Enzymatic synthesis of dicarboxylate diesters for bio-based plasticizers

Abstract

Plasticizers are one of the polymer additives used to enhance the physical properties and workability of polymers. Traditional plasticizers based on fossil fuels are limited in use due to negative effect on environment and human health, to overcome this problem, there is an increasing demand for environmentally friendly solutions such as bio-based plasticizers, which are also known as "green plasticizers". In this study, enzymatic synthesis of dicarboxylate diesters (DDEs) as potential plasticizers have been investigated. Eighteen types of DDEs were synthesized via enzymatic esterification (Lipozyme 435). The reaction parameters, including molar ratio of reagents, reaction temperature, and immobilized enzyme concentration, were optimized using adipic acid and 2-ethyl-1-hexanol, 2-butyl-1-octanol. The maximum conversion achieved for each alcohol was 31.52% and 23.16%, respectively using Lipozyme 435 (75 g/L), with a 1:2 molar ratio of acid to alcohol, at a reaction temperature of 45 °C. Through air bubbling for removal of water, a byproduct of the reaction, the conversion was improved to 66.4% and 66.7% for each. To scale up the reaction, a packed bed reactor with air bubbling was designed and operated. Furthermore, the plasticizing effect was confirmed by testing plasticized polyvinyl chloride (PVC) and polylactic acid (PLA) films with DDEs. This study aimed to the development of eco-friendly and sustainable bio-based plasticizers and provides a methodology for optimizing reaction parameters and assessing the plasticizing effect, enabling the use of DDEs in actual polymer applications.