Physicochemical Properties of Calcium Lignosulfonate with Different Molecular Weights as Dispersant in Aqueous Suspension

Five purified calcium lignosulfonate (CL) fractions with different molecular weights were obtained by fractionation using ultrafiltration and dialysis. The influence of molecular weight on their physicochemical properties was investigated by determining the properties of five fractions. TEM and ESEM imaging indicated that CL has a globular structure to form locally regular colloidal assemblies with the diameter of approximately 200 similar to 300 nm. Fraction3 (M-w is 7621) with the molecular weight of 5,000-10,000 has more sulfonic and carboxyl group, so the highest zeta potential (-36mV) can be charged on the TiO2 particles. With the increase of molecular weight, the hydrophobicity and surface activity of CL in aqueous solution increase, so Fraction5 (M-w is 21646) which molecular weight is more than 30000 has the biggest adsorption amount. The adsorption characteristic of CL on solid-water interface have great impact on the dispersive properties of TiO2 particle in aqueous solution and the higher adsorption capacity is helpful to improve the dispersive ability of CL. On the other hand, the surface charge of TiO2 particle absorbing CL is another important factor to the dispersive ability of CL. Furthermore, when the CL concentration in TiO2 suspension is less than 4mg/mL, Fraction3 has the best dispersive ability because the electrostatic repulsion effect is controlling factor. The dispersive ability of CL increases with the increase of molecular weight when the CL concentration in TiO2 suspension is more than 4mg/mL, so Fraction5 has the best dispersive ability owing to the steric hindrance effect.