| HS Code | 427637 |
| Fuel Permeation Resistance | Excellent low permeability to automotive fuels |
| Oxygen Barrier Property | Superior oxygen barrier performance |
| Chemical Resistance | Resistant to gasoline, oils, and organic solvents |
| Tensile Strength | High tensile strength, typically 60-80 MPa |
| Elongation At Break | Moderate elongation, approximately 15-30% |
| Melting Point | Approximately 170-190°C depending on ethylene content |
| Density | 1.10-1.21 g/cm³ |
| Water Absorption | Moisture sensitive; absorbs water |
| Ethanol Compatibility | Swelling may occur with ethanol-containing fuels |
| Processability | Suitable for co-extrusion in multilayer fuel tank structures |
| Thermal Stability | Good processing stability within prescribed temperature window |
| Adhesion To Polyolefins | Requires tie layer, often maleic anhydride-modified polyolefin |
As an accredited EVOH for Automotive Fuel Tanks factory, we enforce strict quality protocols—every batch undergoes rigorous testing to ensure consistent efficacy and safety standards.
| Packing | EVOH resin supplied in 25 kg moisture-barrier sealed bags, palletized and wrapped, ensuring purity for automotive fuel tank applications. |
| Container Loading (20′ FCL) | EVOH resin for fuel tanks, packed in sealed bags/drums, loaded 20′ FCL with proper bracing and ventilation. |
| Shipping | EVOH barrier resin for automotive fuel tanks ships as moisture-sensitive pellets in sealed, dry-lined bags or bulk containers. Packaging prevents humidity absorption to maintain performance. Transport is via truck, rail, or ocean freight in standard containers, with proper labeling and documentation for non-hazardous polymer cargo, ensuring safe, efficient delivery. |
| Storage | EVOH for automotive fuel tanks is hygroscopic and must be stored in sealed, moisture-proof packaging to prevent water absorption. Keep in a cool, dry, well-ventilated area away from direct sunlight and extreme temperatures. Avoid contamination, physical damage, and prolonged exposure to air. Store away from oxidizers and follow first-in, first-out inventory practices. |
| Shelf Life | Shelf life is typically 12 months from manufacture date when stored sealed, dry, and at ambient temperature. |
The replacement of a monolayer HDPE 55-L fuel tank with a six-layer coextruded structure comprising HDPE/regrind/adhesive/EVOH/adhesive/HDPE is driven by evaporative hydrocarbon emission limits below 0.3 g/day under 40 CFR Part 86.1811-17 Tier 3 and California LEV III certification. In this configuration the EVOH barrier layer is specified at 1.5% to 3.0% of nominal wall thickness, equivalent to 2 wt% to 5 wt% of finished shell mass, while each adhesive tie layer is held at 1 wt% to 2 wt% and the regrind layer occupies 30 wt% to 45 wt% of the layered stack. The downstream process runs on a six-extruder continuous coextrusion blow molding line equipped with a six-layer spiral-mandrel accumulator head; EVOH pellets are pre-dried at 80°C for 4 h to below 0.1% moisture, extruder barrel temperatures are profiled from 180°C to 225°C, and melt temperature is capped at 235°C because residual exceedance generates gel particles and pinhole defects in the barrier layer. Terminal product types are 40 L to 80 L passenger vehicle gasoline tanks certified to EPA and CARB evaporative limits, with oxygen barrier integrity screened on sidewall samples by ASTM D3985-24 and whole-tank hydrocarbon permeation measured under SAE J1737.
When the certification fuel shifts from E10 to E85, the EVOH barrier layer is not a drop-in replacement because ethanol and water present in the fuel reduce the concentration gradient across the inner HDPE layer and alter the equilibrium moisture load at the tie-layer interface. For flex-fuel and high-ethanol-blend tanks the EVOH layer is increased from 2.0% to 3.5% of wall thickness, and the copolymer ethylene content is selected between 38 mol% and 44 mol% to balance barrier, flex-crack resistance, and melt stability at 215°C to 225°C. Industry compliance is anchored to ASTM D471-16a immersion data for fuel resistance and SAE J1737 permeation with CE10 and CE85 test fuels; production adjusts the outer HDPE melt temperature down by 5°C to 10°C to reduce parison sag while increasing EVOH extruder back pressure for layer uniformity, and the die gap at the pinch-off zone is narrowed so the EVOH layer does not drop below 0.05 mm at the seam. Terminal products include 45 L to 90 L flex-fuel passenger car and light-truck tanks intended for E22 to E85 markets where evaporative loss must remain below 0.3 g/day.
Hybrid and plug-in hybrid evaporative control systems close the tank vent for extended periods, producing internal pressure excursions from 20 kPa to 50 kPa that force fuel vapor into the barrier stack and raise the failure risk at the pinch-off seam. The applicable compliance path is the zero-fuel evaporative requirement under California LEV III for PHEV and PZEV platforms, with leak monitoring validated by pressurization and ASTM D3985-24 oxygen transmission on sidewall laminates. For this condition the EVOH barrier layer is specified at 3.0% to 4.0% of nominal wall thickness, and the inner HDPE layer is maintained at 1.5 mm minimum at the pinch-off to prevent barrier rupture. The downstream process uses a servo-driven parison wall-thickness controller and sequential coextrusion blow molding with inflation pressure at 0.8 MPa to 1.0 MPa; mold cooling time is extended by 8% to 12% to reduce post-mold shrinkage in the EVOH layer. Terminal products are 35 L to 60 L sealed fuel tanks for PHEV platforms, with leak verification performed at 20 kPa for 20 s.
| Standard/Code | Application Boundary | Test Method | EVOH Barrier Layer Thickness Range |
|---|---|---|---|
| 40 CFR Part 86.1811-17 | US EPA Tier 3 light-duty gasoline tank shells | SAE J1737 | 1.5–3.0% wall |
| California LEV III | PHEV/PZEV sealed fuel tanks | ASTM D3985-24 | 3.0–4.0% wall |
| GB 18352.6-2016 | China 6 evaporative emission | GB 18352.6 Type IV | 2.0–3.0% wall |
On a 120 mm multilayer fuel filler pipe line running at 250 kg/h, the barrier layer is coextruded as HDPE/tie/EVOH/tie/HDPE with the EVOH layer maintained at 5% to 7% of nominal pipe wall thickness and each tie layer at 2% to 3%. This configuration addresses diurnal breathing losses from the filler neck that are included in the vehicle evaporative certification rather than only the tank shell. The governing standards are SAE J30 for non-pressure fuel hose assemblies and ASTM D471-16a for liquid fuel exposure. Processing uses single-screw extruders with L/D 30:1 barrier screws and gear pumps feeding a coextrusion crosshead at 200°C to 220°C; vacuum calibration maintains roundness, and a corrugator forms the flexible spout section before cut-to-length. Terminal products include multilayer filler necks, capless fuel inlet spouts, and integrated filler-pipe assemblies for passenger cars and light trucks.
Small off-road engine fuel tanks and portable fuel containers are coextruded with an EVOH barrier layer because the diurnal soak cycles on 5 L to 20 L containers can exceed the 0.3 g/day budget under 40 CFR Part 1060 and CARB SORE provisions; the barrier layer is not optional at the smallest sizes because surface-to-volume ratio rises as capacity declines. In this application the EVOH layer is 2 wt% to 3 wt% of the finished vessel, or 0.08 mm to 0.15 mm in a 3 mm nominal wall, with tie layers at 1 wt% to 2 wt%. Production runs on shuttle blow molding machines with accumulator heads and two-position mold systems; parison drop time is held at 1.5 s to 2.5 s to avoid EVOH cooling before inflation. Terminal products include 5 L portable gasoline containers, 10 L jerry cans, and 1 L to 10 L off-road engine tanks for generators, mowers, and marine outboard engines.
Post-industrial regrind from six-layer EVOH tank production carries HDPE, tie resin, and EVOH into the regrind middle layer, which can reduce barrier continuity if the EVOH domain size exceeds 2.0 mm or if moisture content rises above 0.08%. The relevant quality disciplines are melt flow ratio verification under ISO 1133-1:2022 and oxygen transmission testing of pressed film under ASTM D3985-24 after regrind inclusion. In this scenario the regrind layer is controlled at 25 wt% to 50 wt% of the layered stack, while the virgin EVOH barrier layer remains at 2 wt% to 4 wt% of total wall mass. The process includes granulation of coextruded scrap through a 10 mm screen pack, gravimetric blending with virgin HDPE and adhesive resin, and pre-drying at 90°C for 2 h before the regrind extruder. Terminal product types are six-layer fuel tanks with a post-industrial regrind middle layer for high-volume passenger car platforms, allowing virgin HDPE reduction without forfeiting evaporative certification.
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Ethylene-vinyl alcohol copolymer (EVOH) grades qualified for automotive fuel tank barrier layers are supplied as 27–44 mol% ethylene copolymers. Product examples include Nippon Gohsei Soarnol D2908, Soarnol E3808, and Kuraray EVAL F101A. The base resin is specified under ISO 14663-2:2019, with density of 1.14–1.21 g/cm³, melt flow rate of 1.6–12.0 g/10 min at 210 °C and 2.16 kg, and oxygen transmission rate of 0.4–2.0 cm³·20 µm·m⁻²·day⁻¹·atm⁻¹ at 20 °C and 65 % relative humidity. The intended use is as the hydrocarbon barrier core in multilayer high-density polyethylene fuel tanks produced by coextrusion blow molding. In automotive fuel tank service, the material is never used as a monolayer structural component; its contribution to wall stiffness is negligible, and its function is restricted to diffusion control.
In production-scale coextrusion blow molding, the barrier layer is typically positioned between adhesive tie layers within a six-layer or seven-layer die head. The EVOH extruder commonly uses a 24:1 to 30:1 L/D screw with a compression ratio of 3.0:1 to 3.5:1 and barrel zone settings of 190–230 °C. Melt temperature is held below 230 °C and residence time below 15 min to limit gel formation and acetic-acid odor. Pre-drying at 80–90 °C for 4–6 h is required when surface moisture exceeds 0.3 wt% or when the resin has been stored at relative humidity above 60 %. On accumulator-head machines, layer-to-layer temperature variation should not exceed ±3 °C at the die entry; otherwise, interfacial flow instabilities create visible layer thickness variation and localized barrier thinning in pinch-off zones. A representative production configuration is a 6-layer accumulator-head blow molder with an 80 mm main HDPE extruder and a 45 mm barrier extruder; the EVOH layer is injected through a spiral mandrel die and its thickness is monitored by ultrasonic wall-thickness scanning after trimming.
Monolayer HDPE tanks exhibit steady-state hydrocarbon permeation controlled by solubility and diffusion coefficients of toluene, xylene, and ethanol in polyethylene. In SAE J1737 testing, replacing the monolayer wall with a six-layer structure containing a 30–80 µm EVOH layer reduces fuel permeation by one to two orders of magnitude at 40 °C under low humidity. The EVOH barrier works because the strongly hydrogen-bonded vinyl alcohol segments create a tortuous path for nonpolar hydrocarbon molecules; however, this same hydrogen bonding makes barrier performance sensitive to absorbed water and ethanol. A 38 mol% ethylene grade, such as Soarnol E3808, is commonly selected when the tank must survive E10 and E85 fuel blends. Published data for this specific configuration is limited for long-term E85 exposure, so tank-level qualification under EPA 40 CFR 86.1813 and CARB LEV III evaporative emission cycles is required. Oxygen barrier is also relevant: the EVOH layer slows oxygen ingress and reduces oxidative fuel aging, but the primary regulatory driver remains hydrocarbon permeation. In addition, the barrier layer must withstand the pinch-off compression during mold closing without cracking; this requirement alone limits the usable ethylene content to grades above approximately 27 mol%.
Permeation is inversely proportional to barrier layer thickness under steady-state conditions. Increasing the EVOH layer from 30 µm to 60 µm doubles the diffusion path length and reduces hydrocarbon flux by approximately 50 %, provided that the layer remains continuous and free of gel-induced pinholes. Below 20 µm, thickness variation from die-head asymmetry or pinch-off thinning creates local breaches that are not detected by average wall-thickness measurement. Ultrasonic thickness scanning across the barrier layer is therefore used with a minimum tolerance of ±5 µm.
At 20 °C and 65 % relative humidity, oxygen transmission rate values listed for EVOH are 0.4–2.0 cm³·20 µm·m⁻²·day⁻¹·atm⁻¹. At 20 °C and 85 % relative humidity, the same films exhibit oxygen transmission rates from 2.0 cm³ to as high as 15 cm³·20 µm·m⁻²·day⁻¹·atm⁻¹, depending on ethylene content. This water-induced plasticization is reversible when the polymer is dried, but tank-level barrier loss can be permanent if the protective HDPE skin is breached and liquid water pools near the tie resin. Ethanol in E10 can increase moisture absorption in EVOH because ethanol acts as a plasticizer and carries water into the layer. The resulting barrier loss is not uniform across the tank; it is concentrated in lower sections where fuel contact time is longest.
Moisture uptake at equilibrium under 65 % relative humidity is typically 3–5 wt% for 32 mol% ethylene EVOH and 2–3 wt% for 38 mol% ethylene EVOH. Under 95 % relative humidity, uptake can exceed 8 wt%. The glass transition temperature falls with water content; hence, the barrier layer in a fuel tank can undergo localized plastication when the tie resin is not continuously fused. This is a critical threshold risk because a layer that plasticizes at the pinch-off becomes susceptible to cracking during tank burst testing.
Six-layer tank structures usually comprise an HDPE outer skin, a regrind layer, a maleic anhydride grafted polyethylene tie resin, the EVOH barrier layer, a second tie resin, and an inner carbon-black-loaded conductive HDPE skin. The conductive inner skin typically exhibits surface resistivity below 10⁶ Ω per ASTM D257-14 to dissipate electrostatic charges during fuel fill. EVOH layer thickness is 30–80 µm within a total wall thickness of 5–7 mm, corresponding to 0.5–1.5 % of wall thickness. Regrind containing EVOH is limited to the regrind layer and should not exceed 30–50 wt% of total shot weight because exceeding this level raises melt pressure fluctuations and creates gel specks that appear as barrier discontinuities after burst testing. Compatibility with the accumulator-head die is maintained when the EVOH melt stream has a viscosity within ±20 % of the adjacent tie resin; larger mismatches generate interfacial waviness and layer inversion at the pinch-off.
Parison sag is a further constraint. The EVOH layer must not flow independently and create local thinning during parison inflation. Grades with melt flow rate below 2.0 g/10 min, such as EVAL F101A, provide better melt strength but require higher barrier-extruder pressure; grades with melt flow rate of 8.0 g/10 min or higher, such as Soarnol E3808, process more easily in thin layers but may promote interfacial waviness when paired with a high-molecular-weight HDPE outer skin. The viscosity ratio between EVOH and tie resin at the die lip is typically controlled to 1:1 to 1:2 to avoid layer inversion.
| Grade | Ethylene content | Melt flow rate | Density | Oxygen transmission rate at 20 °C, 65 % RH | Flexural modulus |
|---|---|---|---|---|---|
| Soarnol D2908 | 29 mol% | 8.0 g/10 min | 1.21 g/cm³ | 0.4 cm³·20 µm·m⁻²·day⁻¹·atm⁻¹ | 3.7 GPa |
| EVAL F101A | 32 mol% | 1.6 g/10 min | 1.19 g/cm³ | 0.6 cm³·20 µm·m⁻²·day⁻¹·atm⁻¹ | 3.4 GPa |
| Soarnol E3808 | 38 mol% | 8.0 g/10 min | 1.17 g/cm³ | 1.0 cm³·20 µm·m⁻²·day⁻¹·atm⁻¹ | 3.0 GPa |
| Soarnol A4412 | 44 mol% | 12.0 g/10 min | 1.14 g/cm³ | 2.0 cm³·20 µm·m⁻²·day⁻¹·atm⁻¹ | 2.5 GPa |
Grade selection follows the humidity and flex-crack requirements of the tank geometry. Lower ethylene content grades such as Soarnol D2908 provide the lowest oxygen transmission rate but are more sensitive to moisture uptake and flexural cracking after exposure to E10 or E85 fuel. Higher ethylene content grades such as Soarnol E3808 or Soarnol A4412 sacrifice some barrier performance to gain impact resistance and processing stability in deep-draw areas. This is the primary difference among EVOH products for the same application; the choice is not simply barrier level but the balance of barrier retention, flexural fatigue, and coextrusion process window. For saddle tanks with deep draw ratios exceeding 2.0:1, a 38–44 mol% ethylene grade is generally preferred because the higher ethylene content reduces crack propagation in the thinned corner sections.
PA6 is sometimes specified as an alternative barrier layer for fuels with high methanol or ethanol content because it does not lose barrier as sharply with moisture. However, PA6 has a higher baseline hydrocarbon permeation coefficient; typical published values place PA6 fuel permeation at 0.5–2.0 g·mm·m⁻²·day⁻¹ at 40 °C, while a 32 mol% ethylene EVOH remains below 0.1 g·mm·m⁻²·day⁻¹ under the same conditions. PVDF and ETFE fluoropolymers offer the best E85 barrier retention and chemical resistance but require melt processing temperatures above 250 °C and are higher in resin cost. EVOH is therefore selected when the barrier requirement is dominated by hydrocarbon emission limits under low to moderate humidity and when the coextrusion line is already configured for moisture-sensitive materials. In direct fuel contact, EVOH must be protected by tie layers because its water uptake can exceed 8 wt% at 95 % relative humidity. The difference in processing window is also significant: PVDF requires chrome-plated dies to prevent corrosion, while EVOH is processed on conventional low-corrosion tooling.
| Property | Test method | Typical acceptance range |
|---|---|---|
| Melt flow rate | ISO 1133-1:2022 | 1.6–12.0 g/10 min at 210 °C, 2.16 kg |
| Density | ISO 1183-1:2019 | 1.14–1.21 g/cm³ |
| Oxygen transmission rate | ISO 15105-2 | 0.4–2.0 cm³·20 µm·m⁻²·day⁻¹·atm⁻¹ at 20 °C, 65 % RH |
| Hydrocarbon permeation | SAE J1737 | tank-level limit under EPA 40 CFR 86.1813 or CARB LEV III |
| Fuel resistance | ISO 175:2010 | no cracking or delamination after immersion in Fuel C for 500 h at 40 °C |
In service, EVOH barrier tanks are installed with fuel level senders and rollover valves that require sealing bosses molded into HDPE. The barrier layer is interrupted at these insert points; therefore, the sealing boss design must include HDPE-to-HDPE fusion weld details to prevent exposed EVOH from contact with liquid fuel and condensate. Long-term durability testing is carried out under temperature cycling from −40 °C to +60 °C at 95 % relative humidity with E10 and E85 fuel blends. Field failures on production-scale equipment are most commonly traced to moisture-induced barrier reversion at pinch-off regions or to gel formation from extended residence time in the accumulator head. Residence time extensions beyond 15 min typically produce gel specks of 0.5–2.0 mm diameter in the barrier layer; these are detected only after SAE J1737 permeation testing shows a measurable increase in tank-level emissions.
