Migration Testing for Polyethylene: What Food-Contact Approval Really Requires

Food-contact approval for polyethylene (PE) is not an intrinsic property of the resin. Under 21 CFR 177.1520 and Regulation (EU) No 10/2011, the finished article must be evaluated for total or specific migration under conditions that simulate the intended food contact. The binding overall migration limit for general food-contact plastics under Article 12 of Regulation (EU) No 10/2011 is 10 mg/dm² of contact surface, except for materials intended for infants and young children where the limit is expressed as 60 mg/kg food simulant. The U.S. system uses a different control: olefin polymer extractives in hot n-hexane, specified in 21 CFR 177.1520(c). A PE grade can therefore be compliant in one jurisdiction and non-compliant in another if the density, melt-flow category, additive package, processing history, or article geometry differs from the tested condition.

This distinction matters because migration from PE is dominated by low-molecular-weight oligomers, process aids, antioxidant degradation products, and intentionally added slip and antistatic agents. A high-density polyethylene closure injection-moulded from a pellet with a melt mass-flow rate of 4.0 g/10 min at 190 °C under a 2.16 kg load may show low overall migration in aqueous simulant, but the same formulation blown into a 0.025 mm film can release a higher specific migration of a slip additive per unit mass of food because surface-to-volume ratio increases and thickness-controlled diffusion dominates. Migration testing therefore begins with resin characterisation and ends with finished-article exposure geometry, not a single material certificate.

What Limits Apply to Polyethylene Beyond the Base Polymer?

Under Regulation (EU) No 10/2011, ethylene monomer is listed in Annex I, but approval requires all additives, co-monomers, and starting substances to be authorised and, where applicable, tested against specific migration limits. Typical PE concentrates contain a hindered phenolic primary antioxidant at 300–1,000 mg/kg, an organophosphite secondary antioxidant at 500–1,500 mg/kg, a primary amide slip additive at 500–1,200 mg/kg, and an inorganic acid scavenger such as hydrotalcite or zinc stearate at 500–1,000 mg/kg. Each substance carries an SML under Annex I or II, and the compliance documentation must identify the chemical by CAS number together with the measured migration under the assigned simulant.

Specific migration methods for polyethylene are selected under EN 13130-1 and EN 13130-2, with detection by gas chromatography or liquid chromatography. Because many slip agents and antioxidants are polar or semi-volatile, the test temperature and simulant polarity become decisive. A PE film exposed to 10 % ethanol simulant A at 40 °C for 10 days will typically underestimate the migration of non-polar erucamide compared with 50 % ethanol simulant D1 or vegetable oil. This is not a failure of the resin; it is an analytical consequence of partition coefficients, simulant swelling, and diffusion path length. In practice, migration testing for PE approval is therefore a matrix of simulant-specific and article-specific measurements, supplemented by GC-MS screening for non-intentionally added substances formed during extrusion.

For U.S. olefin polymer clearances, the controlling analysis is not a food-simulant migration test but an extraction of the base polymer. Under 21 CFR 177.1520(c), polyethylene is extracted with n-hexane for 2 h at 50 °C, and the maximum extractable fraction is 2.6 % or 5.5 % depending on the melt-flow and density category assigned in the regulation. Melt index is measured at 190 °C with a 2.16 kg load per ASTM D1238 or ISO 1133-1:2022; density is measured per ASTM D1505 or ISO 1183-1:2019. This extraction test is a polymer-purity screen for wax, oligomer, and loosely attached additive, not a substitute for EU overall migration. A converter may also need to secure separate food-contact clearance for every colorant, slip masterbatch, or processing aid added during compounding, because the base olefin polymer clearance does not automatically cover those ancillary components.

When Vegetable Oil or Tenax Absorption Changes the Gravimetric Meaning of Overall Migration

Fatty simulants introduce a measurement artifact because low-density polyethylene absorbs oil into the amorphous phase. In total immersion tests according to EN 1186-2, the oil absorbed into a plaque must be extracted and quantified separately; otherwise the apparent overall migration can be too low or too high depending on whether oil is lost with the residue or retained in the polymer. The effect is more severe for low-crystallinity PE, for thin films, and for testing at 70 °C or above. Extraction corrections use diethyl ether and saponification of triglycerides; repeatability is controlled by EN 1186-2, but the corrected gravimetric value can still be affected by residual unsaponifiables from the test oil. Differential scanning calorimetry per ISO 11357-3 can quantify PE crystallinity and assist in interpreting oil absorption risk.

Tenax MPO, poly(2,6-diphenyl-p-phenylene oxide), avoids oil absorption because it is a solid adsorbent. EN 1186-5 and EN 1186-8 configure the test as a pouch or article filling; the Tenax is extracted and the residue is determined gravimetrically. This approach is preferred for dry and fatty foods at high temperatures where vegetable oil would penetrate the PE and make gravimetric correction unreliable. However, Tenax is not a perfect simulant for all fatty foods; its adsorption behaviour for low-volatility silicone oils or high-molecular-weight migrants can differ from lipid partitioning. Published migration data for PE-specific high-molecular-weight migrants in Tenax remains limited.

On a production blown-film line, migration-relevant residuals are not controlled by the resin supplier alone. A 55 mm grooved-feed single-screw extruder with a 30:1 L/D barrel and melt temperature of 215 °C may impose sufficient thermal residence time to consume the phosphite antioxidant and generate phosphate ester hydrolysis products. When the same resin is processed on a lower-shear extruder, the resulting film can differ in the specific migration of degradation products by an analytically significant margin. The converter must therefore validate the worst-case processing condition, not the resin supplier’s laboratory plaque. Batch-to-batch variation in catalyst residues, comonomer distribution, and additive metering can also shift extractables; a change from 0.920 g/cm³ to 0.918 g/cm³ LLDPE should trigger a review of the migration data and, where required, new Declaration of Compliance documentation under Article 16 of Regulation (EU) No 10/2011.

Documents and Test Designations That a Compliance File Must Contain

A defensible polyethylene food-contact file links the resin specification to the finished article, the intended food type, and the migration test methods. The presence of a supplier declaration is insufficient if it does not state the density class, melt-flow rate, additive package, article thickness, contact surface-to-volume ratio, and the test designation used for overall or specific migration. Under Regulation (EU) No 10/2011, supporting documents must permit official verification of the Declaration of Compliance; under the U.S. scheme, the file should identify the specific olefin polymer clearance and any additional food-contact notifications or threshold-of-regulation exemptions for additives.

Test failures in polyethylene rarely occur as gross OML exceedances; they occur as specific migration of a slip additive, an unexplained NIAS peak in GC-MS screening, or an undetected oil-absorption correction error. A compliance file must therefore record density, melt index, additive concentrations, extruder melt temperature, residence time, article thickness, and the scoped simulant tests with their standard designations. Without those variables, a polyethylene compliance statement is a resin classification rather than a finished-food-contact approval.