Characterization and structural modification of ammonic lignosulfonate by methylolation

The methylolation of softwood and hardwood lignosulfonates was studied. Six different lignosulfonate samples (three from hardwoods and three from soft woods) were characterized in order to assess their suitability for methylol ation. The techniques employed in characterization were UV/vis spectroscopy , Fourier transform infrared (FTIR), and H-1-nuclear magnetic resonance (H- 1-NMR). The best properties were shown by softwood ammonium lignosulfonate (LAS), which was used to optimize the operation conditions to promote the L ederer-Manasse reaction. The methylolation variables studied were the sodiu m hydroxide-to-lignin molar ratio, the formaldehyde-to-lignin molar ratio, time, and temperature. The reaction was followed by the changes in the conc entration of free formaldehyde. IR and NMR spectra of nonmodified and modif ied samples were used to study the structural changes. Under optimum operat ion conditions, softwood lignosulfonates showed higher reactivity toward fo rmaldehyde than did hardwood lignosulfonates. (C) 2001 John Wiley & Sons, I nc.