REACTIVE COMPOUNDING | PROCESSING


Reacting to new developments


Compounding extruders can be a versatile tool for modification and polymerisation of polymers. Mark Holmes reports on the latest developments in reactive extrusion


Compounding extruders are highly flexible pieces of equipment that can be used for more than just mixing. Reactive extrusion techniques exploit these attributes to allow the modification of polymers on a continuous basis through mass polymerisation, chain breaking, grafting or cross linking. The wide variety of process conditions required for such applications mean it is an advantage to be operat- ing a universal machine system capable of provid- ing high torque and balanced volume over a broad range of viscosities, according to Markus Fiedler, Process Expert for Reactive Extrusion at Coperion. Fiedler says the company’s co-rotating ZSK twin


screw extruders are well suited to reactive extru- sion processing work. “Reactive extrusion process- es possible with ZSK twin screw extruders include mass polymerisation - starting from monomers or pre-polymers - as well as polymer modification by grafting, cross-linking or degradation. Feeding of


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raw materials, such as rubber bales or materials with a low melting point, is a crucial process step. Our in-house expertise at Coperion K-Tron offers customised and approved technologies, for example, for feeding small amounts of solid and/or liquid reactants highly accurately to ensure stoichiometric feeding of all ingredients,” he says. Residence time in the process section is a critical concern for reactive extrusion processing and Fiedler explains that this can be achieved by adjusting the length of the machine and the screw configuration. “Extrusion processes with residence times of up to five minutes have been realised, for example, with an L/D ratio of up to 80,” he says. “Coperion machines that can be used for reactive extrusion include two-lobe twin screw extruders, the high torque ZSK Mc18


, and the high volume ZSK


Mv PLUS. In addition, when extremely high shear rates and mixing capacities are required, Coperion


September 2017 | COMPOUNDING WORLD 27


Main image: Reactive extrusion


techniques use the compound- ing extruder as a tool to enable chemical modification of polymers for a whole raft of applications


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