is the preferential formation of soluble oligomers with a lower molecular weight with longer reaction times and higher grinding ball densities. The weight average molecular weight (Table ) for tungsten carbide decreases and is below that of zirconia and stainless steel. A correspondingly lower molecular weight with longer grinding times is expected for zirconia and stainless steel. While investigating the influence of the grinding ball material, the abrasion of the individual ball materials during the grinding process was examined and compared with the content of the components in untreated cellulose using XRF (Table ). It can be seen that there is an increase of the respective metal in the product after mechanocatalytic treatment for all materials. Zirconia shows the smallest increase of about 10 ppm, while stainless steel and tungsten carbide show an increase of about 70 ppm and 65 ppm.