Soybean oil derived fatty acid alkyl ester estolides to enhance the functionality of poly(lactic) acid (PLA)

Abstract: Five soybean oil-derived fatty acid alkyl ester estolide plasticizers were synthesized with methyl, ethylene glycol, and propylene glycol ester head groups of differing size and polarity. The required fatty acid alkyl esters were synthesized by transesterification and epoxidation followed by ring opening and acetylation. Experimental plasticizers were compounded with PLA, and their properties, glass transition temperature, melt processability, tensile strength, Young’s Modulus, elongation at break, contact angle, water vapor permeability–were measured and compared to those of commercial plasticizer, triethyl citrate (TEC). Based on structure, size, and polarity experimental plasticizers are divided into low and high molecular weight groups. High molecular weight plasticizers had poor compatibility with PLA and showed inferior mechanical and water vapor barrier properties. Low molecular weight plasticizers showed good plasticization and mechanical properties comparable to TEC with improved water vapor permeability, even at low concentrations, indicating suitability for more cost-effective applications requiring better water vapor barrier functionality.