carbon bond region of HTPB-IPDI matrices. Strand samples were evaluated at one atmospheric pressure, and the flame contour was found significantly affected by the position of ignition wire on propellant during combustion process. Beside these, burn rate measurements were performed at chamber pressure 0.1 MPa to 2 MPa using Crawford pressure bomb. The results showed that the value of the pressure exponent n falls between 0.29 and 0.36 under the effect of the AP particle sizes, while the burning coefficient a reduced substantially as the AP particle sizes increased in the samples. The propellant samples were fabricated according to JANNAF standard and tensile measurements were performed using universal tensile machine in UTM, Malaysia. It was found that the samples with AP particle sizes below 90 microns produced the best strain-stress curves in tensile test. A scaledrocket motor loaded with propellant grain sample was fabricated for static firing test and six unique pressure-time curves were successfully obtained in this research. As a conclusion, propellant with AP particle sizes below 90 microns produced the maximum pressure of 57.17 psi on the propellant pressure-time profile.