ExxonMobil EVA 7028FL. Resina de copolímero de CC EVA, 27,5% VA, 7 MI, grau de filme de embalagem

ExxonMobil EVA 7028FL.CC is an ethylene-vinyl acetate copolymer resin positioned as a packaging film sealant and tie-layer material, designated by a nominal vinyl acetate content of 27.5 wt% and a nominal melt index of 7 g/10 min when determined at 190 °C under a 2.16 kg load according to ASTM D1238 or ISO 1133-1:2022. The grade-name structure encodes the two most important specification boundaries: the “28” series corresponds to the high vinyl acetate level, while the “7” series corresponds to the mid-range melt-flow segment used in film converting. In coextruded packaging, the resin functions mainly as a low-temperature sealant layer rather than as a load-bearing core. The high vinyl acetate content depresses polyethylene crystallinity, lowers the crystalline melting point, broadens the heat-seal initiation window, and improves adhesion to polar substrates. The 7 g/10 min melt index places the material in a lower-viscosity class than many blown film EVA sealants, which reduces extrusion torque but requires deliberate bubble-cooling control. Because the grade is supplied as a packaging film resin, food-contact compliance must be confirmed on the finished structure under FDA 21 CFR 177.1350 and Commission Regulation (EU) No 10/2011 as amended, not assumed from the resin alone.

In typical three-layer or five-layer blown film constructions, the resin is applied as the inner sealant layer against a polyethylene-based core or an outer skin of linear low-density polyethylene or metallocene polyethylene. The sealant-layer weight fraction is normally set by seal-strength, drop-impact, tear, and migration testing rather than by a single supplier recommendation. Because the high vinyl acetate fraction reduces melting point and melt viscosity relative to unmodified polyethylene, coextrusion processors commonly run the sealant layer at a lower die temperature than the structural layers to prevent interfacial viscosity mismatch and layer distortion. Relevant finished-film test anchors include ASTM F88 for seal strength, ASTM F1921 for hot-tack, ASTM D1709 or ISO 7765-1 for impact resistance, and ASTM D1003 for haze.

Why Does the 27.5 wt% Vinyl Acetate Content Reshape Crystallization and Seal Performance?

Published data for this specific grade configuration is limited outside the supplier technical datasheet; the following statements are therefore based on the well-established behavior of EVA copolymers in the 27–28 wt% vinyl acetate class. At this vinyl acetate level, the copolymer chain loses much of the long-range crystallinity characteristic of low-density polyethylene. Differential scanning calorimetry by ASTM D3418 or ISO 11357-3 typically shows a crystalline melting peak in the range of 70–75 °C for such copolymers, substantially below that of LDPE or lower-vinyl acetate EVA grades. This reduced crystalline order is the primary reason the resin exhibits low-temperature flexibility, improved clarity, and lower heat-seal initiation than EVA copolymers containing 12–18 wt% vinyl acetate.

The increase in vinyl acetate content also shifts density into the class range of approximately 0.94–0.95 g/cm³ at 23 °C when measured by ASTM D792 or ISO 1183-1. The lower crystallinity reduces stiffness and yield stress while increasing elongation and impact toughness at freezer temperatures. These effects are measurable on finished film by tensile testing under ASTM D882 or ISO 527-3, using specimens conditioned at 23 °C ± 2 °C and 50 % ± 5 % relative humidity for at least 40 h before testing.

The sealing advantage of the 27.5 wt% vinyl acetate content is not simply a lower melting point. Reduced crystallinity also lowers the temperature at which the film surfaces fuse under pressure, which is critical in high-speed form-fill-seal lines where dwell time is short. Heat-seal initiation must nevertheless be measured on the final laminated or coextruded structure because seal bar temperature, pressure, dwell time, and film gauge alter the result. The resin provides a moderate hot-tack and seal-through-contamination window relative to lower-VA EVA grades; however, for applications requiring aggressive seal-through-contamination performance, ionomer sealants are generally specified instead.

Adhesion to aluminum foil, paper, and polar inks is improved by the vinyl acetate functional group. For polyester or EVOH substrates, the resin does not replace a true tie-layer chemistry; maleic anhydride-grafted polyolefins are typically inserted between the EVA sealant and high-barrier layers when structural adhesion is required. The high vinyl acetate content also reduces the corona treatment burden relative to unmodified polyethylene because the resin surface exhibits higher polarity.

Blown Film Die, Bubble Cooling, and Extrusion-Coating Boundary Conditions

The melt index of 7 g/10 min under 190 °C and 2.16 kg identifies a lower-viscosity EVA compared with 2–3 g/10 min blown film grades. On a single-screw blown film line with an L/D of 24:1 to 30:1, the grade generally produces lower motor load and lower melt pressure at equivalent throughput, which can support higher output on screw-limited lines. The same lower viscosity reduces bubble stability in blow-up ratios above approximately 2.5:1 to 3.0:1, requiring chilled air and careful frost-line-height control. Typical die gaps for high-VA EVA blown film fall in the range of 1.5–2.5 mm, with actual settings dependent on die diameter, blow-up ratio, and frost-line requirements.

Barrel temperature profiles for high-VA EVA are normally set lower than for LDPE. A representative profile for a 24:1 L/D single-screw extruder begins at 140–150 °C in the feed zone, increases to 160–180 °C in the compression zone, and reaches 190–205 °C at the metering zone and die. Melt temperature at the die should be kept below 220 °C during normal operation. Sustained melt temperatures above approximately 230 °C can initiate deacetylation of the vinyl acetate units, releasing acetic acid. The resulting acidic volatiles can corrode downstream metal surfaces and contribute to die-lip plate-out. Stainless steel melt-contact components are preferred, and copper-based alloys should be avoided in areas exposed to melt vapors.

In cast film and extrusion coating, the 7 g/10 min melt index supports drawdown to thin gauges more readily than lower-MI EVA grades. The grade can be placed against the substrate to exploit its polar adhesion while a polyethylene layer provides melt strength and down-gauge economics. For extrusion coating of paper or aluminum foil, the high vinyl acetate content improves adhesion but limits heat resistance; the resulting laminate should not be specified for hot-fill above approximately 60 °C without creep testing of the seal area and coating interface. Because EVA does not provide high oxygen or moisture barrier, the resin should not be selected as a barrier layer. Barrier performance must be supplied by EVOH, polyamide, aluminum foil, or metallized layers in the structure.

High-VA EVA films exhibit greater blocking tendency than lower-VA EVA or LDPE. Converter-added antiblock and slip packages are generally required to control coefficient of friction. Surface slip should be verified at the final film level by ASTM D1894 because migration of slip additives is time- and temperature-dependent. Processing with highly alkaline or amine-based additive masterbatches should be evaluated before production; such additives can accelerate deacetylation and promote plate-out at elevated melt temperatures. At shutdown, a low-VA polyethylene purge is recommended to reduce acidic residue in the barrel, die, and downstream cooling equipment.

Pre-drying is generally not required for EVA copolymers stored in closed original packaging under ambient relative humidity at or below 60 %. If surface moisture is observed due to improper storage, drying at 60 °C for 4–6 h may be applied. Prolonged storage above 35 °C should be avoided because high-VA pellets can soften and agglomerate under pallet load.

When the Grade Is Positioned Against Lower-VA and Higher-VA EVA Copolymers

Relative to an EVA copolymer with 18 wt% vinyl acetate, the 27.5 wt% vinyl acetate content in 7028FL.CC lowers the crystalline melting point, reduces stiffness, improves low-temperature impact resistance, and increases adhesion to polar substrates. The trade-off is a greater tendency to block, lower maximum service temperature, and higher gas permeability. Relative to a 33 wt% vinyl acetate EVA, 7028FL.CC offers a more moderate balance of adhesion and handling, with less blocking and better thermal stability during film processing. The following directional table compares classes rather than specific commercial grades.

The table is a qualitative ranking only. Actual commercial grades vary by antioxidant package, slip and antiblock content, and supplier-specific molecular architecture. For a given end use, the selection between a 2 MI, 7 MI, or 25 MI EVA should be made on the converting line where bubble stability, screw torque, and drawdown are measured directly. In general, lower-MI EVA grades are favored for thick blown film and large bubble diameter stability, while higher-MI grades are favored for extrusion coating and high-output cast film where low viscosity is more valuable than melt strength.

When a packaging line is limited by seal-bar temperature or seal dwell time, the 27.5 wt% vinyl acetate content provides a lower seal-initiation window than EVA copolymers with 18 wt% VA. That lower seal-initiation window can reduce energy input and increase line speed in form-fill-seal operations. However, the same low melting point limits use in retort, hot-fill, or boil-in-bag structures where the seal area may be exposed to temperatures above 60 °C. In those structures, a higher-temperature sealant such as polypropylene or a specialty tie-layer system is standard.

In frozen food packaging, the reduced crystallinity of 7028FL.CC improves flexibility at subzero temperatures and reduces brittle fracture in drop tests. The frozen food application still requires validation by ASTM D1709 or ISO 7765-1 at the target service temperature, because orientation, gauge, and coextruded layer structure affect impact failure. The resin is not intended for outdoor long-term UV exposure unless a suitable UV stabilizer package is included in the film formulation.

Compliance Verification Requires More Than the Resin Datasheet

Resin-level data alone are insufficient for food-contact or end-market certification. The finished film or laminate must be tested under the conditions of intended use, including time, temperature, food simulant, and layer structure. The matrix below lists the standard designations most commonly used to verify resin properties and finished packaging compliance. Inclusion in the matrix does not constitute a supplier certification.

The vinyl acetate monomer specific migration limit under the EU framework should be checked against the current consolidated regulation; the value is commonly cited as 12 mg/kg, but formulators must use the regulatory text applicable to the end-use food simulant. For United States food-contact use, the grade may be used only insofar as the finished EVA copolymer meets the compositional and extractive limitations of 21 CFR 177.1350. Converters should request the grade-specific certificate of analysis, product stewardship bulletin, and safety data sheet before commercial production.