food-grade polyolefins have no rulebook

Problem statement

Europe recycles PET beverage bottles back into food-contact bottles at scale because PET is a "low-diffusive" polymer: contaminants from misuse (someone storing pesticide in a bottle) barely penetrate the wall and are removed by established super-clean processes that EFSA has evaluated in a long series of process-specific opinions. Polyolefins — HDPE milk jugs and closures, PP tubs and trays — are the largest plastic packaging stream by volume, but they are "high-diffusive": in EFSA's words, "the diffusivity in HDPE is much higher than in PET," so any contaminant a used container ever held migrates deep into the polymer, and any residue left after recycling migrates back out into the next food at far higher rates. When Starlinger submitted a process to recycle HDPE bottle caps collected with deposit-return PET bottles — about the cleanest polyolefin stream that exists — the CEP Panel found that decontamination efficiency was above 99.5 percent for small surrogate contaminants but only 20.2 percent for the 547 Da surrogate, noted "the limited efficiency of the technology to remove contaminants with a molecular weight above 400 Da," and concluded the applicant "has not demonstrated ... that the recycling process is able to reduce the contamination of the HDPE flakes ... to a concentration that does not pose a risk to human health." As Fraunhofer IVV's Welle wrote in 2025, "While there are evaluation criteria for mechanical PET recycling processes, no such evaluation criteria have been published for recycled HDPE caps in food contact." Welle's same 2025 paper argues that for the deposit-return cap stream specifically, worst-case criteria derived from other polymers put the required cleaning efficiencies "within a range that is technically feasible for today's mechanical HDPE recycling processes" — so the gap is at least as much the absence of agreed criteria as it is the physics. The unsolved problem is thus doubled: the physics makes polyolefins harder to clean and more prone to re-release, and the assessment framework that would tell a recycler what "clean enough" means has never been written for them.

Why this matters

The EU Packaging and Packaging Waste Regulation (Regulation (EU) 2025/40) sets minimum recycled-content targets from 2030 for plastic packaging, including contact-sensitive packaging made of polymers other than PET; without a route for post-consumer polyolefin recyclate into food contact, brands can meet those targets only with chemically recycled or mass-balance material — far more expensive and energy-intensive — or by shifting recyclate into non-food uses that are already saturated, which depresses rHDPE/rPP prices and the collection systems that depend on them. Only two kinds of polyolefin recyclate have cleared EFSA to date: material from "closed and controlled loops" (crates and drums that never left a documented food-industry circuit — e.g., the Morssinkhof Plastics and CAPEC crate processes) and, in principle, novel-technology submissions under Regulation (EU) 2022/1616. The mainstream household stream — HDPE bottles and PP tubs from kerbside collection — has no approved mechanical route at all. Every tonne is therefore capped at "one life in food, then downcycled," which is the opposite of the circular loop PET already runs.

What’s been tried and why it hasn’t worked

The PET playbook has been applied to HDPE and it strains at every joint. EFSA's evaluation logic starts from a reference contamination level of 3 mg/kg for misused PET; the Panel rejected Starlinger's proposal to use 0.5 mg/kg for closures and insisted on 3 mg/kg, and then, because HDPE diffusivity is higher, expected that "highest misuse contamination levels in washed HDPE" would match or exceed those in PET (2,000–6,750 mg/kg). Migration modelling used the Piringer/Hinrichs polyolefin diffusion models recognised in EU legislation and, for the infant scenario, arrived at a migration criterion of 0.034 µg/kg food — a target that demands decontamination efficiencies at the top of what solid-state processes can deliver. The challenge test used surrogates only up to 547 Da (TEHTM) where the Panel asked for coverage to 800 Da; the largest surrogate was barely removed and its concentration actually rose after the decontamination step, unexplained; the input-contamination screening covered "only 24 post-consumer samples ... not sufficiently well described to ensure their representativeness"; and up to 1 percent of the input closures were non-food, whose additives could contribute up to 10 mg/kg — none of which the applicant could resolve. Closed-loop crate approvals sidestep the problem by ruling out misuse through traceability rather than by cleaning, and so cannot be generalised to household waste. Welle's 2025 analysis argues that the required cleaning efficiencies for deposit-return caps "are within a range that is technically feasible for today's mechanical HDPE recycling processes" once evaluation criteria are derived from other polymers — but those criteria remain a proposal, and the applicant of record must still submit under the novel-technology route with no published benchmark. Solvent-based purification (dissolution/precipitation) can strip high-molecular-weight contaminants but adds cost that kerbside polyolefins, worth a fraction of rPET, struggle to bear.

What would unlock progress

Three things, in order of leverage: (1) published, polymer-specific evaluation criteria — surrogate sets, reference contamination levels, migration models and packaging-use scenarios — for HDPE and PP recyclate, so that recyclers know the target and regulators can compare processes; (2) decontamination steps that reach heavier contaminants (>400–800 Da) in a high-diffusivity matrix — longer solid-state residence at higher vacuum, supercritical or solvent-assisted extraction, or hybrid mechanical-solvent processes — proven at industrial not lab scale; and (3) input-stream segmentation, such as deposit-return caps or dedicated milk-jug collection, that lowers the realistic misuse-contamination assumption below the PET default. The adjacent precedent is the PET route itself, whose criteria (a 3 mg/kg reference contamination level, a standard surrogate set and default migration limits) took years to consolidate and then unlocked a steady stream of approvals; polyolefins need the same scaffolding, adjusted for their diffusivity, plus a compliant sensor-based screen (e.g., odour/VOC or spectroscopic) that can catch grossly contaminated flakes before they enter the melt.

Entry points for student teams

A chemistry/food-safety team could run a scaled-down challenge test on post-consumer HDPE caps: spike flakes with a surrogate ladder spanning 100–800 Da, apply a bench solid-state or extraction step, quantify residuals by GC-MS, and model migration into food simulants using published polyolefin diffusion coefficients — producing exactly the decontamination-vs-molecular-weight curve EFSA found missing. A regulatory-science team could draft the missing evaluation criteria for rHDPE closures by comparing EFSA's PET guidance, the Starlinger opinion and Welle 2025, then stress-test them against worst-case use scenarios (infants, fatty foods, long shelf life). An engineering team could survey what contaminants actually occur in deposit-return caps versus kerbside HDPE (screening 100+ samples), addressing the representativeness gap the Panel flagged. Relevant skills: analytical chemistry, polymer diffusion modelling, food-contact regulation, process engineering.