QUALITY | PROCESSING
The institute also has considerable experience building pilot plants; the VTT Bioruukki pilot centre is an innovation platform for new bio-based prod- ucts and circular economy solutions which combines expertise and piloting capabilities under one roof. A recent addition to its piloting infrastructure is an advanced mechanical recycling pilot line. This state-of-the-art process called VAREX was discussed at the Plastics Recycling World Expo in Brussels in September in a conference presentation by Joonas Mikkonen, Senior Scientist/Project Manager at VTT.
Pilot plant The pilot line features innovative pre-treatment technology, the MODIX modular mixer previously developed by VTT, which has a large feeding zone and cylindrical rotor with a large diameter and relatively short length. This enables feeding of heterogeneous and otherwise challenging feed- stock to the VAREX mechanical recycling line (it can also be used for feedstock pre-treatment in chemical recycling operations). “What is unique about the [VAREX] pilot line is
that we have installed an adaptive in-line rheologi- cal control,” said Mikkonen, “which means we can
measure the viscosity of incoming waste plastics and can use that data with the software to control the feeding of additives. If there is variation in the viscosity of the incoming plastics we can compen- sate that variation with this control.” At the Plastics Recycling World Expo, Mikkonen
presented a slide showing the VAREX line in a schematic diagram. At the starting stage, the waste plastics material is fed to a single screw extruder where it is melted and mixed. Then the melt runs through a melt filtration unit. Following this, there is the first capture of viscosity data by an in-line rheometer, and this data is used by an adaptive software controller to predict how additives will affect the viscosity of the polymer melt. If there is variation in the viscosity, the software adjusts the ratio of additives which, in the next stage, are fed into a twin screw extruder along with the polymer melt. Adaptive control of the gravimetric feeders maintains target viscosity for the output material. A second rheometer again captures inline viscosity data for the adaptive software controller. “How does this work?” Mikkonen said: “First we collect data on some steady-state viscosity points and use that data to teach the model, by fitting
RECYCLING SOLUTIONS
HIGH PERFORMANCE CLEANING ADDITIVES & SUPPORT
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