Relaxations in double base propellants

Abstract

Double base propellants are composed of nitrocellulose(NC) plasticized with various amounts of nitroglycerine(NG). A series of propellants was made with NG contents of 10%, 35% and 60% by incorporating with solvents, extruding into cords and then drying. A study of relaxation behaviour of these propellants was made using dynamic mechanical analysis, thermomechanical analysis and differential scanning calorimetry (d.s.c.). Three relaxations were observed, one at about −80°C designated γ, one in the temperature range −10° to −60°C designated β, and one above 35°C designated α. The γ relaxation is attributed to motion of the pendant nitrate side groups of NC. The β relaxation is attributed to motion of NC molecule side groups and associated NG molecules. It causes a peak in mechanical loss, and changes in modulus, thermal expansion and heat capacity. The β relaxation has previously been reported as the glass transition, but there is some doubt and this may be incorrect. The α relaxation occurs in the same temperature range as the glass transition reported in other plasticized cellulosic polymers, but it is unusual in that it involves a large change in modulus and mechanical loss, but no change in thermal expansion or heat capacity.