A new model for the structure of lignosulphonates Part 1. Behaviour in dilute solutions

Lignosulphonates are formed by the cleavages of the alpha-O-4 linkages of the "infinite" lignin network in wood, and a sulphonation of the alpha- and/or gamma-positions of the side chains of the C-9 units. The resulting lignosulphonate molecule forms a randomly branched polyelectrolyte. The molecule coils in solution to make a more ball-shaped molecule with the sulphonate groups enriched on the surface. The scaling laws for this model of the lignosulphonate polymer as well as for other models of the lignosulphonate have been derived. The scaling laws for the randomly branched polyelectrolyte and microgel are the same for most properties except the polyelectrolyte expansion. The scaling laws are compared with literature experimental values for radii and polyelectrolyte expansion. The randomly branched polyelectrolyte model successfully accounts for the behaviour in solution. The dependence of the polyelectrolyte expansion on the molecular weight demonstrates that the lignosulphonate is not a microgel structure. (c) 2007 Elsevier B.V. All rights reserved.