EVATANE 28-03 resina de copolímero EVA, grau macio e flexível

EVATANE 28-03 is a low-melt-index ethylene-vinyl acetate copolymer produced under the EVATANE trade name by Arkema. The resin is classified as a soft and flexible grade because the nominal vinyl acetate comonomer content of 28 wt% reduces polyethylene crystallinity to a level that produces a Shore A hardness of 82 under ISO 868:2003. The melt flow index is 2.5–3.5 g/10 min when measured under ISO 1133-1:2022 at 190°C with a 2.16 kg load. This combination of high vinyl acetate content and low melt flow index gives the material higher melt strength and greater cohesive strength than higher-MFI EVA grades of the same comonomer level. Softness is intrinsic to the copolymer backbone rather than induced by external plasticizers; therefore plasticizer migration is not a service-life mechanism in finished parts.

The numerical suffix “03” refers to the nominal melt flow index in g/10 min, not to comonomer content. EVATANE 28-03 therefore belongs to the 28 wt% VA platform, but differs from EVATANE 28-05 and EVATANE 28-25 primarily in melt viscosity. Typical analytical values are consolidated in Table 1.

These values are typical and do not constitute specification limits. For a 25 kg bag stored at 23°C and 50% relative humidity, moisture uptake is normally below 0.05 wt%; pre-drying in a desiccant-bed dryer at 60°C for 4 h is required if pellet surface moisture exceeds that limit. Drying air with a dew point at or below -30°C is preferred. Pellets held in an open hopper at relative humidity above 60% can become surface-moist within 8 h, and this surface moisture can produce pinholing in extruded film when barrel temperatures approach 170°C.

What Processing Boundaries Apply in Extrusion and Injection Molding?

On single-screw extruders with L/D ratios between 24:1 and 30:1, barrel set points from 120°C to 170°C are typical. The screw should use a compression ratio of 2.5:1 to 3.5:1 and a progressive transition zone to limit shear heating. Die temperatures between 160°C and 180°C are common for profile and tubing. In injection molding, barrel temperatures of 140°C to 180°C and mold temperatures of 10°C to 30°C are used. Melt temperature must not exceed 200°C; above this threshold, vinyl acetate degradation generates acetic acid, which causes corrosion in unplated screw and die surfaces and can produce gel defects. At 190–200°C, residence time should be minimized and the machine should be purged with a low-MFI polyethylene after shutdown. Pellet bridging in the feed throat is a known production bottleneck when the rear zone exceeds 50–60°C; water-cooled feed throats are recommended.

At high screw speeds, shear heating can create local melt temperatures above the barrel set point. Pressure transducer monitoring near the die is therefore used to detect viscosity reduction from degradation; a sudden pressure drop at constant screw speed can indicate vinyl acetate decomposition or gel slip. Compounds containing calcium carbonate above 30 wt% may increase melt pressure and reduce elongation at break, but the magnitude depends on filler particle size distribution and surface treatment; published data for highly filled EVATANE 28-03 systems is limited.

Mechanical Property Loss at Elevated Comonomer Content Is Not Linear

The tensile strength at break of approximately 10 MPa and elongation at break of approximately 800% under ISO 527-2:2012 reflect the loss of crystalline load-bearing domains relative to LDPE. Compared with an 18 wt% VA EVA, EVATANE 28-03 has lower hardness and tensile strength but higher elongation and may exhibit greater environmental stress crack resistance under ASTM D1693, although published values for this specific grade are limited. The crystallinity reduction also raises moisture vapor transmission and oxygen transmission; for packaging films, these values should be measured on the finished film under ASTM D3985 or ISO 15105-2 rather than inferred from raw pellet data.

When compared with EVATANE 18-150, the 28-03 grade has lower melt flow and higher melt strength, making it less suitable for high-speed thin-wall injection molding and more suitable for profile extrusion and blown film. The lower melt index also reduces melt drawing and neck-in in extrusion operations, but the higher VA content increases adhesion to polar substrates. EVATANE 28-03 is not an extrusion-coating grade for high line speeds; for coating processes above 150 m/min, a higher MFI grade is normally selected.

If Lower Melt Flow Index Is Required for Hot Melt Adhesive Formulation

In hot melt adhesive compounding, EVATANE 28-03 functions as the polymeric binder and is typically formulated with 30–50 wt% tackifier resin and 5–20 wt% wax. The low MFI raises the viscosity of the final adhesive and increases cohesive strength at ambient temperature. Formulation viscosity is measured at 180°C by ASTM D3236; values between 5,000 mPa·s and 20,000 mPa·s are commonly targeted for slot-die application, depending on the tackifier softening point. Ring-and-ball softening point of finished formulations, measured under ASTM E28, generally falls between 80°C and 110°C. EVATANE 28-03 provides better adhesion to polar films and aluminium than EVATANE 18-150, but the lower crystalline fraction reduces heat resistance and increases cold flow compared with lower-VA grades.

Because the resin has a melting peak near 72°C, hot-melt equipment must be heated before startup to avoid bridging in the melt tank. Stainless steel or nickel-plated tanks are preferred for continuous operation at 160–180°C; copper alloy components can catalyse discoloration in long campaigns. Nitrogen blanketing is recommended when hold times exceed 4 h at application temperature.

Table 2 compares EVATANE 28-03 with adjacent EVATANE grades that are often considered for the same target applications. The primary difference is melt viscosity; within the 28 wt% VA platform, higher suffix values correspond to higher melt flow index and therefore lower molecular weight. In selecting a grade, a converter should separate the effect of the VA content from the effect of melt index: softness and polarity are driven mainly by VA content, whereas flow length, melt strength, and adhesive viscosity are driven mainly by melt index.

EVATANE 33-25 has a higher VA content of 33 wt% and the same nominal MFI as EVATANE 28-25. It offers higher polarity and increased adhesion to polar substrates, but its thermal stability is lower because the additional acetate ester content accelerates acetic acid formation at elevated melt temperature. EVATANE 42-60 has substantially higher VA content and MFI; it is used only in applications requiring very low viscosity or high surface tack at ambient temperature. Published comparative peel adhesion data on EVATANE 28-03 and EVATANE 33-25 is limited; evaluations should be performed on the final formulated product under the relevant peel standard, such as ASTM D903 or ISO 8510-2, depending on the substrate and bond configuration.

Flexible foam structures based on EVATANE 28-03 are produced by compounding with azodicarbonamide blowing agent at loadings of 0.5–1.5 wt% or with exothermic/endothermic blend systems. Because azodicarbonamide decomposition begins near 190–210°C, the blowing agent activation window overlaps the upper processing limit of the resin. Foam lines therefore use a reverse-temperature profile or side-feed the chemical blowing agent masterbatch to delay gas evolution until the melt has passed the restrictive die. Foam density and compression set should be measured under ISO 845 and ISO 1856, respectively; published data for EVATANE 28-03 foam compounds is limited.

Storage, Drying, and Vinyl Acetate Degradation Boundaries

Unopened bags should be stored below 35°C in a dry area, protected from UV radiation. The resin is hygroscopic enough to require moisture control in humid weather, but it is not typically dried in a vacuum oven because pellet fusion can occur above 50°C. A hopper dryer with a dew point below -30°C is preferred. Acetic acid generated during thermal degradation can corrode brass or copper components; stainless steel equipment is recommended for melt temperatures above 180°C. If acrid odour or yellowing appears in purged material, the melt temperature should be reduced and the system purged with a non-reactive purging compound. The resin is not compatible with strongly acidic or alkaline cleaning compounds in hot-runner systems; residues of these agents can accelerate ester hydrolysis.

In many soft-touch applications, EVATANE 28-03 can replace plasticized PVC where phthalate-free or migration-resistant materials are required. The EVA does not contain external plasticizer, so property retention after heat aging is governed by oxidation and crosslinking rather than plasticizer loss. Thermal aging tests should use ISO 188 or the relevant part-specific endurance test; published comparative data against plasticized PVC in specific automotive interior parts is limited.

For food-contact applications, the base resin may be evaluated under FDA 21 CFR 177.1350(a) for ethylene-vinyl acetate copolymers and under European Commission Regulation (EU) No 10/2011. Specific migration limits for vinyl acetate monomer and any additives must be assessed on the finished article using the intended food simulants and temperature conditions. The supplier does not provide a blanket compliance statement for fabricated articles. Medical or pharmaceutical use requires separate biological evaluation under the applicable risk management standard, such as ISO 10993-1, because the polymer may contain process aids and residual monomer below the stated specification.