SOLVENT EFFECTS ON ORGANOSOLV LIGNIN FROM PINUS-CARIBAEA-HONDURENSIS

Lignin from Pinus caribaea hondurensis sawdust (pre-extracted with benzene/methanol 1:1) was obtained by pulping using nine different organic solvents (in 9:1 mixtures with 2.0 N HCI aqueous solutions) in a stainless steel reactor at 125-degrees-C for six hours. The obtained lignins were characterized by chemical analysis (elemental analysis, methoxyl and phenolic hydroxyl groups) and by infrared spectroscopy. Moreover, the average molecular weights (MnBAR, MwBAR and MWD) were determined by vapor phase osmometry and high performance-size exclusion chromatography and shown three different patterns according to the solvent mixtures employed. The yields of lignin depend on the accessibility and nucleophilicity of the solvents as well as on the lignin solubility, and are related to the Hildebrand's solubility parameters (delta) of the solvent mixtures. The plot of lignin yields against delta show a characteristic "Bell shape" curve with maximum at 23 MPa1/2 corresponding to the lignin solubility parameter.