Menthol and organic acid-based hydrophobic deep eutectic solvents as plasticizers in biodegradable poly (lactic acid) films

Abstract

This study examined hydrophobic deep eutectic solvents (DESs) as plasticizers for poly (lactic acid) (PLA) films, comparing their performance to plasticizers like epoxidized soybean oil (ESBO) and di(2-ethylhexyl) phthalate (DEHP). DESs were produced by mixing DL-menthol (hydrogen bond acceptor, HBA) with pyruvic acid (Pyr) and levulinic acid (Lev) (hydrogen bond donors, HBD). The densities of DESs were similar to ESBO and DEHP and exhibited low viscosity and shear-thinning behavior. Chemical and thermal analysis revealed successful production of DESs, indicated by lower melting points and hydrogen bond interactions between HBA and HBD. PLA films plasticized with DESs showed varied properties depending on plasticizer concentration. M-Pyr plasticized films had the lowest water uptake and solubility at a 5 % concentration. DESs imparted a yellowish tint to PLA films, with M-Lev showing higher b* values. Light transmission decreased with increasing plasticizer concentration, enhancing UV barrier properties. Adding 20 % M-Pyr and M-Lev to DES plasticized films enhanced their tensile strength by 21.73-80.60 % while reducing elongation at break by 45.94 % and 39.10 %, respectively. DESs also influenced puncture force, deformation, and heat seal ability. Water vapor and oxygen permeabilities of DES-plasticized PLA films were reduced by 50 % and 38.35 % at 20 % plasticizer concentration. FT-IR analysis verified DESs' compatibility with PLA, indicating negligible shifts in characteristic peaks. DESs exhibited low volatility and migration with high antioxidant capacity, making them suitable plasticizers. Menthol-based hydrophobic DESs demonstrated effectiveness as plasticizers for PLA films, improving mechanical and barrier properties while ensuring stability and low volatility.