Poly(vinyl alcohol) Detergent Films: Analytical Evidence Distinguishing Reversible PVA–Surfactant Phases from Microplastics

Partially hydrolyzed grades of poly(vinyl alcohol) (PVA), typically with a degree of hydrolysis in the range of 87–90%, are widely used in water-soluble detergent films because of their cold-water solubility, film-forming ability, and biodegradability. Under realistic domestic washing conditions, however, PVA-based detergent capsules can occasionally leave visible gel-like residues, raising questions about whether such materials represent reversible, physically associated PVA–surfactant phases or persistent microplastic-like particles. This study investigates the formation and reversibility of gel-like PVA–surfactant phases representative of commercial detergent capsules, using small-angle X-ray scattering (SAXS), filtration coupled with ATR-FTIR and confocal Raman microscopy, dynamic light scattering (DLS), nuclear magnetic resonance (NMR), and size-exclusion chromatography (SEC). SAXS shows that the formation of the gel-like PVA–surfactant phase under low-water, high-surfactant conditions retains scattering features associated with both the PVA film and the detergent-rich phase, without additional SAXS-detectable features indicative of a distinct mesoscale structure. Upon dilution and filtration, vibrational spectroscopy and DLS reveal no detectable PVA microplastic- or nanoplastic-like particles above or below the 0.45 μm filtration threshold. NMR diffusion measurements show hydrodynamic radii of 8.6–9.2 nm for PVA recovered from washing machine residues, consistent with dissolved single chains, while SEC confirms unchanged molecular-weight distributions and no evidence of degradation or cross-linking (PVA Mp = 85.8 ± 2.4 kDa). Together, these results resolve previous ambiguities about the dissolution behavior of detergent films and provide analytical evidence that detergent-grade PVA remains molecularly dispersed upon dilution. Within the detection limits of the analytical techniques employed, no evidence of particulate PVA species was observed, supporting the conclusion that detergent-grade PVA does not form microplastic- or nanoplastic-like particles under realistic domestic use conditions. This dissolved physical state is consistent with the documented mechanism of biodegradability of detergent-grade PVA in aqueous environments.