Chemoenzymatic Epoxidation of Highly Unsaturated Fatty Acid Methyl Ester and Its Application as Poly(lactic acid) Plasticizer

Abstract

It is well known that petroleum-derived plasticizers are causing continuous environmental and health issues. Recently, fatty acid methyl esters (FAMEs), also known as biodiesels, have emerged as sustainable alternatives to produce epoxides that can be used as greener plasticizers. In this regard, enzymatic catalysis has emerged as an ideal alternative for the epoxidation of biodiesels due to the observed high yields and adducts purity. The present study employed Candida antarctica lipase as a biocatalyst to epoxidize FAME from grape seed oil (GSO). Freshly prepared epoxides of grape seed FAME (EGSFA) were studied as plasticizers mixed with poly(lactic acid) (PLA). Subsequently, chemical transesterification of GSO, with potassium methoxide, was achieved in 96% yield, whereas the catalytic enzymatic epoxidation afforded the expected EGSFA in 97% yield. According to dynamic mechanical analysis (DMA), the new blends exhibited a significant elongation versus PLA alone. In addition, Young’s modulus of PLA decreased from 1.23 to 1.10 GPa, indicating a better stiffness. The present study also explored the relationship between EGSFA and FAME–GSO and its effect on the mechanical and thermal properties of PLA. Finally, the mechanical and thermal properties of PLA/EGSFA/FAME–GSO blends were analyzed by thermal gravimetrical analysis (TGA) and differential scanning calorimetry (DSC). The data acquired clearly show that formulations based on EGSFA content, specifically at 0.70 wt %, have superior properties than neat PLA. For example, Youngs’ modulus was 2.2 and 1.2 GPa for the blend and PLA, respectively. On the basis of the results, EGSFA and FAME–GSO have primary and secondary plasticizer attributes, respectively.