A main concern when recycling and reprocessing plastics waste - whether clean industrial waste or contaminated mixed waste from Germany’s Green Dot packaging waste stream - is the quality of the resulting recyclate.
Over the years, the extrusion division at KraussMaffei has gained experienced-based expertise that has enabled the company to tackle the challenges arising during the recycling process.
The plastics recycling space, the company said, is a growth market which it is now able to supply with products designed to address a wide range of applications.
KraussMaffei offers a broad variety of customisable line concepts which, depending on the specific requirements, can be designed as stand-alone or cascade solutions. “Another plus point is the option to use a system solution composed of a single-screw extruder and a twin-screw extruder, especially when it comes to solvent-based plastics recycling. We are the only machine manufacturer worldwide to offer this unique combination as a one-stop solution,”said Carl-Philip Pöpel, Director of Global Application & Product Ownership – Extrusion Technology at KraussMaffei. The systems are based on the company’s highly energy-efficient ZE BluePower extruder series.
Its EdelweissCompounding solution has long proved its value for scrap which has been mechanically crushed, cleaned, sorted by material type and is finally ready for reprocessing; the technology direct converts reclaim material into high-quality compounds in a single heat. The EdelweissCompounding technology is based on two extruders operating in a cascade arrangement. The plastic scrap is fed into the first twin-screw extruder, where it undergoes degassing before being passed through a 100 to 300 µm filter – ‘Depending on the technical specifications of the future product, according to Franz-Xaver Keilbach, Global Application Owner Recycling at KraussMaffei. The first ZE twin-screw extruder also homogenises the often inhomogeneous input material.
“Depending on the planned use of the material to be produced, either a pelletising system is arranged downstream from the ZE extruder or the cleaned melt is directly transferred to the second stage, i.e. a compounding extruder. This extruder is used for controlled material upcycling by incorporating fillers and reinforcing agents, additives, stabilisers and dye,” Keibach explained.
The system can be expanded with an upstream compacting stage, if necessary. KraussMaffei last year launched a cutter-compactor unit, for light and fluffy material fractions that need to be prepared for further processing. In the cutter-compactor, the material fraction is first dehumidified, compacted and homogenised before it is transferred into the first extruder.
Materials that have undergone solvent-based recycling require a different approach.
“The solvent-based process is an interesting alternative especially for recycling composite materials that cannot be separated mechanically. Solvents are used to separate polymers from plastics composites or plastics compounds. However, the solvent has to be removed again afterwards," explained Keilbach.
The solvent-rich material is fed into the first ZE BluePower twin-screw extruder. Its rotating screws create a large and permanently renewed melt surface, from which trapped volatile matter can escape more easily. Via openings in the housing that are connected to a vacuum, the solvents are removed from the process. The solvent removal is carried out in different pressure stages.
In most cases, the twin-screw extruder will reduce the residual solvent content in the material to a purity level that meets most specifications. However, if purity levels in the ppm range are required, a two-stage cascade configuration using a combination of a single-screw extruder with a twin-screw extruder offers a better option, according to KraussMaffei.
“Regardless of whether the material is recycled by a thermomechanical or a solvent-based process, the result is always an optimally cleaned melt. This melt can either be repelletised to a standard polymer or upgraded in an additional compounding step,” said Keilbach.