Study of the Biodegradation Properties of Amorphous Blends of Poly(Lactic Acid) and Poly(3-Hydroxybutyrate-co-4-Hydroxybutyrate) Foamed With Supercritical CO2

Abstract

Poly(lactic acid) (PLA) is the most widely used bio-based and biodegradable polymer because of its versatility and relatively low cost, and PLA foams are increasingly used as alternatives to conventional expanded polymers. However, PLA shows limited biodegradability outside industrial composting, especially when dispersed in the environment. Blending PLA with polyhydroxyalkanoates (PHAs) is a promising strategy to improve its degradation behavior. In this work, fully amorphous blends of amorphous PLA and amorphous poly(3-hydroxybutyrate-co-4-hydroxybutyrate) (aPHA) were studied, with aPHA as the minor component at 10–30 wt.%. The blends were compounded at 185°C. TEM analysis revealed an immiscible morphology with dispersed spherical aPHA domains of 400–600 nm. All blends were successfully foamed by batch pressure-drop foaming using supercritical CO₂. Foam density and morphology depended strongly on foaming pressure and temperature. The lowest density, below 50 g/L, was achieved at 50°C and 90 bar, producing a closed-cell structure with cell sizes of 40–80 µm. Biodegradability under simulated home-composting conditions at 30°C was assessed by respirometry, NMR, SEC, and SEM, showing enhanced PLA degradation and total mass loss up to 84% after 4 months. In marine conditions, degradation was limited and mainly selective for aPHA.