PROCESSING | REACTIVE COMPOUNDING
Right: Ring extruders are a good solution where high free volume and residence time is required, accoridng to CPM
been in commercial produc- tion using twin screw extruders for more than 20 years and is experiencing tremen- dous growth with new applica- tions for TPU. The process requires intimate mixing of monomers with catalyst, long residence time, excellent heat transfer and self- wiping screws – all of which are achieved using twin screw extruders. The scale-up to larger diameter twin screw extruders of more than 100 mm, however, is limited by the decrease in heat transfer. This is just one example of an application that would be an excellent candidate for the RingExtruder, due to the higher surface/volume as compared to a twin screw extruder,” says Dreiblatt.
Combined processing One of the organisations at the forefront of reactive extrusion research is Fraunhofer ICT in Germany and Dr Björn Bergmann, who is Team Leader of the Compounding and Extrusion Research Group, highlights a number of current trends. “Firstly, there is considerable potential to combine processes to save energy and shear force introduced into the material. In addition, there is the possibility to utilise polymeric secondary waste streams, which are only able to be processed using solvent intensive processes or using extruders,“ he says. “For reactive compounding, both a knowledge
from polymer processing/compounding and from chemistry is needed – a combination not always present in companies. Other issues arise in reactive compounding, such as questions involving the handling of hazardous goods in compounding surroundings, which processors usually try to avoid. Finally, particularly when significantly influencing the viscosity of material during reactive compounding – which often happens – new
phenomena can arise during extrusion that have to be considered and the literature may not be of assistance. This has to be answered by alternative process setups and screw configurations,” Berg- mann says. Bergmann also sees new application areas
emerging for reactive compounding. “In my opinion, material optimisation such as upcycling and utilisation of secondary raw materials, as well as efficient polymer modifications – even polymeri- sation in some cases – are all questions that can be answered using reactive compounding,” he says. “For example, recently we developed reactive compounding-based recycling processes for EPDM and the production of polyurethanes and polygly- colic acid through an addition polymerisation and polycondensation reactions. Future developments at Fraunhofer ICT currently involve feasability investigations into other polymerisation reactions to be achieved in reactive extrusion. The question of advanced recycling strategies, including VOC and/or odour removal for primary and secondary raw materials, by advanced compounding technol- ogy is our main focus.” The EPDM project at Fraunhofer ICT involved the devulcanisation or decrosslinking of post production waste EPDM rubber. Part of the REUSE project, which was funded by the German Federal
PHOTO: CPM EXTRUSION GROUP
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