Characterization of syringyl and guaiacyl lignins in thermomechanical pulp from oil palm empty fruit bunch by pyrolysis-gas chromatography-mass spectrometry using ion intensity calibration

Thermomechanical pulp (TMP) was fabricated from the empty fruit bunch (EFB) of oil palm (Elaeis guineensis) by using a laboratory-scale pressurized refiner. The EFB TMP was separated by screens (850, 355, and 180 μm openings) into four fractions. Pyrolysis-gas chromatography-mass spectrometry (Py-GC/MS) indicated analogous chemical features of lignin in the TMP fractions by determining eight pyrolysis products from its syringyl (S) and guaiacyl (G) types. The amount of each pyrolysis product was quantitatively determined through a calibration line obtained by the conversion factor of the main ion intensity to an authentic compound weight. Moreover, S/G molar ratios obtained by Py-GC/MS provided a good correlation with the syringaldehyde/vanillin (Sa/Va) molar ratios obtained by nitrobenzene oxidation for raw EFB material and some hardwoods. The TMP fabrication process slightly changed the lignin structure. Py-GC/MS was found to be a reliable analytical method for the characterization of lignin in EFB TMP.