Abstract

Definitions of microplastics and nanoplastics vary globally, but often with an explicit or implied reference to a hard or well-defined interface between particle and solution. This differentiates them from single molecules dissolved in solution. However, it is difficult to detect this difference at the nanoscale.  This study uses Analytical Scattering techniques to compare the behaviour of water-soluble polymers like Polyvinyl Alcohol (PVA) and Polyethylene Glycol, with nano-sized Polystyrene beads.

Dynamic Light Scattering and Small Angle X-Ray Scattering measured the conformation and size of soluble polymers and dispersed nanoplastics. Differentiating scattering profiles for water-soluble polymers and non-soluble polystyrene at the nano- scale were seen. PVA 18-88 (used in soluble detergent films) and PEG 8000 dissolved into single molecules, presenting a random coil conformation. They did not aggregate over time. Nano-Polystyrene beads showed hard particle characteristics.

Atomic Force Microscopy confirmed these findings, visually distinguishing single flexible PVA molecules in solution from the rigid Polystyrene beads. 

This study highlights the effectiveness of scattering techniques in differentiating water-soluble polymers from micro or nanoplastics.  They differentiate single dissolved molecule vs particle behaviour, and detect hard interfaces characteristic of particles at nano-scale.  So they could provide a better science-based definition of micro- or nanoplastics. This is important, because single molecules in solution can be studied using recognized methods for environmental safety, and their features can open more pathways for environmental degradation. Finally, the results show PVA used in detergent films dissolves to single molecules, and does not form micro nor nanoplastics.