Numerical Simulation of Polylactic Acid Based Polyurethane Reactive Extrusion Using Rheological Kinetics

ABSTRACT Polylactic acid based polyurethane (PLA‐PU) is a high‐performance polymer that can be biodegraded. To achieve its continuous preparation, it is usually synthesized through bulk polymerization in a twin‐screw extruder. During the reaction extrusion process, the physical properties of the material continuously change along the extruder, which is due to the combined effects of flow, heat transfer, and reaction. In this work, the rheological kinetics of PLA‐PU bulk polymerization related to degree of reaction, reaction temperature, and shear rate were established through experiments; the flow and reaction characteristics of conveying elements (CE) and kneading elements (KD) during reactive extrusion were studied through numerical simulations. The results indicate that CE has better pumping ability, but the mixing effect is weaker, which is not conducive to the occurrence of the PLA‐PU polyaddition reaction. KD prolongs the window of the polyaddition reaction by generating reflux, enhances the mixing effect, makes the mixing of various reaction components more uniform, and effectively improves the degree of PLA‐PU polyaddition. Based on the study of the mixing and reaction characteristics of screw elements, the reaction extrusion process of screw element combination was simulated and compared with experimental data under the same geometric shape and reaction conditions. The results indicate that the quality of PLA‐PU can be effectively improved by using more mixing and reverse elements. Through experimental data verification, one‐dimensional numerical simulation of the reactive extrusion process based on rheological kinetics can reveal the flow state and reaction process of the polymerization system, which is beneficial for predicting and optimizing the PLA‐PU reactive extrusion process.