EVOH EVAL F171B

EVOH EVAL F171B is an ethylene-vinyl alcohol copolymer supplied by Kuraray under the EVAL trade name. The grade carries a nominal ethylene content of 32 mol%; within the manufacturer’s series notation, F-series resins are the 32 mol% ethylene family, and the F171B designation identifies a specific melt-flow grade. Typical published data list a density of 1.19 g/cm³ per ISO 1183-1:2019 and a melt mass-flow rate of approximately 1.6 g/10 min at 190 °C under a 2.16 kg load per ISO 1133-1:2022. Differential scanning calorimetry per ASTM D3418 gives a melting endotherm near 183 °C. The oxygen barrier of the dry polymer is high: supplier typical data for a 20 µm film at 20 °C and 0 % RH are below 0.5 cm³·20 µm/(m²·day·atm) when measured per ASTM D3985. This barrier is not static because water plasticizes the hydroxyl-rich amorphous phase; at elevated relative humidity the oxygen transmission rate rises substantially. EVAL F171B is therefore used as an internal barrier layer in coextruded films, sheets, bottles, and thermoformed trays for oxygen-sensitive foods such as processed meat, cheese, sauces, and aseptic liquids. Compared with lower-ethylene EVOH grades, it occupies the standard-barrier position: slightly lower dry gas barrier than 27 mol% ethylene types but improved moisture tolerance and melt stability, and substantially higher barrier than 38 mol% or 44 mol% ethylene types.

How Does the 32 mol% Ethylene Content Govern Crystallinity, Barrier, and Melt Stability?

In ethylene-vinyl alcohol copolymers, the ethylene repeat unit interrupts the continuous hydrogen-bonding network of vinyl alcohol sequences. At 32 mol% ethylene, EVAL F171B retains sufficient vinyl alcohol content to provide high dry oxygen barrier, but the ethylene comonomer lowers crystallinity, melting point, and glass-transition temperature relative to 27 mol% grades. This has three practical consequences. First, the dry oxygen barrier remains high because crystalline domains and hydrogen-bonded amorphous regions restrict oxygen diffusion. Second, water uptake is lower than in lower-ethylene grades because fewer hydroxyl sites are available per unit mass; this reduces the relative humidity sensitivity of the core layer. Third, the lower melting endotherm near 183 °C and the reduced crystallinity widen the processing window in coextrusion, allowing lower die temperatures and less shear-induced gel formation. The melt is pseudoplastic; the ISO 1133-1 melt-flow value should not be used alone for die design. Capillary rheometry at 210 °C and 220 °C is required to characterize viscosity at coextrusion-relevant shear rates, especially for thin core layers below 10 µm.

Because EVOH is hygroscopic, open hopper feeding at ambient relative humidity above 60 % can raise pellet moisture above the recommended processing limit. The resin should be pre-dried with desiccant air to a residual moisture content below 0.3 % by weight. Typical drying conditions on production-scale dryers are 80 °C to 90 °C for 4 h to 6 h, but the actual time depends on pellet bed depth, air dew point, and original moisture load. Melt stock temperature should be controlled between 210 °C and 230 °C in barrier film and sheet lines; excursions above 240 °C accelerate thermal degradation, which can cause gel specks, brown discoloration, and acetic-acid odor at the die. Long residence time above 230 °C is a common production-floor failure mode. The resin should not be left in a hot idle extruder; low-density polyethylene is the usual purge material, and the line should be flushed until visual contamination clears. Contact with PVC or PVDC melt streams is to be avoided because acid evolution can degrade EVOH and corrode downstream tooling.

When EVAL F171B Replaces L171B or H171B in Flexible Barrier Packaging Structures

A grade-to-grade substitution is not a simple drop-in change. Compared with L171B, a 27 mol% ethylene EVOH, EVAL F171B has moderately lower dry oxygen barrier, lower melting point, and better tolerance of incidental moisture exposure. On a cast film line that struggles with unmelted L-grade gels or moisture-related edge defects, moving to F171B can reduce rejects, but the structure thickness or layer ratio may need to be increased to meet the same oxygen transmission target. Compared with H171B, a 38 mol% ethylene EVOH, F171B provides higher gas barrier but lower thermoformability and pinch-off toughness. In deep-draw tray applications where corner thinning and stress whitening are the limiting defects, H171B may be preferred despite its lower barrier. The following gradient summarizes the position of EVAL F171B among common EVAL grades.

Selection is driven by the oxygen transmission requirement under the actual package relative humidity, not by the dry-film datasheet value alone. A converter that must meet a package OTR of 0.2 cm³/(m²·day·atm) at 20 °C and 65 % RH may require a thicker F171B layer than an L171B layer, or a lower-ethylene grade if the line cannot deposit the additional thickness.

At external relative humidity above 75 %, the oxygen transmission rate of EVAL F171B does not increase linearly. Absorbed water molecules interact with hydroxyl groups, increasing free volume and reducing the energy barrier to oxygen permeation. The measured OTR at 85 % RH can be an order of magnitude higher than the 0 % RH value, depending on thickness, temperature, and laminate construction. In practical packages, the EVOH core is therefore not exposed directly to the external environment. Polypropylene or high-density polyethylene outer layers retard moisture ingress, but they do not eliminate it; the design calculation must consider water activity at the EVOH core after the intended shelf life. Protective-layer thickness, tie-layer continuity, and water-vapor transmission rates of the outer layers are as important as the EVOH grade. Published data for EVAL F171B in all possible laminate configurations is limited; converter trials with conditioned barrier testing are required for shelf-life validation.

Screw Design, Residence Time, and Purge Protocols for Barrier Coextrusion

In production-scale barrier lines, EVAL F171B is usually processed on single-screw extruders with L/D 24:1 to 30:1 and a compression ratio of 2.5:1 to 3.5:1. Metallic clearances in the nonreturn valve and die should be maintained to avoid dead zones; stagnant melt degrades quickly above 220 °C. Temperature profiles are typically ramped from 180 °C at the feed section to 210–220 °C at the metering section, with the adapter and die held at 220–230 °C. Actual settings must be trimmed for screw speed, backpressure, and output rate, because shear heating can raise the melt temperature above the barrel setpoint. At the die, layer-to-layer viscosity matching with the tie resin and adjacent polyolefin is critical for interfacial stability; if EVAL F171B is far less viscous than the tie layer at the relevant shear rate, layer waviness and incipient encapsulation can occur. For shutdown, the extruder should be purged with low-density polyethylene and not left filled with EVOH under heat. Startup after idle periods should be preceded by visual inspection of the die exit for crosslinked gels.

In rigid container coextrusion blow molding, EVAL F171B is used as the barrier layer in polypropylene and high-density polyethylene bottles for sauces, ketchup, and edible oils. The layer structure is usually a six-layer or seven-layer arrangement with regrind layers separating the barrier from the skins. The melt temperature of the EVOH is held at the lower end of its range to match the viscosity of the molten polyolefin; if the EVOH is overheated, it wets the die lip unevenly and can form drip strings at the parison cut. When the parison is pinched at the bottom, F171B contributes higher melt strength than a 44 mol% ethylene grade, reducing weld-line thinning, but it is less tolerant of deep pinch deformation than H171B. Blow molding trials that measure barrier retention at the sidewall, shoulder, and pinch-off areas are necessary because wall thickness distribution controls the local oxygen transmission rate.

Under European and United States food-contact regimes, EVAL F171B is normally covered by supplier declarations for ethylene-vinyl alcohol copolymers. In the European Union, finished-article compliance is assessed under Regulation (EU) No 10/2011; the overall migration limit for plastics is 10 mg/dm² unless a stricter specific migration limit applies to a listed substance. In the United States, EVAL resins are generally considered food-contact substances under FDA 21 CFR 177.1360, subject to grade-specific limitations recorded in the manufacturer’s food-contact statement. The converter remains responsible for verifying that adhesion to tie resins, printing inks, and lamination adhesives does not raise migration above the applicable limits. For non-food industrial packaging, supplier documentation typically includes REACH and RoHS statements; heavy metals and substances restricted under Directive 2011/65/EU are not intentionally added, but this does not waive lot-level verification when the package is supplied to regulated electronic or automotive streams.

In multi-layer flexible packaging, EVAL F171B is commonly deposited as a core layer of 5 µm to 15 µm depending on the package oxygen transmission target and the expected distribution relative humidity. On a five-layer cast film line, a typical configuration places the EVOH between two maleic anhydride-grafted polyolefin tie layers, with polyolefin skins providing heat-seal and moisture-barrier functions. The limiting process conflicts on such lines are usually in the die entrance, where unstable layer interfaces produce optical haze, and in edge trim recycling, where EVOH contamination of polyolefin trim can reduce film clarity and seal integrity. Edge trim containing EVAL F171B is more difficult to reuse directly in the skin layer; it is usually directed to an internal layer or kept as mixed-polymer scrap. In retort pouches and hot-filled containers, the post-retort oxygen barrier measured after water absorption is the controlling design value, not the dry-film datasheet oxygen transmission rate. Converters should condition finished packages at the intended worst-case temperature and relative humidity before setting the EVOH layer thickness.