EVOH for Medical & Pharma Barrier Film

Replacement of PVC/PCTFE blister base webs in solid-dose pharmaceutical packaging frequently proceeds on a five-layer flat-die coextrusion line configured with separate extruders for high-ethylene EVOH, anhydride-modified tie resin, and polypropylene homopolymer. The PP skins are extruded on single-screw machines with L/D 24–30, the EVOH core is extruded on a barrier screw with L/D 20–24, and the tie resin is matched to the melt-flow rate of the PP skins to avoid interfacial viscosity mismatch. The EVOH layer thickness is maintained at 15–30 µm within a total sheet thickness of 200–350 µm; below 15 µm, pinhole formation in the barrier layer can increase oxygen ingress, while above 30 µm the stiffer EVOH core reduces cavity corner uniformity and can produce stress whitening. Ethylene contents of 38–44 mol% are specified for thermoforming grades because they exhibit lower zero-shear viscosity and broader thermoforming latitude than 27–32 mol% oxygen-barrier grades. Coextrusion die temperatures are held at 200–230 °C; residence time above 240 °C is limited to less than 10 min to avoid gel and black-speck generation from EVOH degradation. EVOH pellets are dried at 80–90 °C for 4–6 h to reduce surface moisture below 0.3 % before entering the barrier extruder hopper. The coextruded sheet is then processed on a plug-assist pressure former with sheet surface temperatures of 160–180 °C and aluminium mould temperatures of 30–60 °C. For straight-wall cavities, the draw ratio is limited to 0.5:1–0.7:1 because the glassy EVOH core does not yield at the same strain as the PP skins; draw ratios above this range produce corner thinning below 35 % of nominal barrier thickness. Oxygen transmission is verified per ASTM D3985-17 at 23 °C and 0 % RH; water vapour transmission is verified per ASTM F1249-13 at 38 °C and 90 % RH, with acceptance criteria set by the drug product stability protocol under ICH Q1A. Polymeric materials are assessed under USP <661.1> and Ph Eur 3.1.3 for the polyolefin skins. The formed cavities are sealed to lidding foil and peel force is measured per ASTM F88/F88M-21. Published data for this specific configuration are limited where blister geometries include draw ratios above 0.7:1, so corner-thickness validation is required for each cavity geometry.

Does Ethylene Oxide Sterilisation Degrade Seal Strength in EVOH-Based Device Pouches?

Medical device sterile barrier pouches commonly use a peelable or weldable sealing layer of low-density polyethylene or cast polypropylene bonded to a barrier core of EVOH and an outer layer of biaxially oriented poly(ethylene terephthalate) or polyamide. The pouch seal is produced on a constant-heat or impulse sealer with jaw temperature 120–150 °C, dwell 1–3 s, and jaw pressure 0.3–0.7 MPa, followed by conditioning at 23 ± 2 °C and 50 % RH before seal testing. After ethylene oxide sterilisation per ISO 11135:2014, the seal region is subjected to a 35–55 °C aeration cycle and can absorb moisture from the EO process humidity; this transient moisture uptake increases EVOH oxygen permeability until desorption returns the pouch to ambient humidity. Seal strength is measured per ASTM F88/F88M-21 as the maximum force to separate 25 mm wide strips at 200–300 mm/min; a lower acceptance limit of 4.0 N/15 mm is usually applied for non-peelable medical pouches. When electron-beam sterilisation per ISO 11137-1:2006 is used at 25 kGy, high-ethylene EVOH grades retain more elongation at break than low-ethylene grades, but a radiation-induced yellowing index increase above 5.0 is often observed on the outer facing layer. The pouch film is qualified for microbial barrier properties under ISO 11607-1:2019 and ASTM F1608-16, with the non-porous EVOH film validated against the chosen lidding material. Published data on repeated EO cycles above 3 cycles are limited.

In flexible multi-chamber bags for total parenteral nutrition, the coextruded structure is produced on a water-quenched blown-film line with a five-layer A/B/C/B/A distribution: polypropylene skin, maleic-anhydride-grafted tie resin, EVOH core, tie resin, and a polyethylene or polypropylene sealant layer. The EVOH core is placed between two moisture-resistant layers because the oxygen permeability of EVOH rises sharply above 70–80 % RH at 23 °C; the external polypropylene layer retards steam penetration during autoclaving at 121 °C for 15–30 min, which is the terminal sterilisation condition referenced in ISO 15747:2018. The inner sealant layer is selected for low extractables under USP <661.1> and for seal compatibility with polypropylene or ethylene-vinyl acetate port tubes. Film total thickness is commonly 180–250 µm, with the EVOH core at 20–40 µm; the coextruded film is welded into bag perimeters and port fitments by heated tooling at 160–200 °C. Oxygen ingress through the EVOH layer is validated per ASTM F1927-14 at 23 °C and 80 % RH external condition, because the external surface of the bag may be exposed to humid air while the internal solution exerts water activity near 1.0. Physical integrity after autoclaving is tested by dye penetration per ASTM F3039-15 and by visual inspection for delamination at the tie interfaces; delamination usually propagates from port welding zones if the tie resin thickness is below 8 µm. Cytotoxicity is assessed per ISO 10993-5:2009 and sensitisation per ISO 10993-10:2010. Published data on oxygen ingress under combined high-humidity and autoclave cycling are limited; therefore, package performance must be verified on the actual bag geometry.

For desiccant packaging of lateral-flow assay cartridges and blood glucose test strip vials, the lidding laminate consists of oriented PET, aluminium foil, EVOH sealant web, and a peelable heat-seal coating; the EVOH layer functions as a pinhole barrier and chemical barrier rather than the primary moisture barrier. The foil thickness is usually 20–38 µm, while the EVOH layer is kept at 10–20 µm to limit cost and maintain deadfold. Lamination is performed on a solventless or solvent-based adhesive line, with total laminate thickness of 80–120 µm. The lidding is sealed to polypropylene or PETG vials at jaw temperatures of 130–180 °C for 0.5–2.0 s; the peel force is measured per ASTM F88/F88M-21 and is maintained between 3.0–8.0 N/15 mm for adult-openable but child-safe vial designs. Because the desiccant headspace is maintained at <60 % RH, the EVOH oxygen-barrier property is not the controlling variable; the critical defects are flex cracking and micro-voids in the foil. Water vapour transmission through the complete lid is measured per ASTM F1249-13 and is usually specified below 0.5 g/(m²·day) at 38 °C and 90 % RH. Regulatory compliance is established under FDA 21 CFR 177.1360 for ethylene-vinyl alcohol copolymers, and residual solvents from lamination are controlled per USP <467>. Published data for EVOH-specific adhesion to peelable heat-seal coatings in diagnostic vial lidding are limited.

When Ostomy and Medical Fluid Collection Bag Film Replaces PVdC-Coated PET in High-RH Wear Conditions

Because ostomy pouches and urinary collection bags are worn against the body, the film is exposed to liquid water, urine, and skin perspiration; this imposes a high-humidity service environment in which a bare EVOH layer loses its oxygen-barrier advantage. The film structure therefore places the EVOH layer between two polyolefin or elastomer-modified polyolefin layers: the external layer may be an ethylene-vinyl acetate or polypropylene elastomer blend for softness and low crinkle noise, while the internal sealing layer is a low-density polyethylene or EVA. The EVOH layer thickness is typically 10–20 µm, sufficient for odour containment only after moisture is blocked by the outer polyolefin skins. Odour barrier is assessed qualitatively by panel tests, but oxygen permeability is measured quantitatively per ASTM D3985-17 at 23 °C and 0 % RH, and humidified oxygen transmission per ASTM F1927-14 at 23 °C and 80 % RH; the increase between the two conditions is frequently an order of magnitude or more, which is why the outer moisture barrier is essential. The film is fabricated on a blown-film or cast line with a melt temperature of 190–220 °C and a blow-up ratio of 2.0–3.0 for tubular pouch manufacturing. Sealing is performed by radio-frequency or heat welding at 150–180 °C; seam strength is checked per ASTM F88/F88M-21. Biocompatibility is evaluated under ISO 10993-5:2009 for cytotoxicity and ISO 10993-10:2010 for skin sensitisation because the film may contact peristomal skin. Published data on EVOH flex-crack resistance after repeated body movement cycles are limited; therefore, the film must be tested on a Gelbo flex tester according to ASTM F392/F392M-11 with a minimum 50 cycles before oxygen transmission is re-measured.

Transdermal Patch Barrier Overwrap Film for Oxygen-Sensitive Actives

Transdermal delivery systems for nicotine, fentanyl, or rivastigmine require an overwrap that prevents oxygen- and moisture-induced degradation of the drug-in-adhesive layer before application. The primary overwrap is commonly a three-side-sealed pouch produced from a laminate of biaxially oriented polypropylene, adhesive, EVOH, adhesive, and linear low-density polyethylene sealant. The total thickness is 60–90 µm, with EVOH at 10–20 µm; the polypropylene outer layer provides gloss and puncture resistance, while the linear low-density polyethylene sealant layer is chosen for peelable opening without fibrous tearing. The pouch is sealed at 140–170 °C on an intermittent-motion pouch machine with sealing dwell 0.5–1.5 s and jaw pressure 0.4–0.8 MPa. Oxygen permeation through the pouch is tested under ASTM F1307-14 or flat film ASTM D3985-17, with a target oxygen ingress of less than 0.10 cm³/(m²·day·atm) at 23 °C and 0 % RH for the barrier layer. Because the drug-in-adhesive layer may contain volatile amines, organic esters, or fatty acids, the EVOH layer is not placed in direct contact with the active matrix; the polyethylene sealant layer functions as a chemical barrier to migration. Extractables are assessed per USP <1663> and leachables per USP <1664> using headspace GC-MS and LC-MS methods. Water vapour transmission is measured by ASTM F1249-13 and is normally controlled below 0.5 g/(m²·day) at 38 °C and 90 % RH to prevent crystallisation of the drug in the adhesive matrix. Published data for specific drug-EVOH interaction are limited; compatibility testing is performed on the filled pouch.

On a vertical form-fill-seal cleanroom line, single-dose oral liquid sachets are produced from a printed polyester/adhesive/EVOH/adhesive/linear low-density polyethylene laminate at speeds of 60–120 cycles/min. The EVOH core is 10–15 µm within a total laminate thickness of 70–100 µm; the polyethylene sealant layer is designed for a frangible seal that retains the liquid under normal storage but opens with 20–40 N peel force. The sealing jaws are set to 140–170 °C and the dwell is 0.4–1.0 s; jaw pressure is 0.3–0.6 MPa. The sachet is qualified for oxygen-sensitive oral liquids such as paediatric iron drops or vitamin D formulations; oxygen transmission through the laminate is measured per ASTM D3985-17 at 23 °C and 0 % RH, and water vapour transmission per ASTM F1249-13 at 38 °C and 90 % RH. The barrier film is tested for peel initiation and propagation per ASTM F88/F88M-21; control of cohesive failure in the sealant is necessary to prevent fibre shedding or particulate contamination. Extractables testing follows USP <1663>, and elemental impurities in the packaging material are screened per ICH Q3D when the packaged formulation is an oral liquid for chronic use. Published data on EVOH retention of barrier properties after high-speed flexing on continuous fill lines are limited.