Aging and degradation behaviour of poly(lactic acid) composites in alcoholic and acidic food simulants

Abstract

The increasing demand for sustainable, high-performance materials in food packaging highlights the need to understand how bio-based additives and metallic nanofillers influence the stability and degradation behavior of polylactic acid (PLA) composites under food-contact conditions. In this study, PLA-based composites containing grape pomace and silver or copper nanoparticles were developed and evaluated in terms of physico-chemical stability, thermal behavior, and degradation mechanisms. Two commercial PLA grades (PLA1 and PLA2) were blended with Proviplast 2624 plasticizer and doped with grape pomace powder or Ag-PEG/Cu-PEG nanofillers. Nine composite formulations were prepared by melt processing and immersed for six months in three food simulants (10% ethanol, 3% acetic acid, and 20% ethanol) to investigate mass variation, Vickers hardness, surface morphology, and chemical and thermal changes. Scanning electron microscopy (SEM), electron paramagnetic resonance (EPR), Fourier transform infrared spectroscopy (FTIR), and differential scanning calorimetry (DSC) were used to correlate morphological, chemical, and structural modifications occurring during exposure. The results showed that both composite formulation and simulant type significantly affected the structural, mechanical, and degradation behavior of the materials. Grape pomace–reinforced samples exhibited increased Vickers hardness after immersion, particularly in ethanolic media, attributed to the rigid structure of the filler and its stabilizing effect on the polymer matrix. Composites containing Ag-PEG and Cu-PEG nanofillers showed improved nanoparticle dispersion and partial stabilization of the PLA matrix, with enhanced performance at 8% nanoparticle loading. However, prolonged exposure to simulants resulted in polymer degradation characterized by mass variation, surface damage, and free-radical formation detectable by EPR. FTIR and DSC analyses indicated structural and thermal changes consistent with hydrolysis-induced chain scission, while acetic acid proved to be the most aggressive medium, accelerating hydrolytic degradation and structural fragmentation.