PLA is one of the most promising bio-compostable and bio-degradable thermoplastic polymers made from renewable sources. PLA is generally produced by ring opening polymerization (ROP) of lactide using the metallic/bimetallic catalyst (Sn, Zn, and Al) or other organic catalysts in a suitable solvent. 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. Ultrasound energy source was used for activating and/or boosting the polymerization as an alternative energy (AE) source. Ludovic ® software, designed for simulation of the extrusion process, had to be modified in order to simulate the reactive extrusion of lactide and for the application of an AE source in an extruder. A mathematical model for the ROP of lactide reaction was developed to estimate the kinetics of the polymerization process. The isothermal curves generated through this model were then used by Ludovic software to simulate the "reactive" extrusion process of ROP of lactide. Results from the experiments and simulations were compared to validate the simulation methodology. It was observed that the application of an AE source boosts the polymerization of lactide monomers. However, it was also observed that the predicted residence time was shorter than the experimental one. There is potentially a case for reducing the residence time distribution (RTD) in Ludovic ® due to the 'liquid' monomer flow in the extruder. Although this change in parameters resulted in validation of the simulation, it was concluded that further research is needed to validate this assumption.
International audienceIn this paper, numerical simulations of flows in a co-rotating intermeshing twin-screw extruder are performed using a previously presented 3D finite elements model. Some numerical improvements recently introduced are presented. The computations are performed for several processing conditions and screw arrangements. Values of specific energy, pressure and filled length are compared to the results issuing from the 1D Ludovic software in order to compare both approaches. The 3D simulation method is found to be more accurate to describe the effect of varying staggering angle and thickness of kneading discs. On the other hand, 1D model provides very satisfactory results for flows in screw elements
This work focuses on the development of a general finite element code devoted to the three-dimensional direct simulation of mixing processes of complex fluids. The code, developed from the CimLib© Library, is based on a domain immersion method coupled with a “level-set” approach to represent the rigid moving boundaries, such as screws and rotors, as well as free surfaces. These techniques, combined with the use of automatized parallel computing, allow calculating the time-dependent flow of generalized Newtonian fluids in large and complex processes, involving moving free surfaces which are treated by a level-set/Hamilton-Jacobi method. Three examples of flow case studies are presented in this paper: the flow within the mixing section of a twinscrew extruder, the flow in an internal mixer and the flow in a batch mixer.
Despite its complexity, reactive extrusion is continuously developing for the production of new and performing materials. Due to the strong coupling between flow, rheology and chemistry, optimizing this process for a given reaction remains a difficult task. Moreover, the scale-up from the laboratory to the production scale is another crucial question, which cannot be solved by conventional techniques. In this paper, we show how the use of numerical modeling may help answer these complex questions by providing realistic solutions, rapidly and without excessive costs. The example of a transesterification reaction was chosen because this reaction has been carefully characterized in previous studies. The reaction kinetics and the kinetic constants are well known and the modeling of this reactive extrusion process has proved to be realistic and accurate.
The most commonly used batch process to manufacture PLA is ring opening polymerization (ROP) of lactide monomer in a suitable solvent, in the presence of a metallic/bimetallic catalyst (Sn, Zn, and Al) or other organic catalysts. However, this process does not lend itself to safer/cleaner and high throughput (and high volume) manufacturing. Continuous reactive extrusion of lactide monomer using a suitable reaction input has the potential to increase the throughput, and this route has been explored in the literature. 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 the microwave as an alternative energy (AE) source for activating and/or boosting the polymerization. Implementation of a microwave generator in a section of the extruder is one of the novelties of this research. A simulation model of ROP of PLA was formulated to estimate the impact of reaction kinetics and AE source on the polymerization process. Ludovic® software was used for the simulation of continuous reactive extrusion of the process. Experimental and simulated results were compared for the validation of the methodology. This work also highlights the advantages and drawbacks of most conventional metal catalysts, the effect of alternative energies on reaction mechanism, and safe and efficient production of PLA.
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