Synthesis and performance study of potassium-based flame-retardant groups grafted onto nitrocellulose

To analyse the issues of high muzzle flame intensity and the easy migration of insensitive agents in conventional insensitive propellants, this study synthesizes modified nitrocellulose grafted with carboxymethyl potassium groups by a two-step process, starting from the molecular structure of nitrocellulose (NC), the principal component of propellants. First, the denitration reaction was performed to reduce part of the nitrate ester groups on the surface of NC to hydroxyl groups, followed by an etherification reaction to achieve directional grafting of carboxymethyl potassium groups. Compared with conventional flame retardant/insensitive systems based on nitrogen, phosphorus, or DBP (dibutyl phthalate), potassium-based functional groups exhibit superior thermal stability and environmental friendliness. FTIR, XPS, SEM, ICP, and EA characterization techniques were used to confirm the successful synthesis of carboxymethyl nitrocellulose potassium (CMNC-K). Theoretical calculations revealed that this structure improves the oxygen balance value of the material; TG-DSC analysis indicated a more stable thermal decomposition process and a slower heat release rate, and the flame-retardant capability was highly positively correlated with the potassium ion content; TG-FTIR further revealed that CMNC-K continuously releases K⁺ dominated flame-suppressing species during pyrolysis, thereby reducing the release of combustible gases such as NO and CO, which enhances the gas-phase flame suppression during combustion. Firing tests demonstrated that the introduction of CMNC-K significantly reduced muzzle flame intensity and increased projectile initial velocity, exhibiting excellent low-visibility flame characteristics. This study provides a new strategy for designing propellant materials with both high energy safety performance and low muzzle flame intensity, and offers theoretical and experimental support for the functional modification of nitrocellulose energetic materials.