EVOH EW-3801

EVOH EW-3801 is an ethylene-vinyl alcohol copolymer grade identified by a nominal 38 mol% ethylene co-monomer fraction and supplied as cylindrical pellets for coextruded barrier layers in rigid and flexible packaging. Melt mass-flow rate, determined according to ISO 1133-1:2022 at 190°C under a 2.16 kg load, is 1.6 g/10 min; density is 1.17 g/cm³ per ISO 1183-1:2019. Differential scanning calorimetry per ISO 11357-3:2018 shows a peak melting endotherm near 173°C and a glass transition temperature near 58°C. The oxygen permeability coefficient at 23°C and 0% RH is 0.010–0.030 cm³·mm/(m²·day·atm) per ASTM D3985-17. The EW-3801 designation places this grade between lower-ethylene grades of approximately 29 mol% ethylene and higher-ethylene grades of approximately 44 mol% ethylene. Lower-ethylene copolymers provide lower dry oxygen permeability but exhibit a larger increase in permeability above 65–70% RH. Higher-ethylene copolymers offer wider processing latitude and lower moisture sensitivity but sacrifice oxygen barrier. The resin is hygroscopic and requires moisture control before melt processing; total moisture above 0.3 wt% produces hydrolytic degradation, gel particles, and acetic acid release during extrusion.

What Processing Envelope Applies to EW-3801 on Multilayer Extrusion Lines?

On a single-screw extruder with 24:1 to 30:1 L/D and a compression ratio of 2.5:1 to 3.0:1, zone temperatures should be profiled from 180°C at the feed throat to 220°C at the metering section. Barrel temperatures above 230°C accelerate degradation of the vinyl alcohol segments and release acetic acid; a 50 µm screen pack test then shows gel counts above 100 particles/kg. Melt temperature should be maintained between 210°C and 225°C. The screw should use a low-shear metering section without high-intensity mixing elements because localized shear heating above 240°C generates cross-linked gels. Residence time from hopper to die exit should not exceed 15 min. For interruptions longer than 15 min, purge with a low-density polyethylene having a melt index of 8–12 g/10 min at 190°C/2.16 kg. Adapter and die temperatures should be held at 215–230°C. Feedblock and die internals should be free of stagnant regions; dead spots increase the residence-time distribution and produce periodic gel streaks in the barrier layer.

Moisture control is the limiting pre-processing step. EW-3801 should be dried at 90°C for 4–6 h in a dehumidifying dryer with a dew point no higher than -40°C and an airflow of at least 3.7 m³/kg·h. This reduces pellet surface moisture below 0.05 wt% and total moisture below 0.3 wt%. Drying above 110°C should be avoided because pellet agglomeration occurs at the hopper inlet. Return air temperature above 75°C indicates incomplete desiccant bed regeneration. If ambient relative humidity exceeds 60%, the hopper must be sealed or nitrogen blanketed. Inadequately dried resin loses 15–30% of its melt viscosity during extrusion, produces bubble defects in cast film, and increases the oxygen transmission rate of the finished film by 2–3 times compared with correctly dried resin.

When a Seven-Layer Coextrusion Line Replaces a Symmetrical Three-Layer Configuration

The EW-3801 layer is normally encapsulated between two tie layers composed of maleic anhydride-grafted polyolefin with a graft content of 0.3–1.0 wt% and a thickness of 2–4 µm. In a seven-layer structure of polypropylene / tie / EVOH / tie / polypropylene / regrind / polypropylene, the EVOH core thickness is typically 3–10 µm. Interlayer adhesion should be evaluated per ASTM F904-16; values below 4 N/15 mm after 24 h conditioning at 23°C and 50% RH indicate inadequate bonding. The feedblock should route EW-3801 through a dedicated barrier-layer extruder, not through a combined regrind stream. Die pressure on a seven-layer line is typically 8–15% higher than on a three-layer line at the same total throughput because of the higher melt viscosity of the EVOH layer. Pressures above 35 MPa reduce tie-layer wetting and promote edge delamination. For this reason, die geometry should be modified when a seven-layer product is introduced into an existing line.

In sheet extrusion for thermoformed barrier containers, the EW-3801 layer is usually 5–8 vol% of the total sheet thickness. On a 1.2 m wide flat die with a 0.8 mm die gap, die lip temperature should be maintained at 220°C with transverse variation not exceeding ±2°C. Larger temperature spreads produce edge curl and nonuniform barrier thickness. Thermoforming temperature for a 1.0 mm polypropylene/EVOH sheet is 160–175°C. Below 155°C the EVOH layer may crack because its elongation at break at 150°C is below 75% at a strain rate of 100 mm/min per ISO 527-3. Plug-assist speed should not exceed 25 cm/s to avoid localized thinning of the barrier layer below 3 µm. For draw ratios above 1.5, EVOH layer thickness should be increased to 8–10 µm because wall thinning can reduce oxygen barrier by more than 50%.

Blown-film coextrusion of EW-3801 is most stable with a 5-layer spiral mandrel die. Blow-up ratio should be limited to 2.2:1; at ratios above 2.8:1 the EVOH layer is stretched beyond its elongation at break and forms transverse microcracks. Frost line height for a 0.6 mm LLDPE/EVOH film is maintained at 250–350 mm with die temperature 210°C. Nip speed and screw speeds must be matched to keep the EVOH layer at 4–7 µm. Thickness deviations greater than ±0.5 µm produce visible haze banding and roller-map oxygen transmission variation across the web.

In injection molding of polypropylene barrier containers, EW-3801 is metered into the mold as an inner barrier layer by a dedicated secondary injection unit with barrel temperature 210–220°C and injection pressure 80–120 MPa. The mold surface temperature should be 30–50°C for polypropylene; lower mold temperatures reduce adhesion between the PP and EVOH layers. Sequential injection molding requires a shut-off nozzle with a wear-resistant check ring because molten EVOH is more corrosive to steel than polypropylene. The barrier layer thickness in a 500 mL container is typically 50–120 µm. Gate freeze time must be extended by 0.5–1.0 s compared with neat PP because EVOH solidifies at higher temperature and can be pulled from the gate area if the gate freezes prematurely.

Purging procedures are governed by the thermal sensitivity of EW-3801. The transition from a previous resin to EW-3801 should use a cast acrylic purging compound or LDPE with a melt index of 8–12 g/10 min. Direct transition from a polyamide or PVC-based resin can produce cross-contamination and interfacial gels; a purge volume of 3–5 times the barrel capacity is required. At shutdown, the barrel should be filled with LDPE and cooled without EW-3801 remaining in the feedblock. If EVOH remains in the feedblock during cooling, solidified EVOH can crack die lips during restart because of its high stiffness and low elongation at room temperature.

The oxygen transmission response of 38 mol% ethylene EVOH diverges from lower-ethylene grades once relative humidity exceeds 65–70%. At 23°C and 0% RH, a 10 µm EW-3801 layer contributes an oxygen transmission rate near 1.2 cm³/(m²·day·atm) when measured according to ASTM D3985-17 on a coextruded sheet. At 85% RH, the same layer may transmit 12–18 cm³/(m²·day·atm), a loss factor of 10–15 caused by water absorption in the vinyl alcohol phase. This humidity threshold places EW-3801 on the dry side of the package or behind polyolefin layers of at least 50 µm thickness. In retort applications at 121°C and 100% RH, oxygen barrier performance after 30 min exposure may degrade by more than 90%. Shelf-life models therefore use moisture-dependent permeability coefficients rather than a single dry OTR value. Package-level validation should follow ASTM F1927-20 and ASTM F1307-20 under the intended fill temperature and storage humidity.

Comparative Oxygen Transmission and Processing Latitude Across EVOH Comonomer Fractions

Table 1 reports typical indicative values for 29 mol%, 38 mol%, and 44 mol% ethylene EVOH grades. The EW-3801 entry is the middle column. For package-level applications, published conversion data for this specific grade remain limited; values therefore require validation on the intended line and package geometry.

Flex cracking is a measurable limitation of EW-3801. In Gelbo flex testing per ASTM F392, a coextruded film with a 10 µm EVOH core develops pinholes after fewer cycles than a comparable 44 mol% ethylene EVOH film. The failure mode is not uniform barrier loss but discrete microcrack formation; oxygen transmission map tests then show localized hot spots at the flexed regions. For liquid pouch applications subject to repeated flexure, EVOH layer thickness should be increased to 12–15 µm or a higher-ethylene grade should be considered. Published cycle-to-failure data for EW-3801 specifically are limited, but the comonomer trend is well established in flexible packaging.

Moisture uptake at 23°C and 80% RH for a 38 mol% ethylene EVOH film reaches 5–7 wt% at equilibrium, as measured by ISO 62. The diffusion coefficient of water in the polymer is approximately 1.2 × 10⁻⁸ cm²/s at 23°C. Sorption is nonlinear with relative humidity; below 30% RH, water uptake remains below 1 wt%. This sorption behavior explains why the oxygen barrier loss is modest until 65–70% RH and then becomes steep. Package designs that place EW-3801 between hydrophobic layers reduce the local relative humidity by 20–30%, delaying the barrier loss threshold to higher external humidity.

Food-contact status for EW-3801 is established through supplier certifications under Regulation (EU) No 10/2011 and FDA 21 CFR 177.1360 when the resin is incorporated into a coextruded structure and not used in direct contact with aqueous foods at pH below 3.5 or above 8.5. The vinyl alcohol segments hydrolyze slowly under strong acid or base conditions at elevated temperature; prolonged contact with acetic acid solutions above 3 wt% at 100°C should be avoided. Residual vinyl acetate monomer is below 5 mg/kg by headspace gas chromatography per EN 13628-1. The resin is not recommended for use with chlorinated solvents, strong oxidizing acids, or dimethyl sulfoxide. Post-industrial EW-3801 edge trim may be recycled only after pre-drying and blending with virgin material at no more than 20 wt%, because reprocessing above 220°C increases gel particle content and lowers the melting endotherm by 2–4°C.