The recovered products of hydroxymethylated lignins (HL60 and HL85) were thereafter used for formation of hydrocolloids and later hydrothermally cured to internally cross-link the colloidal particles (Figure ) and further evaluate their stability under challenging solvent conditions. Successful hydroxymethylation of lignin was analyzed using spectroscopic techniques. As can be seen from the FTIR spectra of different samples (SKL, HL60, and HL85), obvious differences in the absorbance bands of SKL after hydroxymethylation are noticeable (Figure ). Firstly, there is an increase in the hydroxyl content of reacted lignin which can be seen in the increase of absorbance intensity at 3350 cm -1 . Secondly, the disappearance of the band at suggest that more extensive hydroxymethylation reaction occurred at 85 °C than at 60 °C. These results are in agreement with the literature and our quantitative P NMR data (Table ). A marked increase in the content of aliphatic hydroxyl groups in the hydroxymethylated lignins was determined compared to the parent kraft lignin (Figure ). For instance, it is visible that by increasing the reaction temperature in the presence of formaldehyde the content of non-condensed guaiacyl (free 5-position in the aromatic ring) decreased by 52% in HL85 and 20% in HL60, while that of condensed guaiacyl (carbon-carbon or ether linkage at the 5position) increased by 64% in HL85 and 41% in HL60. At the same time, the phenolic hydroxyl content remained essentially unchanged compared to the parent lignin. Based on the 31 P NMR data the mass fraction of hydroxymethyl groups in HL85 was about 3 wt%.