Tailoring of Mechanical Properties of Highly Filled Nano‐Aluminized Propellants by Modifying Binder Polymer Microstructure

Abstract

Use of nano sized aluminium powder in place of micron sized powder leads to increase in specific impulse of solid composite propellants. However, poor mechanical properties of nano-aluminized propellants prevent their use in actual rocket motors. An attempt has been made here, to improve the mechanical properties by using different HTPB resins having different functionality type distribution. Adjustment of isocyanate to hydroxyl ratio, and ratio of the chain extender, Butane-diol, to the cross-linker, Tri-Methylol-Propane, had also been tried to investigate their effect on mechanical properties. Nano-aluminium content in the propellant samples could be raised to the conventional level of 18 % by use of Iso Decyl Pelargonate as plasticizer in place of Dioctyl Adipate. This made the samples at par with the conventional micro-aluminium propellants, and the experimental results comparable. The microstructural changes of HTPB significantly improved the tensile strength of the nano-aluminium propellants to 0.65 MPa and break elongation to 17 % respectively. Recorded heat of combustion values are at 5990 J/g. These figures meet industrial tolerance and make the propellant acceptable for use while increasing its specific impulse beyond today's conventional levels. The technology established has potentials to increase nano-aluminium content further, and augment ballistic properties of solid motors, upholding the required industrial restrictions of rheological and physico-mechanical parameters.

A review on the effect of ageing on the ballistic properties of solid gun and rocket propellants

“…For solid rocket propellants, the Specific impulse, I SP , is a parameter describing the energy efficiency of propellant combustion. It is a measure of performance and represents the thrust per unit propellant 'weight' flow rate [6] and gives the effective time to generate thrust and sustain the propellant mass [7,8].…”

“…Many researchers have reported attempts to improve I SP , which would augment the ballistic properties [7], through the use of, for example, RDX [8], CL-20 [9] or Nano aluminium in place of micron sized aluminium powder [7,10]. Singh et al [11] attempted to develop propellant compositions with an enhanced performance in terms of density and I SP compared to conventional composite propellant compositions, through changes to the binder system and the introduction of nitroglycerine (NG) as a plasticiser.…”

“…Many researchers have reported attempts to improve I SP , which would augment the ballistic properties [7], through the use of, for example, RDX [8], CL‐20 [9] or Nano aluminium in place of micron sized aluminium powder [7, 10]. Singh et al.…”