PROCESSING | REACTIVE COMPOUNDING


Coperion’s wet bushing


technology (left) provides more intensive barrel cooling than conventional cooling channels (right)


Source: Coperion


Fiedler emphasises that there is more to achieving a successful reactive extrusion process than just residence time. Cooling, particularly where exothermic reactions are taking place, is also a major issue. “Coperion has developed a barrel in a new cooling design with ‘wet bushing’,” he says. “Barrels equipped with ‘wet bushing’ allow intensive cooling of the product inside the extruder at a temperature range of below 100°C. Compared to a barrel with normal cooling channels that circle around the eight-bore of the extruder, the barrel with the wet bushing allows more intensive cooling as the liner is directly cooled with water.”


Right: Leistritz expects its recently introduced elongational rheometer to find applica- tion in reaction process control


Economic concerns The engineering team at Leistritz agrees that, for economic reasons, reactive compounding process- es are being moved from non-continuous produc- tion systems to continuous processes. The com- pany says that the long residence time that can be achieved in conventional batch systems, such as an agitated vessel, can be compensated for in a twin screw extruder through smart process control, tight temperature control or by generating additional surface area through the mixing charac- teristics of the screw profile. New application areas


emerging for reactive com- pounding include polymerisation reactions, degassing and crosslinking. In order to meet these requirements, Leistritz says that it has extended the length of the processing unit of its twin screw extruders. The company has recently supplied extruders in lengths up to 72 L/D and a model up to 84 L/D is in development. One recent reactive compounding


project deliverd by Leistritz involved TPU polymerisation and the production of


28 COMPOUNDING WORLD | September 2018


special TPV compounds. In this example, compound- ing of all the ingredients and the necessary crosslink- ing reaction was all achieved in one process step. Due to the extended processing length for the extruder used, Leistritz says it was able to design the system to optimally compound the several compo- nents and then carry out chemical crosslinking of the EPDM component in the final step. Leistritz adds that reactive compounding is also a potential application area for its recently devel- oped Elongational Rheometer, which facilitates much improved inline process monitoring. It says strategies are under development to use data from the unit within an integrated control loop. The move from reactive compounding to continuous processing is also identified as a key industry trend at JSW, where engineers also confirm that control of polymer temperature and residence time are the prime considerations in maintaining stable reaction processing. One current trend it sees for reactive extrusion, particularly in Europe, is in chemical recycling of waste polymer. JSW says that a high torque extruder can control polymer temperature while optimised mixing screw elements are needed to obtain enough residence time. The company says its TEX-αIII extruder can deliver the torque required while its TEX-FAN


simulation software can analyse polymer behaviour, predicting temperature and residence time inside the extruder.


Performance demands Meanwhile, Adam Dreiblatt, Director Process Technology at CPM Extrusion Group, says new developments in reactive compounding are being driven by demand from the market for high performance materials that cannot be


www.compoundingworld.com


PHOTO: LEISTRITZ


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