Polyelectrolyte complexes based on natural macromolecules for chemical sand/soil stabilization

Soil erosion is a global problem with grave social, economic and ecological consequences. To stabilize the top soil layer, various approaches have been developed, including the use of synthetic and natural water-soluble polymers capable of binding to soil particles and forming a protective layer (crust) on the topsoil. Individual water-soluble polymers give crusts which lose mechanical stability after re-watering. We describe in the article effective stabilizers of model unstructured soil, sand, polyelectrolyte complexes (PECs), composed of two oppositely charged ionic polymers (polyelectrolytes), cationic poly(diallyldimethylammonium chloride) (PDADMAC) and anionic potassium humates (PH). By varying the PDADMAC-to-PH ratio, the total charge of PECs and their solubility in water was adjusted. The PECs as well as PDADMAC and PH were deposited on the surface of monomineral quartz sand, with a mean diameter of particles from 0.15 up to 2.1 mm. After drying, polymer-sand crusts were formed; their mechanical strength increased upon elevating the cationic content in the polymer formulation. Re-watering caused both polyelectrolytes and PECs with a great excess of cationic or anionic groups to be removed from the crusts, which was additionally accompanied by loss of sand and decrease in the mechanical strength of the crust. The slightly positive PECs with a significant degree of mutually neutralized charges (hydrophobized blocks) formed the most stable crusts due to electrostatic and hydrophobic contacts with sand particles. A correlation was thus revealed between the PEC composition and the anti-erosion resistance of the polymer-sand crusts. It is shown that the use of non-stoichiometric polycomplexes makes it possible to manipulate the mechanical strength of the resulting coatings. The described approach is promising for fabrication of polymer formulations for environmental protection, conservation/rehabilitation of landfill sites, desertification control, anti-erosion treatment of agricultural land, conservation of mining dumps, treatment of road slopes, etc.