Impact of Ultrasound-Assisted Dehydration on the Properties of Poly Lactic Acid Produced by Ring-Opening Polymerization

Abstract

The synthesis of polylactic acid (PLA) using Ring-Opening Polymerization (ROP) is composed of several stages, including pretreatment or dehydration, polycondensation, depolymerization, and polymerization. Dehydration is an important stage, which aims to remove the water content in lactic acid raw material. The water content can affect the polymerization and general properties of PLA formed. Therefore, this study aimed to maximize the dehydration process by using ultrasonic technology for lactic acid. The remaining water content was analyzed using Karl Fisher titration, while the final PLA product was assessed by Gel Permeation Chromatography (GPC), Differential Scanning Calorimetry (DSC), Fourier Transform Infrared (FTIR), and X-Ray Diffractometer (XRD). The results showed that the optimum conditions for ultrasonic dehydration optimized by Response Surface Methodology (RSM) were obtained at 98.85 minutes and a power rate of 109.60 watts with a moisture content of 1.9%. Subsequently, dehydrated lactic acid was polycondensed and depolymerized to form lactide. Ring-Opening Polymerization was carried out for 4 hours at 140°C, with the addition of a 0.2% w/w Stannous Octoate catalyst. The final result of PLA obtained by ultrasonic dehydration showed better characteristics than commercial products, with a crystallinity of 60.01%, and a melting temperature (TM) of 165.0°C. Additionally, the molecular weight obtained was 40,567 g/mol.

Keywords

• dehydration
• lactic acid
• response surface method
• ring-opening polymerization
• ultrasonic irradiation