Improving Bond Strength at Propellant

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Improving Bond Strength at Propellant–Liner Interfaces

Liao, Chih Yeh / Lee, Shyong

In solid rocket motors, a strong bond at the propellant–liner interface ensures that the propellant functions as designed. If the interface degums, the propellant burn surface area will change and the performance of internal ballistics will be adversely affected. In this study, two cases of motor failure are considered to investigate methods for improving the bond strength between the propellant grain and the liner interface, with the aim of achieving a tensile strength exceeding the $8 kg / {cm}^{2}$ requirement. Hydroxyl-terminated polybutadiene was used as the liner material. This hydroxyl-terminated-polybutadiene-based material was conditioned and processed under the conditions of 5–20 torr pressure and 60–70°C temperature. Further, toluene diisocyanate was considered as the hardener and its contents were increased in the liner by 0 (i.e., original content), 2, 5, 10, and 15% to obtain diisocyanate NCO/OH equivalence ratios of 1.035, 1.057, 1.087, 1.144, and 1.187, respectively. Thereafter, bond strength tests and analyses were conducted. The tensile strength gradually increased with increasing toluene diisocyanate content in the liner. The bond strength was found to increase after improving the liner, performing hydroxyl-terminated polybutadiene heating and vacuum extraction pretreatments, and increasing the toluene diisocyanate content by 10%.