All experiments were performed in a ball mill (Fritsch Mini-Mill PULVERISETTE 23) in a 10 mL stainless steel beaker with two 10 mm stainless steel balls. Lignin was placed in the lower half of the stainless-steel beaker and then SPC was added. Optionally, NaOH was added for some of the experiments. The total weight was always 1 g to keep the volume in the grinding container constant. The mass ratio of lignin, SPC and NaOH was 1:1:0.25. The molar ratio of SPC to NaOH was 1:1. The ball mill operated at constant 50 Hz.