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Parallel twin-screw reaction extruder and its working characteristics

Update:05-07-2018
Summary:

Reactive extrusion is a process for continuously polyme […]

Reactive extrusion is a process for continuously polymerizing monomers and modifying existing polymers. The most important feature is the synthesis, modification and processing of traditionally separated polymers into a single process. . There are significant chemical changes in the reaction extrusion, such as polycondensation, addition between monomers, polymerization of the ring-opening polymer, grafting reaction between the polymer and the monomer, and cross-linking between the polymers. Joint reaction, etc.

The barrel of the reaction extrusion generally has a plurality of feeding ports according to the needs of the axial direction. Various reactants, including polymers and monomers, as well as catalysts, initiators and the like, can be arranged along the screw according to the laws of various chemical reactions. The axial direction is added stepwise in a certain procedure and in the most suitable manner to control the chemical reaction in a predetermined sequence and direction. These characteristics of reactive extrusion are the main reasons why reactive extrusion typically requires parallel twin-screw extruders with larger aspect ratios.

For example, in the reactive extrusion of polyoxymethylene, the most important one is the "bulk dynamic continuous copolymerization" mode, that is, the polymerization of monomeric trioxane, dioxane, butyral and catalyst, polymerization and finally formation. In polyoxymethylene products, a large amount of heat of reaction is released throughout the polymerization process, accompanied by a phase change from liquid to solid. Since the polymerization of polyoxymethylene is an exothermic reaction, the cooling water running in the cooling system of the open-loop structure inside the barrel plays a very important  temperature regulating effect on the reaction body. The comon monomer needs to undergo several stages of mixing, melting, degassing, and remixing in the reaction extruder. If the temperature is improperly controlled, it will cause a problem of monomer reaction, affecting the quality of the polymer, and even serious. The chaos caused the phase change, and the extruder had to stop working due to severe vibration.

In most reactive extrusions, a common feature is that the material is in a relatively large aspect ratio reaction zone, the reactants are in a liquid or molten state, and the entire flow of the reactants forms a virgin polymer as it flows from the liquid phase to the solid phase. During the phase change process, its volume rapidly expands, and the length of the section that completes this phase change is relatively short.

More Details: Conical Twin-screw Barrel