Repurpose of used frying sunflower oil as an ecofriendly plasticizer for polylactic acid

The development of competitive and sustainable additives for use in semicrystalline polymers is currently an area of growing interest in scientific and engineering areas. However, the feasibility of using waste oils as raw materials to produce effective plasticizers for these polymers has not yet been thoroughly investigated. In this work, the plasticization of polylactic acid (PLA), which is essential to improve its ductility, was studied using different contents of low molecular weight plasticizers: one synthesized from sunflower (Helianthus annuus) oil used in frying (USOP) and the bio-based commercial tributyrin (TB), selected as a control plasticizer. The experimental results revealed changes in the properties of pure PLA matrix that were explained considering the shape and chemical structure of the different plasticizers. Both compounds drastically decreased the glass transition temperature of PLA as well as the elastic modulus and tensile strength, although increase the elongation at break. The greatest plasticizing effect was obtained by adding 15 percent by weight of TB to the biodegradable matrix. However, the synthesized bio-based plasticizer exhibits a desirable low volatility, thus its thermal degradation occurs at higher temperatures in comparison with that of TB. Furthermore, the water vapor permeability of the PLA is not affected when USOP is used as plasticizer, which is a very interesting result for applications in which the material is in contact with food or humid environments.