Composition optimization and characterization of combustible cartridge cases with polyvinyl acetate (PVAc) as a binder

Abstract

Combustible cartridge case samples composed of nitrocellulose (NC), polyvinyl acetate (PVAc), kraft cellulose (KC), dibutyl phthalate (DBP) and diphenylamine (DPA) were prepared to study their structures and chemical and mechanical properties. Taguchi’s experimental design method was used to design the experimental formulations. First, simultaneous thermogravimetry-differential scanning calorimetry (STA TG-DSC), scanning electron microscopy (SEM), Brunauer–Emmett–Teller analyser (BET), bomb calorimeter (BC), vacuum stability tester (VST) and a tensile testing machine (TTM) were employed to analyse the thermochemical characteristics, structure, explosion heat, chemical stability and compatibility, and mechanical strength of all formulated samples. Based on the analysis results, the weight loss of the combustible cartridge case sample obtained by the TG experiment was chosen as the quality characteristic. The results of the Taguchi analysis indicated that the optimal parameter combination was an NC/KC weight ratio of 80:20, an NC/PVAc weight ratio of 85:15, an additional DPB of 3.5 wt.% and a density of 1.25 g/cm3. The results of the chemical stability and compatibility test, explosion heat test and mechanical strength test show that the test samples prepared with the optimal parameter combination can meet the requirements of combustible cartridge cases. Furthermore, the combustion performance of the combustible cartridge case sample prepared with the optimal formula was measured by a high-temperature combustion furnace (HTCF) and burning rate measurement device (BRM). The experimental results indicated that the autoignition temperature and ash content were 231 °C and 0.28%, respectively. In addition, the burning rate increased with increasing combustion chamber pressure but was lower than that of ordinary gun propellants at the same pressure. These combustion characteristics can meet the quality requirement of combustible cartridge cases. Finally, an actual combustible cartridge case was prepared and verified. The result of the performance verification test indicated that the average ash content was 0.30%, which was similar to that of the previous test samples and met the quality requirement.