EVAL EVOH resin

EVAL EVOH resin is a random ethylene-vinyl alcohol copolymer supplied in pellet form by Kuraray. The product is not a water-soluble polyvinyl alcohol; the ethylene comonomer, present at 27–48 mol%, imparts melt processability and allows the material to be coextruded as a discrete barrier layer. Commercial grade designations include F101, H171, E105, G156, and L171. Melt mass-flow rate is determined according to ISO 1133-1:2022 at 190°C/2160 g and typically spans 1.0–15 g/10 min across the product line. Density is 1.12–1.17 g/cm³ by ISO 1183-1:2019. Melting point measured by differential scanning calorimetry under ISO 11357-3:2018 decreases from approximately 191°C at 27 mol% ethylene to approximately 158°C at 48 mol% ethylene. The resin is used in five-layer and seven-layer coextruded films, sheets, tubes, blow-molded containers, and deep-draw thermoformed trays where oxygen barrier is required at total packaging thicknesses that cannot accept foil or metallised barriers. The functional EVAL EVOH layer is commonly 3–20 µm thick, and the surrounding polyolefin layers protect it from liquid water and high relative humidity.

The combined effect of vinyl alcohol hydrogen bonding and ethylene segments is reflected in the resin specification. Oxygen permeability is dominated by the vinyl alcohol phase, while melt processability and water resistance are dominated by the ethylene phase. The glass transition temperature, measured by ISO 11357-2:2020, is typically in the range of 55–70°C. At dry conditions, oxygen transmission is lower than that of PA6 at equal thickness by roughly an order of magnitude. These properties explain why EVAL EVOH is selected for oxygen-sensitive food, pharmaceutical, agricultural chemical, and automotive fuel tank applications. The same hydrogen bonding also requires careful drying because the resin can absorb several tenths of a percent of moisture before processing.

How Does Ethylene Content Shift Oxygen Transmission and Moisture Sensitivity?

Increasing ethylene content from 27 mol% to 48 mol% reduces oxygen-barrier performance but improves moisture tolerance, flex-crack resistance, and melt flow. Table 1 lists representative grade families and supplier-reported values. The oxygen transmission rate is not a single product constant. For a 20 µm film at 20°C/65% RH, OTR increases from approximately 0.2–0.4 cm³/(m²·day·atm) for the lowest-ethylene grades to approximately 5.0 cm³/(m²·day·atm) for the highest-ethylene grade. At 0% RH, the same low-ethylene grades can fall below 0.1 cm³/(m²·day·atm); at 90% RH, oxygen permeability can increase by 10–100× because water plasticizes the amorphous EVOH phase. This is the rationale for embedding EVAL EVOH between polyethylene or polypropylene skins. The skin layers create a moisture barrier that delays the rise in local relative humidity at the EVOH surface.

MFR and OTR values in Table 1 are representative supplier-reported values for comparison; lot acceptance is controlled by the certificate of analysis. Low-ethylene grades such as L171 shift the barrier curve toward lower OTR but require more aggressive drying and tighter melt-temperature control. The humidity dependency arises from plasticization of the amorphous EVOH phase; water molecules replace some of the interchain hydrogen bonds and increase fractional free volume. At low relative humidity, the high barrier is due to low oxygen solubility and low diffusion coefficient. At high relative humidity, the diffusion coefficient increases more rapidly than solubility. Low-ethylene grades have higher vinyl alcohol content and therefore show the greatest relative change from dry to humid conditions. High-ethylene grades sacrifice dry barrier for flatter humidity response and better flex-crack resistance.

Oxygen transmission measurement under ASTM D3985-17 uses a coulometric sensor and is typically reported at 20°C/65% RH for EVOH because that condition reflects many dry-packaged shelf-life simulations. However, OTR under ASTM F1927-20 at 85% RH or 90% RH is a better predictor for high-moisture food contact. The selection of the correct relative humidity condition is critical because EVAL EVOH permeability follows a nonlinear humidity-dependent function, not a linear correction factor. In multilayer films, the oxygen transmission rate of the finished structure is not estimated by simply dividing the EVOH OTR by layer thickness. Layer adhesion, curling, and local relative humidity at the barrier layer control actual package performance. Oxygen transmission test methods should therefore be run on the final package under ASTM F1307-20 when shelf-life modeling is required.

Melt Rheology, Drying, and Extrusion Boundaries

Pre-drying is mandatory before melt processing. The resin absorbs atmospheric moisture, and hydrolysis at melt temperature reduces molecular weight and generates gel-like defects in film and sheet. Desiccant drying at 80–100°C for 4–8 h to a pellet moisture content below 0.3%, preferably below 0.1%, is specified. In plants where ambient relative humidity exceeds 60%, hopper dryers with a dew point of −40°C or lower are required. Hot-air dryers alone are generally inadequate for low-ethylene grades. Dried pellets reabsorb moisture during long hopper residence; material should be consumed within 2 h after drying when ambient relative humidity exceeds 60%. High-ethylene grades fuse more easily in the drying hopper if temperatures exceed 100°C.

Melt temperature control is the critical operational boundary. Low-ethylene grades are processed at 210–225°C; high-ethylene grades are processed at 215–235°C. Temperatures above 240°C initiate rapid thermal degradation, visible as brown specks and odorous volatiles. Screw designs with compression ratios of 2.5:1–3.0:1 and no high-shear mixing elements are used because shear heating can raise melt temperature above the degradation threshold. In twin-screw compounding or reprocessing of EVAL EVOH, the maximum melt temperature limit is unchanged; high-shear kneading blocks should be reduced or eliminated because local shear heating can exceed the set temperature by 15–25°C. That local temperature excursion is sufficient to initiate degradation even when the barrel setting remains below 240°C. Backpressure should be held below 20 MPa. Start-up and shutdown are performed with a low-melt-index polyolefin purge. At melt temperatures above 230°C, residence time should not exceed 20–30 min. These limits are relevant to 5-layer coextrusion lines with 75 mm, 30:1 L/D barrier extruders and flat dies with die gap settings of 0.6–1.2 mm. Melt pressure instability at constant screw speed, typically above ±0.5 MPa, has been documented on 5-layer blown-film lines before gel outbreaks.

High-ethylene grades such as E105 and G156 have higher MFR and lower melt strength; they are preferred for extrusion coating and deep-draw forming but require narrower die gaps and faster quench to maintain layer uniformity. Low-ethylene grades such as F101 and L171 have higher melt strength and are suited to blown-film and cast-sheet structures where gauge uniformity is more easily maintained. Grooved-feed extruders are avoided for the barrier layer because they introduce excessive energy into the melt. Barrier screws with deeper channels reduce shear heating and help prevent gel formation during extended runs.

When EVAL EVOH Is Coextruded Beneath 10 µm

Interfacial instability and melt curtain streaks are documented when the EVAL EVOH layer falls below 10 µm in flat-die coextrusion without adequate tie-layer thickness. The EVOH layer is normally maintained at 10–15% of total structure thickness. Below 8 µm, even minor variation in die gap or melt temperature produces observable barrier-layer breaks and pinholing. Tie layers of maleic anhydride-grafted polyolefin at 2–5 µm are required on both sides for adhesion to polyethylene or polypropylene. The tie layer also isolates the EVOH from acidic or low-molecular-weight contaminants in the skin layers that can accelerate degradation. The choice of tie-layer resin is influenced by vinyl alcohol content. Low-ethylene grades generally require a higher maleic anhydride graft level or a thicker tie layer to maintain interfacial adhesion after retort. Peel strength measured by ASTM F904-16 on coextruded film should be monitored after retort; reductions below 1 N/15 mm indicate inadequate tie-layer wetting or contamination at the interface.

Edge trim containing EVAL EVOH is not compatible with neat polyolefin recycle streams. On blown-film lines, blending multilayer trim into polyethylene skins above 5–10% recycled content has been documented to increase gel formation and optical haze because the EVOH domains do not melt at polyethylene processing temperatures. Converters either divert trim to compatible tie-layer-rich regrind or use separate recovery streams. In rigid barrier containers, the EVAL EVOH layer is typically 3–10 µm, but the same lower-thickness constraint applies. Injection blow molding and thermoforming require matched die and preform layer distribution because an EVOH layer below 3 µm can become discontinuous at the container heel and shoulder. Dart drop and squeeze testing of containers with insufficient EVOH encapsulation shows delamination at the tie-layer interface, not cohesive failure in the polyolefin.

PVDC, PA6, and MXD6 Occupy Different Barrier Performance Bands

EVAL EVOH differs from PVDC, PA6, and MXD6 in oxygen transmission, moisture response, and conversion equipment requirements. Table 2 compares representative 20 µm films at 20°C/65% RH using ASTM D3985-17. The values are representative ranges, not product specifications.

PVOH cannot be melt processed and is confined to solution coating. EVAL EVOH retains melt processability because ethylene segments disrupt the strong hydrogen bonding of vinyl alcohol units. PVDC offers high barrier with low moisture sensitivity, but it contains chlorine and requires corrosion-resistant extrusion hardware or is applied as a coating. PA6 provides abuse resistance and moderate oxygen barrier but requires a much thicker layer or a lower ambient humidity to approach EVAL EVOH performance. PA6 also absorbs significant water and expands, which can alter package dimensions and increase oxygen permeability. MXD6 offers better moisture-independent barrier than EVOH at high relative humidity, but its oxygen barrier remains below that of low-ethylene EVAL EVOH under dry conditions and its melt temperatures are higher. PVDC has a lower water vapor transmission rate than EVAL EVOH and remains a barrier at high humidity, but its density and halogen content complicate disposal. EVAL EVOH is not a drop-in replacement for PVDC in existing coating lines, nor is it a direct substitute for PA6 in cast film. It requires a dedicated extruder, tie layers, and a protection strategy against moisture.

Food-contact compliance is grade-specific and must be confirmed against the current Kuraray regulatory statement. U.S. clearances are referenced through FDA 21 CFR 177.1360 and applicable Food Contact Notifications; European compliance is assessed under Commission Regulation (EU) No 10/2011. REACH registration is confirmed by the manufacturer under Regulation (EC) No 1907/2006. Lot-specific migration testing is not inferred from the resin certificate alone; finished packaging must be tested under the intended food simulant and condition because EVOH migration behaviour depends on layer position, tie-layer composition, and retort conditions. For structures subjected to steam retort above 121°C or high-shear microwave conditions, published data for specific multilayer configurations is limited; the converter must qualify the finished structure under package-specific barrier tests.