In the field of shock physics, flat plate impacts are used to characterize the dynamic tensile strength (spall strength) of a material. In particular, prior work has observed that the presence of secondary phases influences the overall material, typically reducing spall strength. In the study presented here, surface effects were investigated using polymer matrix composites reinforced with alumina particles. Interface adhesion between the matrix and filler was tailored with silanes, while filler morphology effects were assessed using spherical and irregular particle geometries. Two matrix materials were used, polydimethylsiloxane and polyurethane. These composites were characterized through spall experiments, using a single stage light gas gun at Carleton University. Varying particle morphology was found to have no effect on spall strength, while composites with impeded adhesion saw a drastic reduction in spall strength, associated with a loss of adhesion at the interface.