Reactive extrusion of profile parts

A possible design of an extruder for reactive processing is shown in Fig. 4.34.240 Two screws are installed on the same axis inside a common barrel 1 but they have independent drives. This design eliminates stagnation zones, where the extruder is obstructed by the polymeric product. Independent drives for both screws permits the choice of optimal rotation speeds, i. e., to synchronize the polymerization rate with the residence times of the reactive mass in both stages of the process. 

The operating temperature is controlled by the regulated heaters 6 and 7. Volatile products, which can appear as a result of chemical reactions or evaporation of low-molecular-weight components (water residues and others) are removed through the outlet tube 5. 

Reactive extruders and extrusion dies of different designs can be easily included in standard technological scheme of polymer production plants, such as those for polycaproamide synthesis, as shown in Fig. 4.39. In this case, a reactive material premixed in a tank 1 is fed into a static device 2 for prepolymerization, where part of the polymerization process takes place. Then the reactive mixture enters the extruder-reactor 3. The necessary temperature distribution is maintained along the extruder. Transfer of the reactive mass proceeds by a system of two coaxial screws mounted in series in a common barrel. Controlling the relative rotation speed of both screws provides the necessary residence time for the reactive mass in the extrader, so that the material reaching the outlet section of the die is a finished polymer. 

This lubrication principle is also used in this plant a lubricant gas or liquid pumped through a ring sleeve leads to a decrease in the required pressure and improved quality of the end product. Clearly the lubricant gas or liquid must be inert in relation to the reactive mass and must not interact with the die material. Crystallization of the newly formed polymer takes place inside a calibrating 

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