OH groups involved in the polyesterification and an overall reduction of hydrogen bond interactions, the latter due to a lower content of hydroxyl groups close enough to form hydrogen bonds. The ring-opening esterification leads to the formation of secondary alcohol with a signal at 3530 cm - 23 that falls in the already present wide signal from the primary hydroxyl and unreacted carboxyl groups. Thus, such a signal could not be identified from the FT-IR spectrum. The band deriving from the mid-chain unsaturation (3003 cm -1 ) was still present in the final film, showing that it did not participate in the network formation. Finally, lignin-like species can still be recognized in the film's spectrum (1516 and 1599 cm -1 ).