Ethylene-Vinyl Alcohol Copolymer

Coextrusion of five-layer blown film for modified atmosphere packaging of processed meat positions an ethylene-vinyl alcohol copolymer (EVOH) barrier core between two maleic anhydride-grafted tie layers, which are enclosed by low-density polyethylene skins extruded at a die temperature of 210–225 °C. The EVOH grade selected for this structure has an ethylene content of 27–32 mol% and a melt flow index of 1.6–4.0 g/10 min when measured under ISO 1133-1:2022 at 190 °C and 2.16 kg. Pre-drying in a desiccant hopper at 80–90 °C for 4–6 h is required to reduce residual moisture below 0.1 wt%; direct processing of undried resin leads to hydrolytic chain scission and visible gel particles at the die lip. The EVOH layer constitutes 5–10 µm of a total film thickness of 90–130 µm, corresponding to a mass fraction of 7–12 wt% based on an EVOH density of 1.17 g/cm³ and a polyethylene density of 0.93 g/cm³. Food-contact compliance is established under Commission Regulation (EU) No 10/2011, Annex I, as amended, and under FDA 21 CFR 177.1360; oxygen transmission rate is measured on the finished laminate according to ASTM D3985 at 23 °C and 0 % RH, while water vapour transmission rate is measured according to ASTM F1249 at 37.8 °C and 90 % RH. On a production-scale line, the five-layer blown film die gap is set at 1.8–2.2 mm, the blow-up ratio is maintained between 2.2:1 and 2.8:1, and the frost line height is adjusted by closed-loop control of the cooling ring to prevent EVOH wrinkling caused by differential crystallisation shrinkage. Terminal packaging configurations include modified atmosphere lidding films for cured meat slices, vacuum skin packages for fresh beef and poultry, and thermoformed base webs for cheese blocks with residual oxygen levels below 0.5 % in the sealed package headspace.

Two failure modes recur on commercial blown film lines. First, viscosity mismatch between EVOH and skin polyethylene at the die manifold produces interfacial instabilities when the tie layer thickness drops below 8 % of total thickness; the visible symptom is a cyclic haze band in machine direction. Second, prolonged residence time above 230 °C in the barrier-layer extruder initiates carbonyl formation and crosslinked gel accumulation in the screen pack. The EVOH extruder is specified with an L/D ratio of 24:1 to 30:1 and a compression ratio of 2.5:1 to 3.0:1, and the barrel is purged with a low-melt-index polyethylene before shutdown to avoid stagnant EVOH degradation. When the EVOH mass fraction is increased above 12 wt%, the film loses impact puncture resistance under ASTM F1306, and gel count rises under a 50 µm optical film inspection threshold. Conversely, a reduction below 7 wt% fails to maintain the oxygen barrier target of 2.0 cm³/(m²·day·atm) at 23 °C and 65 % RH. Published data for the exact oxygen transmission rate of this five-layer configuration at all relative-humidity steps is limited; converter validation by gas chromatographic headspace analysis over 21 days is therefore used to confirm packaged-product shelf-life.

When EVOH Replaces PVDC in Rigid Agrochemical Barrier Bottles, Which Processing Limits Apply?

Six-layer coextrusion blow molding of HDPE/tie/EVOH/tie/regrind/HDPE bottles for emulsifiable concentrates and chlorinated solvents requires the EVOH layer to remain between 30 µm and 70 µm in a container wall of 1.0 mm to 1.6 mm, equivalent to 2–4 wt% of the bottle mass. The outer HDPE layers are processed at 220–230 °C, while the EVOH melt stream is held at 210–225 °C to avoid gel formation above 230 °C. A maleic anhydride-grafted polyolefin tie layer with a melt flow index of 1.0–3.0 g/10 min under ISO 1133-1:2022 is inserted on both sides of the EVOH, and regrind content is limited to 30–40 % of total wall thickness because regrind boundary layers reduce interlayer adhesion when the bottle is exposed to xylene-containing formulations. Compliance for the transport of dangerous goods is evaluated under the UN Model Regulations, Chapter 6.1, and specific chemical compatibility is determined by ASTM D543 immersion testing at 23 °C and 50 °C for 30 days. Oxygen transmission rate is measured on bottle sidewall specimens according to ASTM D3985 at 23 °C and 0 % RH; moisture vapour transmission rate is measured according to ASTM E96/E96M at 38 °C and 90 % RH. Terminal containers include 1–10 L multilayer bottles for agricultural emulsifiable concentrates, organic solvent-based wood preservatives, and industrial cleaning concentrates.

On rotary and shuttle blow molding machines, accumulator head pressure drop across the six-layer die is maintained below 240 bar to prevent barrier-layer melt fracture; parison programming adjusts thickness distribution to maintain the EVOH layer above 25 µm at the pinch-off zone. A production bottleneck occurs when EVOH is coextruded with HDPE containing post-consumer recyclate: the recyclate layer raises shear viscosity and shifts the EVOH layer toward the inner wall, producing an eccentric layer distribution measurable by optical microscopy after microtome sectioning. In such cases the inner HDPE layer thickness is increased from 15 % to 25 % of total wall thickness to prevent barrier layer breakthrough at the pinch-off. Barrier performance after drop impact according to ASTM D2463-15 at -18 °C must show no visible delamination; EVOH adhesion strength measured by peel testing on the sidewall is typically above 4 N/15 mm. Published data for the exact oxygen transmission rate of this six-layer bottle under aggressive solvent contact is limited, and pack testing with the actual formulation is mandatory.

In six-layer coextrusion blow molding of automotive fuel tanks for gasoline and gasoline-ethanol blends containing up to 10 vol% ethanol, the EVOH layer is placed between two tie layers and is not directly exposed to the inner or outer HDPE surface. The EVOH layer thickness is 100–180 µm in a total tank wall of 5–8 mm, giving an EVOH mass fraction of 2–3 wt%; this narrow fraction balances permeation resistance against impact toughness and pinch-off weld integrity. The outer and inner HDPE layers are processed at 220–235 °C, while the EVOH stream is maintained at 205–220 °C to limit residence-time degradation; the tie layers use maleic anhydride-grafted high-density polyethylene with a melt flow index of 1.0–2.0 g/10 min under ISO 1133-1:2022. Regrind content from post-industrial trimmings and rejected tanks is allowed up to 40 wt% of the total parison provided the regrind particle size is below 500 µm and the regrind is dried to below 0.05 wt% moisture before re-introduction. Compliance for evaporative emissions is conducted under US EPA 40 CFR Part 86.1813-17, CARB LEV III, and Euro 6 evaporative requirements; barrier validation uses ASTM D3985 at 23 °C and 0 % RH on tank wall samples, and fuel permeation is evaluated by sealed-tank diurnal breathing loss testing on the final assembly. Terminal products include passenger vehicle fuel tanks, fuel filler pipes, and small off-road engine tanks for lawn and garden equipment.

The critical process conflict on a production-scale accumulator blow molder is the narrow EVOH temperature window against the high HDPE melt temperature required for parison sag resistance. If the melt temperature of the HDPE skin is raised above 235 °C to improve parison hang time on a 1.5 m accumulator head, the EVOH layer receives excessive heat at the die manifold and begins to form gel particles that appear as black specks in the barrier layer under transmitted light. Conversely, lowering the HDPE temperature below 220 °C increases parison sag and produces uneven wall distribution at the tank corners. Processors therefore specify a six-layer spiral mandrel die with dedicated barrier-layer temperature control and a flow crossover designed to maintain a melt temperature difference no greater than 15 °C between the HDPE and EVOH streams at the die entry. Clamp force on the blow molding machine is selected between 1,200 kN and 2,000 kN for tanks up to 80 L, and the blown part is subjected to a post-mould cooling cycle with internal air at 10–15 °C for 120–180 s. After moulding, the tank is leak-tested under 30 kPa pressure for 30 s and subjected to a drop test at -40 °C according to automotive OEM specifications. Published data for the exact fuel permeation rate of this six-layer structure with every ethanol blend is limited; OEM validation therefore includes sealed-tank diurnal breathing loss testing on the final assembly.

If oxygen diffusion through PE-RT piping must remain below 0.1 g/(m³·d) at 40 °C, what layer configuration is feasible?

Five-layer PE-RT/tie/EVOH/tie/PE-RT pipe for underfloor heating and closed-loop cooling systems typically uses an EVOH barrier layer of 50–150 µm in a pipe wall of 2.0–3.5 mm, corresponding to 3–5 wt% of the total pipe wall. The EVOH grade has an ethylene content of 38–44 mol% to provide flexibility during pipe coiling, and the PE-RT layers are tailored to thermal stability at continuous service temperatures up to 70 °C with peak exposure at 95 °C. The oxygen barrier requirement is specified in DIN 4726 for plastic heating pipes, with an oxygen diffusion limit of ≤0.1 g/(m³·d) at 40 °C; compliance is verified by oxygen permeation testing on the finished pipe at 40 °C according to the method referenced in DIN 4726. The five-layer line uses separate single-screw extruders with a spiral coextrusion die; EVOH is pre-dried at 80–85 °C for 4–6 h to below 0.1 wt% moisture, and the EVOH melt temperature is kept at 205–220 °C. Haul-off speed is adjusted to a pipe outside diameter tolerance of ±0.2 mm, and wall thickness is monitored by ultrasonic sensors at 4 points around the circumference to ensure the EVOH layer does not drift below 50 µm. Terminal products include floor heating pipes in residential and commercial buildings, radiator connection pipes, and chilled ceiling panels for office climate control.

During bending and coiling, the EVOH layer is subjected to hoop strain; if the EVOH layer thickness exceeds 150 µm, stress whitening occurs at the inner radius. Adhesion between EVOH and PE-RT through the tie layer is tested according to ASTM F904 on pipe wall specimens, with a minimum peel force of 3 N/mm at 23 °C. Production lines running above 25 m/min can encounter melt fracture at the EVOH interface if the die land length for the barrier layer is below 10 mm; die design must maintain a barrier-layer land length of 10–15 mm to stabilise the annular flow. Published data for the exact oxygen diffusion rate of this five-layer pipe at every operating temperature is limited; design validation is therefore performed on the finished pipe under DIN 4726 rather than on flat film.

Laminated Tube Barrier Core for Cosmetic and Personal Care Packaging

For laminated tubes used in toothpaste, cosmetic creams, and hair colourant pastes, EVOH is introduced as a core layer in a coextruded blown film that is subsequently laminated to a printed outer web and an inner polyethylene sealant film. The EVOH layer thickness in the barrier film is 15–25 µm within a total laminate thickness of 250–350 µm, resulting in an EVOH mass fraction of 5–10 wt% in the finished tube laminate. Packaging compliance under EU Cosmetics Regulation (EC) No 1223/2009 is achieved through the safety assessment of the finished article, and the food-contact status of the EVOH layer is covered under FDA 21 CFR 177.1360 for formulations marketed with oral-care claims. Oxygen transmission rate is measured on the laminate according to ASTM D3985 at 23 °C and 65 % RH, and side-seam bond strength is tested on the welded tube at 23 °C with a minimum value of 15 N/15 mm. The blown film process uses a three-layer die with EVOH pre-dried at 80–90 °C for 4–6 h and a melt temperature of 210–225 °C; die gap is 1.2–1.8 mm and blow-up ratio is 2.0:1–2.5:1. Terminal products include toothpaste tubes, cosmetic cream tubes, and hair colourant tubes for retail distribution.

Layer adhesion is measured after the laminate is exposed to a sterilising peroxide solution at 40 °C for 24 h; delamination at the EVOH/tie interface indicates insufficient tie-layer thickness below 8 % of total laminate thickness. Published data for the exact oxygen transmission rate of this three-layer film in all cosmetic formulation contact conditions is limited, and barrier validation is performed on the finished tube laminate with the actual product fill.

Against a background of oxygen ingress in bag-in-box liners for wine, post-mix syrups, and bulk edible oils, a three-layer coextruded liner places EVOH between linear low-density polyethylene skins, with the EVOH layer thickness held at 4–6 µm in a total film thickness of 70–100 µm. The EVOH mass fraction is 5–8 wt%, and the ethylene content of the EVOH is 27–32 mol% for barrier performance at chilled storage temperatures. The film is produced on a three-layer blown film line with a die temperature of 210–225 °C, a blow-up ratio of 2.0:1–2.5:1, and a frost line height selected to minimise interlayer haze. Pre-drying at 80–85 °C for 4 h reduces residual moisture below 0.1 wt%; undried pellets generate pinholing at the EVOH layer during stretching. Compliance for direct liquid food contact is established under Commission Regulation (EU) No 10/2011, Annex I, as amended, and FDA 21 CFR 177.1360; oxygen transmission rate is measured according to ASTM F2622 at 23 °C and 0 % RH, and tensile properties are measured according to ISO 527-3:2018 on machine and transverse directions. Terminal products include bag-in-box liners for wine, bag-in-box post-mix syrup packs, and bulk edible oil liners for food-service dispensing.

Because EVOH is hygroscopic, the liner must not be stored in direct contact with high-moisture liquids for prolonged periods unless the LLDPE skins remain intact; loss of skin integrity exposes the barrier layer to plasticisation and reduces oxygen barrier. Published data for the exact oxygen transmission rate of this three-layer liner at every relative humidity is limited; end-use validation with the filled beverage is required.