Mechanism of AP effect on slow cook-off response of HTPE propellant

Due to safety requirements, insensitive behaviour under slow cook-off conditions is the desirable behaviour for HTPE (Hydroxyl-terminated block copolyether) propellant. In this paper, in order to study the effect of AP (ammonium perchlorate) on slow cook-off response of HTPE propellants, the slow cook-off behaviour of AP and the effect of HTPE binder on AP were investigated firstly. The results showed that, the weightlessness rate of AP was only 2.2% in closed system till heated to 250°C, but the figure was 35.91 % in opened system. Then the slow cook-off behaviour of two groups of HTPE propellants with different AP content and diameter respectively were tested. The results indicated that, as the AP content increased from 52% to 67%, or the diameter of AP decrease from 400 μm to 5 μm, the violence of slow cook-off response all increased. The possible mechanism was proposed. It expressed that, thermal damage of propellant produced during the slow cook-off test, the combustion sensitivity to pressure of damaged propellant increased as the AP content rise and the AP diameter decrease, leading a more violent response to slow cook-off.