Novel multifuctional geomimetic soil conditioner based on multilayer hybrid composites of clay-paa-lignin: Synthesis and functional characterization

Abstract

Soil conditioners are products of natural or synthetic origin that aim to improve the physical–chemical properties of poor or degraded soils. Recently, geomimicry has emerged as a novel strategy for obtaining geomimetic materials, which have been designed to imitate the structure and functions of soils, and potentially be used as soil conditioners, by improving their structure, increasing their capacity for water retention (WRC) and cation exchange capacity (CEC), restore the microbiota, etc. Thus, the development of hybrid composites has proven to be an appropriate strategy for obtaining novel materials that combine and improve the properties exhibited by their predecessors; being the systems based on clays and polymers capable of imitating the clay-humin-humic acid structures present in the soil particles and their properties. Therefore, the objective of this work was to develop new geomimetic soil conditioners based on multilayer hybrid composites, MHCs, of clay-PAA-lignin. For this, bentonite and kaolinite surfaces were chemically modified with trichlorovinylsilane to produce surface activation of the clay. Subsequently, chains of poly(acrylic acid), PAA, were inserted into the surface active clay by free radical reactions, in order to generate carboxylic acid groups on the surface. On the other hand, lignin was obtained from sugarcane bagasse by the basic delignification method and was incorporated into the polymeric matrix by urethanization with 4,4-methylenebis(phenyl isocyanate). By this method, lignin coatings on inorganic particles were obtained using urethane bonds. In addition, different clay-lignin ratios were evaluated. Finally, the material obtained was characterized by infrared spectroscopy, FEDS, nuclear magnetic resonance and thermogravimetric analysis. In addition, their WRC, CEC and bacterial viability properties were evaluated. The results showed that MHCs based on clay-PAA-Lignin can be obtained through the proposed methodology and mimic the structures and properties of soil. The WCR and CEC of the synthesized MHCs were lower than that of their predecessors, produced by the change in hydrophobicity of the materials. In addition, the developed MHCs showed a high microbial viability, >83 %, which suggests a high compatibility with the soil microbiota.