EVOH EVAL L101A

Kuraray EVAL™ L101A is a standard ethylene-vinyl alcohol copolymer resin supplied as cylindrical pellets for coextruded barrier films, sheet, and blow-moulded containers. The nominal ethylene content is 27 mol%, with a published melt flow rate of 3.2 g/10 min at 190 °C/2160 g per ISO 1133-1:2022. Density is 1.18 g/cm³ per ISO 1183-1:2019. Oxygen transmission rate on coextruded film with a 20 µm barrier layer, conditioned at 20 °C and 65 % RH, is reported at approximately 0.4 cm³·20 µm/(m²·day·atm) per ASTM D3985. The product is intended as a buried barrier core rather than a monolayer surface layer because direct contact with liquid water disrupts the interchain hydrogen-bonded network responsible for oxygen barrier.

Before pellet L101A enters an extruder, moisture content must be reduced below 0.1 % because the resin is hygroscopic and releases acidic volatiles when processed wet. Pellets stored at 60 % RH and 23 °C can absorb more than 0.2 % moisture in 8 h. Desiccant drying at 80–90 °C for 4–6 h with inlet air dew point below -20 °C is standard in film production. Wet EVOH generates bubbles in the barrier layer, reduces tie-layer adhesion, and accelerates acetic acid formation. Operators should verify moisture analyser readings below 0.1 % before start-up rather than relying solely on hopper residence time.

What Process Conditions Trigger Gel Formation and Acetic Acid Evolution in L101A Extrudate?

Thermal degradation of L101A is a time-temperature autocatalytic process. At melt temperatures above 230 °C, vinyl alcohol units undergo acid-catalysed dehydration, releasing acetic acid and forming conjugated unsaturation that colours the extrudate yellow and creates crosslinked gels. Barrel temperature profiles of 180–220 °C are common on chrome-plated screws; die adapter settings up to 230 °C are permissible only when residence time is kept below 10–15 min. Screw geometries above 24:1 L/D and compression ratios above 3.0:1 can generate shear heating that raises melt temperature above set point. Production-scale purging uses low-melt-flow LDPE or PP at 210–230 °C after each run. Vinyl acetate copolymers and acid-containing purge compounds are avoided because they accelerate gel formation. Melt pressure at the EVOH die adapter is monitored; a drift of more than 10 % without throughput change indicates degradation or wet pellets.

Thermal analysis of L101A per ISO 11357-3:2018 at 10 °C/min from 25 °C shows a melting endotherm near 191 °C, a crystallization exotherm near 162 °C, and a glass transition near 62 °C. These transitions define heat-seal and thermoforming limits. In sheet extrusion for thermoforming, surface heating to 140–150 °C does not destroy barrier-layer continuity if residence time is short. Heating above 160 °C begins to melt the EVOH crystal network and can produce thin spots after forming. The crystallinity of L101A is process-dependent. Rapid quenching on a chill roll at 15–25 °C limits spherulite growth and preserves transparency, while slow cooling or annealing at 90–110 °C for 1 h increases crystalline fraction and reduces oxygen transmission but reduces flex-crack resistance and formability.

Capillary rheometry of L101A indicates non-Newtonian shear-thinning behaviour over 100–1000 s⁻¹. At low shear rates, high viscosity assists layer uniformity; at die shear rates, viscosity approaches that of polypropylene tie resins, which reduces interfacial instability. Melt elongation at 190 °C is sufficient for deep-draw thermoforming but lower than that of higher-ethylene EVAL grades. In blow moulding, L101A is coextruded as a thin core under polyolefin melts, and parison sagging is controlled primarily by skin-layer viscosity rather than by the EVOH core.

Because the oxygen barrier of L101A is generated by interchain hydrogen bonding, barrier loss follows the water activity around the core layer rather than the external humidity alone. In dry snack packaging stored at 23 °C and 50 % RH, polyolefin skins restrict moisture transport and the EVOH core can remain below 65 % RH, maintaining oxygen transmission near the published value. In pasteurized or retorted wet food containers, core-layer humidity can exceed 85 % RH; oxygen transmission then rises by a factor of 5–10. A thicker L101A layer does not fully compensate for humidity-driven barrier loss. For such conditions, a higher-ethylene EVOH grade, a desiccant sealant layer, or an inorganic barrier layer may be required. Published data for this specific configuration is limited, so shelf-life testing should be conducted on the complete multilayer structure.

Oxygen transmission through a finished package contains two terms: permeation through the barrier layer and leakage through pinholes, seal defects, or score-line cracks. L101A contributes only to the permeation term. A pinhole density above 0.2 holes/m² in laminated film can dominate oxygen ingress and mask differences between EVOH grades. In controlled-atmosphere packaging, carbon dioxide permeability of L101A is approximately 3–5 times higher than oxygen permeability. Therefore, carbon dioxide transmission values should be measured per ASTM F2476 on the complete film rather than derived from oxygen transmission data. For nitrogen-flushed packages, oxygen is usually the limiting permeant because nitrogen permeability is lower.

Comparative Barrier and Moisture Trade-Offs Across EVAL Ethylene Grades

L101A belongs to the 27 mol% ethylene class, which provides the highest dry oxygen barrier among standard EVAL film grades but also the steepest relative humidity sensitivity. Compared with 32 mol% and 38 mol% ethylene grades, L101A exhibits lower oxygen transmission at 20 °C/65 % RH, but the ranking can reverse at >75 % RH. The selection boundary is not fixed; it depends on expected core humidity, target shelf life, and package mechanical requirements. Higher-ethylene grades also offer lower melt viscosity and improved flex-crack resistance, which can be decisive for bag-in-box films and high-speed pouch lines. Direct replacement of L101A with a higher-ethylene grade should be preceded by coextrusion adhesion tests and oxygen transmission tests per ASTM D3985 on film conditioned at the product’s worst-case humidity.

Tie-layer selection for L101A starts with maleic-anhydride-grafted polyolefins formulated for EVOH adhesion. Peel adhesion above 4 N/15 mm per ASTM F904 is typically required for flexible packaging, but contaminated EVOH surfaces, low die lip temperatures, or insufficient tie-layer thickness can reduce adhesion below 2 N/15 mm. In five-layer cast film, L101A is usually 5–15 % of total thickness, with tie layers each 1–2 % and polyolefin skins as the balance. Barrier-layer thickness must be monitored independently of total film gauge; a variation of ±5 % in the EVOH core can create local oxygen ingress. Die gap settings of 0.5–0.8 mm and moderate draw-down ratios reduce neck-in and maintain core encapsulation. Screen packs of 100–250 µm are commonly used to trap degraded particles, with pressure drop monitored to avoid heat build-up at the screen.

When L101A Replaces a Higher-Ethylene EVOH in an Existing Coextrusion Line

Substitution of L101A for a 32 mol% or 38 mol% ethylene grade on an existing line requires changes to temperature and screw-speed profiles. Because the lower ethylene content increases melt viscosity and crystallization rate, barrel set points are often reduced by 5–10 °C to prevent shear over-heating and gel formation. The EVOH layer may set faster at the die lip, which improves layer sharpness but increases the risk of edge encapsulation defects. If the line previously ran a higher-ethylene grade, feed-section temperature should be verified to avoid pellet bridging in hot hoppers above 70 °C. Pellet geometry and the additive package influence feed consistency; L101A feeds uniformly on grooved-throat extruders but can exhibit feed interruptions if hopper throat temperature exceeds the pellet surface softening point.

L101A is supplied in moisture-barrier packaging, typically 25 kg or 500 kg bags and octabins. Opened containers should be resealed with dry-air purge or used within 4 h in high-humidity environments. Clean EVOH edge trim can be incorporated at up to 10 % into the EVOH layer without measurable loss of oxygen barrier, but the regrind must be dried to the same moisture specification and must not be contaminated with polyolefin or tie-layer trim. Cross-contamination with nylon or polyester trim produces hazy gels and is not permitted.

Typical application zones include coextruded polypropylene cups and trays for processed meat, dry cereal liners, lidding film for modified-atmosphere packages, and stand-up pouches for dry and semi-dry foods. L101A is used in structures where external humidity remains below 65 % RH for most of shelf life and where product water activity does not force the core above 75 % RH. For high-water-activity products, barrier-layer options are selected case by case, with shelf-life testing on the complete package per ASTM F1927 or ASTM F2622 as appropriate.

Residual acetaldehyde in EVOH can migrate into sensitive products. L101A is normally positioned behind a polyolefin functional barrier that reduces migration below organoleptic thresholds. For direct contact with semi-solid foods under FDA 21 CFR 177.1360, residual acetaldehyde is often specified at less than 5 µg/g resin, measured by headspace gas chromatography per ISO 17052 or equivalent. Final package acceptance should include sensory evaluation because barrier performance and flavour performance are independent criteria.

Compliance documentation for L101A commonly includes FDA 21 CFR 177.1360 for food-contact applications, EU 10/2011 for plastic materials intended to contact food, and REACH registration statements. Heavy metal content is below the limits of EU 2011/65/EU RoHS recast for packaging components. The product is not recommended for unprotected monolayer packaging because direct contact with liquid water or high-moisture foods causes opacity and a sharp loss of oxygen barrier. It is also not recommended as the sole barrier layer in retort applications; if used in retortable structures, L101A must be encapsulated with high-temperature tie resins and polypropylene skins, and oxygen barrier under humid retort conditions should be verified rather than inferred from dry-film data.