Influence of fillers on the mechanical and thermal characteristics of rocket motor liners based on HTPB

Abstract. Case bonded solid rocket motors hold significant importance in both the defense and aerospace industries which typically consist of an insulating layer, a solid propellant, and a liner layer serving as an adhesive between the insulator and solid propellant. The importance of liner layer is that it secures the propellant grain to the rocket motor chamber by adequate bonding. Therefore, determination of its properties is crucial for the design of a case bonded system. In this investigation, the aim was to assess the critical mechanical properties of five different HTPB based liner formulations under ambient conditions, as well as at elevated and reduced temperatures. The liners formulations incorporated micro carbon black, nano carbon black, nano silica, and nano titania as fillers. A comprehensive characterization study encompassing mechanical and thermal properties was conducted to evaluate the performance of these potential rocket motor liners. All mechanical properties of filled liner formulations enhanced significantly compared to unfilled formulation at all temperatures. At lower temperatures, mobility reduction of polymer chains as well as bond strengthening led to the enhancement in mechanical properties of all filled and unfilled liners. Contrary to that, at elevated temperatures, a decrease in the mechanical properties of all filled and unfilled liners has been observed due to the polymer chains being able to move more easily and the interactions at the molecular level being weaker. Augmentation in mechanical properties were more pronounced with carbon blacks as fillers. Thermal analyses of each formulation revealed that there are improvements in the thermal properties of filled liners compared to unfilled one. Three stage decomposition was observed for all liner formulations based on thermogravimetric analyses. Thermomechanical investigations revealed that thermal expansion of filled liners were lower than that of unfilled liner.