Lignin from the pulp and paper industry is a potential abundant resource for making more sustainable polymeric materials. By converting the hydroxyl groups of lignin into esters, the derivatized lignin shows an improved compatibility with compostable polymers such as polylactic acid and polybutylene adipate terephthalate. These polymer blends or composites can be potentially applied for 3D printing inks, single use packaging, and agriculture plastics. However, traditional esterified reactions using anhydride and acid chloride compounds have drawbacks, considering requirements of sustainable chemistry and industrial economic efficiency. In this study, we developed three greener innovative routes to obtain esterified lignin: 1) direct esterification using organic acids as solvent and reagent, without adding catalyst, at 90-160 °C for 24-48h, 2) direct esterification using organic acid as solvent and reagent, with the addition of immobilized lipase as catalysts, at 90 °C for up to 96 h, and 3) transesterification using lipase as a catalyst to react with vinyl esters at 40~90 °C for 24-48h. In order for these reactions to proceed at high efficiency, hydroxyethyl lignin (HELignin, 90% aliphatic OH group) was synthesized utilizing ethylene carbonate as the solvent and reagent. Based on this HELignin, all of these routes reached a degree of substitution between 80%-90% for both short chain acid (propionic acid) and fatty acid (stearic acid and oleic acid) based on <sup>13</sup>C nuclear magnetic resonance analysis. The immobilized lipase was able to promote the directly esterification at milder temperature and shorter time. The molecular weight and thermal properties before and after these esterified reactions were in line with traditional esterified methods using anhydride and acid chloride compounds. Moreover, these esterified routes were greener considering principles of green chemistry including safer reagents, reaction efficiency, and lower E-factor.

Simple, greener and robust routes to make esterified lignin

2019 Spring National Meeting

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