EFFECT OF MOLECULAR WEIGHT DISTRIBUTION ON CHEMICAL, STRUCTURAL AND PHYSICOCHEMICAL PROPERTIES OF SODIUM LIGNOSULFONATES

Authors: Nidal Madad, Latifa Chebil, Christian Sanchez and Mohamed Ghoul

*E-mail: mohamed.ghoul@ensaia.inpl-nancy.fr

Chemical, structural and physicochemical properties of six sodium lignosulfonates (SLS) fractions with high purity and narrow molecular weight distribution (M_w) ranked between 2307 and 19583 g.mol^-1 were studied. Structural characterization of these fractions, using ³¹Phosphor Nuclear Magnetic Resonance (³¹P NMR) and Fourier Transformed InfraRed (FTIR) analysis, was reported. ³¹P NMR and FTIR analyses show that these fractions present an important variability of hydroxyl, carboxyl and sulfonic group content. The adsorption isotherms of SLS fractions; fitted by Guggenheim–Andersen–de-Boer model; present different isotherms profile and different values of binding energy and adsorption capacities. SLS fractions were found to be highly charged and present the behaviour of soft particle. Intermediate fractions with M_w of 4297 and 2471 g.mol^-1 give the highest surface activity and antioxidant capacity. Moreover, fractions with the highest molecular weight, M_w more than 6953 g.mol^-1, present the greatest charge density and apparent viscosity. This data can help to develop new niche applications for the SLS.

Keywords : Sodium lignosulfonates, diafiltration, physicochemical properties, antioxidant capacity.