Abstract
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 π*. 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 31P 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.
Highlights
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
This method is attractive with the simplest cyclic carbonate, ethylene carbonate (EC), since it allows the introduction of primary aliphatic OH groups of high reactivity on the lignin
This specific variation in solubility depending on the solvent nature has been exploited to develop a sequential solvent fractionation
Summary
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. Many studies have focused on the use of lignin as component of polymer materials in the past decade.[7,8,9] A large part of the developed polymeric systems relies on the reactivity of lignin chemical functions, phenolic OH groups. The modification of polyphenols, including various lignins, with cyclic carbonates has been recently developed in our laboratory.[15,16,17] This method is attractive with the simplest cyclic carbonate, ethylene carbonate (EC), since it allows the introduction of primary aliphatic OH groups of high reactivity on the lignin Such lignins modified with EC can be directly esterified by fatty acids in the absence of catalyst or solvent.[18,19] They show a higher reactivity towards isocyanates and can be employed in the synthesis of polyurethane foams.[20]. Organosolv pretreatments have proven to be among the most promising for such purpose, and recent years have seen considerable developments.[1,2,3,4,5,6] The efficient use of all the individual constituents of lignocellulosic biomass is crucial for the economic viability of biorefineries, and has raised increased attention to the valorization of lignins
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