Ozonolysis of regular and crosslinked lignin nanoparticles: closing the loop

Crosslinked lignin nanoparticles have been developed to produce chemically robust grades suitable for demanding applications. However, their end-of-life degradation has remained elusive. In this work, we studied oxidative degradation of regular, non-covalently assembled LNPs and crosslinked hydroxymethylated LNPs (HLNPs). The results suggest that HLNPs degrade in the same fashion as regular LNPs through the transformation of aromatic rings into muconic acid moieties. This transformation was studied by UV-vis, 31 P-NMR, 2D-NMR and FTIR and it was found to be rapid within the first 120 min of ozonolysis. During ozonolysis, the LNPs degrade into smaller nanoparticles, as shown by SEM and DLS, until their ultimate degradation and conversion into acetals and small organic acids, supported by LC-MS data. The oxidative degradation of regular and crosslinked lignin nanoparticles was studied. Despite different solvent stabilities, both degrade at similar rates during ozonolysis, forming smaller oxidized particles and eventually water-soluble molecules.