INTRODUCTION
Disposable packaging materials (DPMs) are typically single use items and commonly used for enclosing or protecting food products during storage, sale, delivery and for the regular use mainly at restaurants (Tallentire and Steubing Reference Tallentire and Steubing2020). For packaging applications, a variety of materials are used, comprising plastic, bioplastics, paper or pulp-based products, metal, wood, glass, and a variety of composites made from multiple elements(Davis and Song Reference Davis and Song2006). In Europe, from 2009 to 2019, paper and cardboard (32.3 million tons in 2019) were the main packaging material followed by plastic (15.4 million tons in 2019) and glass (15.2 million tons in 2019) (Eurostate 2022). The aim of this paper closely falls within the European waste Directive (EU) 2018/852, which intends to harmonize national measures for packaging and waste management policies in order to prevent environmental impacts (Davis and Song Reference Davis and Song2006; Directive2018/852(EU)).
Reuse and recycling are the two most crucial techniques in the development of the circular economy (Di Foggia and Beccarello Reference Di Foggia and Beccarello2022). In Europe the recovery in total waste treatment increased significantly from 46% in 2004 to 60% in 2020 (39% for recycling, 15% for backfilling, and 6% for energy recovery), whereas the disposal in total waste treatment decreased from 54% in 2004 to 45% in 2020 (Eurostate 2020).
Regarding energy use, greenhouse gas emissions, and their contribution to an increase in trash, plastic food packaging has an impact on the environment (Jeżewska-Zychowicz and Jeznach Reference Jeżewska-Zychowicz and Jeznach2015). Biodegradable polymers have become the topic of current research due to their potential biodegradability and nontoxicity, but still there is a long way to go in order to overcome the global plastic pollution through biodegradable plastics (Shen et al. Reference Shen, Song, Zeng, Zhang, Huang, Wen and Tang2020). Growing emphasis has been paid in recent years, especially in European (EU) members, to the development of biodegradable packaging materials made from renewable natural resources (mainly from corn and sugarcane) in order to contribute for sustainable development and also can reduce environmental impact upon disposal, if managed properly (Davis and Song Reference Davis and Song2006).
Green packaging is the one of the main aspects of green logistics activity, which aimed to minimize resource utilization and environmental pollution. Green packaging is being developed to make packages that are lightweight, recyclable, reusable, and biodegradable and to prohibit the use of non-ecological products (Zhang and Zhao Reference Zhang and Zhao2012).
By using agro-industrial plants products and by-products to produce biodegradable packaging can be turned into goods with a high added value while using less conventional nonrenewable packaging. The pandemic scenario increased the food packaging market (Barone et al. Reference Barone, Matheus, de Souza, Moreira and Fai2021).
According to Directive2018/852(EU), bio-based recyclable packaging and compostable biodegradable packaging could be a way to promote renewable sources for packaging production. DPMs prepared from sugarcane or paper can be a source of valuable resources and can overcome the plastic problem. Sugarcane plates are made from renewable sugarcane pulp so the compositing takeaway packaging minimizes the greenhouse gas emissions and improves the soil quality (APSnet 2022). Production or recycling of DPMs in industries causes CO2 emission, which is seen as a global hazardous because of its properties like greenhouse gas. CO2 emission can be reduce by the use of renewable (biogenic/bio-based) resources (Rodin et al. Reference Rodin, Lindorfer, Böhm and Vieira2020). New paper production from waste paper requires less energy and emits less amount of greenhouse gases than producing the same amount of paper from virgin materials, thus the recycling of waste paper could be beneficial to the environment (Merrild et al. Reference Merrild, Damgaard and Christensen2008). Recycling of about 1 ton of paper can save slightly more than 2 tons of wood. The energy information administration that 40% reduction in energy paper is produced by paper recycling verses paper production by unrecycled pulp, while the Bureau of International Recycling (BIR) claims a 64% reduction (WKPD). Radiocarbon analysis can distinguish between fossil and bio-based carbon by detecting 14C/12C isotope ratio in the sample (Haverly et al. Reference Haverly, Fenwick, Patterson and Slade2019; Gill et al. Reference Gill, Michczyńska, Michczyński, Piotrowska, Kłusek, Końska, Wróblewski, Nadeau and Seiler2022). After about 50,000 years, samples do not contain 14C isotope, as its half-life is 5700 years (Kutschera Reference Kutschera2019). Several methods have been used to determine the biocomponent content in different materials, but the radiocarbon method is known to distinguish between carbonaceous material of fossil and biological origin (Krajcar Bronić et al. Reference Krajcar Bronić, Barešić, Horvatinčić and Sironić2017). Many studies have been done to check the renewability in different kinds of materials in terms of biogenic carbon determination. Stable carbon isotope ratio measurements have proved to be an acceptable method of distinguishing between C4 plant plastics and petroleum plastics (Santos et al. Reference Santos, Macario, Jou, Oliveira, Cardoso, Diaz, Anjos and Alves2019). Quarta et al. (Reference Quarta, Calcagnile, Giffoni, Braione and D’Elia2013) determined biobased content in plastic (polyester resins). Ploykrathok and Chanyotha (Reference Ploykrathok and Chanyotha2017), Santos et al. (Reference Santos, Macario, Jou, Oliveira, Cardoso, Diaz, Anjos and Alves2019), and Telloli et al. (Reference Telloli, Rizzo, Canducci and Bartolomei2019) measured biogenic carbon fraction in plastic materials, and Huels et al. (Reference Huels, Pensold and Pigorsch2017) and Pigorsch et al. (Reference Pigorsch, Kiessler and Hüls2022) analyzed paper materials.
In this paper 14C isotope concentration in DPMs was monitored, to make sure if indeed, the materials contain some concentration of biogenic carbon to cause a green effect in recycling.
MATERIALS AND METHODS
In this study we examine 10 different kinds of DPMs, which include paper, wood, sugarcane, and wheat bran type materials. Samples were collected from different packaging production companies in order to investigate different varieties of typical packages: paper cups, plates, straws, food boxes, and also baking paper, wheat bran plates, and wooden cutlery.
14C Analysis by AMS
All of the samples were prepared and analyzed at Gliwice 14C and Mass Spectrometry Laboratory in Institute of Physics – Centre for Science and Education, Division of Geochronology and Environment Isotopes. A VarioMicroCube Elemental Analyzer (EA) coupled to an AGE-3 graphitization system by IonPlus AG was used for the determination of total carbon content in samples and for graphitization, as it is the efficient, fast and convenient sample preparations for radiocarbon measurement (Wacker et al. Reference Wacker, Němec and Bourquin2010b). Tin boat capsules were used with ∼4 mg of sample. CO2 is produced by the sample combustion with the Elemental Analyzer, and Automated Graphitization Equipment (AGE) produces graphite by reducing this CO2 with H2 on iron powder. The obtained graphite is pressed into the target holders (cathodes), two times at a pressure of 4 bar for the proper pressing. A Cu pin is used to seal the graphite.
MICADAS accelerator mass spectrometer was used for 14C concentration measurements (Synal et al. Reference Synal, Stocker and Suter2007) and BATS software for calculations of 14C concentration (Wacker et al. Reference Wacker, Christl and Synal2010a). Oxalic Acid II was used as standard. Anthracite, phthalic acid, and fossil fuel were used as backgrounds.
For DPMs, no chemical pretreatments were used for AMS measurements. Only small masses of the tested material are used for AMS measurements, which in the case of samples with complex structures may be a source of non-representative results if only one subsample is selected for measurements. Therefore, two batches of samples were analyzed. In the first batch, a small subsample was taken from a random place in the case of each sample, whereas in the second batch, different layers of samples were tested. Other than baking paper and wooden cutlery, all DPMs samples are taken as outer layer, inner layer, mixture of outer and inner layer. In case of paper cup samples, three AMS measurements were performed for each of the tested layers to check the consistency of the results. The measurements for the thin outer layer which potentially contains plastic seemed particularly interesting. In the case of baking paper, only two types of subsamples were analyzed, including the original form (two random subsamples) and carbonized form. In the case of wooden cutlery, samples from the fork, knife, their mixture, were analyzed. We examine the different subsamples to test whether plastic or bioplastic was used to make the waterproof layer.
Due to the different weight ratio of the possible plastic or bioplastic layer to the inner layer, depending on the sampling site, small samples may not be representative. In order to avoid the influence of different mass proportions of the waterproof layer and the inner paper layer, and its effect on the results of 14C concentration measurements, samples need to be homogenized. Mechanical homogenization of samples can be time-consuming. The best solution would be to combust a larger mass of the sample in vacuum conditions in the presence of reagents (Ag and CuO), and then convert the resulting CO2 into graphite. This is typical solution used for small samples in AMS laboratories. Due to the lack of dedicated vacuum line for combustion larger masses of samples, it was decided to test applicability of carbonization with limited oxygen available. Carbonization of large mass (∼24 g) of samples was carried out in a metal reactor with a small hole in the lid, minimizing the access of air, in a muffle furnace at a temperature of 700°C for 7 to 10 minutes and grinded into powder form after cooling.
RESULTS
14C concentration results of DPMs from AMS laboratory (with lab code GdA) are listed in supplement. 14C concentration in samples is reported as percent modern carbon (pMC), according to (Stuiver and Polach Reference Stuiver and Polach1977). Total carbon concentration data is obtained by combusting samples in EA with different masses in three experiments, mean of the three values are provided in Supplementary Material.
DISCUSSION
Determination of 14C concentration in disposable packaging was conducted. Supplement represents the total carbon content, 14C concentrations, and δ13C of each sample. It should be noted that the given δ13C values are values measured using the AMS method and therefore also take into account the isotopic fractionation that takes place during the measurement. Figure 1 presents the graphical view of pMC values with uncertainties.
Comparison of the 14C isotope measurements (see Supplementary Material).
All samples gave a mean of 14C concentration higher than 100 pMC, which means the samples are modern thus the recycling of such samples will be a green recycling. All DPMs from paper material gives 14C concentration between 100–112 pMC in random subsamples, corresponding to the 14C concentration in packaging paper reported in (Huels et al. Reference Huels, Pensold and Pigorsch2017; Pigorsch et al. Reference Pigorsch, Kiessler and Hüls2022).
It is well visible that for samples of sugarcane plates (QSCP-1) and boxes (BSCB-9), paper plates (QPP-5, QBPP-7 and BPP-10), backing paper (QBP-3), and wheat bran plates (VWBP-8), the 14C concentration values for small subsamples are consistent within a single or double uncertainty. This agreement is confirmed by the results of the chi-square test presented in Table 1, and for these samples, the weighted mean, as a measure of the 14C isotope content in the whole tested sample, can be calculated. The remaining three tested packages (QPC-2, QPS-4, QWC-6) are characterized by a large dispersion of results. This can be a result of the non-homogeneity of the samples. We selected one of these samples, namely QPC-2, to test which layer was causing the scatter. For that sample, we performed three measurements for the outer layer, the inner layer and the mixed outer and inner layers (see Supplement).
Results of testing the consistency of received results. A) testing the consistency of small subsamples (random, inner layer, outer layer, and mixed) results by meaning of chi-square (χ2) test. Critical χ2 values for confidence level α = 0.05 and for 4 measurements = 7.81, for 3 measurements = 5.99, and for 2 measurements = 3.84. For consistent results weighted mean was calculated. B) testing the consistency of weighted mean for small subsamples and result for large (carbonized) sample by meaning of t-test.
The sample QPC-2 was a paper cup, coated with waterproof material in outer most part (both sides) with a thin inner layer. The 14C concentration from the outer layer are varied between 93.95 ± 0.28 and 105.46 ± 0.33 pMC showing non-homogeneity of this layer. These values are much lower than for the inner layer. Similar, lowered pMC values in plastic packaging materials are reported in Ploykrathok and Chanyotha Reference Ploykrathok and Chanyotha2017; Santos et al. Reference Santos, Macario, Jou, Oliveira, Cardoso, Diaz, Anjos and Alves2019; Telloli et al. Reference Telloli, Rizzo, Canducci and Bartolomei2019.
Measurements for the inner layer are highly consistent, and weighted mean for this layer is equal to 114.54 ± 0.19 pMC. The mixture of outer and inner layer subsamples gives 14C concentration from the value range 106.07 ± 0.30 - 108.37 ± 0.34 pMC, which is consistent with the average value calculated from results of outer and inner layers (106.79 ± 0.32 pMC). The sample with lab code of GdA-6806.1.1 (random sample) yielded 14C concentration of 100.61 ± 0.34 pMC. As random sample was taken directly without selecting any layer so the decreased 14C concentration could be the result of the bigger proportion of outer to the inner layer in it. The carbonized sample yielded 113.7 ± 0.36 pMC. This value is between the extremes obtained for the small subsamples. It may therefore represent a realistic average value for the concentration of 14C in the total sample.
For sample QPS-4, there is visible high variation in 14C concentrations for all subsamples. The sample was from the paper straws, composed of thick waterproof layer and a thin paper layer. The 14C concentration from the outer layer is 100.04 ± 0.33 pMC which is little lower than the 14C concentration from the inner thin layer i.e., 101.47 ± 0.33 pMC. The mixed layers sample yielded the lowest 14C concentration i.e., 98.21 ± 0.33 pMC. This indicates that the sample material is highly inhomogeneous. Carbonized sample gave a measurement result 108.46 ± 0.35 pMC. Even the highest 14C concentration for small subsample GdA-6808.1.1 (random sample) is far away from such result. The hypothesis that the lighter carbon isotopes may have been preferentially removed as a gas fraction during the carbonization procedure and that this was not sufficiently corrected by the measurement of the δ13C can be considered in this situation. However, the results for six samples: QSCP-1, QBP-3, QPP-5, VWBP-8, BSCB-9, and BPP-10 contradict such a hypothesis. This suggest the selected small subsamples were not representative of the packaging tested.
For sample QWC-6, the subsamples were from the wooden cutlery in knife and fork forms. The 14C concentrations for the fork, knife, mixed form of fork and knife, random and carbonized samples, are high and coming from the range 136.53 ± 0.42 to 114.72 ± 0.37 pMC. We got quite different 14C concentrations for each subsample, as the samples are not prepared only from a single tree which significantly affect the 14C concentrations. According to (Krajcar Bronić et al. Reference Krajcar Bronić, Barešić and Horvatinčić2015) if wooden products are produced from wood grown in the second half of the 20th century, 14C activities may vary between 105 and 190 pMC depending on the year of growth.
For sample QBPP-7, there is a little variation in 14C concentrations for all subsamples. The sample was from the brown paper plates, composed of waterproof layer and inner paper layer. All subsamples other than carbonized give the 14C concentrations between 107.22 ± 0.36 pMC and 108.35 ± 0.35, whereas for carbonized sample is 109.63 ± 0.28 pMC. Thus, the situation for this material is analogous to that for sample QPS-4.
Admittedly, measurements of the δ13C at AMS do not correctly reflect its value in the samples, but they do make it possible to observe certain trends. For carbonized samples we received the lowest δ13C values as during carbonization the lighter isotopes of carbon evacuated from the sample with other gases. δ13C values for QSCP-1 and BSCB-9 samples are the highest (between –13‰ to –18‰) as the samples are from sugarcane material, the values are in the range of δ13C values measured in sugarcane-based plastic bags (Santos et al. Reference Santos, Macario, Jou, Oliveira, Cardoso, Diaz, Anjos and Alves2019).
Instead of carbonization complete combustion would be a better way of homogenization. Such combustion of the samples carried in a vacuum line with the ability to control the temperature rise and combustion time and using (Quarta et al. Reference Quarta, Calcagnile, Giffoni, Braione and D’Elia2013) would be necessary. It would prevent light carbon loss and reduce isotope fractionation which we observe in the case of carbonization.
One more thing to be noted here, the outer surface of three samples: QPC-2, QPS-4 and QBPP-7 was more waterproof and greasy as compared to the rest of the samples.
CONCLUSIONS
the AMS 14C technique was tested in Gliwice 14C and Mass Spectrometry Laboratory for the determination of 14C concentration in disposable samples. The research was carried out on paper, wheat bran, sugarcane, and wooden materials from different production companies.
According to the current, post-bomb changes in 14C concentrations in the biosphere, the highest 14C concentration values could be expected for samples made from wood, followed by samples containing paper (produced from wood and/or recycled). In contrast, the lowest concentrations should yield materials from current plant crops. The results obtained are as expected. The highest values were obtained for sample QWC-6 (wooden cutlery) and the lowest for sugarcane (QSCP-1, BPP-10) and wheat bran (VWBP-8) products. Paper packaging gives intermediate results.
All samples turned out to be contemporary. The mean concentration of the 14C isotope for all samples is above 100 pMC, indicating that the disposables tested were produced from modern biomass. Relatively high 14C concentrations for the outer (waterproof) layer indicate that bioplastic was used. However, in the case of paper cups, one of the subsamples gave the lowest measured results, which may indicate a small addition of ordinary plastic. Significant differences and high 14C concentrations in the wooden samples indicate the production of samples from different trees with different ages.
Four packaging samples tested are characterized by a large scatter in the results of 14C isotope concentration measurements. This demonstrates the need to homogenize a larger volume of samples, since a sample selected for analysis from a random part may not be representative. Such homogenization may be particularly important when determining the biomass content of material used for co-firing in energy production.
Simple carbonization is not an appropriate way for the homogenization of sample although 6 of the 10 packaging types tested, the results obtained for the large sample subjected to simple carbonization are in agreement with the results for the small subsamples. The results are promising, but further comparative studies with a specially designed line and carbonization of samples in an oxygen-free atmosphere are needed to conclusively answer the question of whether carbonizing a sample can be a good way for homogenization.
ACKNOWLEDGMENTS
The research work was supported under the Rector’s pro-quality grants, Silesian University of Technology, no 14/020/RGJ22/0019 and 14/020/SDU/10-05-01 and young scientists’ competition BKM-707/RIF2/2022.
Supplementary material
To view supplementary material for this article, please visit https://doi.org/10.1017/RDC.2024.35
