Micro-Sized Polymer Hydrogels as Model Microplastics: Interaction with Polycationic Toxins in Solution and Precipitate

The problem of polymer waste has reached a level that requires immediate solution. Microplastics (MP), potentially toxic polymer particles of 5 mm or less in size, are an important part of this problem. In the article, two types of micro-sized polymer particles are described, mimicking behavior of real MP. The first are soft anionic 570 nm microgels with a developed surface, which reproduce the structure of "aged" MP. The second are 380 nm microspheres with a solid polymer core and a thin outer anionic layer, which are taken as a model of the "initial" MP. Both types of anionic species electrostatically adsorb cationic polymers, toxic compounds, widely used in water treatment/purification, food industry, and cosmetics. The adsorption is accompanied by neutralization of the particle charge and aggregation of the species at mutual neutralization of the particles and polycation charges. Polycations pass from their complexes with microgels to free microgels, which results in dissolution of the aggregates and formation of homogeneous solutions, but the same polycations are not desorbed from microspheres when free microspheres are added, and the aggregates are preserved. No redistribution/dissolution is observed in the microgel-polycation-microsphere ternary systems. This picture reflects the different behavior of the aged and initial real MP when they are in contact with toxic polymer compounds. A possible mechanism for this difference is discussed. The results of the study clarify the details of the MP interaction with the environment and the role of MP in the spread of toxic components.