plastic packaging recycling using intelligent separation ...€¦ · plastic packaging recycling...

PLASTIC PACKAGING RECYCLING USING INTELLIGENT SEPARATION

TECHNOLOGIES FOR MATERIALS (PRISM)

Edward Kosior1, Dr Jon Mitchell1, Kelvin Davies1, Dr Martin Kay1, Dr Rafi Ahmad1, Edwin Billiet1

and Prof. Jack Silver, Nextek Ltd1 and Brunel University2

Abstract

A new way of rapidly sorting packaging into high purity

streams (> 99%) has been developed based on intelligent

labels with invisible markers that can be detected and

sorted using existing high-speed optical sorting systems

used in MRFs with minor modifications.

The principles have been proven using a range of

commercially available UV responsive fluorescent markers

with high emission yields. A full-scale commercial optical

sorting trial was conducted at the MRF facilities of Tomra

in Germany.

Sorting of used plastic packaging for closed loop recycling

back into food packaging requires positive identification

and sorting of the recycled materials to a higher standard.

The operators of commercial food grade recycling

processes are required to demonstrate the recycled

materials meet relevant European Food Safety Authority

(EFSA) criteria; these require at least 95% (PET) and 99%

(HDPE) of the feed material must have been used for food

contact in their first life. The initiation of closed loop food

grade recycling of PP packaging is awaiting a viable

technical solution to differentiate the food grade packaging.

From previous sorting trials, it can be estimated that of the

143,000 tons of PP food packaging used annually [1],

77,077 tons could be recovered each year in the UK. The

objective of this project was to further develop the

fluorescent marker technology investigated in earlier

projects that has the potential to meet EFSA requirements

and to extend the scope to different applications, enabling

and facilitating the sorting of different polymers to a high

degree of purity. The scope of the project included the

optimisation of fluorescent compounds, evaluation of their

stability in the supply chain and the ability of the

compounds to be effectively removed during the cleaning

and decontamination process. The project investigated the

viability of the technology and its capacity to be

implemented in the UK and elsewhere.

Unlike existing NIR sorting systems [2], this technology

uses commercial labeling and decoration methods to sort

targeted streams potentially including food-contact plastics,

bioplastics, chemical packaging, automotive plastics, black

plastics and different grades of one plastic. This technique

has the potential to create new recycling loops for food

grade PP, milk bottle sorting and PET products. The project

demonstrated that the use of commercial labels

incorporating fluorescent markers can be used to sort

plastic bottles and packaging with high yields and purity.

Introduction

A major challenge in producing recycled plastics from post

consumer recycling feedstock is to sort the material into

high purity mono-material streams since small quantities,

often as little as 0.1%, of a non-compatible plastic can

significantly reduce the quality of the final product. In

order to keep costs low while processing high volumes,

sorting is typically realized with automatic sorting

machines using Near Infrared (NIR) detection.

The stimulus for this investigation was the need to have an

automated method for sorting mixed PP packaging waste

into a separate a stream that consists of at least 99% PP

previously used for food applications [3,4], from other non-

food PP packaging that could be present at levels as high as

50% in the input stream.

A previous project [5] evaluated techniques such as

polymer additives, surface markings such as diffraction

gratings and fluorescent markers.

The use of fluorescent markers compounded into plastics

was pioneered by Ahmad et al [6,7]. They investigated the

feasibility of using single and multiple combinations of

fluorescent dyes in a range of polymer materials to identify

and sort the packaging at commercial rates.

More recently Langhals [8] reported the possibility of

identifying polymers based on their auto fluorescence and

doping with fluorescent dyes. The article highlighted the

possible use of fluorescent dyes to identify special batches

of a basic polymeric type.

This project investigated the use of machine readable

fluorescent markers that can be applied to the surface of

packaging or packaging labels so that existing NIR sorting

equipment can be utilized with no or minimal modification.

The machine readable markers needed to be invisible to the

naked eye under normal lighting so not to affect branding

and aesthetics, but be detectable at with existing MRF

infrastructure at commercial sorting speeds and sorted at

high efficiencies. To achieve this, markers were applied as

a surface varnish on an existing package or label to provide

an adequate means of identification and separation. The

labels and markers can then be removed during the normal

recycling processes so that the materials can be free of any

markers prior to being used in any new applications to

prevent false sorting responses in the next cycle of

application.

PRISM Project

PRISM is a new way of rapidly sorting packaging based on

intelligent labels with invisible markers that can be detected

SPE ANTEC® Anaheim 2017 / 500

and sorted using existing high-speed optical sorting

systems used in MRFs with minor modifications. This

technology uses commercial labelling and decoration

methods which are coded with high performing

luminescent compounds to sort targeted streams including

food-contact plastics, bioplastics, chemical packaging,

automotive plastics, black plastics and different grades of

one plastic. Sorting is accomplished using modifications to

existing NIR sorting machinery. The new technology can

boost recycling plant yields with efficient ways of sorting

materials such as PP packaging used for food, HDPE milk

bottles and sleeved PET and increase recovery of food

grade plastics and open up new markets for recovered

plastics.This technology will be compatible with all NIR

sorting equipment. It will help brand owners to ensure that

packaging reaches the recycling loop and boost UK

recycling performance. The partners in the project are :

Closed Loop Recycling, Nextek, Brunel University,Tomra,

CCL, Sun Chemicals, Johnson Mathey, Addmaster,

Enlightened Lamp Recycling (ELR) and WRAP.

This PRISM project builds on recent WRAP funded

feasibility studies [9][10], lead by Nextek Ltd.

Plastic packaging is a continually produced waste of which

the UK recycles 640,000 tonnes annually which is only

25.5% of UK plastic packaging consumption. Defra has set

the recycling target to 57% by 2017. Recoup forecasts that

UK plastic packaging consumption will increase to over 2.9

million tonnes by 2017 with recovery needing to increase

rapidly to 1.6 million tonnes per year. This means that

additional high value plastic packaging that is currently

sold as low-value unsorted material needs to be more

effectively recovered and sorted to maximise the their value

and meet these targets. Currently 556kt of rigid packaging

is described by Recoup as pots tubs and trays made up

principally by PET (329kt) and PP (123kt) goes largely un-

recycled or to low value applications.

This project delivers a new technique for identification of

materials and parts as a “plug-in” to existing high speed

automatic identification systems. This provides cost

effective separation of PET, PP and HDPE milk bottles to a

recyclate quality of greater than 99% purity that is required

for high value, food-grade applications that can sell at

virgin resin pricing. In addition to HDPE milk bottles

which face special purity sorting challenges, food grade

post consumer PP recycling has been identified as a new

key opportunity for recyclers to maximise value from the

recycling stream and it remains a hard-to-recycle material

since there has previously been no way of separating out

the non-food grade packaging materials. PET bottles that

are covered with full body plastic sleeves are usually mis-

identified representing a further critical loss of yield of

approximately 10%. The current project will develop

commercial, intelligent labels and adaptations to high speed

NIR visible sorting equipment to identify and sort materials

based on both the polymer signature and prior-use

categorization (i.e. food grade or other) and be capable of

meeting stringent European Food Standards Agency

(EFSA) guidelines. The project has spin off benefits in

being able to be applied to the sorting of many difficult-to-

sort materials including, sleeved PET bottles, black

plastics, bio-plastics and also many non packaging items

such as textiles, automotive plastics and WEEE. It has the

potential to also be used to monitor the composition,

authenticity and contamination level of many products

since the principle of identification and sorting is based on

labels that have luminescence under UV light. It will

investigate using luminescent materials recovered from

recycling of fluorescent lighting as one source of unique

markers thereby creating a high value market for these

otherwise hazardous materials.

This paper highlights the latest published data from the

WRAP funded feasibilty study and challenges which the

PRISM project will continue with.

Bench scale trials of fluorescent compound

deactivation during recycling

To progress the technology, it was important to

demonstrate that when the packaging was recycled into

new applications it did not transfer marker compound

functionality from its previous use, which could lead to

incorrect identification in any subsequent uses of the

recyclate. To demonstrate this, bench scale trials were

conducted at the beginning of the project to determine if the

fluorescent markers were deactivated by minimal recycling

and polymer process conditions.

Subsequent testing demonstrated that labels with

fluorescent pigments were able to remain active throughout

the supply chain. Therefore, packaging articles could be

positively identified and separated when they reached the

sorting stage of recycling.

A high emission intensity was obtained from the SR-1

pigment throughout the initial project work with WRAP[9]

and was therefore used in this recycling trial. Using the

hand drawn label coating, samples were prepared with a

12,500ppm concentration and applied to PP pots, and

fluorescent activity tested as shown in Figure 1.

Figure 1: PP pots with 12,500ppm SR-1 on PP self-

adhesive labels.

Labelled and unlabelled pots were then put through a

laboratory scale grinder separately, to produce flake as is

typical at the start the recycling process. At this stage of the

process, some labels became detached, but were retained in

the sample.


Figure 2: Granulated labelled and unlabelled PP pots

exposed to UV light.

The flakes were then oven treated for 5min at 220oC to

simulate PP melt extrusion time and temperatures. No

fluorescence remained in the flakes after oven treatment.

Figure 3: Fluorescence before and after simulating

extrusion conditions.

Figure 3 shows the fluorescence of the flakes before, during

and after the oven test, clearly showing that no fluorescence

remained after the oven test at PP processing conditions.

The black specks that were seen after the oven test were

found to be degraded residue of the label adhesive, not the

PP or the fluorescent compound. Further analysis at

reduced oven temperatures was conducted to determine

minimal conditions to eliminate the fluorescent properties

of the compound. The fluorescence was significantly

diminished after 10 minutes at 100oC and after 150oC for

10 minutes the fluorescence was completely destroyed.

This initial study shows the ability of fluorescent

compounds to be removed during cleaning and

decontamination processes. Commercial labels and markers

were shown to be removed efficiently without any residues

during the food grade recycling operations ensuring that

they would not persist in future applications. In addition,

the high temperature extrusion processes encountered in

remelting of plastics created irreversible changes to most of

the fluorescent chemical structures and deactivated the

markers. One of the markers was stable at extrusion

temperatures and this would limit its application to only

those labels that are efficiently removed during the

recycling stages.

Assessment of stability of fluorescent compounds in the

supply chain

The markers investigated can withstand the environment

conditions in the packaging supply chain encountered by

milk bottles (refrigeration and moisture) without significant

change in performance. Exposure to UV either as outdoor

UV light or (to a lesser extent) fluorescent lighting used by

retailers to illuminate the shelves reduced pigment

fluorescence and sorting efficiency after outdoor exposure

still needs to be validated even though baling of packaging

will protect the bulk of the labels.

Bench scale environmental stability tests included:

A range of label samples were mounted in slides and

exposed to varying environmental conditions and the

change in emission intensity was monitored regularly over

a fourteen-day period.

The exposure conditions were as follows:

Outside: South facing at 30 degree angle @

1.5metres above ground.

Fridge: Door shelf in polythene bag @ 5o C.

Freezer: Upper shelf in polythene bag @ -25o C.

Fluorescent lamp: 30cm front of the tube.

Dynamic testing of pigments – Sorting Trial

Demonstrations

These trials were conducted on production scale equipment

at the Tomra testing facility to evaluate performance under

commercial conditions. Although relatively minor

modification of the sorting equipment is required in the

form of a UV LED light system, it would not be possible to

make these modifications and conduct trials at a

commercial MRF in the UK due to their production

demands. The Tomra facility emulates MRF operating

conditions, using a number of processes prior to NIR

sorting operating at about 1 tonne per hour.

Optimisation of fluorescent compounds and dynamic

testing

The objective was to identify pigments that could be

strongly excited by suitable UV light sources (at 365nm)

and be detected by existing commercial sorting equipment.

If pigments with different emission profiles could be

identified this may provide a wider range of application in

which different packaging articles could be identified by a

specific wavelength or a combination of wavelengths.

Pigments sourced from a number of suppliers were

analysed for their fluorescent capabilities

An important objective was to identify pigments which

fluoresce in discrete regions of the visible spectrum to

allow the development of a ‘code’ to identify a wider range

of plastics packaging. Three pigments with strong

fluorescence in the red, yellow and blue region were

selected as follows:

DR-1- emission red region

DY-1- yellow region

SC-1 blue region.


It was observed that the fluorescence emission from DR-1

was approximately 3 times greater than that recorded for

DY-1 and that higher concentrations of DY-1 may be

required to ensure labels carrying this pigment are correctly

identified during commercial sorting. It was also evident

that pigments such as DR-1, which emit within a distinct

and ‘narrow’ wavelength range, are desirable to ensure

correct package identification. Obtaining pigments that

exhibit this feature also allows for a greater number of

pigments that can be clearly identified across the visible

spectrum to ‘code’ a wide range of plastics packaging.

Figure 4: DR-1,Control, SC-1+DR-1 combined,SC-1,DY-1

Figure 4 shows hand-made labels that were trialled at

12,500ppm as calibration runs. At this concentration the

yields and purity levels were 100% in detection and

ejection on the UV LED modified automated sorting

equipment at Tomra.

Sorting trials using commercially prepared labels

Figure 5: All types of labels with fluorescent pigments for

sorting trials.

CCL Labels prepared pressure sensitive adhesive (PSA),

shrink sleeve and stretch sleeve labels for testing on PET

and HDPE bottles at reduced concentration levels down to

2,000ppm. A number of fluorescent pigments and pigment

combinations were utilised, as well as un-pigmented

control labels.

The fluorescent markers could be used effectively at low

addition levels in commercially prepared inks between

2,000 and 6,000ppm and be effectively sorted on high

speed automatic sorting systems running at throughputs of

3m/s and 1 tonne per metre of belt width that are typically

found in industry. The project was able to demonstrate

yields in the range of 88% to 96% and purity levels up to

100% in a single pass.

This is illustrated in the following example. 200 PET

bottles with DR-1 pigmented shrink sleeve labels were

mixed with a further 50 PET bottles (unpigmented). 190

pigmented bottles were recovered during sorting (95%)

with 100% purity.

Figure 6: PET bottle with CCL shrink sleeve containing

DR-1 (2000ppm) and illuminated under UV at Tomra.

Table 1: Sorting for DR-1 shrink labels on PET bottles

Pigment Concentration

(ppm)

Total

number

of bottles

Number

of bottles

targeted

Yield

1st

pass

(%)

Purity

(%)

DR-1 2,000 250 200 95 100

Sorting of fluorescent label packaging mixed with

brightly coloured shrink sleeved PET bottles

The presence of coloured wavelengths close to the target

pigment wavelength could result in bottles being falsely

identified as discovered in trials at Tomra. To facilitate this,

small adjustments to the current sorting system allowed

simultaneous signatures of fluorescence and NIR to be used

to identify the labels being sorted and at the same time

supressing the effect of the presence of coloured bottles. To

test this arrangement, bottles with three fluorescent labels

(DR-1, SC-1, and DY-1) were mixed with sleeved bottles

that had a wide range of colours that overlapped the colour

of the fluorescence of these labels as shown in Figure 7 and

the results of the sorting are shown in Table 2.


Figure 7: Mixture of labels with fluorescent pigment and

coloured sleeved bottles.

Table 2: Sorting fluorescent labels from coloured bottles


(ppm)

Total

number of

bottles

Number of

bottles

targeted

Yield

1st

pass

(%)

Purity

(%)

DR-1 2,000 240 50 96 98.5

SC-1 2,000 240 50 85 100

DY-1 2,000 240 50 73 100

The results were particularly notable for the high level of

purity of the selected label in the range of 98.5-100%. This

showed that the modified sorting equipment particularly

effective in excluding the presence of the many colours

from the sleeved bottles. The yields achieved for SC-1 and

DY-1 (73% and 85%) could potentially be improved with

further sorter setting optimisation as demonstrated by the

high yields for DR-1.

Sorting of fluorescent label packaging mixed with MRF

bottles

The real challenge for sorting bottles with fluorescent

labels would be to examine the sorting efficiency when

they were mixed with many bottles obtained from Evolve

Polymers, a UK MRF. This was done in two stages, firstly

with mixed, coloured PET and then with mixed coloured

HDPE bottles to simulate the worst-case scenarios

encountered in the sorting operations as shown in Figure 8.

Figure 8: Coloured PET (left) and Coloured HDPE (right)

used in the sorting trials.

In each case 50 bottles with fluorescent labels were mixed

with 990 other bottles and then sorted using the new

modified sorting system with the results shown in Table 3.

Table 3: Sorting fluorescent labels on PET in mixed MRF

coloured bottles


(ppm)

Total

number

of bottles

Number

of bottles

targeted

Yield

1st

pass

(%)

Purity

(%)

DR-1 2,000 1040 50 94 99

SC-1 2,000 1040 50 68 31

SC-1 optimised

2,000 1040 50 90 100

DY-1 2,000 1040 50 84 65

The results for pigment DR-1 showed very high purity

(99%) and high yield of 94% in one pass demonstrating

that this pigment could be readily selected from the other

coloured bottles at levels suited for food grade applications.

The results for SC-1 showed lower purity (31%) and yield

(68%) when initially tested due to the selection of other

types of bottles with paper labels that included optical

brightener that also produced fluorescence in the same

wavelength range as SC-1.


Figure 9: Optical brightener in paper labels ejected along

with SC-1.

This result shows that the presence of optical brightener is

relatively common and can lead to false positives if these

bottles are not eliminated from selection. In order to

prevent selection of the labels with optical brightener the

sorting equipment was calibrated with the specific NIR and

fluorescence spectrum of the label. This resulted in the

specification of a new material (SC-1 optimised) with a

very specific signature and consequently sorting yield of

90% and a purity of 100%.

Coding protocols for packaging development

In the sorting of mixed plastic packaging (with or without

fluorescent labels) it is typical to initially sort the materials

into single stream materials such as HDPE, PET and PP. In

terms of priority for marking containers, the materials of

key interest would be where higher valued materials would

be separated or where regulations must be met. This

situation is directly applicable to the opportunity to identify

food grade HDPE, PP and PET. In the future, new

materials like polyethylene furanoate (PEF) or new

biobased plastics may emerge as high value targets for

recycling. It has been shown that a unique signature of the

label material and the fluorescence pigment on a specific

package (PET, HDPE, PP etc) can be generated using the

combined NIR and fluorescent signals. It is possible to

designate food grade status across all the main packaging

polymers as well as new materials to be introduced in the

future.

The signal used for food grade status should be readily

identified by the sorting equipment and not be confused

with other materials that might inadvertently create false

signals such as optical brighteners that are in commercial

use. It has been shown that ranges of packaging products

already use optical brighteners in the plastic (PET ad

HDPE), in the paper label and in the contents (as found in

detergent). This means that SC-1 (blue light emission)

should not be used on its own as it fluoresces in the same

wavelength region as optical brighteners even though it is a

particularly bright and readily discriminated pigment. For

packaging that uses full body sleeves that cover the base

polymer, the key issue is whether the base polymer is clear

or opaque and whether it is food grade or not.

In the case of PET, where sleeves are extensively used, the

food grade marker (DR-1) would be used for bottles that

were clear and food grade. This would mean that these

bottles would be directed in the clear food grade bottle

stream.

In order to separate bottles from pots, tubs and trays (all un-

pigmented), a combined marker of DR-1 & DY-1 would be

used. This would be particularly useful for PET recycling

where there is a desire to separate the two streams due to

the differing recycling behaviour.

Since coloured PET bottles (except light blue and light

green) are usually directed away from bottle applications

and directed into textile and non-food markets, it is

expedient to use a combination marker to differentiate then

from the clear food grade stream. The marker for this

category is DR-1 & SC-1.

The use of a marker or marker combination for each

category allows the sorters to be used in either positive

sorting mode or negative sorting mode depending on the

needs of the sorting operation allowing savings in utilities,

energy and cost.

The same principles can be used for HDPE and PP and any

other plastic.

Packaging that is food grade and natural in colour would be

designated by the food grade marker DR-1 and coloured

packaging or any products that need to be especially

removed from a stream (non-food that contained toxic

products) would be designated by DY-1.

In the case of sorting packaging that was food grade and

also coloured, then a combined marker (DR-1 & SC-1)

could be used. For natural un-pigmented pots, tubs and

trays the combined marker DR-1 & DY-1 could be used

provided there was a requirement to differentiate them from

bottles. The signal from this combination would be

different from the natural food grade marker and the

coloured non-food grade marker (DY-1).

The protocol is summarised in Table 5. Each combination

is unique even though the fluorescent pigment is the same,

allowing a simple and effective way of discriminating each

material and any new materials that may need to be added

in the future.

Table 5: Packaging Sorting Protocol

Bottle type Food grade

natural

bottles and

full length

sleeves

Food grade

natural

Pots, Tubs

and Trays

Food grade

coloured and

full length

sleeve

Non-food

grade natural

or coloured

full length

sleeve

PET DR-1 DR-1 &

DY-1

DR-1 &

SC-1 DY-1

HDPE DR-1 DR-1 &

DY-1

DR-1 &

SC-1 DY-1

PP DR-1 DR-1 &

DY-1

DR-1 &

SC-1 DY-1

Other

polymers DR-1

DR-1 &

DY-1

DR-1 &

SC-1 DY-1


Overall Conclusions

This project demonstrated that the use of commercial labels

incorporating fluorescent markers can be used to sort

plastic bottles and packaging with high levels of yield and

purity achieved. The addition of UV-LED illumination to

existing full-scale commercial sorting equipment enabled

sorting of packaging with a range of fluorescent pigments.

Trials were able to demonstrate yields in the range of 88%

to 96%, with purity levels up to 100% in a single pass. This

performance will meet the sorting requirements for food

grade plastics, especially recycled HDPE and PP that

require purity levels greater than 99% and 95%

respectively. The recycling processes in food grade

recycling operations remove the labels and markers,

ensuring that they would not persist in future applications.

In addition, any high temperature extrusion process creates

irreversible changes to their chemical structures and

deactivates the markers. The markers investigated

withstood the conditions in the packaging supply chain

encountered by milk bottles with limited impact on its

performance. These markers were, however, affected by

exposure to outdoor UV light and the durability after

outdoor storage still needs to be validated, even though

baling of containers will protect the bulk of the labels. The

labels can be used effectively at low addition levels in inks

at between 2,000 and 6,000ppm and be effectively sorted

on high-speed automatic sorting systems running at 3 m/sec

and 1 metric ton per hour per meter of belt width.

The big potential of this sorting process is as an extension

to the methods of sorting packaging that requires an

additional level of information to allow further sub-

categorization. The food grade recycling of PET packaging,

HDPE milk bottles and PP rigid packaging are likely

starting points for the application of this technology.

References

1. Burke, H, Freegard, K, Morrish, E, Morton, R,

“UK market compositional data of polypropylene

packaging”. WRAP, July 2012

2. Kenny, R Garry, Vaughan, Derek, “Optimization

of plastic bottle sorting”, Report, Soc. Of Plastics

Engineers, Chicago, Nov. 3-4, 1994.

3. Dvorak, R, Kosior, E, Moody, L “Development of

a food-grade recycling process for post-consumer

polypropylene”. WRAP, Sep 2011

4. Kosior, E, Dvorak, R, Moody, L, Evans ,R, “Food

grade decontamination trials of household PP

waste”. WRAP, July 2012

5. Morton,R, Williams, R, Omoboke, S, Morrish E<

“Sorting plastics for food use” WRAP, July 2012

6. Ahmad, S Rafi, Rogge, C, Billiet, E “A

Fluorescence Tracer Based System for Automatic

Identification of Doped Plastics in a Mixed Waste

stream”, Measurement and Control, 32(2), 50-

52(1999).

7. Ahamad, Rafi “A new technology for automatic

identification and sorting of plastics for recycling”

Environmental Technology 25, 1143-1149, 2004.

8. Langhals, H., Zgela, D. and Schlücker, T. “High

Performance Recycling of Polymers by Means of

Their Fluorescence Lifetimes”. Green and

Sustainable Chemistry, 4, 144-150 2014.

9. WRAP IMT003-106 Optimising the use of

machine readable inks for food packaging sorting

(September 2014)

10. WRAP PMP003-001 Recycling of food grade

packaging using fluorescent markers (March

2016).


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