Fiber-to-Fiber Recycling: Unique OMNImax Technology enables Efficient Fiber Recycling in a Single Extrusion Step

With increasing emphasis on sustainability, more and more fibre producers are looking for ways to use recycled material to make fibres, whether it is recycling post-consumer PET bottle flake into high quality yarn or recycling PET fibre waste from fibre production. The use of PET Bottle Flakes is now state of the art, allowing direct production of staple fiber, carpet fiber or even POY / DTY. However, the source of Bottle Flakes is becoming more and more limited, as these flakes are being absorbed by bottle manufacturers who want to close their loop, so that the remaining Bottle Flakes are quite expensive or of very low quality.

One problem with polyester as a raw material is the high affinity of the molecules to moisture, which results in the shortening of the molecules (hydrolysis) during processing in the extruder and significantly reduces the mechanical properties of the polymer.

When using bottle flakes, the multi-rotation extruder MRS from Gneuss has proved its worth. By using very large polymer surfaces and creating a simple vacuum, the moisture accumulated during the extrusion process is removed and the degradation is reversed.

On the other hand, when fibres are made from PET, the problem of recycling production waste is much more difficult to solve. One problem is the very low “bulk density” of the waste, often less than 100 g/l, which makes it very difficult to feed back into the extruder. The other difficulty is the high residual moisture content and the coating of post-industrial fibre waste with spin finish oils. This fibre waste is notoriously difficult to recycle.

OMNImax Recycling System for processing industrial and post-consumer fibre reclaim

With the powerful OMNImax recycling systems, Gneuss offers a complete, compact recycling system for processing waste fibres.

An OMNImax recycling system consists of a combination of different Gneuss products and technologies optimised for a specific end application.

The system typically consists of a 3C rotary feeder, an MRS extruder with extended multi-screw section, a specially optimised vacuum system, a fully automated RSFgenius melt filtration system and an online VIS viscometer.

The 3C rotary feeder allows low density materials to be processed without the need for external processing. A conveyor belt feeds shredded regrind into the hopper where a fast-rotating disc with knives cuts, compacts and preconditions the material. The knives add energy to the material and start the heating and degassing process before the material is automatically fed into the MRS extruder.

This MRS extruder offers a longer, modified version of the Multi Rotation Section, providing both longer material residence time and more surface exchange under vacuum. The longer Multi Rotation Section, combined with a powerful vacuum system operating at 1 mbar, can be used to increase the viscosity of R-PET and keep it stable despite variations in the input material. This eliminates the need for liquid phase polymerisation (LSP) or solid state polymerisation (SSP). By stabilising and/or increasing the intrinsic viscosity in the extrusion process, the MRS is particularly suitable for recycling, e.g. PET fibre regrind – for which direct recycling with a single extrusion step was previously impossible due to low intrinsic viscosity or variable input viscosities.

In combination with Gneuss Rotary Filtration Technology, high melt purity is guaranteed. For quality assurance, the melt viscosity can be measured with an on-line VIS viscometer.

The compact OMNImax recycling line requires very little space and can either be easily integrated into existing production lines or directly adapted to a fibre production line without the need for an intermediate pelletising step. The compact design also results in very low energy consumption. Any energy used in the extrusion process is designed to be used in the next process step. This not only has a noticeable effect on electricity and gas consumption, but also significantly reduces the CO2 footprint of the recycling process.

The cleaning efficiency of the MRS extrusion process and Rotary Filtration Systems is unique in the world. In a single, simple extrusion step, harmful contaminants can be removed so thoroughly that the resulting recycled materials are safe for use in demanding applications. Due to the short residence time in the system, thermal damage is largely eliminated so that the chemical properties of the recycled material are virtually identical to those of virgin material.

Back in 2011, Mogilev Khimvolokno in Belarus pioneered the use of the MRS extruder to process agglomerated, wet, spin finish oil-treated PET post-industrial fibre waste. This highly successful application of the MRS extruder demonstrated how both the moisture and spin finish oils can be efficiently and reliably extracted under vacuum in the extruder’s multi-rotation degassing section. Since then, MRS technology has been successfully applied to fibre recycling worldwide.

With the OMNImax, a compact recycling system is now offered that recycles fibres directly and can be easily integrated into existing fibre systems, significantly reducing labour and energy requirements.