EVOH for Fresh Food Trays

Red meat case-ready tray production begins from a five-layer PP/tie/EVOH/tie/PP cast sheet in which the EVOH layer occupies 5–8 vol% of total sheet thickness. In a 650 µm sheet, the food-contact PP layer is commonly 180–220 µm, the two maleic anhydride-grafted PP tie layers are each 20–35 µm, and the EVOH core is specified at 12–20 µm. The sheet is produced on a five-layer coextrusion line with the PP skin melt at 238–245 °C, the EVOH melt at 195–215 °C, and the tie resin at 205–220 °C. EVOH residence time in the adapter and flat die is limited to 15–20 min because longer hold-up at 220 °C initiates gel formation and crosslinking. The cast sheet is then plug-assisted pressure formed at a surface temperature of 155–165 °C and 4.5–5.5 bar forming pressure. Corner draw ratios approach 1.8:1; when the plug geometry is not optimised for EVOH-containing sheet, local core-layer thinning exceeds 55 % of the original thickness and oxygen transmission in the corner increases disproportionately. The formed trays are used for modified-atmosphere packaging of beef mince, beef steaks, and pork chops under a headspace gas mix of 70 % O₂ / 30 % CO₂. High oxygen partial pressure retains oxymyoglobin colour in red meat, while the EVOH layer limits oxygen ingress from the outside so the headspace ratio remains stable over 7–14 days at 4 °C. Finished-tray oxygen transmission is tested by ASTM D3985 at 23 °C and 50 % external RH, with a typical acceptance limit of 0.05 cm³/(package·day·atm) for a 500 g pack. EU 10/2011 compliance is demonstrated through overall migration testing in food simulant C at 5 °C for 10 days on the final container; the PP food-contact layer carries the direct-contact clearance, and the EVOH core remains separated from food by the tie and PP layers. Interlayer peel strength is measured on the preformed sheet by a 180° peel method, with a minimum acceptance value of 1.5 N/15 mm.

What Limits Corner Barrier Integrity in High-Humidity Poultry Trays?

Poultry trays operate with internal RH values above 90 % because purge exudate and muscle surface moisture equilibrate with the headspace. EVOH oxygen transmission is a function of water activity; at 85 % RH a 20 µm film made from a 38 mol% ethylene EVOH can increase from 0.30–0.45 to 2.0–3.5 cm³/(m²·day·atm). The inner PP or PE layer delays moisture diffusion but does not eliminate it, so the barrier layer approaches the humidity of the meat cavity over multi-day storage. Corner thinning from thermoforming compounds the problem because the same moisture-plasticised EVOH is also the thinnest in the corner sidewall. The practical correction is not a thicker EVOH layer alone; tray producers shift to 44 mol% ethylene EVOH for high-moisture poultry, accepting a higher dry barrier in exchange for flatter OTR across the humidity range. On a PP/EVOH/PP sheet for chicken drumsticks and marinated poultry pieces, the EVOH layer is often 15–20 µm before forming, with a maximum draw ratio of 1.5:1 in the corner to keep post-form EVOH thickness above 6 µm. The sealed pack typically uses a 70 % N₂ / 30 % CO₂ or 50 % CO₂ / 50 % N₂ mixture, because high CO₂ suppresses Pseudomonas and Enterobacteriaceae growth on poultry surfaces. EVOH oxygen barrier is measured on the formed tray at 85 % internal RH and 23 °C with an OTR limit of 0.05–0.08 cm³/(package·day·atm) for a 400 g tray. Migration testing under EU 10/2011 uses simulant B for acidulated poultry marinades and simulant D2 for fatty skin-on portions at 5 °C for 10 days.

Typical supplier datasheet ranges for oxygen transmission rate of 20 µm EVOH film at 23 °C

EVOH ethylene content	OTR at 0 % RH	OTR at 85 % RH
27 mol%	0.08–0.12 cm³/(m²·day·atm)	5.0–8.0 cm³/(m²·day·atm)
32 mol%	0.15–0.25 cm³/(m²·day·atm)	3.5–5.5 cm³/(m²·day·atm)
38 mol%	0.30–0.45 cm³/(m²·day·atm)	2.0–3.5 cm³/(m²·day·atm)
44 mol%	0.80–1.20 cm³/(m²·day·atm)	1.2–2.0 cm³/(m²·day·atm)

Because the package is not retorted, the EVOH remains below its practical hot-fill ceiling, and the high-humidity barrier loss is managed by grade selection and geometry rather than by protective lamination alone. Producers validate the package by measuring headspace oxygen after 24 h and again after 7 days; an increase above 1.0 % O₂ in a 400 g tray commonly triggers rejection of the thermoforming setup.Seafood tray structures place the EVOH layer in the base sheet and combine it with a separate lidding film carrying its own EVOH or metallised layer. In a chilled fish pack the headspace gas is commonly 30 % CO₂ / 70 % N₂ for white fish, or 40 % CO₂ / 60 % N₂ for salmon and tuna, because very low residual oxygen retards lipid oxidation and trimethylamine-producing bacteria. The EVOH layer is specified not only for oxygen ingress control but also for retention of volatile sulfur compounds that arise from fish purge; however, EVOH is not an absolute odour barrier when the film approaches 85 % RH and moisture plasticisation opens free volume. To protect the EVOH, a PE-rich inner layer of 40–60 µm is coextruded on the food-contact side, and the sheet is immediately thermoformed at a processing moisture level below 0.3 % after pre-drying at 80–90 °C for 4–6 h in a desiccant dryer. The base tray is sealed with a PET//EVOH//PE lidding structure in which the EVOH layer in the lid is 5–8 µm; the total package OTR is targeted at 0.02–0.05 cm³/(package·day·atm) for 250 g salmon portions. Because fish exudate contains alkaline amines, the tray must be qualified for interlayer adhesion retention after 10 days of chilled contact; peel strength is measured before and after filling by ASTM F904 and must remain above 1.0 N/15 mm. Regulatory clearance for fish contact is established under EU 10/2011; for fatty fish, overall migration is measured in simulant D2 at 5 °C for 10 days, while lean fish uses simulant C.In fresh-cut produce applications, the EVOH layer is buried behind a polyolefin skin that delays liquid water from contacting the barrier resin, but the package design must balance oxygen barrier against the produce respiration requirement. Leafy greens such as baby spinach respire at rates commonly above 80 mL CO₂/kg·h at 10 °C; if the tray and lidding are fully hermetic, the headspace oxygen fraction drops and anaerobic metabolism generates ethanol and acetaldehyde. The base tray is therefore not the primary gas-exchange pathway; laser micro-perforated lidding or patch-based differential permeability creates an OTR of 5000–15000 cm³/(m²·day·atm) on the lidding, while the PP/EVOH/PP base remains at 0.05–0.10 cm³/(package·day·atm) to prevent contamination from outside. Condensation on the inner tray wall is unavoidable at distribution temperatures of 3–7 °C; the product-contact PE or PP layer is specified at 50–80 µm to slow moisture migration such that the EVOH layer remains below 70 % RH over the intended shelf life. The end applications include cut melon, mixed leaf salads, shredded carrot, and fresh pineapple spears. Compliance for cut fruit with low acid conditions is assessed under EU 10/2011 with simulant A at 5 °C for 10 days; for mixed products with oil-based dressing, simulant D2 may also be required. Published OTR data for specific laser-perforation patterns in EVOH-lidded trays is limited, so packaging developers qualify gas composition empirically using headspace analysers at 24 h intervals.

When Chilled Ready-Meal Trays Encounter Hot-Fill and Microwave Reheat

Chilled ready-meal, fresh pasta, and sauce-coated chicken trays are produced from PET/EVOH/PE or PP/EVOH/PP structures. The EVOH layer is adjusted to 38–44 mol% ethylene because the tray undergoes hot filling at 80–85 °C, followed by blast chilling to 2–4 °C within 90 min. Thermal shock creates interlaminar shear at the tie layer because PET, EVOH, and PE have different coefficients of linear thermal expansion. A hot-fill grade EVOH with a melt flow rate of 3.0–4.0 g/10 min at 210 °C and moisture content below 0.3 % is fed through a dedicated extruder at 195–215 °C, while the PET skin layer is processed at 265–280 °C; a barrier feedblock with polymer-specific channel lengths prevents thermal degradation at the PET/EVOH interface. The lidding film uses a biaxially oriented PET//adhesive//EVOH//PE structure with a heat-seal layer that peels at 8–12 N/25 mm measured according to ASTM F88. The final pack is filled with lasagne, filled pasta, or chicken in sauce, then sealed without vacuum. The oxygen barrier is tested by ASTM D3985 on the tray sidewall and flange, with an accepted OTR of 0.03–0.06 cm³/(package·day·atm) for a 350 g portion. These trays are not automatically suitable for full retort at 121 °C; most fresh-food EVOH trays are validated only for hot-fill below 90 °C and microwave reheating at 800 W for 2–3 min. The EVOH layer must be protected from direct contact with food oils that can plasticise tie layers; repeated microwave exposure above 100 °C in oil-contact areas can increase delamination risk at tray corners.

Compliance and physical test matrix for chilled ready-meal EVOH tray structures

Parameter	Standard / regulation	Typical condition
Oxygen transmission	ASTM D3985 / ISO 15105-2	23 °C, 50 % RH, formed tray or sheet
Heat-seal strength	ASTM F88	25 mm strip, 300 mm/min
Interlayer adhesion	ASTM F904	180° peel, 254 mm/min
Overall migration	EN 1186-1, EU 10/2011	Simulant C, 5 °C, 10 d
US food contact	21 CFR 177.1360	Indirect contact, functional barrier

Edge-Trim Regrind in PS/EVOH/PE Deli Tray Sheet

PS/EVOH/PE sheet for deli trays, bakery items, and fresh pasta side cups produces a thermoforming skeleton that may be ground and reincorporated. The EVOH layer in this structure is typically 3–5 vol% of a 500–700 µm sheet, with the PS layer on the outside for rigidity and the PE layer inside for sealing and moisture resistance. Regrind from the thermoforming skeleton contains EVOH as discrete elongated particles after grinding; when the regrind is added directly to the PS skin, the immiscible EVOH domains create surface gels and low-gloss patches. Processors therefore limit regrind addition to 15–25 wt% of the PS layer, or blend the regrind into the PE cap layer where the softer matrix accommodates the dispersed EVOH particles more readily. If the regrind fraction exceeds 30 wt%, notched impact strength of the thermoformed tray falls below the value required for refrigerated distribution, and corner cracking appears after flexing at 2 °C. An upstream melt filter of 120 mesh is recommended on the regrind stream to remove oxidised EVOH gels larger than 125 µm. Barrier performance of the finished tray is not improved by regrind; the freshly coextruded EVOH core remains the only functional oxygen barrier, and thinning of the core during forming is measured by microtome cross-section. Compliance with indirect food-contact regulations for this structure is based on the functional barrier doctrine; EVOH is cleared under 21 CFR 177.1360, PS and PE belong to the outer layers, and overall migration is tested according to EN 1186-1 with simulant C for refrigerated deli contact. Published data for regrind-induced OTR variation in PS/EVOH/PE tray sheet is limited; most converters qualify regrind levels through barrier testing of a 48-tray sample set from the start, middle, and end of a production run.