The grinding ball material and the grinding ball diameter influence the energy input per impact on the mechanocatalytic partial depolymerization. With increasing grinding ball density and grinding ball diameter, the energy input increases due to the kinetic energy of the grinding balls. The yields by varying the grinding ball material zirconia, stainless steel and tungsten carbide and the plot of the soluble fraction against the grinding ball density are shown in Figure . As expected, the oligomer fraction increases with increasing density of the grinding ball material.