Physicochemical Insights into Enzymatic Polymerization of Lignosulfonates

The enzyme-catalyzed polymerization of lignosulfonates was investigated. Molecular formulas for the initial material (LS) and the final polymerized lignosulfonates (pLS) were determined by mass balance calculations combined with elemental analyses, allowing the elaboration of the reaction equation. Structural and chemical changes during the reaction were followed. Rheology and size exclusion chromatography showed that viscosity and molecular weight increased 90-fold and 4-fold, respectively. The thermal stability of pLS was investigated by thermogravimetric analysis and was found to be rather low compared to those of other polymers. The specific heat capacity (c(P)) was determined by differential scanning calorimetry and was higher for pLS than for LS, depending on the final formulation of the polymer. Determination of the higher heating value together with the reaction equation allowed the determination of the reaction enthalpy of -61 kJ/kg(feed). Only minor structural changes were revealed by NMR and FTIR analyses. However, these are responsible for the gained insolubility properties of pLS. Higher solubility in organic solvents of varying polarity (heptane, toluene, isopropanol, and acetone) was found for polymer films. The perturbed chain statistical associating fluid theory equation of state was found suitable to model the solution behavior of pLS films.