Copolímero de acetato de vinilo de etileno ELVAX 9770

ELVAX 9770 is a high-pressure free-radical copolymer of ethylene and vinyl acetate, supplied as translucent pellets. The grade identifier denotes a product within the manufacturer’s ELVAX line; the numerical designation does not provide a direct reading of comonomer content or melt flow rate. Current supplier technical documentation lists a nominal vinyl acetate content of 25 wt% and a melt flow rate of 4 g/10 min measured at 190 °C under a 2.16 kg dead load in accordance with ISO 1133-1:2022. Typical density is 0.95 g/cm³ at 23 °C per ISO 1183-1:2019. Differential scanning calorimetry according to ASTM D3418-21 records a broad melting endotherm between 72 °C and 78 °C, consistent with disruption of polyethylene crystallinity by the acetate side groups. Tensile testing of 2 mm compression-moulded plaques per ASTM D638-14 typically indicates tensile strength at break of 15–20 MPa and elongation at break above 700%. These values are typical lot averages, not release limits; the lot-specific certificate of analysis is the controlling specification.

How Does Vinyl Acetate Content Modify Adhesion, Flexibility, and Thermal Response?

The 25 wt% vinyl acetate in ELVAX 9770 introduces polar ester side groups that reduce crystallinity and increase specific adhesion to aluminium, polyester, and cellulose. Compared with low-density polyethylene, the comonomer lowers the peak melting endotherm from roughly 110 °C to below 80 °C, broadens the melting range, and shifts the low-temperature transition measured by ISO 6721-1:2019 to between -30 °C and -20 °C. In adhesion testing according to ASTM D1876, EVA resins in this vinyl acetate range typically produce higher flexible-packaging peel strengths than 12 wt% vinyl acetate grades such as ELVAX 660, because the polar acetate groups interact with surface oxides and hydroxyl groups on metal foils and corona-treated films. The same polarity reduces the methylene sequence length and lowers flexural modulus; comparative ISO 178:2019 three-point flexure data should be evaluated on conditioned specimens because EVA modulus is humidity-dependent through plasticisation of the amorphous phase. Relative to 40 wt% vinyl acetate resins such as ELVAX 40W, ELVAX 9770 exhibits higher tensile strength and heat resistance but lower tack and slower substrate wet-out on high-surface-energy substrates; surface energy of corona-treated film should be checked by ASTM D2578 and maintained above 38 mN/m for lamination.

Capillary rheometry according to ISO 11443:2021 at 190 °C characterises ELVAX 9770 as a pseudoplastic melt; apparent shear viscosity declines as shear rate increases from 100 s⁻¹ to 1,000 s⁻¹, although exact curves are lot-dependent. On single-screw extrusion lines with 24:1 to 30:1 L/D and corrosion-resistant screw and barrel metallurgy, barrel set points from 150 °C to 230 °C are typical. The feed throat must be water-cooled because pellet softening occurs above approximately 50 °C, and pellet bridging in the throat is a known production bottleneck. Screw designs with compression ratios of 2.5:1 to 3.5:1 and without severe Maddock mixing elements are used to limit shear heating. Extrusion coating lines with a 90 mm single-screw extruder and flat die generally operate at melt temperatures from 220 °C to 240 °C; the higher temperature improves draw-down but residence time above 230 °C should stay below 20 min to reduce deacetylation. Desiccant drying at 60 °C for 4 h is recommended when pellet surface moisture exceeds 0.05 wt%, particularly at ambient relative humidity above 60%; published supplier moisture-threshold data for ELVAX 9770 is limited and should be confirmed with a Karl Fischer moisture analyser calibrated to ISO 15512:2019.

EVA copolymers with 25 wt% vinyl acetate are swollen by aromatic hydrocarbons, chlorinated solvents, ketones, and esters; solubility parameter approximations place the resin in the 8.5–9.0 (cal/cm³)^0.5 region, but published data for ELVAX 9770 is limited. Exposure to methyl ethyl ketone, ethyl acetate, or toluene in printing and laminating lines therefore requires dry-bond or wiped lamination cell design with controlled extraction ventilation. The resin maintains acceptable service resistance in contact with dilute acids, alkalis, and alcohols at ambient temperature, although environmental stress-cracking performance should be evaluated under ASTM D1693 for aggressive service environments. Because the vinyl acetate comonomer increases oxygen and moisture permeability relative to LDPE, barrier specifications in packaging must be confirmed by oxygen transmission rate under ASTM D3985 and water vapour transmission rate under ASTM F1249 on the finished laminate, not on the resin alone.

Thermal Degradation and Additive Compatibility Boundaries

Thermogravimetric analysis under ISO 11358-1:2022 in nitrogen typically positions the onset of mass loss above 280 °C for EVA grades with 25 wt% vinyl acetate; the exact value varies with heating rate, sample mass, and purge-gas flow. Thermal deacetylation of the acetate side group begins at lower temperatures and becomes process-relevant above 230 °C, releasing acetic acid. Continuous production lines therefore specify nitrided steel, bimetallic barrel liners, or corrosion-resistant alloys for adapters, melt pipes, and dies. Batch-to-batch variance in surface moisture and residual stabiliser concentration can shift the observable degradation onset; stabiliser consumption should be monitored by melt flow retention after multiple extrusion passes. Primary amine-based stabilizers are generally avoided in EVA formulations because reaction with acetic acid degradation products can reduce their long-term thermal stabilising efficiency. Acid scavengers such as zinc stearate or calcium stearate at 0.5–1.5 wt% are incorporated in hot-melt adhesive compounds to buffer residual acidity. In peroxide-crosslinked systems, compounding must remain below the dicumyl peroxide decomposition threshold of approximately 120 °C to prevent scorching; cure behaviour should be characterised by a moving-die rheometer according to ASTM D6601-21.

In hot-melt adhesive compounding, ELVAX 9770 is melt-blended with hydrocarbon tackifiers and paraffin or microcrystalline waxes in heated sigma-blade mixers or twin-screw kneaders at 170–190 °C. Brookfield viscosity is measured according to ASTM D3236-15 at 180 °C; a ternary formulation containing 30 wt% ELVAX 9770, 35 wt% tackifier, and 35 wt% paraffin wax may produce viscosities in the 1,500–2,500 mPa·s range, though supplier-published data for this specific ternary formulation is limited. Open time and set time depend on wax crystallisation and thermal diffusivity of the substrate; comparative measurements should be carried out with the same coat weight and substrate temperature. In extrusion coating and lamination of aluminium foil and polyester film, ELVAX 9770 is applied at coat weights from 12 g/m² to 25 g/m², and bond strength is tested by ASTM D1876 after conditioning at 23 °C and 50% relative humidity for 24 h.

In polymer modification and masterbatch carrier applications, the polar acetate groups improve wetting of mineral fillers and organic pigments; dispersion quality can be assessed as filter pressure rise on a 40:1 L/D twin-screw extruder fitted with a screen pack, but published data for ELVAX 9770 in masterbatch carrier service is limited. The grade is also used in wax modification, where its addition raises melt viscosity and low-temperature flexibility of paraffin systems. Food-contact compliance is not intrinsic to the resin; finished articles must be evaluated under 21 CFR 177.1350 or EU Regulation 10/2011 for migration limits appropriate to the intended food type and use temperature. Electrical and electronic applications require supplier declarations for RoHS Directive 2011/65/EU and REACH SVHC obligations, preferably assessed against IEC 63000; these declarations are supplier- and lot-specific and should be verified against current documentation.

Unlike ethylene methyl acrylate copolymers, ELVAX 9770 has higher hydrocarbon character and a stiffer backbone at equivalent comonomer content; unlike metallocene polyolefin plastomers, it provides greater polarity for adhesion to polar substrates but lower thermal oxidative stability. These differences affect stabiliser selection and maximum continuous service temperature; oxidative stability should be assessed by ISO 11357-6:2018 or ASTM D3895-19 using the specific stabiliser package, not the base resin.

The following comparative data place ELVAX 9770 between lower-vinyl-acetate and higher-vinyl-acetate resins in the same manufacturer line. The entries are nominal typical values, not release limits.

Relative to ELVAX 660, ELVAX 9770 reduces melt processing temperature and improves adhesion to aluminium and corona-treated polyester, but lowers tensile strength and creep resistance. Relative to ELVAX 40W, ELVAX 9770 offers higher cohesive strength and better heat resistance, but lower initial tack and slower wet-out on high-surface-energy substrates. The melt flow rate of 4 g/10 min is higher than that of low-MFR 25 wt% grades such as ELVAX 360, which increases substrate penetration and may improve wetting in porous board at the cost of reduced melt strength. In extrusion coating, ELVAX 9770 exhibits greater neck-in than low-MFR grades; the difference is managed by reducing the air gap, increasing draw ratio, or adjusting die lip geometry, with coating-width stability measured optically at the chill roll.