Mathematical modelling and simulation of continuous, highly precise, metal/eco-friendly polymerization of Lactide using alternative energies for reaction extrusion

Polylactic acid (PLA) is one of the most promising bio-compostable and biodegradable thermoplastic made from renewable sources. PLA, is typically obtained by polymerising lactide monomer. The technique mainly used for ring opening polymerization (ROP) of Lactide is based on metallic/bimetallic catalyst (Sn, Zn, and Al) or other organic catalysts in suitable solvent. However, the PLA synthesized using such catalysts may contain trace elements of the catalyst, which may be toxic. In this work, reactive extrusion experiments using stannous octoate Sn(Oct)2 and tri-phenyl phosphine (PPh)3 were considered to perform ROP of lactide monomer using ultrasound as an alternative energy (AE) source for activating and/or boosting the polymerization. Mathematical model of ROP of lactide, was developed to estimate the impact of reaction kinetics and AE source on the polymerization process. Ludovic® software, a commercial code was used. It was adopted for the simulation of continuous reactive extrusion of PLA. Results from experiments and simulations were compared to validate the simulation methodology. Results indicate that the application of AE source in reaction process boost the PLA formation rate. Result obtained through Ludovic simulation and experiments were validated. It was shown that there is a case for reducing the residence time distribution (RTD) in Ludovic due to the ‘liquid’ monomer flow in the extruder. This change in the parameters resulted in validation of the simulation. However, it was concluded that the assumption would have to be established by doing further validations.The simulation model includes the details of kinetics of reactions involved with in the process and helps to upscale the reaction output. This work also estimates the usefulness and drawbacks of using different catalysts as well as effect of alternative energies and future aspects for PLA production.