Production of carboxymethylated lignin and its application as a dispersant
Kraft lignin is currently combusted in the pulping process to produce heat. It can be
extracted from the process and converted to value-added products, but its limited water
solubility hampers its end use applications. The main objective of this study was to
investigate the carboxymethylation of hardwood kraft lignin to produce an anionic water
soluble product. The results showed that the optimal conditions for carboxymethylation
were 1.5 M NaOH concentration, 3 mol/mol sodium chloroacetate (SCA)/lignin ratio,
40 C, 4 h and 16.7 g/L lignin concentration. The produced lignin had a charge density
and carboxylate group of 1.8 meq/g and 1.68 mmol/g, respectively. The carboxymethylated
lignin was further characterized using thermogravimetric analyzer (TGA), Fourier
Transform Infrared (FTIR) spectrophotometer, Nuclear magnetic resonance spectroscopy
(H NMR) and elemental analyses. Moreover, the application of carboxymethylated lignin
as a dispersant for a clay suspension was successfully analyzed by means of a photometric
dispersion analyzer.