Saves energy and costs: two-stage process makes plastics recycling more efficient

In recycling, plastics are usually sorted, cleaned, ground, compounded and regranulated to be reprocessed as regranulate. The material must therefore be melted twice – first for granulation, then for injection moulding. ENGEL has now developed a process in which plastic waste can be processed as flakes in injection moulding directly after grinding. This makes it highly energy-efficient.

In an interview with K-MAG, Bianca Gubi explains how the new process works, the benefits for the climate and customers, and what to expect at the ENGEL booth at K 2022.

You have developed a new process for processing plastic waste. How does this work exactly? What is different from the conventional process?

Bianca Gubi: The special feature of the two-stage process is that plastic waste can be processed as flakes in injection molding directly after grinding. For this purpose, we have divided plasticizing and injection into two independent but coordinated process steps. In the first stage, the raw material, i.e. the plastic flakes that come from the yellow bag, for example, is melted in a conventional plasticizing screw. The melt is transferred to another screw for injection into the cavity in the second process stage. A melt filter and a degassing unit can be integrated in the transfer from the plasticizing screw to the injection screw. This enables high-quality products to be obtained even from contaminated plastic waste.

How is the corresponding production plant structured?

Gubi: Instead of a large plasticizing screw, which would normally be used in standard injection molding, there is a smaller plasticizing screw and a shorter injection screw. The two screws are arranged one above the other, which makes for a comparatively compact design of the system. The melt filter and the degassing unit are optional. They form the transition from the plasticizing screw to the injection screw. The degassing unit is a proprietary ENGEL development. Degassing is necessary because certain impurities, such as residual moisture as well as low-molecular compounds originating from material degradation or ink residues, can pass through the melt filter. If these impurities are not removed before the melt is injected, this can lead to pores in the interior and defects on the surface of the component and thus reduce its mechanical load-bearing capacity. The degassing unit thus makes a significant contribution to ensuring that recyclates can also be used for high-quality applications. The modular design makes the process very flexible.

To what extent does the process contribute to climate protection?

Gubi: The great achievement of the process is that a complete work step, namely regranulation, is eliminated. Regranulation is an energy-intensive process that usually also requires a logistical effort, as different companies sort, clean and grind, regranulate and process the plastic waste. If this work step is omitted, the CO2 balance of the recycling process improves. According to our calculations, energy requirements drop by around 30 percent.

What advantages does this offer your customers?

Gubi: Less energy input naturally also means lower recycling costs, which makes it even more attractive for industry to use processed plastic waste. Without economy, there is no ecology - unfortunately, this is what practice shows. At ENGEL, we therefore always keep an eye on efficiency and economy in all our developments. Our goal is to significantly expand the range of applications for recyclates. Only in this way can the Circular Economy function.

You will also be presenting the process at this year's K and have some project partners on board for this. One of them is the R-Cycle Initiative, which you joined in the spring. To what extent do you contribute to the initiative's goal with your newly developed process?

Gubi: The dolly pallets we produce at K are marked with a QR code. Via the QR code, visitors to the trade fair can call up information on the material and the recycling process live from the R-Cycle database. The aim of the cross-company initiative is to introduce digital product passports for plastic products. All recycling-relevant information is automatically recorded as early as the product manufacturing stage so that waste sorting plants, for example, can identify recyclable plastics more precisely and provide unmixed fractions for recycling. In this way, it is possible to stop the downcycling that has prevailed up to now and to recycle plastics of equal or even higher value. Many different building blocks are needed to drive the development of the Circular Economy. Data transparency and innovative processing methods are among them.

What can visitors expect to see at your booth?

Gubi: We are dedicating a separate booth to the new process, to be found in the Circular Economy Forum on the open-air site between Halls 11 and 16, where the dolly pallets mentioned above will be produced on an ENGEL duo injection moulding machine equipped for the two-stage process. Flakes obtained from post-consumer materials are used. For the injection molder, who is used to feeding granulate onto the screw, this is an unfamiliar sight, and it is exciting to watch how the injection moulding machine forms very stable, high-quality products from it. We will be there with our entire Circular Economy team and look forward to talking to trade show visitors - about the two-step process, but also about all other topics related to recyclate processing.