Abstract:
HTPB is polymer of 1, 3-butadiene terminated at each end with hydroxyl group. It is considered
as a workhorse of propellant binder and is used all over the globe. This liquid prepolymer has
excellent physical properties such as low glass transition temperature, and good chemical
résistance. It is capable of taking solid loading up to 88% without sacrificing the ease of
processability. It reacts with isocyanate to form polyurethane polymer. The mechanical properties
of elastomer of HTPB vary widely depending on the physical properties of polymer such as
molecular weight, molecular weight distribution, functionality, degree of branching and
microstructure.
A systematic study has been done on HTPB resin with varying hydroxyl value with a view to
achieve the maximum possible strain capability and moderately high tensile strength keeping all
other parameters constant. The influence of increasing hydroxyl content (0.7-0.8) (Mn remain
same) on mechanical properties of the finished propellant is studied. The filler used is calcium
carbonate. The cured elastomer were subjected to be analyzed for the determination of dynamic
thermo-mechanical analysis (DTMA), differential scanning calorimetry, uniaxial tensile properties
such as tensile strength, percentage elongation, Young's modulus and hardness. It was found that
thermal properties of prepared elastomers did not change significantly by varying OH number of
polymer. Hardness and tensile strength increases while % elongation decreases by increasing
NCO/OH ratio while mechanical properties (tensile strength) decreases by increasing OH value of
polymer.
