Since 2019, the start-up Wildplastic has been bringing plastic waste by the container load from cities and wild waste dumps in India, Ghana, Haiti and other countries back to Europe. Here, the plastics are washed, regranulated and processed into trash bags. So far, Wildplastic has returned a good 300 tons of LDPE plastics to the cycle. In the future, the company also plans to produce shipping bags for mail order company Otto.
However, to be able to produce higher-quality plastics from the collected waste, the printing inks in particular have to be removed. This is because they impair the quality of the granules through discoloration and the formation of gases and odors. In a joint project Siegwerk, the Siegburg-based printing ink manufacturer, the Institute for Circular Resource Engineering and Management (CREM) at the Technical University of Hamburg and Wildplastic, are currently investigating the possibilities and conditions under which printing inks can be efficiently removed.
On the one hand, the aim of the project is to find the best washing process for deinking, says Ingo Fehr, Senior Product Manager Advanced Recycling and Deinking at Siegwerk. Which agents and temperatures achieve the best results? Because in principle, deinking is nothing more than an "alkaline hot wash". On the other hand, they try to find out which ingredients in the printing inks, such as ink pigments and binders, make deinking easier or more difficult. "In the end, the goal is to develop printing inks that can be deinked easily", Fehr says.
Mechanical recycling
For the Siegwerk engineer, ink removal is a key step on the way to a truly circular plastics industry - "so that, in the best case, food packaging can be turned into food packaging again." To date, he says, this is still a "fairly linear process in which only virgin material is used." According to Wildplastic, for example, of 6.3 billion tons of plastic produced each year, only nine percent is recycled, and twelve percent is incinerated. A full 79 percent "litters the environment."
For Fehr, mechanical recycling is the option of the future to break this linear system from production to environmental waste. Chemical recycling is also possible, but is expensive and CO2-intensive. On top of that, only half a kilo of recyclate is produced from one kilo of plastic waste. "Mechanical recycling is clearly the better solution if we can get the deinking right."
The long-term goal could be as follows: In the future, only deinking-friendly printing inks will be used. At the same time, recycling companies will be setting up deinking plants on a large scale to produce higher-quality granules. "This is mutually dependent," Fehr knows. To support this process, he says, Siegwerk is working with the DIN Institute, among others, on a standard that can be used to objectively and quantitatively measure the deinkability of printing inks.
Siegwerk is also active in other areas. For example, the company has already developed a deinking detergent and a de-lamination primer that allows different plastic layers to separate from each other during deinking. Because this is also a problem in plastics recycling: composites that are difficult to separate again. "For recycling, such laminates are the ultimate MCA," says Fehr. Tha is why, in cooperation with partners such as Henkel, Exxon Mobil and Windmöller & Hölscher, they have recently developed the first stand-up pouch made of monomaterial, which can be made entirely of PE thanks to a new type of oxygen barrier.
It will probably be some time before plastics recycling reaches the level of paper recycling, where deinking as the most important process has a decades-long tradition and recycled papers can replace primary raw materials in almost all areas. On the one hand, this will require less complex packaging structures, and on the other hand, the development of efficient deinking processes - so that at some point every chip bag can be turned into one again.
