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Swelling in the Eye of Secondary Interactions
Summary
Scientists used computer models to study how tiny plastic particles (from materials like polyurethane foam and PET plastic bottles) soak up liquids and swell, since this affects how they move through the environment and potentially our bodies. They found that PET swells gradually and steadily, while polyurethane swells in a more complex, step-by-step way because its stronger internal bonds must break first — differences that matter for predicting how these nanoplastics behave once they're in water, food, or human tissue. This research is still basic science modeling, but it helps build the foundation for understanding how different types of nanoplastics might interact with our bodies down the line.
Swelling is expected to be an inherent property of nanoplastics, defining their interactions with their environment. First, we created models for polyurethane (PUR) and polyethylene terephthalate (PET) nanoplastics, which, based on structural descriptors, including density, these particles were found to exhibit realistic geometries. Using these models, we identified the sequence of steps that result in the swelling of these nanoplastics in water, trifluoroacetic acid, and dimethylformamide. For PET, bearing weaker polymer-polymer interactions, swelling was found to be a continuous process. In the case of PUR, in which hydrogen bonding forms a dominant type of intermolecular interactions within the polymer, these hydrogen bonds first have to be broken by the solvent, thereafter, solvent molecules penetrating the particle can cleave off individual chains in separate steps, resulting in a more complex swelling mechanism. The resulting mechanistic picture is consistent with earlier models of polymer swelling deduced from second order kinetics.