Plasticizing PLA with Biobased Fatty Esters: Comprehensive Study on Film Properties

ACETEM (E472a) and CITREM (E472c) are fatty acid esters used as additives in the food industry to improve quality, stability and sensory properties of food products due to their emulsifying, stabilizing properties, and antioxidant and antimicrobial activities. Herein, we have explored their use as active plasticizers in one of the most used biobased polymers, polylactic acid (PLA). Initially, different CITREMs (LR10, SP70, RO and VEG) and ACETEM (SOFT-NSAFE), with a variety of compositions and physical states at room temperature, were characterized. The studied fatty acid esters demonstrate good thermal stability and moderate to good antioxidant properties. Subsequently, PLA films containing 10% of the tested fatty acid esters were prepared by melt extrusion and posterior compression molding. The obtained films were analyzed by different characterization techniques to evaluate their role as active plasticizers. Raman confocal microscopy showed that SOFT-NSAFE is homogeneously distributed in the PLA films, whereas CITREMs form microdomains due to their immiscibility with PLA. The incorporation of these plasticizers decreases the tensile strength, Young’s modulus and glass transition temperature. However, only CITREM-LR10 is able to significantly enhance the elongation at break of PLA up to 42%, due to the elongation and orientation of the microdomains along the cracks formed during the tensile test. Additionally, their incorporation provides antioxidant properties to the PLA films, being CITREM LR10, SP70 and SOFT-NSAFE that impart higher activity. In terms of antimicrobial activity, CITREM-LR10 showed effectiveness against S. aureus, while SOFT-NSAFE was active against L. innocua bacteria. These results open the possibility to use such CITREM and ACETEM food additives as plasticizers in films for a variety of applications such as active food packaging.