Poly(lactic acid) (PLA) has become a material of interest in the packaging industry due to its sustainability. It has very low extensional viscosity, which causes problems for the manufacture of high-quality foams. This can be mitigated by increasing its extensional viscosity through chain extenders (CE). Therefore, this study evaluated the effectiveness and efficiency of two food-grade multifunctional epoxies chain extenders (CE) with low and high epoxy equivalent weights (EEW) in branching PLA and improving its foamability.

The chain-extension reaction of PLA with CE was followed by torque rheometry as well as shear and elongational viscosities. The cell morphology, void fraction, volume expansion ratio, and cell-population density of PLA batch-microcellular foamed with CO₂ were evaluated. Both CE grades were effective in increasing PLA’s viscosity. However, CE with low EEW was more efficient than CE with high EEW due to its high reactivity.

Neat PLA foams showed poor cell morphology and had low expansion, owing to their low elongational viscosity. The chain-extended PLA foams showed uniform cell morphology with higher expansion, irrespective of CE content and grade. High void fraction (up to ~85%) and expansion ratio (up to ~ 8 times) were achieved by chain-branching PLA, suggesting that their melt properties were appropriate for optimum cell growth and stabilization during foaming.

Overall, this study identified the chain extender with low EEW as the most effective grade and 0.25% the threshold of CE content to produce PLA foams with homogeneous structure, small cells, as well as high void fraction, volume expansion ratio, and cell-population density.