In the direct spinning process, PET is polymerised in several steps before being fed directly to the spinning beam. The final reaction stage typically takes place in a ring disc reactor or finisher, where the viscosity is lifted from approximately 0,3 dl/g to 0,64 dl/g by the extraction of ethylene glycol. The waste created in the production process (fibre waste, coated with spin finish oils) is typically disposed off or sold off at a low price. With the Gneuss recycling concepts, this waste can be directly reprocessed, without detrimentally affecting the quality of the end product. The size-reduced and agglomerated waste is melted in the MRS extruder where it is devolatilised – volatile contaminants such as absorbed or surface water, spin finish oils or other processing oils are extracted. Further, the required viscosity is adjusted in the MRS extruder. The intensive surface area exchange rate in the MRS extruder makes it especially suitable for this application. The low-maintenance water ring vacuum system condenses the volatile contaminants and concentrates them in the process water, which is filtered atmospherically. Once the volatile contaminants have been removed and the viscosity is adjusted, solid contaminants such as glass, wood, paper and ceramics are filtered out with the Gneuss Rotary Filtration System RSFgenius or SFXmagnus.
With the Online Viscometer VIS, the melt viscosity is measured in real time and directly adjusted. Depending on the recycling process, the viscosity is specifically reduced by means of ethylene glycol injection or in a further step specifically increased in the IV boost system JUMP. Subsequently, the polymer melt is merged with the main, virgin polymer melt flow either upstream or downstream of the finisher.

Advantages of direct recycling with the Gneuss recycling concepts

  • Direct processing of waste to fibre without loss of quality
  • Highly energy efficient – no need for an additional melting process
  • Exact viscosity adjustment to a set point
  • Simple, direct introduction of TiO2 possible
  • Few (and automated) control interventions in the main process

Material introduction upstream of the finisher

Downstream of the MRS extrusion process, ethylene glycol is introduced into the melt flow and mixed with it. In this way, differing viscosities in the input material can be equalized. The glycolised melt is then be filtered in the Rotary Melt Filtration System RSFgenius. Thanks to the low viscosity, fine filtration with a relatively small filtration system is possible. The purified polymer flows then through the Online Viscometer, which controls the quantity of ethylene glycol which is injected into the melt and in this way maintains a constant viscosity. With the help of a booster pump, the polymer is fed into the main polymer flow upstream of the finisher. With a static mixer, the reprocessed, glycolysed material is mixed with the main material flow and the blend of recycled and virgin material passes into the finisher where the polycondensation takes place under vacuum and the PET melt passes on to the spinning beam from there.

Material introduction downstream of the finisher

After extrusion and filtration, the purified polymer melt is fed via a booster pump into the IV boosting system JUMP. Agitating and mixing devices within the JUMP reactor also achieve – under a deep vacuum – high polymer melt surface exchange rates and so achieve a set IV. The viscosity is set by means of the Online Viscometer and the process control system. The polymer melt is pumped out of the vacuum and directly into the polymer melt pipe downstream of the finisher, with an IV which matches that of the main polymer flow and the recycled content is mixed with the virgin polymer melt.