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Key components and know-how for plant optimisation in sheet extrusion
PET Sheet Lines: Fit for recycled material thanks to retrofitted line components by Gneuss
"The demand for PET packaging sheet, which contains a high proportion of recycled material or is even made of 100 % of it, has recently increased enormously due to public discussion and legal requirements.“ - Dr. Carl-Jürgen Wefelmeier, Head of Business Unit Sheet.
In order to be able to meet these requirements, many processors are confronted with high investment costs for equipment that can process recycled materials. After all, the quality of the end product must be good.
An ideal possibility to combine low investment costs with an extended processing window for recycled material is offered by Gneuss Kunststofftechnik GmbH from Bad Oeynhausen with a special retrofit service.
One of the companies that has used this service is Cotnyl S.A. from San Martín, thus being the first company in Argentina to obtain local approval to produce packaging made of 100 % r-PET.
On the one hand, the demand for plastic packaging is constantly increasing worldwide due to changing consumption and consumption habits, especially in the food and beverage sector. On the other hand, plastic packaging in particular has fallen into disrepute and has received new, often negative attention from the public.
The call for waste reduction and reasonable recycling of plastic packaging is becoming ever louder. The European Union has drawn up legal directives which stipulate that by December 31, 2025 50 % of plastic packaging placed on the market in an EU member state must be recycled.
By the end of 2030 it should be 55 % and from 2040 onwards all plastic packaging should be 100 % reused or recycled so that a closed cycle is achieved.
The market is already responding: according to a recent report by the British consultancy firm Eunomia, consumption of r-PET in the EU in 2018 was around 1.4 million tonnes, accounting for 26 % of the total demand for PET of 5.3 million tonnes. By 2030, experts expect an increase in demand for r-PET of up to 55 %. Approximately 20 % of the existing r-PET is used for PET trays throughout Europe, with the average proportion of recycled material already at 50 % – and the trend is rising.
Retrofit as an economic alternative to new investment
This increased use of recycled materials poses problems for many packaging manufacturers. A recycling rate of up to 100 % and the required recyclable design do not always meet the requirements for packaging, especially for food packaging.
Food authorities and consumers expect the highest quality in terms of colour, purity, odour and mechanical properties. The desired properties often cannot be achieved with existing equipment designed for processing virgin materials. Investments in completely new lines, with which the processing of recycled materials is successful, are not always possible for economic or space reasons.
An interesting alternative is the Gneuss retrofit.
“With the know-how in PET processing and recycling as well as the customized key components, existing plants can be optimised and the processing window significantly extended“ - Dr. Carl-Jürgen Wefelmeier, Head of Business Unit Sheet.
Filtration system indispensable for high contamination levels
Gneuss has already proven to many customers worldwide that retrofitting is a good alternative for processing recycled materials. For example, a customer from Chile has been using Rotary Filtration Systems from Bad Oeynhausen for several years now to produce PET thermoformed trays with a 70 % recycled content. Thanks to the patented filter disc technology, Rotary Filtration Systems operate continuously, with constant pressure and fully automatically.
The high and fluctuating levels of contamination of the input material are a major problem in recycling processing. Especially due to the increasing demand for packaging with a high recycled content, the high-quality recycled material, which mostly come from sorted bottle fractions, have become scarce and processors have to fall back on inferior recycled materials with higher degrees of contamination.
This has enormous effects on the filtration process. Screens get dirty faster and as screen contamination increases, the pressure upstream of the filter increases, which in turn can lead to temperature and viscosity fluctuations, and finally the available area for the melt to pass through is reduced.
This is where the RSFgenius Filtration Systems with back-flushing technology fully show their advantages. The screen cleaning is carried out fully automatically during the running production process via an integrated back-flushing piston system, in which only a small portion of filtered melt is regularly shot through the dirty screen via a narrow gap by means of high-pressure pulses. The quantity required for this is freely adjustable and in practice corresponds to about 0.01 to 1 % of the throughput. This means that the loss is significantly lower than with other systems available on the market, which operate with losses of up to 5 %, which on the one hand reduces the margin and on the other hand leads again to scrap production that has to be recycled or disposed of. Even with high degrees of contamination, the screens of the RSFgenius can be reused up to 400 times, depending on the filter fineness, which allows fully automatic production without the need for personnel for several weeks.
Retrofit extruder allows food contact
There are many factors involved in the processing of PET in general, and of recycled material in particular. In addition to the mechanical cleaning of the melt by the filtration system, the extruder has the task of thermal cleaning. Here, the processing unit should work gently in order to exert as little mechanical stress as possible on the sensitive polymer.
Through simultaneous vacuum degassing, low-molecular components such as monomers, oligomers or decomposition products can be removed from the plastic melt on the one hand, while on the other hand moisture escapes here, which would initiate chain degradation and thus viscosity reduction.
Finally, even more happens in the vacuum zone: contaminants that can never be ruled out in recycled goods, such as solvents, stabilizers, acetaldehyde scavengers or oils, must escape.
All these functions are combined in the Gneuss Multi-Rotation System (MRS) extruder based on a single screw extruder. This extruder processes PET melt gently and provides a particularly large melt surface in the multi-screw section with degassing zone. In this way, even with a simple vacuum of 25 to 30 mbar an enormous degassing and decontamination performance is ensured. Reason enough for the American FDA authority to grant Gneuss MRS Extrusion Technology a Letter of Non-Objection. As well as in Europe, where the Gneuss recycling process received EFSA approval for the processing of 100 % post-consumer PET on thermoforming sheet processing line.
Convincing arguments for many customers
The above-mentioned advantages of the MRS extruder not only convinced the Argentinian customer Cotnyl, the first company in the country to produce certified packaging made of 100 % recycled material, but also many other processors worldwide. One of them is another customer from South America, which, after purchasing the filtration systems from Germany, has now also opted for an extruder from Bad Oeynhausen. This producer was thus able to increase the proportion of recycled material in the PET thermoformed trays to up to 100 %. A perfect retrofit solution.
Online Viscometer completes retrofit solutions
A customer in South America decided, in addition to the MRS 130 with a capacity of around 1,000 kg/h, to purchase a complete Gneuss Processing Unit which includes an RSFgenius 150 as well as an Online Viscometer. The latter is also available separately and is ideal as a retrofit solution. It measures both the temperature and the pressure of the small amount of melt diverted into the precisely manufactured slot capillary during ongoing production.
Based on internal calculations, the online viscometer constantly provides the representative shear rate and dynamic viscosity. Depending on the values determined, the vacuum in the degassing zone of the MRS extruder is readjusted to keep the melt viscosity within the specified tolerances. The installation of these key components of the extrusion process (MRS extruder and/or melt filtration system, as well as online viscometer if required) makes it possible to process recycled material and still produce a high-quality PET sheet. In combination with Gneuss’ consulting services, an optimum solution can be found for almost any application.
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