PROCESSING | QUALITY
these data points to a multi-parameter empirical mixing model. Then when the model has been calculated, we can set the target viscosity for the software to reach. It automatically adjusts the feeding of the additives to the incoming polymer to reach the required viscosity level.” VTT says the pelletised end product from the
VAREX line is a high-quality stabilised recycled plastic with upgraded rheological properties. The line can be used for developing recycled and virgin material formulations by recyclers, compounders, converters and OEMs. The main concept with the system is that it is a model-based control of the material feeding and the resulting blend viscosity, said Mikkonen. “The benefits are that you can control several interde- pendent viscosity parameters, for example shear, extensional viscosity and MFI. You can compensate using the system within-the-batch and batch-to- batch viscosity variation and get constant-viscosity upgraded plastics, even if there is change in the incoming plastics streams.” VTT has had experience with in-line rheology
control of a wide range of recycled polymers, in both technical plastics (including ABS, PC/ABS, PC/ PBT) and commodity plastics (such as PP, PE, PS, multi-layers). It also sees application potential in reactive extrusion (peroxides, chain extenders etc.)
Applications Mikkonen presented a slide at the expo on how the system works with recycled PP. Viscosity charts for a mixture of two different recycled PP batches, with high and medium MFI, demonstrated compensa- tion of viscosity change in the melt when the rheology controller was activated. One application example he showed was the upgrading of recycled PP for use in the automotive sector. He said: “By using melt filtration and process design and several additives, we have been able to upgrade the properties so that the required recycled content of
51% has been achieved and also [achieved] the mechanical properties required.” Examples of applications for recycled engineer- ing plastics were also shown by Mikkonen. These included recycled polycarbonate from a mixed WEEE feedstock and recycled ABS from electrical devices. VTT also tested a recycled PC/PBT blend for use in the crash box of electric vehicles, where he said that the mechanical properties were good enough that it was able to replace metal in that application. “We have developed several functional formulations with over 65% recycled content and impact strength that is high enough for this application,” he said. VTT’s rheology-based technique is being used in various collaborative projects, including the EU-funded CIMPA multi-partner project focused on improving recycling of multilayer films from packaging and agricultural applications. Samples from the project were on display in an exhibition stand at the Plastics Recycling World Expo in Brussels run by CIMPA, together with partners from the Circular Plastic Cluster. In another conference session at the event, CIMPA Coordinator Céline Chevallier from IPC presented key results and challenges from the project. VTT intends to develop further functionalities for
the VAREX pilot plant beyond the rheology measurement and control that it initially focused on. Plans for the pilot line include more types of analysis such as in-line VOC emissions measure- ment, which will help understanding of the influ- ence of polymer degradation, legacy additives and contaminants. Another analysis area is in-line spectroscopy to examine composition, colour and chemometrics.
CLICK ON THE LINKS FOR MORE INFORMATION: �
www.lbf.fraunhofer.de �
www.vttresearch.com �
https://cimpa-h2020.eu
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