Wood particleboards produced with unmodified and esterified Kraft lignins

Abstract

Hardwood Kraft lignins were esterified with succinic anhydride and chemically, thermally and morphologically characterised compared to their unmodified counterparts. Esterification was confirmed by NMR and Fourier transform infrared spectrometer (FT-IR). Esterified lignins were found to be porous, less thermally stable and slightly more hydrophilic than unmodified lignins because esterification with cyclic acid anhydride is accompanied with the simultaneous liberation of carboxylic acid groups. These free carboxylic acid groups are interesting for panel production as they could create new ester groups with wood components. The wood particleboard panels were produced via compression moulding using different concentrations of unmodified and esterified Kraft lignins as sole binders (10, 20 and 30%). All the mechanical properties [impact strength, modulus of elasticity (MOE) and modulus of rupture (MOR)] of the studied wood particleboard panels significantly increased with the addition of the succinated and unmodified Kraft lignins. However, the best mechanical properties were determined for panels containing 20% of unmodified Kraft lignins. Therefore, the condensation reactions of the unmodified Kraft lignins taking place during the compression moulding seem explain why these lignins act as a more efficient binder than the succinated lignins.