Study on the Preparation and Application of Lignin-Derived Polycarboxylic Acids

Abstract

Lignin was oxidized by NaOCl, and the main product of the reaction was named lignin-derived polycarboxylic acids (LPCAs). The effect of the reaction conditions was studied. With the mix ratio [n(NaOCl)/m(lignin)] increasing, the content of carboxyl of LPCAs increased. When the reaction temperature or the reaction time increased, the content of carboxyl decreased in different degrees. After the oxidation by NaOCl, the content of hydroxyl and methoxyl of lignin decreased, and the molecular weight of lignin decreased as well. The FT-IR and 1 H-NMR spectrum of lignin suggested that the benzene rings of lignin were disrupted after the oxidation. A possible mechanism of the oxidation of lignin by sodium hypochlorite is supposed to briefly demonstrate the reason that the benzene rings were disrupted and the content of carboxyl increased. Finally, an application example shows that LPCAs can strengthen the mechanical properties of waterborne polyurethane elastomers.