Combustion of Polystyrene and Oxygen-Styrene Copolymer/Ammonium Perchlorate Propellants

Burning rate, heat of combustion, flame temperature, and surface temperature of the two composites have been measured. Studies on thermal degradation kinetics and differential scanning calorimetry (DSC) of the propellants have also been made. The inhibitor-free styrene was polymerized by benzoyl peroxide. To prepare the oxygen-styrene copolymer, azobis isobutyronitrile was used as the intiator and oxygen was passed at 1 atm pressure for 24 hr through the styrene. The reaction was completed by adding benzoyl peroxide and maintaining the solution in thermostat at 50°C for another 24 hr until it became sufficiently viscous. The yield of styrene peroxide was of the order of 21-22%. Styrene peroxide was characterized by microanalysis and infrared spectroscopy. Infrared spectra have weak characteristic absorption bands at 7.42 // and 11.15 n and a broad absorption band at 9.75 characteristic of peroxide linkage. Burning rate was measured in a manner described earlier. The products of combustion were analyzed by an Orsat Gas Analyzer. The heat of combustion of the PS and copolymer propellant was determined by a Parr Bomb Calorimeter. Thermal degradation of the propellants was determined by the weight-loss method. The flame temperature was measured by the sodium-line reversal technique. The stray light incident on the spectroscope was minimized by putting a diaphragm between the flame and the lens. The measured temperature was corrected for a shift in wavelength on account of the red filter in the pyrometer which was used for calibration. For the polystyrene +70% AP propellant, the flame temperature was found to be 1550±30°C whereas for the corresponding copolymer propellant, the value was 1850±30°C. The surface temperature of the PS and copolymer propellants during burning was determined by using a Pt-Pt (Rh 10%) thermocouple (0.45-mm-diam). The hot junction was kept touching the surface by putting a load of 60-80 g. The cold junction was kept in water at room temperature. The thermocouple was calibrated beforehand by taking measurements on the melting points of silver nitrate, potassium dichromate, and