How digital watermarking technology can make recycling more efficient

Plastic packaging plays an essential role in our daily lives, serving multiple purposes — cosmetic or functional. For instance, it is commonly used to wrap food, keeping it fresh for longer periods, reducing food wastage.

However, plastic packaging is too often discarded after a single use, ending up in landfills and polluting the environment. Because plastic is durable and takes years (often decades) to decompose, its ecological impact cannot be taken lightly. Only 9% of all plastics ever produced have been recycled, and only 10% of this proportion have been recycled more than once.

Plastic packaging is often made up of a mix of different types of plastics or combined with other kinds of materials. For example, multimaterial food packaging such as beverage cartons is often composed of polyethylene, aluminium and paperboard to increase the product's shelf life.

The complex makeup of plastic packaging makes it even more difficult to recycle. Current sorting technology cannot analyse the material composition in plastic packaging in fine detail. As a result, only a small fraction of plastic packaging waste is recycled correctly and can be reused.

New identification and sorting technologies need to be deployed to address this problem and improve the quantity and quality of plastic packaging recycling.

Digital watermarking technology offers an innovative solution to this problem. Digital watermarks are the size of a postage stamp and can carry data, similar to QR codes. They offer information on the different attributes of a plastic packaging product, including packaging type, material and usage category.

Digital watermarks are printed or embossed on plastic consumer goods packaging. They are invisible to the human eye. Instead, high-resolution cameras are used to read these digital watermarks.

The aim of the HolyGrail 2.0 initiative, a project driven by AIM – European Brand Association, and powered by the Alliance, is to prove the technical viability of digital watermarks for accurate sorting of packaging waste as well as the economic viability of the business case at large scale.

During the prototyping process, the team looked at three factors:

1. Speed: The detection unit should be scanning waste on the conveyor belt at 3m/s.

2. Accuracy: Each piece of waste must be accurately identified by its material makeup and type of usage.

3. Detection and Ejection Efficiency: Once identified, waste must be sorted into the appropriate categories to produce a high-quality feedstock for recycling.

The information displayed by the watermark helps to efficiently and correctly sort different kinds of plastic packaging and, among other features, distinguish between food and non-food packaging applications.

The aim is that once the packaging has entered a waste sorting facility, the digital watermark can be detected and decoded by a high-resolution camera on the sorting line, which then, based on the transferred attributes (e.g. food vs. non-food), can sort the packaging into corresponding streams.

This would result in better and more accurate sorting streams, thus resulting in higher-quality recyclates that benefit the complete packaging value chain.

Building the technology

Gian De Belder, Technical Director – R&D Packaging Sustainability at Procter & Gamble, conceived the concept of digital watermarking for plastic packaging in 2016.

“I was running a lot of sortation tests, and even though the packaging was perfectly designed, we saw a lot of tests failing. To improve the sorting, there was a need to make it better and more intelligent. Hence, we came up with the concept of adding a digital watermark,” said De Belder.

The digital watermark can potentially offer a lot of value to consumers too, said De Belder, as it can give them the confidence and ability to make more informed choices about recycling.

The data captured by the digital watermarking technology can also enable facilities to track accurately how much each type of plastic waste is collected, sorted and recycled. This can help companies better measure the effectiveness of their sustainability or Extend Producer Responsibility (EPR) efforts, for example.

From industrial trials to commercialisation

Recently, HolyGrail 2.0 conducted industrial-level trials at the Hündgen Entsorgung material recovery facility (MRF) in Swisttal, Germany, to assess the efficiency of digital watermarking to sort post-household rigid packaging waste.

The facility, which processes over 100,000 tonnes of waste annually from three million households, was equipped with detection prototypes and add-on modules co-developed by technology provider Digimarc and machine supplier Pellenc ST.

This solution combined near-infrared (NIR) spectrometry and digital watermark detection technology to enhance sorting accuracy.

The NIR provides insights into products' chemical composition, while digital watermarks deliver the SKU—each product's unique commercial reference as defined by its barcode. Together, these technologies enable instant access to detailed product information, such as whether the item is food or non-food, and much more.

The trials focused on four types of post-consumer rigid packaging waste: PET non-food bottles, rigid PP, rigid PE (including tubes), and PET trays.

Companies that participated included Aldi, Arlafoods, Edeka Zentrale, Haleon, Hochland, Mondelez International, Orkla and Procter & Gamble.

Other brands that joined the trials included Coca Cola and McDonald’s, which provided digitally watermarked drinking cups. Another participant, Imperial Brands, provided tobacco canisters.

The industrial trials were a success. The modules achieved a detection efficiency rate of between 87.9% and 93.8%. Additionally, they were able to process nearly 56,000 detections per day, totalling 5.66 million detections of 5,949 unique products over a 100-day period. Click here for the full breakdown.

The speed and level of precision of sorting were even more remarkable, given that there was some material overlap and heavy containment under industrial-scale conditions.

HolyGrail 2.0's success proves that the digital watermarking technology is ready for commercialisation, though work is still being done to refine the technology.

Since high-resolution cameras are required to scan large volumes of digital watermarks quickly and for long periods, a lot of computing power is needed.

“Big progress has been made by implementing Graphics Processing Units (GPUs) in order to reduce the computing power needed. We are still planning to improve this implementation further and also reduce the cooling requirements to implement the commercialisation of the machines,” said  Antoine Bourely, Chief Scientific Officer at Pellenc ST.

The next phase, HolyGrail 2030 – Circular Packaging initiative, aims to prove the economic viability of smart sorting and reprocessing into high-quality recyclates, which can be used again in packaging applications such as food packaging for all packaging chain stakeholders.

Early-adopter market demonstrations will be launched in Belgium (for flexible PP food packaging) and Germany (for rigid PP food packaging), to further scale the technology and allow participants access to dedicated recycled PP food-grade materials.

Giving recyclers the ability to access crucial product information easily opens more opportunities for them. By identifying key product properties such as adhesives, glues and inks, recyclers can create the right ‘recipe’ to develop high-value applications with recycled material.

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