An experimental study and model development have been performed to better understand the reactive extrusion of polyethylene terephthalate. A process was developed using a 34 mm counter-rotating twin screw extruder to depolymerize a commercial grade of polyethylene terephthalate into an acceptable pre-polymer for reactive extrusion experiments. Residence time distribution experiments were conducted at different screw speeds and feed rates to characterize the flow patterns of the extruder. Based on these results an idealized plug-flow model was developed to simulate this process. An experimental design using the controllable process variables of zone temperature, feed rate and nitrogen flow sweeping across the surface of the polymer melt was developed to study the individual effects of each of these variables as well as any interactive effects.
The results indicate that the feed rate and nitrogen flow have an effect on the degree of polymerization of the product. However, the study clearly shows the dominant effect to be the average residence time of the polymer melt in the vent zone.
The idealized plug-flow model presents a reasonable representation of this process. The predicted product degree of polymerization is slightly higher than the experimental results due to the exclusion of any degradation reactions. The model reinforces the importance of residence time and devolatilization effectiveness in the condensation reaction.