Long- and short-term stability of plasticized poly(lactic acid): effects of plasticizers type on thermal, mechanical and morphological properties

In this work, PLA was plasticized with poly(ethylene glycol) (PEG) having different molecular weights such as 400, 8000 and 35,000 g/mol at various concentrations ranging from 5 to 20%. In addition, a new plasticizer, PEG-functionalized polyhedral oligomeric silsesquioxane (PEG-POSS), was used for comparison. The short- and long-term mechanical, thermal, and morphological properties of PLA and plasticized PLA were determined by tensile tests, differential scanning calorimetry, and scanning electron microscopy (SEM), respectively. All the blends were found to be miscible in the entire composition range, since a single Tg was observed. Blending with PEGs and PEG-POSS decreased the tensile modulus and yield strength and increased the elongation at break. The plasticized samples were stored under ambient conditions of temperature and humidity for 4 months and 1 and 2 years to determine their long-term properties. Physical aging was only seen in PEG-400-plasticized PLA samples for 4 months after production. It was found that glass transition temperature, tensile modulus and yield strength increased and the elongation at break decreased for 1-year-old samples. Migration of plasticizers with time was proved by SEM analysis.