At the same time, the temporal development of the band around 1210 cm -1 is interesting. Already after 5 min reaction time, an intensity decrease of the band at 1210 cm -1 as well as the formation of a pronounced shoulder around 1185 cm -1 can be observed. After 15 min, two overlapping bands have formed, reaching intensity equilibrium at 30 min milling time. This pattern of changes has similarity with the absorption of the C-O stretching vibrations in phenyl acetate. Using solution chemistry, Kadla and Chang were able to demonstrate this on various lignin model compounds . The use of SPC and NaOH is thought to cause cleavage of the β-O-4 bond of the lignin skeleton and introduce carbonyl functions so that the fragments have phenyl acetate-like structural features. A similar reaction behaviour is observed for the SPC series of experiments without NaOH as additive (Fig. ).