Toward Sustainable Food Packaging: Monomer Composition as a Lever to Balance Structure–Property Trade-Offs in PLGA Films

Abstract

Poly(lactic-co-glycolic acid) (PLGA) has recently emerged as a promising biobased alternative to conventional packaging plastics because of its promising biodegradability in soil and water and its inherently low oxygen permeability. However, the lack of a comprehensive structure–property framework spanning both low- and high-GA compositions has limited its development. Here, we systematically investigated PLGA films with glycolic acid (GA) contents ranging from 32 to 90 mol % to establish how composition governs microstructure, density, mechanical behavior, and transport properties relevant to food packaging. Differential scanning calorimetry, polarized optical microscopy, tensile testing, and water-vapor and oxygen-permeation measurements revealed clear composition-dependent trends. Increasing GA content led to denser molecular packing and reduced free volume, whereas the mechanical properties remained statistically unchanged, likely due to the similar molecular weights and glass transition temperatures. Water-vapor permeability was highest for PLGA32, likely owing to its lower density and higher diffusivity, whereas compositions ≥50 mol % GA exhibited uniformly lower WVP. Oxygen permeability decreased markedly with increasing GA content, dropping from 3.77 to 0.07 mm·cm3 m–2 bar–1 day–1 between PLGA32 and PLGA90. This decrease reflects increased polarity and tighter chain packing, which respectively hinder O2 sorption and diffusion, respectively. This work provides a predictive structure–property map that enables the rational tuning of PLGA performance for targeted sustainable-packaging applications.