Hydroxymethylation of technical lignins from south-american sources with potential use in phenolic resins.

Abstract

This work investigates the valorization of sodium lignosulfonate, kraft, and organosolv lignins from South America. A detailed characterization of the lignins and their chemical modification by hydroxymethylation, a reaction between lignin and formaldehyde, were performed. The characterization included measurements of moisture, ash, and carbohydrate contents, elemental and thermogravimetric analysis (TGA), and functional groups and molar mass distributions by Fourier transform infrared spectroscopy (FTIR) and size exclusion chromatography (SEC), respectively. Also, reactive aromatic hydrogens (—HAr) were quantified by the measurement of phenolic hydroxyl groups (P-OH) content by UV-Vis spectroscopy. The different initial formaldehyde/lignin weight ratios (0.07, 1.47), temperatures (40 ºC, 50 ºC, 70 ºC) and pHs (9, 11); and the following of hydroxymethylation reactions by UV-Vis spectroscopy were investigated. All lignins resulted attractive for the use as replacement of phenol in phenolic resins but sodium lignosulfonate was the most appropriate due to its water solubility.