Lignins as macromonomers for polyurethane synthesis: A comparative study on hydroxyl group determination

Abstract The hydroxyl group contents of four technical lignins [Indulin AT (Meadwestvaco), Alcell (Repap), Curan 27‐11P (Borregaard LignoTech), and Sarkanda (Granit SA)] were investigated in view of their valorization as polyols in polyurethane synthesis. The different hydroxyl group contents were determined by the following methods: titration and 1 H‐NMR, 13 C‐NMR, and 31 P‐NMR spectroscopy. The titration method chosen was on the basis of a standard method commonly used to characterize commercial polyols for polyurethanes synthesis. The values of the total and phenolic hydroxyl contents determined by the different techniques were found to be in good agreement. For the total hydroxyl contents, coefficients of variation of 5.6% (Alcell), 3.2% (Indulin AT), 2.3% (Sarkanda), and 6.2% (Curan 27‐11P) were established. For the phenolic hydroxyl contents, a good correlation was observed between data obtained from 31 P‐NMR and 13 C‐NMR for all lignin samples, except for the Sarkanda lignin, for which a relatively high coefficient of variation (12.6%) was found. For softwood lignins (Indulin AT and Curan 27‐11P), the phenolic hydroxyl content determined by 1 H‐NMR was always lower than that deduced from 31 P‐NMR and 13 C‐NMR spectroscopy. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008