Plastic Recycling : Any plastic, any day: The hard reality of multi-material extrusion

Ask any extruder manufacturer what keeps them busy, and they will tell you: it is not plastics in general – that challenge has largely been solved – but the bewildering and ever-growing variety of plastic waste streams that recyclers are being asked to process, often on the same machine, often on the same day. From sticky, contaminated post-consumer film to the precise demands of food-contact-grade PET, the world of mechanical recycling has become a battlefield of competing material requirements, regulatory obligations and economic realities. 

It is a challenge that extruder manufacturers know all too well.

There is broad consensus about which material is causing the most engineering pain right now: highly variable post-consumer polyolefin packaging, and particularly film-rich streams. Markus Huber-Lindinger, Managing Director at EREMA, is blunt about why. The problem is not the polymer chemistry alone, he explains, but the combination of low bulk density, fluctuating moisture, and a wide contamination and odour spectrum that simultaneously stresses feeding, melt stability, filtration uptime and final pellet quality.

Low bulk density – the notorious fluffiness of shredded post-consumer film – is perhaps the single most-cited problem. When film waste is size-reduced, it becomes a light, voluminous mass with a great deal of trapped air. Simply feeding this material into a standard extruder at any meaningful throughput rate is a serious engineering challenge. Coperion developed its MegaFeed unit specifically to address this: a side feeder with a conical twin-screw design and a very wide opening, enabling much higher output rates by getting low-bulk-density material into the machine in the first place. “Once it is in the machine, you are melting it anyway and the density climbs,” notes Coperion General Manager Peter von Hoffmann, “but getting it in is the important thing.”

ICMA San Giorgio's Giorgio Colombo echoes the challenge, noting that lightweight, low-bulk-density materials demand high-efficiency force feeders and optimised intake geometries to guarantee stable throughput. ICMA's ONE-STEP UP-CYCLING concept goes a step further, bypassing upstream agglomeration entirely by feeding lightweight flakes directly into the twin-screw extruder. This approach avoids an additional thermal cycle, reduces energy consumption, and simplifies the plant layout, according to Colombo, who is candid about its limits: when high-performance compounding is required, such as adding fillers or blending recycled and virgin polymers to specific targets, a second downstream extruder in a cascade configuration may still be necessary.

Contamination adds another layer of complexity. Paul Niedl, Commercial Head at Starlinger, describes how newer materials are often more contaminated, requiring systems that can handle higher impurity levels while withstanding increased mechanical demands. The company continuously adapts elements such as degassing units, filters, and odour-reduction modules to ensure reliable, uninterrupted operation. Starlinger's PCUplus pellet conditioning unit can be added at the end of the recycling process to strip residual odours, enabling the resulting material to be used even in sensitive applications such as food packaging or cosmetics.

>>> EREMA's Markus Huber-Lindinger on building recycling lines that handle variability without sacrificing output quality

For demanding recycling applications, the co-rotating twin-screw extruder is effectively the industry's consensus platform – and the reasons are worth unpacking. Hoffmann identifies the point at which its advantage becomes decisive: above approximately one tonne per hour throughput. Below that threshold, single-screw systems can still deliver adequate quality. But at higher outputs, the twin screw's ability to simultaneously achieve excellent homogenisation, effective degassing and minimal product degradation – without generating gels – sets it apart. When China closed its borders to imported plastic waste, Hoffmann recalls, suddenly much larger waste streams needed processing domestically, and the twin screw's advantages at scale came sharply into focus.

A key practical advantage is modularity. Unlike single-screw extruders, where the screw is typically a single-piece unit, twin-screw screws are composed of interchangeable segmented elements. When a customer wants to switch polymer families or when incoming material changes character, the screw profile can be physically reconfigured rather than replaced wholesale. On a medium-sized machine, a screw change can be completed within one to two hours. ICMA’s Colombo adds that processors who need to run different polymer families on the same line might invest in a second pre-configured screw set, preserving performance while maintaining versatility. “Flexibility must be engineered, not assumed,” he says.

EREMA's engineering response to material variability is structured around three concrete levers. First, gentler and more stable plasticising to protect melt quality across varying viscosities and bulk densities, addressed with its EcoGentle technology, which lowers melt temperature and reduces drive power in multipurpose HDPE/PP applications. Second, boosted degassing performance to manage volatiles and odour-critical components, where the company's VOLEX technology provides high-performance degassing including VOC reductions at full throughput. Third, high-performance filtration combined with downstream odour management via the ReFresher system, targeting the post-consumer realities of premium output.

>>> Giorgio Colombo, ICMA San Giorgio, on why reconfigurable twin-screw platforms beat dedicated machines

Food-contact-grade PET recycling occupies its own category. Bottle-to-bottle applications must satisfy EFSA (European Food Safety Authority) and FDA (US Food and Drug Administration) approval requirements, involving rigorous challenge testing to verify that the recycling process eliminates potential contaminants to concentrations well below permitted limits. Starlinger has developed its recoSTAR PET systems specifically to meet these standards, including intrinsic viscosity restoration essential for maintaining PET's mechanical properties after processing.

A common assumption is that food-grade capability necessarily makes a machine significantly more expensive or locks it into material-specific use. Hoffmann pushes back on this. The cost of regulatory certification and challenge testing is real, but the twin-screw extruder itself does not require a fundamentally different or more expensive configuration to achieve food-grade output. The same core machine architecture – with appropriate vacuum degassing and process control – can serve both food-contact and standard industrial recycling applications.

Niedl raises an important complication on the regulatory side. Whilst EFSA and FDA requirements represent the minimum quality standard, to stay competitive on international markets, customers must often meet the far more stringent conditions set by individual brand owners. As major consumer goods companies tighten their recycled-content specifications, brand owner requirements are increasingly becoming the effective performance benchmark. The result is that extruder manufacturers end up designing to brand owner specifications just as much as to regulatory ones.

When a customer asks for a machine that can handle multiple plastic types, what trade-offs must be honestly communicated? The answers from all four companies are consistent: flexibility is achievable, but physics sets limits. Huber-Lindinger is direct: when you try to run everything on one line, you typically compromise in at least one of three areas: throughput, quality or operating cost. His approach with customers is to frame this clearly upfront: EREMA can engineer a broad process window, but if the business case depends on premium-grade output, either the feedstock corridor must be defined tightly, or the line must be configured with the right combination of modules.

This modular platform philosophy is the industry's structural answer to the flexibility challenge. Rather than building one universal machine, manufacturers are building flexible platforms with a menu of add-on modules that processors can activate or reconfigure as their feedstock mix evolves. Starlinger's modular design allows customisation to specific materials. ICMA's platform is built for application-driven specialisation on a flexible foundation. Coperion's twin-screw systems allow barrel segments to be swapped, screw profiles to be reconfigured, and feeding and degassing setups to be adapted without redesigning the base machine.

Chemical recycling – particularly pyrolysis-based processes that convert mixed plastic waste into (pyrolysis) oil – is increasingly entering the extruder manufacturers' orbit, though it involves quite different machine requirements from mechanical recycling. The key difference in the processing philosophy is this: in mechanical recycling, the goal is to carry out the task at as low a temperature as possible to avoid damaging the polymer. In chemical recycling feedstock preparation, the aim is the opposite: to get the product as hot as possible as efficiently as possible, feeding a continuous melt into the pyrolysis reactor at temperatures approaching 350 degrees Celsius.

The machine scales differ sharply too. A mechanical recycling line might run at one tonne per hour on a 70 mm screw. A chemical recycling feedstock preparation system may need six tonnes per hour from a 133 mm machine. EREMA's CHEMAREMA approach addresses the specific challenge of reliable, continuous, energy-efficient feeding despite widely varying input properties upstream of the pyrolysis reactor. Coperion already has pilot chemical recycling lines running in Europe, with Hoffmann noting that the technology is not quite booming yet, but large players are gaining firsthand experience and seeking to understand how much of their waste problem it can realistically address.

All four companies maintain dedicated test centres where customer materials can be trialled and processes validated before any investment decision is made. Coperion, EREMA, Starlinger and ICMA San Giorgio have all invested significantly in recycling-specific facilities in recent years – reflecting a broader shift in R&D priorities. Material-specific customisation is claiming a growing share of budgets, driven by the circular economy's demand for processing ever more varied and complex waste streams. But investment in core platform improvements – torque, energy efficiency, process control – cannot stop either. 

When asked to look three years ahead, all four manufacturers converge on the same somewhat paradoxical prediction: the industry will move simultaneously towards greater specialisation and greater flexibility – both trends co-existing rather than one replacing the other. As Niedl explains: with recycling rates rising and quality demands increasing, some applications will require specialised equipment whilst technological advances will allow more flexible systems to reliably handle a wide range of materials. Huber-Lindinger puts it neatly as “specialisation at the edges, flexibility in the core” – food-contact and highly regulated uses will push towards dedicated configurations, whilst modular platforms will improve their ability to quickly adapt to defined material families.

Colombo is emphatic about the dominant direction: flexibility will prevail. The growing variability of recycling streams favours adaptable processing platforms, and co-rotating twin-screw technology, with its modular and reconfigurable architecture, is naturally positioned to lead this transition. Hoffmann points to scale as the other key variable: large, consolidated streams justify dedicated high-throughput lines optimised for a specific material, whilst smaller or more fragmented streams demand flexibility. His most compelling opportunity is turnkey plant solutions combining a pre-processing washing line with a compounding back-end – delivering a market-ready product from raw waste input in a single integrated system.

For the waste management professionals who invest in this equipment, the picture that emerges from these four conversations is one of rapidly improving but genuinely complex technology. Modern extrusion systems are more capable than ever: better at handling low-bulk-density materials, more effective at degassing and decontamination, more modular in design. But the technology does not eliminate the need for careful planning, clearly defined input streams and honest assessment of acceptable trade-offs. The diversity of plastic waste will not simplify over time. As recycling mandates push processors to deal with increasingly difficult feedstocks, the extruder manufacturers, for their part, seem ready for the challenge.