EP4630807A1

EP4630807A1 - Method for quantifying the recycled pet (rpet) content within a given pet containing plastic material

Info

Publication number: EP4630807A1
Application number: EP23818446.9A
Authority: EP
Inventors: Emmanouil TSOCHATZIS; Milena CORREDIG
Original assignee: Aarhus Universitet
Current assignee: Aarhus Universitet
Priority date: 2022-12-07
Filing date: 2023-12-06
Publication date: 2025-10-15
Also published as: WO2024121196A1

Abstract

The present invention relates to a method for determining the amount of recycled polyester in a polyester containing material, the method comprising a) providing a polyester containing material; b) determining the δ13C value in the polyester containing material from step a); c) comparing said determined δ13C value to a corresponding reference table; and d) determining the amount of recycled polyester in the polyester containing material by comparing to the corresponding reference level.

Description

METHOD FOR QUANTIFYING THE RECYCLED PET (rPET) CONTENT WITHIN A GIVEN PET CONTAINING PLASTIC MATERIAL

Technical field of the invention

The present invention relates to a method for the determination and quantification of rPET content within a PET containing material, preferably using elemental analyser-isotope ratio mass spectrometry (EA-IR/MS) and 6¹³C values.

Background of the invention

Plastics are products large economic field being used extensively for the production of a large variety of different industrial products, such as textile fibers, machinery, equipment, toys, and packaging materials for food, food contact materials as well as pharmaceutical products etc.

Food packaging is one of the fields employing the largest variety of polymers, mainly due to the necessity for different properties depending on the type of food, its shelf life and the supply chain involved. The most notable is polyethylene terephthlatate (PET), currently recognized as the most circular plastic food contact material (FCM), and suitable to be recycled back into new FCMs. Its high recyclability potential is due to a combination of intrinsic unique material properties that allow it to be mechanically recycled, almost endlessly. Important points of concern still exists, with the most relevant being all the existing delays in integrating the EFSA positive opinions for the production of recycled plastic FCMs in EU regulation.

According to the European Food Safety Authority (EFSA) publication repository, a significant number of different technologies can be applied for the decontamination and recycling of food contact PET, such as Starlinger iV+technology (Lambre et aL, 2021), Vacurema prime (Lambre et aL, 2022), EREMA basic (Silano et aL, 2019), and Kreyenborg IR Clean+ (European Food Safety (EFSA), 2022). Throughout these technologies, different decontamination conditions and extrusions steps (single screw, twin screw) are applied.

However, there is a significant lack of analytical methods to assess the content of rPET with a given plastic materials and to verify, or even quantify them. Although producers claim that a PET material has been produced from 100% rPET, in reality this is not possible to be verified, with the present analytical methods and the lack of potential marker compounds (Tsochatzis et al 2022).

Isotope ratio mass spectrometry (IRMS) is a technique that accurate measures the abundances differences of different elemental isotopes, such as hydrogen (²H/¹H), carbon (¹³C/¹²C), nitrogen (¹⁵N/¹⁴N) and oxygen (¹⁸O/¹⁶O) (Pico 2020). IRMS has a broad and significant applicability, among various scientific fields, onto food authenticity and traceability. The main type of IRMS is the elemental analyzer (EA-IRMS), in which solid samples are being introduced to a combustion chamber (analysis C and N) transforming them to gas, transfer to a gas chromatography column introduction to the ionization source and finally analyzed by a sector-field mass spectrometer (Pico 2020). IRMS was recently investigated as a complementary tool for monitoring environmental plastic debris, where carbon isotopic ratio (¹³C/¹²C) for a variety of common plastic pollutants and expressed as 6¹³C values (Birch et al 2021).

Very recently on 15^th September 2022, the European Commission adopted and placed into force a new Regulation, namely European Commission Regulation (EU) 2022/1616, where the all FCM containing recycled plastic, shall be clearly labelled, while the recycled plastic content must be labelled indicating the by weight of the recycled content (w/w) and the maximum percentage by weight of the recycled content that final recycled plastic materials and articles containing the recycled plastic may contain, if this is less than 100% (EU 2022).

Therefore, we developed, validated and applied an EA-IRMS method for the determination and quantification of rPET content within a given PET material. At the moment, no identical method or similar analytical exists for the evaluation of rPET content within a given PET material.

Birch et al. is silent in respect of quantifying based on establishing a correlation between 6¹³C values and rPET levels in a given product (Birch et aL 2021), although being in respect of qualitatively analyse PET, rPET, and other type of plastics, within a given aiming, aiming to develop a method in respect of differentiating microplastics.

Berto et al relates to the characterization of carbon stable isotopes (6¹³C) of different plastic polymers (petroleum- and plant-derived) in order to increase the dataset of isotopic values as a tool for further investigation in different fields of polymer research as well as in the marine environment surveillance (Preliminary study to characterize plastic polymers using elemental analyser/isotope ratio mass spectrometry (EA/IRMS) (Berto et aL 2017). Berto et al. is silent in respect of quantifying rPET content within a given plastic.

A report from "Deutsche Gesellschaft fur Internationale Zusammenarbeit (GIZ) GmbH" from 2021, establishes that there is a "Need of a third-party control system as the recycled content cannot be physically or chemically determined at the level of the final product or packaging to supported market surveillance and enforcement" (page 4). (Recycled content in plastic material with focus on PET, HDPE, LDPE, PP. Deutsche Gesellschaft fur Internationale Zusammenarbeit (GIZ) GmbH. January 2021).

Currently, most of the approved recycling processes for food-grade plastic FCM, aims to the production of rPET, which shall comply not only with the previously mentioned EU regulations, but also with any national legislation existing at any member state. A notable restriction in the production of food-grade rPET as recommended by EFSA, is the presence of a maximum proportion of 5% w/w of non-food plastic material in the post-consumer PET streams for recycling processes IEFSA 2011; Tsochatzis et aL 20221, which shall be assessed and evaluated prior production of the material.

Hence, an improved method for determining amounts of rPET in a sample PET product would be advantageous, and, in particular, a more efficient and/or reliable method for determining amounts of rPET in a sample PET product would be advantageous.

Summary of the invention

In here is disclosed a method for the determination and quantification of rPET content within a given PET material.

Thus, an object of the present invention relates to the provision of an improved method for the determination and quantification of rPET content within a given output PET material as well as in input PET material. Example 1 presents all the tested materials from PET plastics, either vPET, rPET or in-purpose contaminated vPET. Furthermore, it reports all the experimental conditions, including sample preparation, instrumental analytical conditions and performed statistical analysis.

Example 2 shows that processing, such as heating, of the material to be analysed may affect 6¹³C values. An evaluation of this effect was performed, in order to assess the effect of the sample preparation and in particular grinding of the material. This step is crucial in order to validate and confirm that the obtained results.

Example 3 shows that knowing how the material to be analysed has been prepared is important to establish correct reference levels. It highlights that different extrusion technologies (the main 2 currently used, including single-screw and twin-screw extrusion) present significant differences to the carbon isotope ratio. Knowing the applied technology (single r tin-screw) it is applicable and reference values can be determined, thereby allowing for correct determining of rPET amounts in a sample. However, a different approach for the calculation and assessment of the rPET content (w/w) within a given PET plastic is based on the applied technology.

Example 4 is applied to the assessment of the input of virgin PET plastic that will be used for the assessment and evaluation of the maximum proportion of 5% w/w of non-food plastic material in the post-consumer PET streams for mechanical recycling processes. Thus, example 4 shows that input reference levels can indeed be determined for input material for mechanical recycling of PET, thereby allowing for correct determining of rPET amounts in a sample.

Thus, in a first aspect the invention relates to a method for determining the amount of recycled polyester in a polyester containing material, the method comprising: a) providing a polyester containing material; b) determining the 6¹³C value preferably by EA-IR/MS, in the polyester containing material from step a); c) comparing said determined 6¹³C value to a corresponding polyester containing material reference table; and d) determining the amount of recycled polyester in the polyester containing material by comparing to the corresponding reference table.

In a preferred embodiment, the polyester is PET.

Another aspect of the present invention relates to the use of the 6¹³C value in a polyester material, preferably PET, preferably determined by EA-IR/MS, to determine the amount of recycled polyester material in the material.

Still another aspect of the present invention is to provide a device or system adapted to determine the amount of recycled polyester in a polyester containing material, the device comprising: optionally, a homogenizer, such as a grinder or cutter, adapted to homogenize the polyester containing material, preferably at a low temperature, such as below the melting point temperature (T_m) of the polyester, such as below 260°C for PET, or not exceed the glass transition (Tg) of the polyester material; a mass spectrometer, preferably a stable isotope mass spectrometer, EA- IR/MS; a processor configured with a reference table, said reference table corresponding to reference levels of a 6¹³C value of one or more polyester containing material and the processing/production method of the reference polyester containing materials; wherein the device or system is adapted to receive the polyester containing material, optionally via the optional homogenizer to homogenize said material; determine the 6¹³C value of the material by the mass spectrometer; comparing the determined 6¹³C value of the sample to the reference table; and determining the amount (% w/w; mass fraction) of recycled polyester within the sample by the processor. Yet another aspect of the present invention is to provide a computer implemented method of determining an amount of recycled polyester in a polyester containing material, the method comprising: providing a 6¹³C value of a polyester containing material, providing a production method of the polyester containing material, providing a mathematical model comprising reference levels of 6¹³C within a corresponding polyester containing material, said reference levels being correlated with various production methods of said polyester containing material, determining the amount of recycled polyester in the polyester containing material by the mathematical model, providing the determined amount of recycled polyester in the polyester containing material to a system or a user.

Brief description of the figures

Figure 1

Figure 1 shows regression analysis for twin-screw extrusion of PET trays with different estimated rPET (% w/w) content.

Figure 2

Figure 2 shows regression analysis for twin-screw extrusion of PET trays with different estimated rPET (% w/w) content.

Figure 3

Figure 3 shows linear regression of 6¹³C values of vPET flakes contaminated with specific concentrations (% w/w) of PBT cyclic oligomers (FCM885).

The present invention will now be described in more detail in the following.

Detailed description of the invention

Definitions

Prior to discussing the present invention in further details, the following terms and conventions will first be defined: Polyesters is a category of polymers that contain the ester functional group in every repeat unit of their main chain. The most common polyester polymers are: polyethylene terephthalate (PET), polytrimethylene terephthalate (PTT) and polybutylene terephthalate (PBT).

Polyethylene terephthalate (or poly(ethylene terephthalate), PET, PETE, or the obsolete PETP or PET-P), is the most common thermoplastic polymer resin of the polyester family and is used in fibres for clothing, containers for liquids and foods, and thermoforming for manufacturing, and in combination with glass fibre for engineering resins.

In the present context the term "recycled polyethylene terephthlatate" or "rPET" refers to PET which has been recycled, such as from recycled plastic bottles.

Virgin polyethylene terephthlatate CvPET)

In the present context the term "virgin polyethylene terephthlatate" or "vPET" refers to PET (see previous paragraph entitled "Polyethylene terephthalate (PET)") when it is in its purest form. Thus, this plastic material is considered as "new" and will have never been used or mechanically processed or recycled before and is therefore in peak performance.

5¹³C value

The stable isotope-number ratio (R) for a particular substance refers to the ratio of the number of atoms of a heavier stable isotope (e.g. ¹³C) to the number of atoms of a lighter one (e.g. ¹²C) of the same chemical element in the same system. In the case of carbon, R follows the following relation: where n is the number of atoms of a given isotope in a given "substance". By convention, stable carbon isotope amount ratios [n(¹³C)/n(¹²C)] are expressed relative to the ratio for an international standard (Pee Dee Belemnite [PDB] or Vienna PDB [VPDB]). Results are reported as 5¹³C values, in parts per thousand (%o), calculated as follows:

Higher 5¹³C values (less negative) indicate enrichment of the sample in the rarer and heavier ¹³C isotope.

Method for determining the amount of recycled polyester in a polyester containing material

As also outlined above, in here is disclosed a method for the determination and quantification of rPET content within a given PET material. Thus, in a first aspect the invention relates to a method for determining the amount of recycled polyester in a polyester containing material, the method comprising: a) providing a polyester containing material; b) determining the 5¹³C value preferably by EA-IR/MS, in the polyester containing material from step a); c) comparing said determined 5¹³C value to a corresponding polyester containing material reference table; and d) determining the amount of recycled polyester in the polyester containing material by comparing to the corresponding reference table.

Again, as also outlined in the example section, comparing 5¹³C values measured from a given sample and comparing it to a corresponding reference level/table, it is possible to determine the amount of recycled polyester in a polyester containing material. No such methods have previously been provided.

Step a)

Different polyesters may be tested in the method of the invention. Thus, in an embodiment, in step a) the polyester is selected from the group consisting of polyethylene terephthlatate (PET), polybutylene terephthalate (PBT), polytri- methylene terephthalate (PTT), polyolefins, including low-density polyethylene (LDPE), high-density polyethylene (HDPE) and polypropylene (PP) polystyrene (PS), preferably the polyester is PET. PET was tested e.g. in examples 1-3, whereas PBT was demonstrated in Example 4. PTT is used e.g. in textiles and clothing.

In a preferred embodiment, the polyester is PET.

Is it plausible that the method will also work for other recycled/virgin plastic packaging materials, such as polyolefins, including low-density polyethylene (LDPE), high-density polyethylene (HDPE) and polypropylene (PP) as well as polystyrene (PS). The latter materials are of high relevance as they represent a high fraction of the packaging material market.

The polyester containing product may have different origins. Thus, in an embodiment, in step a) the polyester containing product is selected from the group consisting of

- food contact material (FCM), such as bottles, food packaging crates, trays and films;

- textile, such as clothes, such as apparel and footwear; and packaging for pharmaceutical and healthcare packaging materials.

In a preferred embodiment, in step a) the polyester is a food contact material (FCM).

In another embodiment, in step a) the polyester is a textile selected from the group consisting of clothes, such as apparel, and footwear.

In a preferred embodiment,

• in step a) the polyester is PET and the product is a food contact material (FCM); and

• in step b) the 6¹³C value is determined by EA-IR/MS.

The provided material is preferably homogenized before step b). Thus, in an embodiment, in step a) the provided material is homogenized before step b), such as by melt mixing and/or particularization such as by cutting, chopping, milling grinding or extrusion.

In a preferred embodiment, the homogenization step is performed without heating, such as by cutting of chopping, such as by using a cryogenic grinder. As shown in the example section milling may develop heat (Example 2), which can impact the 6¹³C value. Thus, only processing shall be considered, which in most of the cases is similar and affects the material in an identical way. Thus, preferably temperatures that are equal or above the melting point (T_m) of the tested polymers must not be exceeded and avoided during sample preparation. For PET these temperature (melting point, T_m) is around 260°C. Moreover, it is preferred the material not having any heat effect during sample preparation (e.g. milling, melting, heating, softening). The advantage of the methodology is the direct analysis representing only the applied process. Thus, in an embodiment, the homogenization step shall not exceed the respective glass transition (T_g) of the plastic/polyester material. For PET, the T_g is around 70°C.

Thus, is in an embodiment, the homogenization step does not exceed 70°C, such as not exceeding 60°C, such as not exceeding 50°C.

In an embodiment, the provided material in step a) is processed by cutting, milling, or grinding followed by sieving, such as with a sieve with a cut-off below 5 mm such as in the range 0.1-5 mm, such as 0.1-4 mm such as 1-4 mm such as 1-3 mm such as around 2 mm. In case of grinding, the temperature shall preferably follow the aforementioned requirements and restrictions.

Step b)

In a preferred embodiment, in step b) the 6¹³C value is determined by EA-IR/MS. This is also the method used in the example section.

Step c)

In an embodiment, the reference table in step c) is a predetermined standard curve and/or regression model for a corresponding material, preferably produced by a mechanical recycling technology, such as a technology including extrusion, such as single-screw extrusion and twin-screw extrusion. In an embodiment, the reference table in step c) comprises at least a predetermined reference table for a corresponding material, which has also been produced in a similar manner, such as by a mechanical recycling technology, such as a technology including extrusion, such as single-screw extrusion and twin- screw extrusion. Recyclers know the applied technology, and this is an information that can be provided in advance and prior analysis of the material with EA-IR/MS.

In another embodiment, the predetermined reference table has been determined using a regression model for the material in question, such as PET, and production method of the material in question, such as single-screw extrusion or twin-screw extrusion. As shown in example 3, different regression models are applicable for different types of processing, including extrusions (single-screw or twin-screw). Based on the information provided in here, the skilled person will be able to establish references tables for other materials and types of processing.

In an embodiment, in step d) the amount of recycled polyester is determined by comparing to the predetermined table in step c).

In another embodiment, in step d) the predetermined reference level is a standard curve or table, such as a regression model, such as a linear regression model or a non-linear regression model, such as a polynomial regression.

In yet another embodiment, in step d) the amount of recycled polyester determined, is the ratio of recycled polyester to virgin polyester or the mass fraction percentage of recycled polyester in the material (by weight % w/w; mass fraction).

Uses

An aspect of the invention also relates to the use of the 6¹³C value in a polyester material, preferably PET, preferably determined by EA-IR/MS, to determine the amount of recycled polyester material in the material. As outlined in the example section is has been determined that this can be done. Device or system

The method of the invention can also be implemented in a device or system.

Thus, a further aspect of the invention relates to a device or system adapted to determine the amount of recycled polyester in a polyester containing material, the device comprising: optionally, a homogenizer, such as a grinder or cutter, adapted to homogenize the polyester containing material, preferably at a low temperature, such as below the melting point temperature (Tm) of the polyester, such as below 260°C for PET, or not exceed the glass transition (Tg) of the polyester material; a mass spectrometer, preferably a stable isotope mass spectrometer, EA- IR/MS; a processor configured with a reference table, said reference table corresponding to reference levels of a 6¹³C value of one or more polyester containing material and the processing/production method of the reference polyester containing materials; wherein the device or system is adapted to receive the polyester containing material, optionally via the optional homogenizer to homogenize said material; determine the 6¹³C value of the material by the mass spectrometer, comparing the determined 6¹³C value of the sample to the reference table; and determining the amount (% w/w; mass fraction) of recycled polyester within the sample by the processor.

In an embodiment, the device or system comprises a user interface, the user interface adapted to receive input from a user relating to the production method of the polyester containing material to be analyzed.

In another embodiment, the homogenizer is a cryogenic grinder.

In a related embodiment, the homogenizer comprises a controller and a temperature sensor and wherein the controller is adapted to control a homogenization speed (such as grinding speed) and temperature of a material being homogenized, based on a measured temperature and a temperature threshold, wherein the homogenization speed is reduced if the temperature threshold is exceeded.

Computer-implemented method

The method of the invention can also be a computer-implemented method. Thus, yet a further aspect of the invention relates to a computer-implemented method of determining an amount of recycled polyester in a polyester containing material, the method comprising: providing a 6¹³C value of a polyester containing material, providing a production method of the polyester containing material, providing a mathematical model comprising reference levels of 6¹³C within a corresponding polyester containing material, said reference levels being correlated with various production methods of said polyester containing material, determining the amount of recycled polyester in the polyester containing material by the mathematical model, providing the determined amount of recycled polyester in the polyester containing material to a system or a user.

An aspect of the invention also relates to a computer system comprising an input/output device and a processor, the system being enabled to execute the method according to the invention on the processor.

It should be noted that embodiments and features described in the context of one of the aspects of the present invention also apply to the other aspects of the invention.

All patent and non-patent references cited in the present application, are hereby incorporated by reference in their entirety.

The invention will now be described in further details in the following non-limiting examples. Examples

Example 1 - Materials and Methods

Polymer samples

The analysed food contact materials were originated from the same company, producing either vPET or rPET pellets as well as the production of food packaging trays using different technologies (single screw or twin-screw extrusion) at different contents of rPET. Samples are given in Table 1. Samples were stored at dry conditions at room temperature (25°C), in a dark place.

Table 1. Samples of pellets and FCM trays analysed in this study produced with different technologies and at different estimated content of rPET.

* Referring to high purity mixture of PBT cyclic oligomers (regulated FCM No885) used for the preparation of materials 11-14, as described in Annex I, European Regulation (EU) No 10/2011 (EU 2011).

For samples 1-10, real samples were provided from recycling facilities, representing different mixtures of ground PET materials, collected from different industrial production locations/facilities, using different extrusion technologies. Samples 11-14 were Polyethylene terephthalate samples (PET) contaminated with cyclic polybutylene terephthalate (PBT) oligomers, following the requirements of Annex I of the Commission Regulation (EU) No. 10/2011 were prepared. Thus, samples were prepared by melt mixing in a spherical flask heated by a salt bath, under nitrogen atmosphere at 300°C for 20 min. A mechanical stirrer was used for the mixing, at a speed of 300 rpm. The produced material was collected and cut into small flakes.

Sample No.15, representing the officially regulated compounds mixture of PBT cyclic oligomers, as reported in Commission Regulation (EU) No 10/2011 was tested as well (EU 2011).

Samples 16-18 were input materials from kerbside collection facilities to be used for FCM mechanical PET recycling facilities having to respect the maximum of 5% non-food PET polymers. These materials were tested in order to validate the methodology and verify the assessment of the 5 % w/w threshold, according to the recycling regulation (EU 2022).

Sample preparation

For the EA-IR/MS analysis of the trays and the flakes, samples followed a simple preparation. Thus, the tray samples were cut in small square size pieces (ca. 1 mm x 1 mm) using a laboratory scissor. For the pellets, two approaches were applied, to assess potential differences and effects. For the 1^st approach, the pellets were ground using a Retsch ZM200 mill (Haan, Germany) using a 2.0 mm sieve, while for the 2^nd approach the pellets were tested directly without any grinding prior analysis. A portion of 2.0 mg was wigheted and placed within an alum Elemental analysis-isotope ratio mass spectrometry (EA-IR/MS)

We used an NC 2500 Elemental Analyzer (EA) (Carlo Erba) with a Thermo Conflo III coupled to a DeltaPlus (Thermo Finnigan) stable isotope mass spectrometer (EA-IRMS) to obtain 6¹³C values of the studied polymers. The samples were dropped by an autosampler carousel into an oxidizing furnace (chromium cobaltous oxides) at 600°C, where they were flash combusted under a stream of oxygen, generating CO2, NOx (oxides of nitrogen), H2O, and SO2. A portion of 100-250 pg of polymer samples and standards (nicotinamide, acetanilide and benzoic acid). Small pieces (<4 mm largest dimension) were cut from the plastic packaging and pellet samples and weighed in tared tin capsules. The capsules were gently crimped closed and placed in the autosampler. The stable isotopenumber ratio (R) for a particular substance refers to the ratio of the number of atoms of a heavier stable isotope (e.g. ¹³C) to the number of atoms of a lighter one (e.g. ¹²C) of the same chemical element in the same system. In the case of carbon, R follows the following relation : where n is the number of atoms of a given isotope in substance S. By convention, stable carbon isotope amount ratios [n(13C)S/n(12C)S] are expressed relative to the ratio for an international standard (Pee Dee Belemnite [PDB] or Vienna PDB [VPDB]). Results are reported as 6¹³C values, in parts per thousand (%o), calculated as follows:

Higher 6¹³C values indicate enrichment of the sample in the rarer and heavier ¹³C isotope. The values for the standards and samples were corrected with a blank. Furthermore, if the standard deviation (SD; n > 3) for the standards was less than 0.6 %o, no drift correction was applied. The raw/blank-corrected values for the standards were plotted against their expected values (known). Calibration curve presented a R² value above 0.99. The tested method was validated by testing real samples, either raw material (vPET and rPET pellets), final products (FCM trays) with known amount of vPET/rPET, real samples from the input of a recycling process (prior decontamination) and vPET samples containing up to 5% w/w (mx threshold for recycling FCM) with PBT cyclic oligomers (dimer up to pentamer) representing regulated mixture FCM No.885 (EU 2011).

Statistical analysis

Statistical analyses were performed using Microsoft Excel office software (Microsoft Inc, USA), where differences of 6¹³C values within were tested using ANOVA test. Furthermore, and wherever it was needed, a multivariate statistical analysis was performed using Simca-P V17.0.2 software (UMETRICS AB Sweden). Principal component analysis (PCA) and Orthogonal Partial Least Squared Discriminant Analysis (OPLS-DA) were used for modelling differences between the 6¹³C values for the trays, using single or twin-screw extrusion, as well as for the comparison between the virgin and recycled flakes.

Example 2 - Determining that sample preparation treatment influences the results

Aim of study

The aim of this study was to evaluate if grinding of the material is statistically significant or not, regarding the assessment and evaluation of 6¹³C values obtained from rPET/vPET plastics.

Materials and methods

Samples tested were trays (samples 1-7) and pellets (8-10) as reported in Table 1 of Example 1. Furthermore, Elemental analysis-isotope ratio mass spectrometry (EA-IR/MS) and statistical analysis was identical as reported in Example 1.

Sample preparation:

Apart from the sample preparation, as reported in Example 1, an additional sample preparation treatment was tested. Hence, the plastic materials samples of trays and pellets, were undergone grinding using a grinder (Retsch rotor mill,ZM 300) using a 2 mm sieve and with just directly placing the pellet and trays to be analysed. In all cases, the goal was to perform the analysis with a size less than 5 mm, as it was recommended in respective studies (Berto et aL 2017; Birch et aL

Results

After performing the desired tests and applying the EA-IR/MS methodology, we identified that the grinding of the polymers presented significantly different 6¹³C values among rPET and vPET, especially for pellets. Especially the non-ground pellets, either rPET or vPET, presented lower 6¹³C values compared to the nonground ones. The results are presented in Table 2, supporting the findings obtained for the PET pellets. In addition, and in relation to the instrumental results, during milling/grinding, it was observed that temperature of the plastic polymer material and of the mill compartment was increased, due to the hardness of the material (plastic) and the increased frictional energy from the rotor centrifugal milling. A melt of the material was observed on the used sieve (2 mm) as well as the increased temperature in the mill.

Table 2. Statistical analysis and overview of the vPET and rPET results.

* Values are means of triplicate measurements. Values followed by different letters within a row are significantly different (p < 0.05). Conclusion

The effect of sample preparation (grinding) was assessed and proved to have an impact on the analysis. Milling/grinding of the material shall be avoided in order to avoid heating of the material due to frictional energy. Moreover, it must be avoided in order to exclude variation in the obtained 6¹³C values that will reflect to the accuracy of the results.

Example 3 - Identification of recycled content of PET in single-screw and twin extruded recycled PET plastic FCM

Aim of study

Different pellets and plastic trays for food contact materials (FCM) production, coming from either 100% virgin PET (not recycled), 100% recycled PET as well as trays from different processes, with single-screw extrusion systems or twin-screw systems, representing the majority of systems applied to mechanical recycling of PET for FCM in Europe.

The analyzed food contact materials were originated from the same company, producing either vPET or rPET pellets as well as the production of food packaging trays using different technologies (single screw) at different contents of rPET (see Example 1; Table 1).

Materials and methods

Samples are given in Table 1 of Example 1 (see samples 1-11). All samples were stored at dry conditions at room temperature (25°C), in a dark place. Sample preparation, EA-IR/MS and statistical analysis were applied as reported in Example 1. For this example, no multivariate statistical analysis was applied.

Results

1. Single-screw

Pellets and trays, resulting from single-screw extrusion and containing different amounts (% w/w mass fractions) were analysed with the developed EA-IR/MS methodology as reported in Example 1. The obtained 6¹³C values for single-screw experiments are reported in Table 3. The data were implemented to perform regression analysis and to reveal potential correlation between the 6¹³C and the known rPET contents. Table 3. Statistical analysis and overview of the analysed single-screw extruded pellets and trays samples of vPET/rPETs. rPET= recycled PET; vPET=virgin PET (non-recycled); ** Values are means of triplicate measurements. ^a Values are means of triplicate measurements. Values followed by different letters within a row are significantly different (p < 0.05).

Analysis of variance (ANOVA) statistical analysis highlighted a statistical difference between the 6¹³C values and the amount of rPET content. Following the ANOVA of the results, the data were implemented to perform regression analysis and to reveal potential correlation between the 6¹³C and the known rPET contents, for twin-screw extruded samples (Figure 1). The results indicated that rPET pellets and trays had reduced 6¹³C values (more negative) compared to the vPET or the non-recycled PET pellets and trays tested.

Moreover, linear regression analysis presented a linear regression coefficient (R²) of 0.99 is indicating an excellent linear behaviour, for this type of materials, either including the 100% rPET. The regression analysis coefficient (R²) was 0.9882 indicating excellent linear relationship between the studied factors (rPET content and 6¹³C values). 2. Twin-screw extrusion

Pellets and trays, resulting from twin-screw extrusion (see Example 1, Table 1) and containing different amounts (% w/w mass fractions) were analysed with the developed EA-IR/MS methodology as reported in Example 1. The obtained 6¹³C values for single-screw experiments are reported in Table 4. As in case of singlescrew extrusion, the data were implemented to perform regression analysis and to reveal potential correlation between the 6¹³C and the known rPET contents, for twin screw-extruded samples (Figure 2).

Table 4: Statistical analysis and overview of the analysed twin-crew extruded pellets and trays samples of vPET/rPETs.

* rPET= recycled PET; vPET=virgin PET (non-recyc ed); ** Values are means of triplicate measurements. ^a Values are means of triplicate measurements.

Values followed by different letters within a row are significantly different (p < 0.05).

Analysis of variance (ANOVA) statistical analysis highlighted a statistical difference between the 6¹³C values and the amount of rPET content. Following the ANOVA of the results, the data were implemented to perform regression analysis and to reveal potential correlation between the 6¹³C and the known rPET contents, for twin-screw extruded samples (Figure 2). The results indicated a polynomial correlation between the 6¹³C and the known rPET contents for twin-screw extruded samples with a regression coefficient of 0.9998, indicating excellent linear relationship between the studied factors (rPET content and 6¹³C values). The analysis of the real samples proved to be in accordance with the established calibration curves as mentioned above, depending on the type of extrusion for the production of the pellets.

Conclusion

The knowledge of the production of mechanically recycled PET plastic for FCM in combination with EA-IR/MS analysis, can be used to determine the amount of rPET (w/w) within a given plastic material. In this case, the two main production techniques, such as single-screw and twin-screw, can be differentiated and appropriate calibration curves. In case of single-screw extruded, linear regression analysis, while for twinOscrew extruded PET, a polynomial regression analysis is applied.

Example 4 - Differentiation of virgin content of PET contaminated with food contact material PBT polyester

Aim of study

The analysed FCM were produced under laboratory conditions for establishing a methodology to assess and evaluate the differentiation of virgin content of PET contaminated with food contact material PBT polyester, in order to verify the regulated input of 5% w/w for non FCM application for PET mechanical recycling (EU 2022).

Materials and methods

Samples are given in Table 1 of Example 1 (see samples 11-15). All samples were stored at dry conditions at room temperature (25°C), in a dark place. Sample preparation, EA-IR/MS and statistical analysis were applied as reported in Example 1. For this example, no multivariate statistical analysis was applied.

Results

Therefore, PET plastic flakes were contaminated at specific levels and used as input for the EA-IR/MS method developed and applied (see Example 1). In this approach we would lie to verify and assess the limit of 5% non-food grade PET can be achievable to be analysed by the present EA-IR/MS technique. The results are presented in Table 2. A visual representation of the data (Figure 3) supports the findings obtained from the analysis of the PET pellets.

Table 5. Analysis and overview of the analysed contaminated PET flakes with PBT oligomers, analysed by EA-IR/MS method.

* Values are means of triplicate measurements. Values followed by different letters within a row are significantly different (p < 0.05). The results reported in Table 5 are certainly indicating that EA-IR/MS can provide direct information and estimation in respect to the threshold of 5% w/w.

Furthermore, knowing the 6¹³C of the tested PET/FCM885 material, a regression analysis was performed in order to assess the mass fraction of contaminants in relation to their respective 6¹³C results (Figure 3). The results indicated an excellent linear relationship with R² higher than 0.99, indicating that the method can certainly be considered as a quality tool for their assessment. However, lower 6¹³C were observed for the vPET used (6¹³C = -40.3095) were higher than the values obtained from the industrial materials tested in Examples 2 and 3. These results were already explained in Example 2, where the increased temperature might lower the 6¹³C, as clearly indicated in Example 2. Considering that tested samples (11-15) were prepared by hot melting at 300°C for 20 min, under nitrogen atmosphere, indicated the potential effect to the initial material. However, in order to produce ad-hoc materials, the application of heating is unavoidable and therefore we consider the final results as valid.

Conclusion

The developed and applied methodology is capable to differentiate a given input PET material (vPET) containing up to 5% (and even with higher amounts) of another given polyester, (PBT), considering being contaminated at the threshold level. Therefore it is feasible not only the control of the output and quantification of the rPET content (% w/w mass fraction) but also for the input materials. The assessment and evaluation of the regulated input of 5% w/w of non-FCM application for PET mechanical recycling (EU 2022).

Summary of data

An EA-IR/MS method was developed and applied for the assessment of rPET content in plastic FCM applying statistical analysis and multivariate analysis. The effect of sample preparation (grinding) was assessed and proved to have an impact on the analysis.

Subsequently, the same methodology was applied for the analysis of raw vPET and rPET pellets was performed. Real FCM trays containing a different ratio of vPET/rPET and produced with different extrusion were tested and compared. Assessment and evaluation of the rPET is feasible, based on the EA-IR/MS method, although different regression models may be applied based on the production method (extrusion).

The same EA-IR/MS was applied to assess the regulated limit of 5 %w/w non-food FCM PET material , including non-PET. The method was assessed with other polyester such as PBT and proved to be efficient for differentiation and assessment of the input material. The preparation of the calibrant material proved to have an effect and shall be considered during the analysis. References

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Claims

1. A method for determining the amount of recycled polyester in a polyester containing material, the method comprising : a) providing a polyester containing material; b) determining the 6¹³C value preferably by EA-IR/MS, in the polyester containing material from step a); c) comparing said determined 6¹³C value to a corresponding polyester containing material reference table; and d) determining the amount of recycled polyester in the polyester containing material by comparing to the corresponding reference table.

2. The method according to claim 1, wherein in step a) the polyester is selected from the group consisting of polyethylene terephthlatate (PET), polybutylene terephthalate (PBT), polytrimethylene terephthalate (PTT), polyolefins, including low-density polyethylene (LDPE), high-density polyethylene (HDPE), polypropylene (PP) and polystyrene (PS), preferably the polyester is PET.

3. The method according to claim 1 or 2, wherein the polyester is PET.

4. The method according to any of the preceding claims, wherein in step a) the polyester containing product is selected from the group consisting of

5. The method according to any of the preceding claims, wherein in step a) the polyester is a food contact material (FCM).

6. The method according to any of claims 1-3, wherein in step a) the polyester is a textile selected from the group consisting of clothes, such as apparel, and footwear.

7. The method according to any of the preceding claims 1-5, wherein

• in step b) the 6¹³C value is determined by EA-IR/MS.

8. The method according to any of the preceding claims, wherein in step b) the 6¹³C value is determined by EA-IR/MS.

9. The method according to any of the preceding claims, wherein the reference table in step c) is a predetermined standard curve and/or regression model for a corresponding material, preferably produced by a mechanical recycling technology, such as a technology including extrusion, such as single-screw extrusion and twin-screw extrusion.

10. The method according to any of the preceding claims, wherein in step d) the predetermined reference level is a standard curve, such as a regression model, such as a linear regression model or a non-linear regression model, such as a polynomial regression model.

11. The method according to any of the preceding claims, wherein in step d) the amount of recycled polyester determined is the ratio of recycled polyester to virgin polyester or the percentage of recycled polyester in the material (by weight (% w/w; mass fraction).

12. Use of the 6¹³C value in a polyester material, preferably PET, preferably determined by EA-IR/MS, to determine the amount of recycled polyester material in the material.

13. A device or system adapted to determine the amount of recycled polyester in a polyester containing material, the device comprising: optionally, a homogenizer, such as a grinder or cutter, adapted to homogenize the polyester containing material, preferably at a low temperature, such as below the melting point temperature (Tm) of the polyester, such as below 260°C for PET or not exceed the glass transition (Tg) of the polyester material; a mass spectrometer, preferably a stable isotope mass spectrometer, EA- IR/MS; a processor configured with a reference table, said reference table corresponding to reference levels of a 6¹³C value of one or more polyester containing material and the processing/production method of the reference polyester containing materials; wherein the device or system is adapted to receive the polyester containing material, optionally via the optional homogenizer to homogenize said material; determine the 6¹³C value of the material by the mass spectrometer; comparing the determined 6¹³C value of the sample to the reference table; and determining the amount (% w/w; mass fraction) of recycled polyester within the sample by the processor.

14. A computer implemented method of determining an amount of recycled polyester in a polyester containing material, the method comprising: providing a 6¹³C value of a polyester containing material, providing a production method of the polyester containing material, providing a mathematical model comprising reference levels of 6¹³C within a corresponding polyester containing material, said reference levels being correlated with various production methods of said polyester containing material, determining the amount of recycled polyester in the polyester containing material by the mathematical model, providing the determined amount of recycled polyester in the polyester containing material to a system or a user.

15. A computer system comprising an input/output device and a processor, the system being enabled to execute the method according to claim 14 on the processor.