Optimierung der Entgasungsleistung von bedruckten LDPE-Folien in der Extrusion am Beispiel einer TVEplus Recyclinganlage

Translated title of the contribution: Optimization of the degassing capacity of a TVEplus recycling machine for printed LDPE-films

Sebastian Sochor

Research output: ThesisMaster's Thesis


Because of an ever growing environmental awareness, it is becoming increasingly economical to recycle contaminated plastics as well. In the case of recycling the heavily printed plastic films, unresolved issues are coming up, especially the degassing of volatiles from ink decomposition. The degassing of printed LDPE-films during extrusion was previously only possible using very small extrusion plants. Using large-scale extrusion plants, the plastic melt exited the extrusion line prematurely in the venting zone through the degassing domes and the quality of the remaining plastic in the extruder was of inferior quality. The aim of this master thesis was to develop an extruder screw, capable of degassing the entire melt stream without any further melt exiting the degassing domes. Therefore, the experience of the company Erema was collected and it was thoroughly examined which factors disturb the proper degassing process. One hypothesis was that wall slipping of the plastic melt occurred, preventing the conveyance along the extrusion screw and thus resulting in a discharge of melt from the venting ports. The assumption was that a degradation product from the ink hinders the conveying of the plastic melt. Since the ingredients of many different inks vary greatly and the recipes are a trade secret of the paint manufacturer, the wall slippage behaviour was determined experimentally. These experiments were conducted using a high pressure capillary rheometer and showed no significant differences between printed and unprinted films of the same origin. Thus, wall slippage could be ruled out as a likely cause. Another hypothesis was that thermal decomposition and the shearing of the ink produced previously unknown large amounts of gas as a resulting product. These large quantities of gas were thought to foam up the plastic melt in such a high degree that the discharge capacity of the venting zone is more than exceeded and the melt is urging from the degassing domes. The envisaged solution to this problem was to optimize the throughput capacity of the venting zone, meaning to create more volume for melt and gas. The parameters which can be optimized are pitch, flight depth, channel width and flight radius. Only flight depth and pitch remain suitable for optimization of the venting zone. These parameters were optimized for all extruder sizes and then implemented using a 180 mm screw. Subsequently this extruder screw was installed at a recycling plant instead of an extruder screw with "old" design and achieved good results right from the start. There was no more plastic melt coming out of the degassing domes and as a positive side effect an improvement in pellet-quality has been achieved.
Translated title of the contributionOptimization of the degassing capacity of a TVEplus recycling machine for printed LDPE-films
Original languageGerman
  • Holzer, Clemens, Supervisor (internal)
  • Schuschnigg, Stephan, Co-Supervisor (internal)
Award date20 Oct 2017
Publication statusPublished - 2017

Bibliographical note

embargoed until 29-05-2022


  • recycling
  • printing ink
  • devolatilization

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