Effect of nano‐sized zinc citrate on the supercritical carbon dioxide‐assisted extrusion foaming behavior of poly(lactic acid)

Abstract

AbstractPoly(lactic acid) (PLA) foams containing various amounts of an epoxy as a chain extender (CE) and nano‐sized zinc citrate as a nucleating agent are prepared by continuous extrusion using supercritical CO2 (sc‐CO2) as a physical foaming agent. Processing parameters such as the CE content, sc‐CO2 flow rate, and foaming temperature are optimized with regard to the apparent density and expansion ratio of the PLA foams. The nano‐sized zinc citrate exhibits a high nucleation activity for the crystallization of the PLA. The addition of 0.5 wt% nano‐sized zinc citrate significantly increases the compressive strength and modulus of the PLA foams from 0.124 MPa and 3.1 MPa to 0.35 MPa and 19 MPa, respectively. The PLA/0.5 wt% nano‐sized zinc citrate foam shows a microcellular structure with an average cell diameter of 17.1 μm.