Advancing PLA synthesis: Creatinine bio-based catalysts and ultrasonic enhancement

Poly Lactic Acid (PLA) has emerged as a leading bioplastic, known for its low environmental impact, biocompatibility, and biodegradability, making it a viable alternative to petroleum-based plastics. Ring-Opening Polymerization (ROP) is a popular technique for creating high-molecular-weight PLA. However, broader access to metal-free catalysts is essential to drive commercial PLA adoption. This study pioneers the exploration of a safer bio-based catalyst, creatinine, in PLA synthesis via ROP. To enhance efficiency, we introduce ultrasonic wave irradiation into the polymerization process. Lactide is placed in a reaction flask with creatinine catalyst at varying doses (1%, 2%, and 3% w/w). An ultrasound probe (5 mm diameter, 250 watts) is immersed in the solution, operating at frequencies between 20 and 30 kHz. Polymerization durations of 1, 3, and 5 hours are employed. We determine the resulting PLA's molecular weight through a viscosity-based method. Further analysis includes Fourier Transform Infrared Spectroscopy (FTIR) and Proton Nuclear Magnetic Resonance (H-NMR) to scrutinize compound and molecular structures. Differential Scanning Calorimetry (DSC) elucidates thermal properties. This innovative approach, merging ultrasonics with ROP for PLA synthesis and introducing a bio-based catalyst, aims to enhance efficiency, yield high-quality PLA, and ensure safety in the production process. The best results were obtained with 2% creatinine biocatalyst and a polymerization time of 5 hours, yielding an impressive 90.24%, molecular weight of 30,855.12 g/mol, melting temperature of 140.1°C, and % crystallinity of 41.32%.