Adsorption of surface-modified silica nanoparticles to the interface of melt poly (lactic acid) and supercritical carbon dioxide

Abstract

With the purpose of fabricating polymer nanocomposite foams and preventing coalescence in foaming processes, the interfacial tension of poly (lactic acid) (PLA) -silica composites is investigated in this work. Synthesized silica nanoparticles(SNs) with a CO2 - philic surface modification are used as the dispersednanoparticles. Interfacial tension is a key parameter in processing of polymer foamssince it directly affects the final foam properties, such as cell size and cell density.Interfacial tension of silica-containing PLA and supercritical carbon dioxide (CO2)is measured using Axisymmetric Drop Shape Analysis Profile (ADSA-P) pendantdrop method at high pressures and high temperatures. The interfacial tensionbetween PLA and supercritical CO2 is observed to decrease as a result ofnanoparticles’ adsorption to the interface. These results indicate that the reductionin interfacial tension with increasing silica content significantly deviates from alinear trend; there is a minimum at 2 wt. % loading of the SNs and then the interfacialtension curve reaches a plateau. Contact angle measurements show an affinity of theSNs for the polymer-supercritical CO2 interface, and these obtained results are usedto calculate the binding energy of the nanoparticles to the PLA / CO2 interface. Inaddition to interfacial properties, the adsorption of silica nanoparticles at theinterface is also studied in detail with Scanning Electron Microscopy.