Surface modification effects on ammonium perchlorate wettability

Solid propellants are commonly used for propulsion systems due to their high volumetric thrust and reliability. Powder bed, binder jetting manufactured propellants will enable unique geometries to be made that are necessary for designers to achieve high thrust levels. However, changes to the particulate wettability from the solvent-based manufacturing technique must be understood such that propellants with adequate mechanical properties are achieved. In this work, the wettability of ammonium perchlorate (AP) crystal surfaces is quantified with solvent and air plasma treatments. Removal of adventitious carbon from AP surface decreases the polybutadiene contact angle from 34 ± 1° to 15 ± 4°. The presence of hydrocarbons from non-polar solvents used in this study with lower vapor pressure was observed to have a similar effect as the adventitious carbon whereas higher vapor pressure solvents have minimal influence on the final wettability of AP surfaces. Polar solvents were determined to alter the surface topology by creating a more hydrophobic surface when compared to the plasma treated samples. An increase in concentration of amine surface groups overcomes the decrease in wettability from carbonaceous residue and surface morphology. The extension and implications of these findings to powder bed, binder jetting manufacturing for propellants is discussed.