ATEVA 1807EG Copolímero de acetato de vinilo de etileno

ATEVA 1807EG is a pelletized ethylene-vinyl acetate random copolymer whose product designation is conventionally interpreted as nominal 18 wt% vinyl acetate comonomer content and nominal melt index 0.7 g/10 min when measured at 190 °C under 2.16 kg load according to ASTM D1238. Typical density is 0.940 g/cm³ per ISO 1183-1:2019. Differential scanning calorimetry under ASTM D3418-15 generally places the peak melting endotherm between 84 °C and 88 °C, and the Vicat softening temperature is near 70 °C when measured using ASTM D1525-17e1 A50 conditions. The unfilled copolymer exhibits Shore A hardness from 90 to 94 under ISO 868. Because vinyl acetate content remains below the 28 wt% threshold at which ethylene crystallinity falls sharply, the material retains enough crystalline fraction for green strength in extruded profiles, foam expansion, and calendered sheet while offering improved polarity, filler wetting, and low-temperature flexibility relative to unmodified LDPE.

Because the pellet surface retains sufficient ethylene crystallinity to resist blocking at ambient temperatures below 25 °C, closed packaging protects the grade from moisture adsorption and UV exposure. Pre-drying at 70–80 °C for 2–4 h is justified when packaging has been opened in an environment exceeding 70% relative humidity, since surface moisture can produce splay and surface defects in extruded profiles. Bulk silo and hopper systems should be purged with dry air at a dew point below −20 °C. The resin is not hygroscopic in the polyamide or polyester sense, but condensation on cold pellets transferred into a warm production hall is a documented processing fault when ambient dew point is above pellet temperature.

What Defines the Performance Difference Across VA Content and Melt Index?

The melt index of 0.7 g/10 min differentiates ATEVA 1807EG from otherwise similar 18 wt% vinyl acetate grades designed for high-speed injection molding with melt indices above 2 g/10 min. In melt processing, the higher molecular weight fraction raises zero-shear viscosity and elongational viscosity, both of which govern foaming, blown-film bubble stability, and thermoforming sag. A higher-melt-index grade with equivalent comonomer content permits shorter cycle times and lower injection pressure but sacrifices die swell, melt strength, and extrusion bubble stability. Published capillary rheometry data for this exact grade is limited; for material substitution, normalized viscosity comparison under ISO 11443:2021 is recommended at shear rates from 100 s⁻¹ to 1000 s⁻¹.

Vinyl acetate content at 18 wt% places the copolymer in an intermediate polarity range. X-ray and DSC determinations on EVA copolymers in this composition window typically show a crystalline fraction of 25–30%, compared with 10–18% for 28 wt% VA grades. That crystallinity contributes to tensile modulus, hardness, and creep resistance, while the amorphous ethylene-vinyl acetate sequences impart low-temperature flexibility and environmental stress-crack resistance. Increasing vinyl acetate content above 18 wt% reduces peak melting temperature from roughly 86 °C to near 73 °C in 28 wt% VA copolymers and broadens the melting range. Those changes lower heat-seal initiation temperature and improve adhesion, but they also reduce upper service temperature and increase surface tack.

Batch-to-batch variation in melt index should be monitored under ASTM D1238. Converter specifications commonly apply a tolerance of ±0.1 g/10 min around the nominal 0.7 g/10 min. A received lot approaching +0.2 g/10 min above nominal can alter foam density and bubble-size distribution because melt strength is disproportionately sensitive to changes at the low end of the melt-index scale.

Blown-Film Bubble Stability and Frost Line Position

The high melt strength of 0.7 g/10 min EVA permits blown-film towers to operate at blow-up ratios of 2.5:1 to 3.5:1 without bubble flutter when the frost line is maintained between 200 mm and 400 mm from the die face. On a 50 mm single-screw blown-film line with a 100 mm annular die, die gap of 0.8 mm, and air ring pressure drop of 25 mbar, melt temperature at the die lip is held at 185–195 °C. Higher-melt-index EVA grades are less tolerant of elevated blow-up ratios because their lower elongational viscosity permits film sag and uneven gauge. Gauge variation measured by a capacitance thickness scanner should remain below ±5% across the web. Bubble instability is often accompanied by gauge bands of ±10% or worse and reduced dart impact strength under ASTM D1709-22.

Foam extrusion benefits from the long relaxation-time distribution associated with low melt index. In chemically blown formulations using azodicarbonamide at 1.0–2.0 phr and zinc oxide at 0.2–0.5 phr, gas release onset occurs at approximately 160–190 °C; adequate melt strength at these temperatures suppresses cell coalescence. Expanded densities of 160–220 kg/m³ are achievable on tandem foam lines with twin-screw primary mixing and single-screw cooling. Crosslinked foam systems based on dicumyl peroxide at 0.6–1.0 phr and triallyl cyanurate coagent at 0.3–0.5 phr are also processable. Scorch time measured by moving-die rheometer at 180 °C is shortened when acidic fillers are present, so pH-neutral fillers should be selected.

Injection molding of ATEVA 1807EG requires clamp tonnage calculations based on projected area and cavity pressure of 400–600 bar. On a 120 t hydraulic injection-molding machine with a 35 mm screw, melt temperature should not exceed 200 °C; barrel zones from feed to nozzle are typically 150/170/180/190 °C. Because the material has a long relaxation time, gate freeze time is shorter than for high-flow grades. Holding pressure should be maintained until gate sealing, which may occur at 8–12 s for a 2 mm wall. Sink marks and warpage arise when the packing phase is terminated before gate seal. Mold temperatures of 20–40 °C are adequate for dimensional stability, but chilled water below 10 °C can create internal stresses and stress-cracking tendency in constrained parts.

As a base resin for mineral-filled compounds, ATEVA 1807EG accepts calcium carbonate loadings up to 40 wt% without excessive melt fracture when a fatty acid–coated carbonate with median particle size 2–3 µm is used. The high melt viscosity improves dispersive mixing in twin-screw extruders with L/D 40:1 and distributive mixing elements at 200–250 rpm, but barrel temperature settings must avoid stock temperatures exceeding 220 °C. Torque is typically higher than for 2.5 g/10 min EVA; drive motor sizing should include a 10–15% safety margin over the calculated specific energy of 0.18–0.24 kWh/kg. Zinc stearate at 0.2–0.5 wt% functions as an external lubricant, but zinc-containing additives above 1 wt% may catalyze deacetylation at high residence times, releasing acetic acid and producing gel specks.

When Low-Temperature Sealing or High Adhesion Becomes the Primary Requirement

For heat-seal layers, ATEVA 1807EG can provide a seal initiation temperature approximately 8–12 °C higher than 28 wt% VA copolymers. In flexible packaging, that difference is significant when seal-bar dwell times are below 0.5 s or when fatty-product contamination is expected. Adhesion performance against aluminum foil and corona-treated polyethylene follows vinyl acetate content. The 18 wt% VA grade is selected when excessive adhesion or cohesive peel is undesirable. If peel strength measured by ASTM F88/F88M-21 must exceed 12 N/15 mm at a seal temperature of 110 °C, a higher-VA grade should be evaluated rather than increasing seal-bar temperature, because the material may thin and fail at the seal root.

In photovoltaic encapsulant sheeting, standard formulations use 28–33 wt% VA copolymers with melt indices above 20 g/10 min to achieve complete melt spreading over glass and cell surfaces at lamination temperatures of 150 °C within 15 min. ATEVA 1807EG is not effective in this application because its melt viscosity remains too high and its crystalline fraction impedes optical coupling. Void retention around busbars and cell edges has been observed when low-melt-index 18 wt% VA copolymers are used. Therefore, photovoltaic-grade EVA, not this product, is specified for encapsulation.

Thermogravimetric analysis of EVA copolymers in nitrogen shows a two-step mass loss: acetic acid elimination begins near 250–280 °C and main-chain degradation follows above 420 °C. In air, radical oxidation lowers the onset by 20–30 °C. For ATEVA 1807EG, melt processing should remain below 220 °C to keep deacetylation below 0.5% conversion per pass. Residence time at 200 °C above 10 min should be avoided because acetic acid release can corrode die lips and promote gel formation. Nitrogen blanketing of hoppers and vent ports is justified when regrind ratios exceed 30 wt%.

When Regulatory Compliance Determines Grade Selection

Food-contact use of EVA copolymers is addressed under FDA 21 CFR 177.1350, which contains compositional and extractives limitations specific to vinyl acetate content and end-use conditions. Users must verify the 18 wt% VA grade against the paragraph applicable to the intended food type and processing history. EU plastic food-contact materials under Regulation (EU) No 10/2011 specify a specific migration limit for vinyl acetate of 12 mg/kg food simulant. Converters must verify that migration from the finished packaging structure does not exceed this limit under EU 10/2011 test conditions. Industrial users are also subject to REACH Regulation (EC) No 1907/2006 SVHC disclosure obligations for additives in the compounded product. The unfilled copolymer contains no halogenated flame retardants and is normally outside the scope of RoHS Directive 2011/65/EU, but cadmium-based pigments or lead heat stabilizers must be excluded by procurement specification.

ATEVA 1807EG is not recommended for continuous immersion in aromatic hydrocarbons, ketones, esters, or chlorinated solvents because the vinyl acetate segments undergo swelling and loss of mechanical integrity. The grade should not be processed with acid-functionalized additives at loadings above 1 wt% because residual acidity accelerates deacetylation and increases melt acidity. Amine-based antistats and certain hindered amine light stabilizers can also displace acetic acid under high-temperature processing; if antistatic performance is required, a non-amine migrating or permanent additive should be selected. Outdoor exposure requires carbon black at 2.0–2.5 wt% or an appropriate UV stabilizer package. Unstabilized service above 60 °C in air may lead to molecular-weight reduction and surface tack. For applications with continuous service below −40 °C, the grade retains flexibility, but impact testing under ISO 179-1:2010 should be performed on the finished part because weld-line strength is geometry-dependent.