Extrusion foaming of biodegradable poly(lactic acid)/nanosilica nanocomposites: Correlations of the phenomena...

In this study, the processing-microstructure-properties interrelationships of poly(lactic acid) (PLA) foams filled with different nanosilica types and particle sizes through a reactive extrusion process were investigated in depth. The simultaneous melt-compounding and foaming extrusion processes of PLA/nanosilica systems, in the presence of a chain extender (CE) and chemical foaming agents, exhibit great complexity. The findings showed that the studied variables, including nanosilica type, nanofiller loading, and CE content, had strong interactions and affected the phenomena involved in the extrusion process. Among the nanofillers, the hydrophobic nanosilica with a lower primary particle size (20 nm) was relatively dispersed and distributed well in the matrix. This type of nanosilica showed a more considerable impact on the PLA's degradation reaction, the chain extension reaction, the melt viscoelastic properties, and the PLA's crystallization rate. As a result, the highest cell density (3.7 × 10⁶ cells/cm³) and the smallest average cell radii (number average radius of 36 μm and volume average radius of 150 μm) were attained for these nanocomposite foams. As proved with chromatography and rheological data, the influences of the CE content on the PLA foamability depended on the nanosilica type and loading. The main objective of this work is to control the continuous extrusion foaming process of filled PLA systems to expand their applications.