Siegwerk, Greiner and Krones spearhead PP and PS cup de-inking and recycling initiative

09 Feb 2024 --- Siegwerk, Greiner Packaging and Krones have pioneered a recycling initiative to convert “non-recyclable” direct-printed PP and PS cups into high-quality recyclates.

Direct-printed PP and PS cups have traditionally been deemed non-recyclable by prevailing Design for Recycling Guidelines. However, Siegwerk, Greiner and Krones were able to employ hot caustic washing, a standard process predominantly used in PET bottle recycling but increasingly adopted in handling polyolefin (PO) and PS rigid streams, to de-ink and convert the rigid containers into white recyclates.

The accomplishment was achieved without altering the ink formulation or print design. The significance of this initiative extends beyond its immediate achievements, emphasizing the need for recycling guidelines to evolve in tandem with technological advancements.

“Caustic hot washing is becoming essential in plastic recycling. Efficient removal of filling good residues, adhesives and inks requires more intense washing systems, particularly when targeting consumer packaging,” explains Michael Auburger, product specialist of recycling solutions at Krones.

Hot washing effectiveness
The collaboration began with laboratory tests on PP and PS cups at Siegwerk’s facilities, adhering to test protocol DIN SPEC 91496, resulting in complete ink removal. This encouraged the validation of the findings under industrial conditions.

At Krones’ pilot plant — a representative version of the set-ups used in the industry for large-scale washing tests — 500 kg of mixed-color PP cups were processed.

The continuous hot washing process was found to be highly effective in removing inks without any deviation from standard washing conditions while using standard offset printing inks.

Additionally, water treatment tests showed that inks could be readily flocculated out of the lye, enabling the washing solution to be used in a closed cycle.Printed cups in blue, black and red utilized in the study as input and the resulting clean, deinked recyclate flakes.

Value chain cooperation for success
Recent years have witnessed a surge in demand for transparent and white recyclates, driven by brand owner commitments and anticipated EU regulations mandating recycled content in all plastic packaging. This growing trend of recycled plastic packaging has intensified discussions on ensuring a consistent supply of uncolored recyclates.

The initiative underscores the necessity for a comprehensive reevaluation of the role of printing inks and coatings in the recycling process. It advocates for a broader assessment of packaging de-inkability under standard hot caustic conditions.

“Indeed, achieving packaging circularity in Europe isn’t just about changing upstream design,” says Andrey Charkovskiy, senior business partner recycling and polymers at Siegwerk.

“The whole value chain has to work together and Design for Recycling Guidelines must be continually reassessed to recognize the latest recycling technology. Cross-value chain industry initiatives like the creation of the standardized de-inking test protocol DIN SPEC 91496 are essential and need to be acknowledged on the European level,” he continues.

The partners say their case study represents a “broader need for similar initiatives in the area of flexible packaging where the prevalence of non-de-inkable systems remains a significant challenge.”

“Design for Recycling Guidelines are important tools to enable a circular economy. However, it is even more important to continuously review and develop them further if necessary,” adds Anita Gruber, Greiner’s global project manager for circular economy.

“As converters, we aim to design our packaging in the best possible way. The entire value chain must work together to drive positive developments.”

By Radhika Sikaria

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