Investigation Changes in Structure and Thermal Properties of Glyoxalated Soda and Kraft Lignins

One of the solutions to increase the applications of lignin molecules is increasing reactive functional groups by chemical modification. Adding reactive functional groups into the lignin structures is one the best proposed methods. The aim of this study was to investigate change in structure as well as glass transition temperature (Tg) of Soda and Kraft lignins after hydroxymethylation them with non-volatile aldehyde entitle Glyoxal. Kraft and Soda black liquors were prepared from Choka and Pars Co, respectively. Lignins were extracted from black liquors by acidic method. Then changes in structure and thermal properties of the glyoxalated lignins were measured with Fourier transform infrared (FTIR) and differential scanning calorimetry (DSC) compared to pure lignins, respectively. The results indicated that glyoxalation increase reactive functional groups in lignins. Also FTIR result indicated that glyoxalation made some changes in lignin structure. DSC analysis showed that Tg of Soda and Kraft lignins reduced by glyoxalation. Finally DSC and FTIR analysis indicated that Soda lignin exhibited better potential for glyoxalation and have lower Tg compared to Kraft lignin.