Foaming of Polylactic Acid/Cellulose Nanocrystal Composites: Pickering Emulsion Templating for High-Homogeneity Filler Dispersions

Polylactic acid (PLA)/cellulose nanocrystal (CNC) composite foams have attracted much attention due to their biodegradability and potential to replace petroleum-based foams. However, the dispersion of (unmodified) CNCs in PLA remains challenging. Here, we used the Pickering emulsion templating method of unmodified CNCs to stabilize PLA microspheres and prepare a concentrated masterbatch. This masterbatch was used in conventional melt blending of pristine PLA to obtain well-dispersed CNCs in PLA with a CNC loading of up to 5 wt %. In comparison, PLA/CNC composites prepared by direct melt blending of CNCs in PLA showed visual agglomerates of CNCs. PLA/CNC composites were batch foamed with CO2 as a physical blowing agent. We demonstrate that the good CNC dispersion obtained by the Pickering emulsion route is favorable for preparing PLA foams with smaller and more uniform cell sizes and with a higher cell density. These results demonstrate that the Pickering emulsion approach to prepare CNC masterbatches for subsequent dispersion in thermoplastics by conventional processing seems promising for numerous industrial applications.