Rheology of HTPB propellant. I. Effect of solid loading, oxidizer particle size, and aluminum content

Abstract

SYNOPSISComposite solid propellants based on hydroxyl-terminated polybutadiene ( HTPB ) have become the workhorse propellants in the present-day solid rocket motors. The other major ingredients of a composite propellant are the crystalline oxidizer and metallic fuel. As the solid loading of such propellants is as high as 86-90%, their rheological behavior is very complex. The propellant slurry needs to have reasonably low viscosity and a long pot life for better casting and, hence, for a defect-free rocket motor. The primary factors affecting the solid propellant viscosity are solid content, particle size, shape, and distribution. The present study concerns the variations of solid loading from 80 to 89% at constant aluminum content, variation of aluminum from 0 to 22% at constant solid loading, and the coarseto-fine ratio of the oxidizer. The plots of yield stress, consistency index, pseudoplasticity index, and thixotropic index at different time intervals are drawn for all these parametric changes. Based on these rheological studies, the optimum ratio of oxidizer coarse-to-fine ratio, aluminum content, and level of solid loading have been determined.

Pseudoplasticity of Propellant Slurry with Varied Aluminium Content for Castability Development

“…The size of aluminium that is used is 30 microns which almost equals to 0,155 times of the size of largest particle used (coarse AP (200 microns)). That size of aluminium is reported thread throughout the binder effectively [8]. With small content of aluminium (6 and 8%), ability of aluminium flow along with the binder, when the shear conducted on it, is represented by pseudoplasticity index that close to 1 which are 0,8 -0,9 and low viscosity.…”

“…It is because of polimerization of liquid contents that forms propellant binder. As the viscosity of liquid contents increase, the effect of the percentage of aluminium in the viscosity of slurry propellant also change [8].…”

“…Therefore, developing knowledges of pseudoplasticity of propellant slurry with the changes in percentage of aluminium is crucial. Based on pseudoplasticity index, Muthiah et al (1992) reported that propellant slurries with 5 -10% of aluminium have the best processibility until 6 hours after mixing. This research involves aluminium of 10 -12 microns.…”

“…This research involves aluminium of 10 -12 microns. Based on Prangili et al (2006), different size of aluminium results different viscosity in propellant slurry, the range that is mentioned by Muthiah et al can be different with the different size of aluminium [8], [19].…”

“…While, based on the packing density of the filler, various parameters such as particle size, interactions between particles, and interactions between particles and suspending fluid play important roles [24] [25]. The percentage of solid contents that are used in this research is 85% of which reported exhibites pseudoplasticity [8]. With the increase in aluminium content, the effects of those mentioned above are vary and to more understanding those effects on pseudoplasticity of slurry, the graph of volume fraction vs pseudoplasticity index is made, as shown in figure 2.…”