In a series of three articles published in the peer-reviewed journal Packaging Technology and Science, scientists from the Wageningen Food & Biobased Research, Biobased Products Business Unit, Wageningen, The Netherlands, examined the influence of recycled polyethylene terephthalate (rPET) quality and levels of recycled content on the properties of PET bottles.
In Part I, published on January 12, 2020, optical and mechanical properties, including haziness, color parameters, environmental stress cracking, and particle contamination were systematically studied in PET bottles containing 25-100% rPET of three different quality types. Particle contamination was studied by “dissolving bottle fragments and counting the insoluble particles.” Higher levels of particle contamination were found in rPET compared with virgin PET, as well as in rPET originating from co-collection systems compared with rPET from mono-collection systems. Particle contamination in turn directly correlated with the haziness and color parameters of PET bottles. The authors noted that “the acceptance of a hazy bottle depends on the color of the beverage and the marketing strategy of beverage company. Haziness could be more accepted by the consumers if they are aware that it indicates the use of recycled content in the bottles. Color and haze are marketing aspects and are not always regarded negatively.” In addition, some color parameters can be “largely influenced with additives.” The occurrence of environmental stress cracking did not correlate with the presence of rPET but was influenced by rPET processing parameters, and particularly by internal viscosity, which “can be ‘tuned’ during rPET production,” the authors explained.
In Part II, published on August 3, 2020, migration data is presented. The authors summarized that “the migrated amounts of acetaldehyde [(CAS 75-07-0)] and ethylene glycol [(CAS 107-21-1)] complied with the limits given in the food contact material (FCM) legislation.” The condensation product of acetaldehyde and ethylene glycol, 2-methyl-1,3-dioxolane (CAS 497-26-7), migrated at concentrations “below the limit of 10 µg/L, which is conventionally applied for non-intentionally added substances (NIAS) not classified as ‘carcinogenic’, mutagenic’ or ‘toxic to reproduction’ (CMR).” Other detected migrants included limonene (CAS 138-86-3), acetone (CAS 67-64-1), butanone (CAS 78-93-3), furan (CAS 110-00-9), benzene (CAS 71-43-2), and styrene (CAS 100-42-5). The authors explained that limonene is a “natural fragrant,” while acetone and butanone are “probably residues from solvents used to clean and protect the mold at the small-scale production facility.” Furan could originate from “various organic impurities,” since this substance is “a known pyrolysis product of biomass and is produced in thermally treated food products.” Benzene and styrene were also suggested to “originate from heat-induced reactions within the PET matrix, which involve contaminants.” The formation of benzene in particular could be “attributed to polyvinylchloride as contaminant,” while styrene “could originate from the thermal degradation of polystyrene, which is present as a polymeric contaminant in lower qualities PET.” Migrated amounts of benzene were characterized as “relatively small” and estimated to represent “a low priority for risk management.” As for the other NIAS, the authors concluded that “depending on the underlying data and exposure scenario, different threshold limits in the food can be derived which can still be considered safe.” However, because “risk assessments . . . can be based on multiple exposure scenarios and hence yield different outcomes,” it appears necessary to conduct a “further risk assessment” before recommendations for a maximum level of recycled content can be made for rPET-containing bottles. The authors further outlined two strategies which could help mitigate the risk of “benzene and other NIAS in rPET,” namely “reducing the chlorine concentration in the rPET and limiting the exposure time to elevated temperatures during injection molding and bottle blowing processing to a [minimum].”
In Part III, published on August 3, 2020, the modeling results for repetitive recycling scenarios are presented. The authors analyzed the contaminants present in pellets and bottles at different steps of the recycling loop and proposed a model “to generically describe the accumulation of these contaminants within closed-loop recycling schemes for PET bottles.” The type of collection system was found to “greatly” influence the accumulation of contaminants in PET bottles, as bottles from mono-collection systems had fewer contaminants than bottles from co-collection systems. Therefore, the authors concluded that “PET bottles within recycling schemes using mono-collection systems can contain more recycled content than those from co-collection systems, without exceeding acceptation limits on critical bottle properties such as haziness, yellowing, and migration.” The allowed levels of recycled content can be calculated using the proposed model.
Chacon, F.A., et al. (2020). “Effect of recycled content and rPET quality on the properties of PET bottles, part I: Optical and mechanical properties.” Packaging Technology and Science DOI: 10.1002/pts.2490
Thoden van Velzen, E.U., et al. (2020). “Effect of recycled content and rPET quality on the properties of PET bottles, part II: Migration.” Packaging Technology and Science DOI: 10.1002/pts.2528
Brower, M.T., et al. (2020). “Effect of recycled content and rPET quality on the properties of PET bottles, part III: Modelling of repetitive recycling.” Packaging Technology and Science DOI: 10.1002/pts.2489.