Incorporation of organically modified inorganic nanoparticles into polypropylene films using supercritical CO2

Incorporating inorganic nanoparticles into polymer films enabled the fabrication of functional polymer materials, but conventional approaches had limitations: melt mixing could bury the particles, while immersion-drying led to poor dispersion and weak adhesion. Supercritical carbon dioxide (scCO 2 ) offered a solvent-free alternative, but the size of the nanoparticles, which was much larger than the dye molecules typically dissolved in scCO 2 , limited their dispersion and long-range transport, thereby restricting loading efficiency. Against this background, two scCO 2 -assisted supply pathways were developed to introduce decanoic acid-modified cerium oxide (CeO 2 ) nanoparticles into polypropylene (PP) films: one was a supercritical dyeing method (SCDM), in which the nanoparticles were dispersed in situ within the bulk scCO 2 phase; the other was a drop-casting-assisted supercritical impregnation method (DC-SIM), where the nanoparticles were pre-positioned on the surface of PP. Loading and distribution were characterised using UV-visible spectrophotometry, SEM/EDX and TEM/EDX. Control experiments confirmed that scCO 2 was indispensable, and the swelling-induced free volume was necessary for incorporation. The bulk-transport-governed SCDM increased with time, temperature, and pressure, but the relationship with dosage was non-monotonic, reaching about 2.2 µg/cm 2 , whereas surface pre-positioning via DC-SIM raised the loading nearly tenfold, reaching approximately 19.8 µg/cm 2 , with near-linear dosage dependence and no saturation. Cross-sectional TEM/EDX revealed a cerium-rich band beneath the surface, confirming effective near-surface penetration. These two pathways thus operated complementarily and offered viable strategies for scCO 2 -assisted polymer functionalisation.