Effects of Accelerated Aging and Primer on the Mechanical Properties and Bond Strength at Propellant–liner Interfaces

This study explores the influence of accelerated aging and primer composition on the bond strength at the solid propellant–liner interface. Tris(methyl-aziridinyl) phosphine oxide (MAPO) was employed as the primary bonding agent, formulated with two curing agents—toluene diisocyanate (TDI) and isophorone diisocyanate (IPDI)—in varying ratios. Propellant samples were subjected to accelerated aging at 70 °C for 0, 8, 16, and 24 days, corresponding to simulated storage durations of 0, 3, 6, and 9 years under ambient conditions. Mechanical testing revealed that increasing aging time resulted in higher tensile strength and hardness, accompanied by a gradual reduction in elongation, indicative of increased crosslink density and polymer matrix stiffening. Bond strength at the propellant–liner interface was evaluated using tensile tests on rectangular specimens coated with primers of different compositions. Among all formulations tested, the MAPO:IPDI ratio of 1:9 demonstrated superior adhesion performance, maintaining the highest bond strength across all aging intervals. Compared to unprimed controls, this formulation improved bond strength by 18 – 55 %, depending on aging duration. These results provide valuable insights for optimizing primer design and aging protocols in the production of solid rocket motors, thereby enhancing the long-term reliability and structural integrity of propulsion systems.