Effect of Different OH Values of HTPB on Thermo Mechanical Properties of HTPB/TDI System Using Inert Filler

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.