Isolation of Low Dispersity Fractions of Acetone Organosolv Lignins to Understand their Reactivity: Towards Aromatic Building Blocks for Polymers Synthesis

Two organosolv lignins extracted during pilot runs of the Fabiola process were analyzed, fractionated and chemically modified with ethylene carbonate (EC) to produce building blocks suitable for polymer synthesis. Isolation of low dispersity fractions relied on the partial solubility of the lignins in organic solvents. Lignins solubility was first evaluated and analyzed with Hansen and Kamlet-Taft solubility parameters, showing a good correlation with the solvents dipolarity/polarizability parameter pi*. The results were then used to select a sequence of solvents able to fractionate the lignins into low dispersity fractions of increasing molar masses, which were analyzed by(31)P NMR, SEC and DSC. The lignins were then reacted with EC, to convert the phenolic OH groups into primary aliphatic OH groups. The reactivity of the organosolv lignins was high, and milder reaction conditions than previously reported were sufficient to fully convert the phenolic OH groups. A gradual reduction in reactivity with increasing molar mass was evidenced and attributed to reduced solubility of high molar mass fragments in EC. Undesirable crosslinking side reactions were evidenced by SEC, but were efficiently limited thanks to a fine control of the reaction conditions, helping to maximize the benefits of the developed lignin modification with EC.

Automated summary

In this study, two organosolv lignins were extracted and chemically modified with ethylene carbonate (EC) to create building blocks for polymer synthesis. The lignins were fractionated using a sequence of solvents based on their solubility parameters, and then reacted with EC to convert phenolic OH groups to primary aliphatic OH groups. The reactivity of the lignins decreased with increasing molar mass, leading to reduced solubility of high molar mass fragments in EC. Efforts to minimize undesirable crosslinking side reactions were successful through careful control of reaction conditions.