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Successful Plastics Recycling

How can plastics processing operations increase the proportion of recycled material used in compounds while maximizing quality?

To this end, recycling experts from Coperion met on location at Aurora Kunststoffe, the successful recycling company, to exchange thoughts and ideas. Also in attendance were Alexander Schweinle, Head of Production at Aurora Kunststoffe, and Marius Schaub, journalist for industry and recycling management.
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Circular economy is the big trending topic right now in the plastics industry. Recycling within the industry, in contrast, is long established, so why all the hype around circular economy all of a sudden?

J. Schofer: Recycling is in fact not new. However, what is new is more and more companies are recognizing that recycling is a key process for the future of the plastics industry. This realization and the increased importance that comes with it, result from end users’ altered consumer habits and environmental consciousness against the backdrop of current climate discussions. Political pressure arising from increased awareness of the problem has persuaded plastics manufacturers and processors to produce more sustainably and increase recycling share in order to contribute to a functioning circular economy.

F. Neuner: We’ve all seen the pictures of plastic waste carpeting the world’s oceans. People just don’t accept plastic anymore that can’t be recycled properly. Trash in the ocean is an absolutely exasperating subject, and rightly so: In 2014, the ratio of plastic to fish in the sea was at 1:5; in 2050, it will be at 1:1 if nothing changes with established practices.

What can the plastics industry do to contribute in a tangible way to a functioning circular economy?

J. Schofer: Particularly in the field of “recycling”, the plastics industry can make a meaningful contribution to a sustainable circular economy. To do so, the plastics industry has to implement the three principles of Reduce, Reuse, and Recycle even more forcefully. Reduce refers to reducing use of virgin polymers wherever possible and sensible. Reuse refers to propelling the reuse of plastics and plastic products and Recycle signifies fundamentally making plastics as recyclable as possible and closing the circuit.

S. Bader: Currently, plastics accounts for only a small portion of the total use of petroleum. The energy revolution is changing that: In 2050, the share of petroleum used for plastics manufacturing will be 20%. Especially when it comes to packaging, conventional plastics such as PET, PE, or PVC will have no competition for the foreseeable future. In order to effectively reduce environmental effects, the plastics industry has to emphasize recycling more forcefully.

In processing recyclate, primarily single screw extruders have been used up to this point, but Coperion manufactures twin screw extruders. How does that fit?

J. Schofer: It seems to be a contradiction, because in practice, twin screw extruders offer tremendous advantages in many recycling applications. Technically speaking, compound quality is a sticking point in processing recyclate. Using twin screw extruders, very good results can be achieved in compounding and recycling. Operators using twin screw extruders profit from the short residence time and very good mixing behavior, even at very high throughput rates. As a result, constant high product quality can be achieved.

Which recycling applications are Coperion’s compounding machines suited for?

J. Schofer: Our technology can be used for various recycling applications: regrinding of plastics such as HDPE, PP, ABS, PS and PVC, manufacturing films, PET recycling, upcycling, and even chemical recycling.

Compounding secondary raw materials is demanding. Which technical challenges are present, and how are those challenges overcome?

F. Neuner: In feeding, the challenge is primarily that waste plastic, in contrast to virgin material, is heterogeneous in size, form, and bulk density. The correct choice of feeding technology is thus decisive in ensuring optimal bulk material flow. Since single screw extruders are usually operated with volumetric feeders, they are better suited for feeding bulk solids at a constant density. With secondary raw materials, irregularities in flow behavior arise quickly. Twin screw extruders are usually operated with gravimetric feeders which operate far more accurately and, thanks to the weight signal, can react better to fluctuations in bulk density and flow disruptions.

J. Schofer: The dispersion and devolatilization performance inside the extruder are crucial to end product quality. Thanks to their high torque and optimally adjusted process parameters, twin screw extruders are able to contain and process high percentages of calcium carbonate, talc, glass or natural fibers or mix recyclate with virgin polymer. Melt homogenization and devolatilization take place with markedly higher intensity – this also positively affects odors that may be present in the secondary raw material, which are effectively removed. Using the twin screw extruder, compounds can be manufactured with constant high quality that match the buyer’s specified properties profile.

When pelletizing recyclate, where do the pitfalls lie?

J. Schofer: The challenge in pelletizing also lies in the usually widely varying characteristics of products that can be potentially highly abrasive. One process that is especially well suited for recycling applications is strand pelletizing. It is used to process melted polymer into cylinder-shaped, dry, easy-to-handle plastic pellets. Coperion offers all the necessary technology, from drying and pelletizing to screening. Semi- or fully automatic conveying of strands to the pelletizer reduces the use of manpower that is necessary and increases productivity, since the process can be started more easily and broken strands are automatically rethreaded into the pelletizer thanks to strand break monitoring.

What do manufacturers need to be mindful of in order to achieve the desired end product quality?

S. Bader: There are a number of things to pay attention to in bulk solids handling of secondary raw materials. Problems can arise, for example, from varying and fluctuating intake quality as well as from hard-to-handle granule shapes are properties. The discharge from containers and silos is critical when conveying ground products, flakes or fibers. Since this material tends to bridge, you have to find the right discharge unit.

Operators can choose between different pneumatic conveying processes in either a dense phase or a dilute phase conveying mode. With our comprehensive expertise, we can specify the conveying system that will match your bulk solids exactly. Factors that are taken into account include the product’s tendency toward dust and fiber formation as well as pipeline wear. Moreover, product-specific customer requirements are important, for example, with regard to residual dust content, as this can significantly influence product quality as well as machine availability.

Likewise, we offer a large bandwidth in technology solutions for pneumatic conveying of saleable recyclates. We take the exact conveying properties of the pellets into account here too, in order to maintain their high product quality.

When manufacturing recyclates, is homogenization of the input material of primary importance?

S. Bader: Yes. For homogenizing input material, a mechanical mixer such as the Coperion MIX-A- LOT, for example, can be provided that transfers a batched mix to a continuous process. If homogenization of the finished product is required to achieve uniform quality, the Coperion Combiflow® Mixer is recommended.

PET recycling is a very complex procedure, as a rule. Can this process be simplified somehow?

J. Schofer: In PET processing, its hygroscopic properties play a large role. Using Coperion technology, shredded PET can be compounded directly — predrying, crystallization and agglomeration of the recyclate are unnecessary. This direct processing into films, fibers, or bottles increases product quality and at the same time, operating costs, energy use and logistical expense all drop. PET processors profit from using twin screw extruders with constant high end product quality, great flexibility that enables quick recipe and color changes, and simpler logistics. Even energy savings can be realized thanks to doing away with predrying and crystallizing.

Politicians and the public expect the industry to use more secondary raw materials. Where can these be implemented and is the whole thing even profitable for companies?

F. Neuner: Thanks to our process know-how, the variety of our products and their sizes, Coperion can cover throughputs of up to 10 t/h using our own technology – depending upon the processed material. End products are implemented, among others, in the demanding automotive industry and by packaging manufacturers, some of whom supply to the food industry where especially high demands are placed upon material purity.

S. Bader: Coperion’s years of experience ensure comprehensive expertise across all process stages and components and a seamless interplay of discharge material handling via feeding, compounding, pelletizing, and conveying the finished product can be ensured. Companies using our machines in their production are not only profitable, but they’re also manufacturing ready-to-use, high-quality pellets for high-value applications, and by doing just that they’re making an important contribution to the circular economy of plastic.

Many thanks go to Aurora Kunststoffe for allowing us to meet there for the valuable exchange of ideas.

Contact

  • Jochen Schofer

    Business Segment Manager Recycling & Direct Extrusion I Compounding Machines