Enhanced thermal performance and hydrochloric acid gas (HCl) emission mitigation in ammonium perchlorate (AP)-Based solid propellants with potassium permanganate (KMnO4)/AP dual oxidisers

The conventional propellant used in rocket boosters and tactical missiles commonly utilises ammonium perchlorate (AP). However, the release of harmful chloride fumes resulting from the combustion of AP during rocket launches contributes to a 1% increase in air pollution. Generally, the perchlorate-based propellants contribute to pollution by hydrochloric acid (HCl), which can contaminate launch sites and potentially deplete the ozone layer. Several techniques have been employed to convert standard AP-based composite solid propellant (CSP) into green propellant. This study designed a minimum chlorine content propellant containing potassium permanganate, KMnO 4 /AP as a dual oxidiser and examined its properties in CSP formulation. This novel KMnO 4 /AP was characterised in terms of morphological structure, elemental analysis, and thermal decomposition properties by using scanning electron microscope (SEM), energy dispersive X-ray analysis (EDX), and differential scanning calorimetry (DSC) and thermogravimetry analysis (TGA), respectively. Additionally, heat of combustion analysis was examined through bomb calorimetry. The chlorine content investigations were experimentally carried out, and the results were compared with conventional AP-based CSP using gas bubbling and Mohr’s titration method. From thermal decomposition analysis, sample KMnO 4 /AP (40:60) shifted high temperature decomposition (HTD) of AP to a lowest temperature of 331.32 °C with the highest heat release of 3721.2 J/g. Besides, sample KMnO 4 /AP (80:20) shows the highest reduction of chlorine concentration content with a reduction percentage of 58.25%. Besides, KMnO 4 /AP (40:60) sample resulted in the highest value of heat of combustion with a value of 1254.01 cal/g. This study contributes to the development of environmentally friendly and sustainable oxidisers for solid rocket propellant applications. • Morphological analysis using Scanning Electron Microscopy (SEM) showed that composite solid propellant (CSP) samples appeared darker and rougher as the potassium permanganate (KMnO 4 ) to ammonium perchlorate (AP) ratio increased. • The KMnO 4 /AP (40:60) CSP sample showed the best catalytic performance by reducing AP's HTD from 392.1 °C to 331.32 °C and releasing the most heat at 3721.2 J/g during decomposition. • KMnO 4 /AP (40:60) CSP sample exhibits the highest heat of combustion value of 1254.01cal/g, thus exhibits the highest combustion efficiency percentage of 100.2%. • A higher ratio of KMnO 4 /AP results in a higher percentage of decrease in chlorine concentration, as the KMnO 4 /AP CSP (80:20) sample resulted in the largest reduction of 58.25% in chlorine content. • This study will contribute to the development of environmentally friendly oxidiser in which providing a promising candidate for solid rocket motor applications.