Effect of aluminium content on pseudoplasticity involving wall slip of high density composite solid propellant (HD-CSP) slurries

Inappropriateness between composition and casting technique of high density composite solid propellant (HD-CSP), a highly energetic fuel, increases susceptibility of the casting process towards explosion. The process can be safer with lubrication effect from wall slip phenomena. Pseudoplasticity involving the phenomena is also important in determining casting technique. Although it has been found that aluminium determined the pseudoplasticity, the controlling mechanism remained unclear. Therefore, revealing the mechanism was the aim of this work. Three types of HD-CSP slurries with solid contents of 87.5–90 wt%, and aluminium amount of 15–20 wt% were fabricated. The other ingredients include bimodal ammonium perchlorate, hydroxyl-terminated polybutadiene (HTPB), toluene diisocyanate, dioctyl adipate, and a partially cyanoacrylated tetraethylenepentamine. The materials were fabricated through sequential mixing in horizontal mixer with Z-shaped blade at 60 ℃ for 2.5 h. It was followed by measurement of stress growth in the start-up of shear flow and the viscosity in a range of low shear rates. Based on particle packing model, a parameter describing volume fraction of aluminium in area adjacent the wall of the instrument controlled pseudoplasticity of the HD-CSP slurry with high correlation level. Analysis on the stress growth discovered that the mechanism involved determination of shear modulus sensitivity towards shear rate.