Addition of Oils to Polylactide Casting Solutions as a Tool to Tune Film Morphology and Mechanical Properties

Poly(L-lactide) (PLLA) films exhibit toughening by the addition of oils to the polymer casting. This was investigated by casting films from solution and evaporation in air; the investigated oils were linear alkanes, cyclic alkanes, and two terpenes (limonene and eugenol). The addition of the oils greatly influenced the morphology and thermal and mechanical properties of the films. Most oils rendered porous films, and a variety of morphologies was obtained. Films prepared with hexane and eugenol showed a solid, nonporous structure similar to neat PLLA films, with similar mechanical properties. The thermal transition temperatures of the films decreased through the addition of oil, depending on the oil used, the decrease could be up to 30°C (glass transition), 45°C (cold crystallization), and 15°C (melting temperature). The films prepared without oil were stiff and brittle. Upon addition of most of the oils, the maximum strength and elastic moduli decreased, but their ductility improved considerably. Limonene, the most extreme case, gave a very ductile film with an elongation at break up to 200%. The main conclusion of this study is that various oils can be used to tune and improve the properties of PLLA film