Fig. 2. Variation of milling frequency and sphere number. (A) Propene flow during milling of 2 g model PP at 25–35 Hz with 5 ZrO₂ grinding spheres (10 mm diameter). (B) Cumulative C_1–3 hydrocarbon yields obtained after 1 h of milling 2 g model PP at 25–35 Hz with 5 ZrO₂ grinding spheres (10 mm diameter). (C) Cumulative total C_1–3 hydrocarbon yields (Y_total) obtained after 1 h of milling 2 g model PP at 25–35 Hz with 5 ZrO₂ grinding spheres (10 mm diameter), and fit (Y_total ∼ f_mill^5.51). (D) Dependency of hydrocarbon formation on f_mill: exponent x_i obtained by fitting Y_i per mg ∝ (f_mill per Hz)^x_i for each product i. Y_i denotes the cumulative yield of i after 1 h with 5 ZrO₂ grinding spheres (10 mm diameter) at f_mill = 25–35 Hz. (E) as a measure for chain cleavage calculated from experimental data viaeqn (15) plotted against milling frequency f_mill together with fit (gray line) using the modified Zhurkov equation (eqn (16)). (F) Propene flow during milling of 2 g model PP at 30 Hz with 3–19 ZrO₂ grinding spheres (10 mm diameter).