In the ambition to reduce plastic waste, by 2025 at least 55% of plastic packaging should be recycled in the EU (FPF reported). In September 2022, the European Commission officially adopted the new regulation on recycled plastic materials and articles intended to come into contact with food, (EU) 2022/1616, which came into effect in October 2022 (FPF reported). The Food Packaging Forum (FPF) commented on the draft with concerns about the chemical safety of recycled packaging (FPF reported). Accordingly, during the recycling of plastic waste into new products known hazardous or unknown chemicals may be carried from the previous into the new product (FPF reported, also here and here).
Due to the number of chemicals present in the material, up to date, high-density polyethylene (HDPE) has not yet been recycled successfully in applications with food contact. In an article published on January 11, 2023, in the journal Food Packaging and Shelf Life, Paula Vera from the University of Zaragoza, Spain, and co-authors analyzed the chemicals migrating from post-consumer HDPE milk bottles. Therefore, the authors first optimized an analytical method based on solid-phase microextraction (SPME) gas chromatography-mass spectrometry (GC-MS) which they then applied in the untargeted assessment and quantification of volatile chemicals in the migrates. They investigated two types of plastic containers made from post-consumer HDPE milk bottle flakes obtained from two European plastic cycling companies. They subjected the two products to migration experiments following the Commission Regulation (EU) 10/2011 using 50% ethanol as a food simulant as well as skimmed milk, soy milk, and horchata (i.e., beverages, which are generally plant-based, but sometimes contain animal milk) as real milk products.
In 50% ethanol, the authors detected a total of 53 chemicals of which 49 migrated from both containers, and 16 could be identified and verified with their standards. The compounds included several common plastic additives, such as antioxidants (e.g., butylated hydroxytoluene, CAS 128-37-0), UV filters (e.g., benzophenone, CAS 119-61-9), and plasticizers (e.g., dibutyl phthalate, CAS 99 84-74-2), as well as non-intentionally added substances (NIAS) such as 2,4-di-tert-butylphenol (CAS 96-76-4) and 7,9-di-tert-butyl-1-oxaspiro(4,5)deca-6,9-diene-2,8-dione (CAS 82304-66-3). Degradation products of antioxidant compounds, residues from cleaning products, detergents, and flavoring agents were also detected. In contrast, only eight chemicals were found to migrate into the real milk products. Since migration experiments into real milk were performed at lower temperatures (6 °C) compared to those into ethanol (60 °C), the authors assumed temperature to affect the compounds’ migration.
Vera and co-authors also performed a risk assessment. Here they reported that only six of the 53 migrating compounds were included in the Commission Regulation (EU) 10/2011. One of the six, 1-dodecane (CAS 112-41-4), migrated in concentrations of 615 ± 36 and 2630 ± 382 ng/g, respectively for the two containers, hereby greatly exceeding its specific migration limit (SML) of 50 ng/g. To classify the toxicity of the remaining chemicals, the scientists used Cramer classes. “Four compounds were above the migration values recommended by Cramer in the simulant 50 % ethanol, but this was not the case in milk and vegetable beverages products.”
On top of the potentially hazardous chemicals present in the material the odor of recycled HDPE may also hinder adoption. HDPE has a high chemical sorption capacity and can adsorb food flavors or the odors from cleaning agents used in recycling processes. In an article published on January 11, 2023, in the journal Polymer Degradation and Stability, Shao-Fu Zeng and co-authors from Jinan University, Guangdong, China, analyzed the changes in odor and volatile organic compounds upon mechanical recycling of HDPE.
The researchers investigated six virgin HDPE pellets, 15 recycled HDPE flakes obtained by crushing, washing, and drying in mechanical recycling, as well as 19 recycled pellets obtained by re-granulation and extrusion in the process. They used E-nose an electronic device mimicking human olfactory perception, headspace-gas chromatography-ion mobility spectrometry (HS-GC-IMS), and HS-GC-MS to assess volatile compounds. The scientists also evaluated the contribution of each volatile substance to the sample’s overall odor by calculating the relative odor activity values (ROAV).
Zeng and co-authors reported that HS-GC-IMS allowed distinguishing the recycled from the virgin HDPE samples based on the different profiles of volatile organic compounds. In the recycled materials terpenes and aliphatic hydrocarbons were present in higher amounts. According to the researchers, “the sources of the volatile organic compounds in recycled HDPE may be the contamination of post-consumer bottles and their thermal oxidative degradation.” Moreover, it was found that the re-granulation process from flakes to pellets removed most of the volatile organic compounds. However, aromatic hydrocarbons, terpenes, and some acids were still present in the pellets. Concerning ROAV, the results showed that d-limonene (CAS 138-86-3) and octanal (CAS 124-13-0) contributed the most to the overall odor of recycled pellets.
The authors think that “the process of mechanical recycling is required to be better optimized to remove the volatile organic compounds from the odorants” to increase the use of recycled HDPE. According to industry association reports published in 2022, in Europe, plastic recycling has not increased substantially over the last years and two-thirds of plastic-packaging pledges from food and drink companies failed (FPF reported).
References
Vera, P. et al. (2022). “Migration of volatile substances from recycled high density polyethylene to milk products.” Food Packaging and Shelf Life. DOI: 10.1016/j.fpsl.2022.101020
Zeng, S.-F. et al. (2022). “Characterization of odors and volatile organic compounds changes to recycled high-density polyethylene through mechanical recycling.” Polymer Degradation and Stability. DOI: 10.1016/j.polymdegradstab.2023.110263
