PROCESSING | REACTIVE COMPOUNDING
Fraunhofer ICT’s ReUse project uses reaction processing to devulcanise EPDM. Images show the vulcanised material at the extruder exit (left) and final raw polymer (right)
Ministry of Education and Research (BMBF) under agreement number 01DL17004A, the consortium works with EPDM concerns from different applica- tion areas. Using twin screw extruders, the fully vulcanised rubber was devulcanised. This involved a proportion of the bonds creating the rubber network being cleaved to leave a secondary raw material suitable for reuse. In order to increase reaction efficiency, the
extruder was equipped with an additional ultra- sound energy input. The additional ultrasound shear forces acting on the material results in improved devulcanisation rates, providing an additional tool in the complex field of reactive extrusion process parameters. To enhance the reaction further, carbon dioxide was also dosed into the extruder. Depending on the chosen screw configuration, the carbon dioxide can be intro- duced in liquid form or in a supercritical state. This additional ingredient in the extrusion process allows the viscosity to be varied significantly - en- hancing the ultrasound energy input. “It is a highly complex field of dependent
interactions,” says Bergmann. “However, after a couple of days we understood the characteristics of the materials provided to us and managed to supply very promising materials to the project partners.” The changes in the material characteristics and the behaviour observed during the extrusion process can be seen in the images above. Al- though the project is only half way through, Bergmann says the project partners are delighted with the results obtained so far and Fraunhofer ICT will show a number of the resulting materials at its booth at Fakuma in October this year.
Demanding reactions In another funded project at Fraunhofer ICT, the demanding process of polycondensation has been addressed. Due to the reaction kinetics and the water produced during polycondensation polymeri-
34 COMPOUNDING WORLD | September 2018
sation, which has to be removed constantly, it poses specific problems in reactive extrusion. Fraunhofer ICT opted to use a cascade setup for the project. Starting from glycolic acid in aqueous solution, a
pre-polymerisation step and subsequent polymeri- sation are performed in a continuous setup. While the initial steps are performed in vessels dedicated to low viscosity materials, twin screw extruders take over the material showing thermoplastic behaviour. This combination ensures that the material is always processed by machinery optimised for the required characteristics. It means each item of machinery is able to work in optimal processing windows, allowing good material properties with minimum stress.
TPU reality The production of TPU through reactive extrusion is even closer to industrial realisation, according to Fraunhofer ICT. Unlike the polycondensation process, this reaction is fast and a cascade setup is not required. In fact, the reaction is so fast that extruder considerations, such as dosing systems, order of dosing and homogenisation of all compo- nents, play a major role in the resulting material properties. To solve these problems, Fraunhofer ICT says it employed its chemical laboratory and expertise in small-scale batch reactions in combina- tion with its highly flexible reactive extrusion labora- tory. Using its 18 and 27 mm extruders, with process- ing lengths of 60 and 30 L/D, combined with options for material addition, degassing and analytics, it says it was able to build a customised line.
CLICK ON THE LINKS FOR MORE INFORMATION: �
www.coperion.com �
www.leistritz.com �
www.jsw.co.jp �
www.centuryextrusion.com �
www.orrex.com �
www.ict.fraunhofer.de
www.compoundingworld.com
PHOTO: FRAUNHOFER ICT
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