Decontamination efficiencies of post-consumer high-density polyethylene milk bottles and prioritization of high concern volatile migrants

High-density polyethylene (HDPE) milk bottles are well-distinguished from other plastics in the mix-collected plastic waste and have potential to be closed-loop recycled. To evaluate this option, volatile substances present in various recycled HDPE (rHDPE) pellets and flakes from postconsumer milk bottles were analysed for similarities between different industrial recycling companies and batches. All substances found were classified in five different levels based on toxicity, from level I to level V (high toxicity). Chemicals present in the samples from different recyclers varied considerably, while those from different batches of a given recycler gave similar results. However, the study of rHDPE stream mixed with high volume of non-milk-bottles provided significant differences between batches. Washing the rHDPE twice and applying extra decontamination techniques reduced to a half the intensities for most chemicals detected, including two toxicity level V substances, butylated hydroxytoluene and diethyl phthalate. Nevertheless, other two high concern compounds, octocrylene, and 2-ethylhexyl-4-methoxycinnamate were not significantly reduced and thus deserve special attention when decontaminating rHDPE and evaluating its feasibility for food contact uses. Extra decontamination was able to reduce the intensities of 1-dodecene and 1-tetradecene. In total, 265 substances were detected in migration tests (95% ethanol and 3% acetic acid) and 58 of them were prioritized by toxicity. Regarding volatile migrants, rHDPE with low content of non-milk-bottle could be safe for direct contact with low-fat content food. For high-fat foods, the main concerns could come from 1-tetradecene, octocrylene, and 2-ethylhexyl-4-methoxycinnamate.

Automated summary

Analysis was conducted on volatile substances in recycled HDPE pellets and flakes from postconsumer milk bottles, showing variations in chemicals among different recyclers but consistency within batches from the same recycler. Double washing and additional decontamination techniques reduced intensities of most chemicals detected, with particular attention needed for certain compounds like octocrylene and 2-ethylhexyl-4-methoxycinnamate. Migration tests revealed 265 substances, with concern raised for 58 based on toxicity, suggesting that rHDPE with low non-milk-bottle content could be safe for direct contact with low-fat food while caution should be taken for high-fat food due to specific compounds like 1-tetradecene, octocrylene, and 2-ethylhexyl-4-methoxycinnamate.