Polyimide-modified epoxy coatings reinforced with functional fillers for enhanced thermal stability and corrosion resistance

The protection of combustible cartridge cases (CCCs) benefits from applying composite coatings, which significantly extend their heat resistance time and improve their waterproof properties and corrosion resistance. In this study, a series of polyimide-modified epoxy resin composite films (NPMFs) was developed and applied as protective coatings. The polyimide-modified epoxy resin was designed through cross-linking reactions between epoxy resin and polyimide, forming the film material. The heat resistance and flame retardation of the NPMFs were attributed to the introduction of inorganic fillers. The results demonstrated that NPMF-3 significantly delayed the ignition of CCCs, withstanding temperatures of 270 °C for 109 s, thus, enhancing heat resistance by 104.1%. Meanwhile, the saltwater absorption rate of NPMF-4 was only 6.92 wt%, which was reduced by 82.10 wt% compared to the uncoated CCC sample. The maximum storage modulus value of all NPMFs exceeded 2000 MPa. Compared to the uncoated CCC sample, the tensile strength and elongation at break of NPMF-3 increased by 203.52% and 570.24%, respectively. Additionally, the corrosion rate of the Zn-Fe alloy samples coated with NPMFs was significantly lower than the uncoated samples, indicating strong protection against salt corrosion. These performance results were among the highest currently observed for CCCs. Therefore, these NPMFs not only possessed excellent thermal stability and corrosion resistance, but may also play an important role in CCC protection and marine corrosion resistance applications.