Soarnol GC3304B

Soarnol GC3304B is an ethylene-vinyl alcohol copolymer manufactured by Mitsubishi Chemical Corporation and supplied through Soarus LLC for coextruded film, sheet, and blow-molded barrier containers. The grade is positioned in the 32–33 mol% ethylene class; the nominal ethylene content is determined by the manufacturer’s internal spectroscopic method and is reported on the certificate of analysis. The melt mass-flow rate is controlled within the range 3.0–4.0 g/10 min when measured at 190 °C under 2.16 kg using ISO 1133-1:2022. Pellet density is normally 1.18–1.20 g/cm³ when tested according to ISO 1183-1:2019. The product is supplied as a uniform pellet with a controlled gel rating and is intended for use as the barrier layer in polyolefin-based multilayer structures. Unlike general-purpose polyolefins, EVOH requires a tie-layer resin, normally a maleic anhydride-grafted polyolefin, on both sides to achieve structural continuity with polyethylene or polypropylene. The material is regulated for food-contact use when used in accordance with the applicable national legislation; in the United States, EVOH copolymers in this composition class fall under 21 CFR 177.1360, and in the European Union the substance is evaluated within the framework of Regulation (EU) No 10/2011 as amended. Users are responsible for verifying the compliance status of the finished multilayer structure, including the tie layer and outer layers, for the intended food type and temperature condition.

Specification values for Soarnol GC3304B should be drawn from the current technical data sheet and the lot certificate of analysis. The following table presents the typical property envelope for this resin class and should not be used as a supply specification.

The grade designation GC3304B is commonly assigned to applications requiring a combination of moderate melt viscosity and high dry-barrier retention. In coextruded cast film and sheet, the resin is matched with tie resins having a melt-flow index in the 1.0–3.0 g/10 min range at 190 °C/2.16 kg; a lower-viscosity tie resin can produce unstable interlayers because the viscosity ratio at the die shear rate is too high. The shear-rate dependence of EVOH is more Newtonian than that of low-density polyethylene, so the EVOH layer does not thin as much in high-shear regions; this can cause layer encapsulation or uneven layer distribution if the feedblock is not adjusted for the viscosity of the grade. Production-scale feedback from cast-film lines indicates that die-lip temperatures should be held within ±2 °C of the center value to avoid gauge bands in the EVOH layer. The use of automatic die bolts is often required when total film thickness is below 40 µm and the EVOH layer is below 3 µm.

For adhesive strength testing, peel adhesion of the tie/EVOH interface is measured according to ASTM F904 on a tensile tester equipped with a 0–50 N load cell. Values above 4 N/15 mm are generally required for lamination films; values below 2 N/15 mm after 85 °C/85% RH conditioning for 168 h indicate an inadequate tie resin or insufficient drying. The failure mode should be noted: a clean interfacial separation indicates adhesive failure, while a film tear within the EVOH layer indicates cohesive strength sufficient for commercial use.

What Limits Melt-Temperature Stability in a 32 mol% EVOH Barrier Layer?

On production-scale coextrusion lines, the practical processing window for Soarnol GC3304B is bounded by gel formation at high temperatures and by viscosity mismatch at low temperatures. A single-screw extruder with 24:1 to 30:1 L/D and a barrier screw with a compression ratio of 3.0:1 to 4.0:1 is commonly used; grooved-barrel extruders are generally avoided for this resin class because excessive shear heating can produce localized temperatures above 240 °C. Barrel zone settings are typically set from 180 °C at the feed throat to 220 °C at the metering section. Melt temperature at the die entrance should remain below 240 °C; excursions above 250 °C can initiate thermal decomposition, producing gels, discoloration, and pressure fluctuations in the feedblock. The actual melt temperature is measured with an immersion thermocouple at the adapter; the value should be recorded as part of lot traceability because batch-to-batch variation in molecular weight can shift the shear heating response.

The resin must be dried to less than 0.3% moisture before extrusion. Moisture above 0.3% leads to hydrolytic degradation and bubble formation in the melt stream. Desiccant dryers with a dew point of -40 °C or lower are specified; drying at 80 °C for 4–6 h is normally adequate for fresh material. Regrind loads above 20% in the EVOH layer are not generally recommended for high-humidity or retort applications, because each heat history increases gel content and reduces interlayer adhesion. On a 75 mm single-screw extruder producing a five-layer film at 300–500 kg/h total throughput, residence time should be kept below 15 min; start-up and shutdown procedures should include purging with a low-melt-index polyethylene or a commercial purge compound until the melt stream is clear. The purge material must be compatible with the tie resin and must not contain amine-based slip or antistatic additives that can react with residual EVOH.

Coextrusion feedblock and die design should maintain the EVOH melt stream between 200 °C and 230 °C. If the die gap is below 0.8 mm or the line speed exceeds 150 m/min, the shear rate in the EVOH layer may exceed the critical value for melt fracture in this molecular weight class; visual defects such as sharkskin or layer waviness are then observed. The use of a lower-viscosity grade should be evaluated instead of raising melt temperature to compensate. Published data for this specific configuration is limited, but production audits have shown that layer thickness variation above ±10% is frequently associated with feedblock temperature imbalance rather than resin lot variability.

When Relative Humidity Exceeds 65% in High-Barrier Packaging

Oxygen barrier performance of Soarnol GC3304B is not constant; it is inversely related to moisture content in the barrier layer. At 20 °C and 0% RH, a 20 µm film from the 32 mol% class can show oxygen transmission rates below 0.2 cm³/m²·day·atm when conditioned to equilibrium and tested according to ASTM D3985. At 20 °C and 65% RH, the transmission rate commonly increases to 0.3–0.8 cm³/m²·day·atm. At 85% RH, the same film can exceed 2.5 cm³/m²·day·atm. This nonlinear increase is characteristic of the EVOH barrier mechanism and must be accounted for in shelf-life models. The performance of a multilayer package therefore depends less on the dry resin spec than on the moisture ingress rate through the outer polyolefin layers and the edge seal quality. In retort or high-humidity applications, the 32 mol% grade is selected as a compromise between the dry-barrier advantage of a 29 mol% grade and the lower process sensitivity of a 38–44 mol% grade.

Water vapor transmission through a 20 µm film is significantly higher than that of polyolefins; values of 30–60 g/m²·day at 40 °C/90% RH are typical under ASTM F1249. This is not a defect but an inherent property of the vinyl alcohol blocks. For this reason, EVOH barrier layers are typically buried between polyolefin cap and tie layers that limit moisture uptake. The structural design should position the EVOH layer away from the package exterior in high-humidity service; dry food and modified-atmosphere packages can tolerate more aggressive EVOH placement.

In comparison with polyamide 6, at 0% RH the EVOH class provides oxygen transmission rates roughly two orders of magnitude lower. At 85% RH, the advantage narrows, with typical 20 µm EVOH films at 2.5–8.0 cm³/m²·day·atm compared with 20–40 cm³/m²·day·atm for PA6 under ASTM D3985 after thickness normalization. PVDC barrier is less humidity sensitive, but processing requires halogen emission controls and the resin is not as easily incorporated into transparent recyclable structures. Soarnol GC3304B differs from higher-ethylene Soarnol grades in that it retains a sharper melting endotherm and higher dry barrier; it differs from lower-ethylene grades in that it shows lower melt viscosity and better tolerance to moisture during processing.

Direct replacement of Soarnol GC3304B with a 29 mol% EVOH such as Soarnol D2908 is not straightforward because the 29 mol% material requires a slightly higher melt temperature to prevent high melt viscosity and may exhibit greater gel sensitivity at high shear. Conversely, replacement with a 44 mol% grade such as Soarnol A4412 reduces viscosity and improves thermoformability but can increase oxygen transmission by a factor of 3–5 at the same thickness and humidity. The choice is therefore tied to the target shelf-life model and the downstream forming process, not to oxygen transmission alone.

When this resin is used for hydrocarbon barrier in blow-molded containers, the barrier requirement is often specified as a permeation limit under US CARB or EPA test protocols for fuel systems. The 32 mol% class is used in multilayer HDPE/EVOH/HDPE structures for small-engine fuel tanks and agricultural chemical containers. The resin layer is typically 2–5% of the total wall thickness; tie-layer thickness is maintained above 0.02 mm per side to prevent delamination during drop-impact conditioning at -40 °C. Blow molding melt temperature is controlled between 190 °C and 220 °C for this grade; higher temperatures reduce melt strength and may cause parison drawdown problems.

Soarnol GC3304B should not be dry-blended with polyamides containing amine end groups, polyvinyl chloride thermal stabilizers based on organotin, or high-acid copolymers without prior compatibility testing; these combinations can generate discoloration or interlayer defects. If a line stoppage exceeds 15 min, the EVOH stream should be purged or the extruder heaters should be reduced to 150 °C to limit residence-time degradation. These limits are operational boundaries, not optional guidelines, for maintaining layer adhesion and barrier retention.