Extrusion Foaming of Compatibilized Multi-Component Poly(lactic acid)/Poly(butylene adipate-co-terephthalate)/Nanosilica Systems: Microstructure-Processing Correlation Insights

Abstract

Multiphasic poly(lactic acid)/poly(butylene adipate-co-terephthalate) (PLA/PBAT) mixtures containing 1, 3, and 5 phr of hydrophilic and hydrophobic silica nanoparticles in the presence of a chain extender (CE) additive were foamed through a continuous extrusion process. The phenomena, involved in the one-step melt-compounding and foaming process, were impacted by the nanofiller type and loading. Melt rheological behavior, crystallization rate, the extent of chain scission and chain extension reactions, and nanofiller dispersion and localization states were studied in depth to correlate the processing with the foam microstructure. The addition of 1 phr of nanosilica particles, especially hydrophobic one, to the chain extended PLA/PBAT blend improved the foamability of system by creating lighter foam with larger bubbles. The increment in the nanofiller loading resulted in the multi-phasic foams with smaller cells at larger quantities and lower foam expansion ratio. Microscopic observations revealed better dispersion state of hydrophobic nanoparticles in the PLA/PBAT blend foam and preferential localization at the interface. Besides, this type of silica had a more profound impact on the chain extension reaction of CE and increasing the average molar mass and network structure content. By affecting the melt viscoelastic properties and accelerating the matrix crystallization process, hydrophobic nanosilica gave the compatibilized PLA/PBAT melt, a higher melt strength. Therefore, cell coalescence and structure collapse were relatively restrained more at higher loading of this nanosilica.