A novel methodology to study the release of fragmented fibres, including microplastics, in laboratory washing conditions.

Fragmented fibres, including fibrous microplastics, are increasingly recognised as a major pollutant originating from textile laundering. While many studies have quantified fibre release, the mechanisms underlying fibre fragmentation and detachment remain poorly understood, partly due to the lack of techniques to capture fibre-flow interactions under controlled conditions. This study introduces a novel methodology for the simultaneous characterisation of turbulent flow and textile fibre dynamics under simulated washing conditions. The approach combines a Von Kármán Swirling Flow apparatus, which generates reproducible shear and turbulence, with dual high-speed imaging to record both the fluid, analysed using Particle Image Velocimetry, and the fibres, analysed using optical flow. Proof-of-concept experiments with polyester and cotton yarns demonstrate that the method can capture fibre motion, deformation, and protrusion in synchrony with surrounding flow fields. A Reynolds number definition for top- and front-loading washing machines is also proposed, providing a basis for comparing washing conditions. This reproducible, non-invasive framework establishes a foundation for systematic investigations of fibre behaviour during laundering by providing mechanistic insight into fibre breakage and release processes that underpin textile-derived pollution, which is not covered by existing gravimetric methods that quantify mass release from textiles.