Lignin-Based Chemicals as Green Dispersants for Liquid Formulation: Better Protection Against Crystal Growth

The development of liquid formulations such as suspension concentrates is increasing in the crop-protection industry. However, Ostwald ripening, also called crystal growth, can irreversibly occur in the aqueous suspension even at low solubility levels of the active material and can cause severe changes in the formulation during storage. Lignosulfonates are natural water-soluble polymers based on wood biorefinery that can be used as crystal growth inhibitors in suspension concentrates. In addition, lignosulfonates are highly efficient dispersants because they rapidly adsorb onto the newly created surfaces during milling of the active material, preventing its re-agglomeration. The purpose of the present study was to characterize the stability of fungicide-based suspension concentrates using different kinds of dispersants. A special-grade lignin-based product from Borregaard LignoTech, Greensperse S7, was tested and compared with kraft lignin, sulfonated naphthalene formaldehyde condensate, acrylic copolymer, and a standard sodium lignosulfonate. The active material was milled down to 1 μm in order to encourage the destabilization of the formulation during “accelerated” storage (i.e., 2 weeks at 54°C). Based on evaluation of formulation stability after accelerated storage, we demonstrated that lignosulfonates represent very interesting alternatives to synthetic dispersants and kraft lignins in suspension concentrates. Our results show that, after accelerated storage, formulations dispersed by Greensperse S7 are stable in terms of particle size and viscosity, reducing the eventuality of crystal growth. This can be explained by the presence of an electrical double layer at the particle/solution interface, leading to electrostatic repulsive forces, combined with steric repulsion of the adsorbed macromolecule.