Polybutadiene structural effects on dynamic wetting

Binder jetting additive manufacturing will increase the design space for composite propellants but the technology is limited in part by a lack of insight into the dynamic wetting process. This effort investigates the structural influences on the spreading of commercially available polybutadiene-based droplets impacting ammonium perchlorate. Analysis indicates that spreading scales with t1/2 immediately after impact indicating inertia dominated spreading whereas a viscous regime occurs later in the event. Droplets from a height of 50 mm displayed shear thinning effects in the viscous regime whereas increased droplet height caused faster spreading as expected by Newtonian flows. The maximum spreading diameter for linear polymer droplets was dependent on the infinite shear viscosity. However, improved wetting and formation of globular entities during the event caused the branched variant to spread up to 25% more, by area, despite being more viscous. Implications of these results can improve binder design for binder jetting-made propellants.