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PIONEERPROJECTHolyGrail: taggingpackaging foraccurate sorting andhigh-quality recyclingPioneer project HolyGrail aims to speed up thetransition to a circular economy for plastics byfocusing on an important pillar to increase recyclingrates, namely improved sorting of post-consumerpackaging with the help of chemical tracers and digitalwatermarks. Next to designing plastics packaging forcircularity and ensuring they are collected after use,high quality sorting is a crucial component to increasecurrent poor recycling rates. Improved sorting canimprove both the quality and quantity of recycledon the market, which would mean more plastics goback to the marketplace and bring value instead ofbecoming waste.The concept of a circular economy is gaining tractionall over the world. We need to move away from thelinear plastics economy, where we take, make, andwaste plastic - towards a circular system, where wekeep useful plastics in the economy and out of theenvironment.To keep plastics in circulation, we will need actionson several fronts. In addition to the elimination ofproblematic and unnecessary plastics, and switchingfrom single-use to reuse models, recycling the plasticsthat we do need is crucial. However, today only a verysmall fraction of plastic packaging is actually recycled.CONTACTProject Leaderdebelder.g@pg.comOne of the biggest hurdles to high volumes and qualityof recycled plastics is the complexity of the packagingdesign. Countless packaging formats with manymaterial combinations are in use while the sortingtechnology on the end-of-use side is capable1

of recognising only a few properties (suchas 3D vs. 2D shapes or different infraredabsorption for different polymers and/orVIS for colour recognition). There are severalexamples where the design of packagingdisrupts the recycling, either by making anitem ‘invisible’ (e.g. black PET trays cannotbe seen by detectors) or leading to falsepositives/negatives (such as the negativesorting of a full-sleeve PET bottle because thesleeve is typically made of a different materialwhich means the PET is not detected).One approach to improve automateddetection and sorting that has received a lotof interest is to ‘tag’ an item with a unique‘code’. There are several ways of doing this.The methods that have received the mostinterest involve chemical tracers and digitalwatermarks. Tagging is accomplished byapplying chemical(s) to the label, sleeveor plastic object (chemical tracers) or byapplying a ‘digital watermark’, which can beprinted on the label (shrink sleeve, in-mouldlabel, paper or other material) or physicallyincorporated as a subtle pattern embossed inthe plastic itself. Pioneer Project HolyGrail wasset up to investigate if such chemical tracersand digital watermarks could provide a reliableand efficient tagging system that couldeventually be deployed on a large scale, andif so how they might contribute to a circulareconomy for plastics.HOW DOES TAGGING WORK?Chemical tracers and digital watermarkstag items use the same basic principle –they introduce a machine-readable codeor identifier into an item. Then, rather thanrelying only on the ability to distinguish oneor several properties of collected items (e.g.shape, density, IR spectrum of the resin,visual identification), detecting and readingthe code provides the sorting system withinformation unique to that item by pointing toa database where that information is stored.The information tells the system in which wayto sort the item (e.g. food grade vs. non-foodgrade) Such information can be updated andexpanded over time, e.g. to allow for changingsorting preferences if an items recyclabilityimproves. The main difference is in how thecode is applied: A chemical tracer is a moleculeembedded in the plastic resin orpackaging component such as a label,acting as a binary ‘code’ as the chemicalis either present or not. The moleculeis detectable due to its spectroscopicproperties (e.g. being fluorescent underUV light). In principle, it is possibleto combine several different tracermolecules, each with unique spectra, toincrease the number of possible codes.Packaging marked with such chemicalscan be identified and sorted usingsorting equipment that is modified withUV lighting. The chemically tagged itemis insensitive to deformation or otherphysical stress which would otherwisereduce the detectability of many items. A digital watermark is an optical codethe size of a postage stamp, applieddirectly within the item’s label artworkor embossed in the mould, usually ina repeatedly-tiled manner. The codeis created by subtly modulating thepixels that make up the design, or byadding micro-topological variations tothe surface of the plastic as a texture- there is no need for added materials.In addition to detection by an addedcamera/processor on a sorting machine,digital watermarks can be detected bybarcode scanners and smartphones, inpractice turning the tagged items intoInternet-of-Things object. The codescan provide a wide range of attributessuch as manufacturer, SKU, type ofplastics used and composition for multilayer objects, food vs non-food usage,etc. The number of available codes isvirtually unlimited, attributes can beadded over time, and false positiveseliminated.There are several intuitive advantages ofchemical tracers and digital watermarks. The technologies enable sorting of muchhigher granularity and quality Retrofitting existing sorting equipmentwith add-on modules for detection ofchemical tracers or digital watermarksis likely less CAPEX intensive thanupgrading recycling facilities with moresophisticated detection technologybased on material properties. The machine-readable codes could alsobe utilised to enable other applicationsthroughout the value chain. Forexample, digital watermarks couldbe used in manufacturing, for fastercheckout in retail applications, and to2

provide information transparency andcommunicate with users. In principle,it could be possible to access data inreal time, and to get accurate actualrecycling figures broken down to formator individual product level. This couldbe used to inform better design choicesto eliminate packaging elements thatcannot be recycled.However, it is important to investigate howthese technologies fit in the broader recyclingecosystem and actually contribute to acircular economy for plastics.Figure 1: Application of chemical tracers and digital watermarksAs seen by thecamera, but no humanrecognizable patternto codeChemical tracers are applied to the shrinklabel or plastic object and can be detectedunder UV lightingDatabase holds product attributes: Manufacturer SKU/Global Trade ItemNumber Composition andpercentage of plastics inlayers Food vs Non-food Other attributes as desiredDigital WatermarkingFor a demonstration, click here.For a demonstration, click here.Methodology and processAt the start of HolyGrail, a small core project team was formed that looked into all availabletechnologies in the market. A handful of chemical tracer programs were studied at that time,but none of them entered the market, likely due to lack of alignment within the full packagingchain on one technology (or several compatible ones). Digital watermarking was a completelynew concept for plastic packaging recycling. The project was motivated by the belief that newsorting technology for plastic packaging truly requires first cross-value chain alignment onwhich technologies to use, so that they ultimately would become the “barcode of recycling”,before market introduction can take place.The project team started with organizing a public workshop (2017) to accelerate interest inthe topic, which with over 85 participants was a real success. Some key items (that 99% ofparticipants agreed to) were identified:i.the packaging industry needs a non-permanent technology (to minimize the risk ofcross contamination in the next cycle);ii.preferably the selected technology is compatible with existing sorting assets (e.g.allowing easy retrofit of existing sorting units with add-on modules),iii. the technology causes no issues with food safety (such as migration risks); andiv. this “additional dimension in sorting” can solve the top 5 needs identified by theparticipants: 1. distinguish food from non-food (not possible with classical NIR/VISsorters), 2. divert easily compostable packaging from Material Recovery Facilities,3. proper identification of all kinds of full-body sleeved (PET) bottles, 4. Allow newmaterial introductions by proper control of their after-use material flow (no risk ofpolluting established streams), and 5. crack the challenge on multi-layer/materialcomponents (film, tray, bottles ).3