Extruded Polylactide Bead Foams Using Anhydrous Supercritical CO2 Extrusion Foaming

Polylactic acid (PLA) is a bio-based and biodegradable polymer. It is challenging to prepare PLA bead foams at a large scale in an efficient manner. Herein, beads of modified PLA are foamed by one-step anhydrous supercritical CO2 extrusion. This dramatically shortens the production time, prevents the PLA from pyrohydrolysis, and avoids wastewater generation. The melt strength of the PLA is increased from 0.8 to 16.7 cN using a chain extender. The morphologies and microstructures of bead foams are analyzed. In the case of the PLA bead foam obtained by extrusion foaming combined with wind-cooling pelletizing technology, the expansion ratio is higher than 13, the pore morphology is typical cellular structures, and the surface is glossy. The advantages and shortcomings of the PLA beads are also investigated. It is beneficial to promote the continuous preparation of PLA bead foams and other polymer beads like PS, and PP, which can be used in the fields of green packing, sound absorption, cold-chain logistics, and so forth.