Starlinger Recycling Technology Increases Recycled Film Quality : IN DEPTH: Closing the Loop on Agricultural Film Recycling

Agricultural films are used across the world in huge quantities. They protect crops from bad weather, pests and disease, but when the enter the waste stream they present a number of challenges for recyclers. Austrian firm, Starlinger, is addressing those and moving the recycled product up the value chain.

In 2013, 510,000 tonnes of films for agricultural use were sold in Europe, the majority in Spain (95,000 tonne), Italy (80,000 tonne) and France (55,000 tonnes). Other major users are Germany, the UK and Poland.

Films account for the biggest share of plastics used in agricultural applications – around 70% – and are mostly made of LDPE. The market has also been experiencing steady growth over the past decade.

However, with many countries implementing restrictions on landfilling, the need to recycle the growing quantities of agricultural film entering the waste stream each year has become increasingly important. And that’s a market which Austrian plastic recycling equipment manufacturer, Starlinger, has been finding growing interest in.

The challenges

While countries such as Germany, Spain and the UK have implemented collection schemes, when it comes to closed loop recycling agricultural films present a number of challenges. Chief amongst these is contamination.

According to Elfriede Hell, general manager of Starlinger Recycling Technology, the washing process for collected materials is “extremely critical”. One of the challenges here is that because the waste film is very often pressed into bales for transportation, it is hard to determine the type and degree of contamination. Solid and/or abrasive contaminants must be removed by means of special melt filtration before pelletising, while the organic matter on the film may have started to decompose.

Due to storage conditions moisture content also poses a challenge for recycling. Humidity from outside storage and/or washing requires special pre-drying. Depending on the moisture content, different drying methods such as venting or air flushing must be employed. Thermic drying is very energy intensive in this case due to the very thin material and the large surface.

“Compared to a shredding a PET bottle where you get a nice flake, when you shred film it tears and sometimes it forms pockets with humidity in it, and maybe some contaminants,” Hell tells WMW.

Technology

To meet these challenges Starlinger launched its recoSTAR dynamic recycling lines – the successor of the recoSTAR basic series. The new machine has been specially designed for the processing of highly contaminated and washed post-consumer film.

Depending on the requirements of the application the lines can be equipped with various types of degassing units. For example the integrated but independent C-VAC module, discontinuous and continuous melt filters, and four different types of pelletisers.

In order to obtain the high quality granulate required for applications such as injection moulding and film extrusion, the melt needs a high degree of purification. Depending on the type and amount of contaminants the melt contains, gas is formed that could cause foaming in the melt and consequently entrapped air in the granulate.

Air bubbles in the regranulate generate problems in the subsequent production process, e.g. specks and holes in the produced film, etc. According to Starlinger its high-capacity C-VAC degassing module can be combined with any of it recycling extruders to increase the degassing surface of the melt and thus enhance degassing efficiency. This module is recommended for difficult-to-recycle plastics, allowing them to be processed into a higher quality and value regranulate which is suitable for use in a wide range of applications.

Also, a significant amount of material can be lost as fluff in the drying process in the cyclone. Depending on the material being processed, and the processing equipment being used, if the moisture content in the input material is less than 2% it can be processed without venting.

However, a moisture content of up to 4% requires venting, and if it reaches up to 6%, air flushing is required. Materials with a very high moisture content – up to 8% – can be processed on recycling lines equipped with air flushing combined with a reinforced agglomerator drive. A cascade agglomerator allows the processing of materials with an even higher moisture content – up to 15% is possible.

Upcycling & Downcycling

When it comes to agricultural film it’s common for different polymers become mixed up. The recycling process therefore needs to be able to cope with this, either by sorting the different polymers, or by processing them together.

“It certainly helps the end quality if you separate the polymers – the PE from the PP,” explains Hell. “But you can also make a decent product out of mixed plastic, but of course the quality if lower and the reapplications are limited. Flexibility to process different materials is extremely important because different kinds of films are used in the different seasons.”

Seasonally fluctuating input material means that the recycling equipment needs to allow the processing of not just different films, but other too such as geotextiles, irrigation pipes and containers.

According to Hell this traditionally leads to a process of ‘downcycling’, whereby not all the contamination can be removed so you end up with a pelletised recyclate , which while not suitable for making thin films, can be used to make a thicker, darker coloured product. “It’s not like virgin, but it’s a usable product she says.

However, Hell says that recently there has been increased interest in “upcycling” plastics.

“Now the washing technologies have changed, and recycling technologies such as extrusion filtration have changed, we see a lot of upcycling in the sense of adding a colour into the material so that the produced regranulate already has a certain regularity in colour. We can also add a UV enhancer and calcium carbonate if required,” she explains.

“The recyclers have become more sophisticated, but also the coordination between the value chain functions better. The people that buy the material are asking the recyclers for this material in a certain quality or colour or price. Upcycling is happening a lot now,” continues Hell.

Conclusions

With the oil price remaining at record lows, and virgin material prices consequently low, recyclers across the board are struggling. “We have the problem that recyclers have very small margins in their business,” notes Hell.

However, with the EU recently agreeing its Circular Economy package, a waste stream of over 500,000 tonnes per year cannot be ignored, and technology that improves the quality of the recycled product, and increases its circular credentials, would seem to be just the ticket.

“We expect that an increase in collected material will drive the price down, but we have to use that material as part of the Circular Economy,” concludes Hell. “That’s going to give a huge boost if investments are facilitated by governments.”