EVAtech EVA 140S/28G Copolímero de acetato de vinilo de etileno

Ethylene-vinyl acetate copolymers containing a vinyl acetate mass fraction of 28 wt% are positioned between semi-crystalline polyethylene and elastomeric ethylene copolymers. The EVAtech EVA 140S/28G Ethylene Vinyl Acetate Copolymer carries a nominal melt flow index of 140 g/10 min when determined under ISO 1133-1:2022 at 190 °C with a 2.16 kg mass. The vinyl acetate content is specified through infrared spectroscopy according to ISO 8985:2022 or ASTM D5594-98. Density at 23 °C is class-typically reported between 0.945 g/cm³ and 0.965 g/cm³ under ISO 1183-1. The high melt-flow index separates the grade from low- and medium-flow EVA resins used in films, encapsulants, and structural foams; those resins commonly display melt-flow values between 1 g/10 min and 25 g/10 min. Because reactor lot data and additive package changes shift final values, specification acceptance should be based on the manufacturer certificate of analysis. Published multi-lot mechanical data for this specific EVAtech configuration are limited in open literature; class-typical ranges are therefore provided as engineering comparisons rather than guaranteed product limits.

EVA resins with this vinyl acetate content are selected where adhesion to polar substrates, low-temperature flexibility, and compatibility with tackifiers are required. Compared with 14 wt% VA copolymers, the 28 wt% material exhibits reduced crystallinity, a lower and broader melting endotherm, and stronger interaction with aluminium, polyester, paper, and untreated polar fillers. Compared with 33 wt% or 40 wt% VA copolymers, the 28 wt% grade retains sufficient ethylene sequence length for blocking resistance and cohesive strength in formulated compounds. These differences direct use toward hot-melt adhesives, wax modification, and polymer compounds where both flow and polar adhesion are required simultaneously.

Why Does a 28 wt% Vinyl Acetate Unit Content Depress Crystallinity and Change Adhesion?

Inserted acetate groups disrupt the regularity of ethylene sequences. The crystalline melting point measured by differential scanning calorimetry under ISO 11357-3 at 10 °C/min generally falls between 55 °C and 85 °C for this VA class, compared with 95 °C to 110 °C for lower-VA EVA copolymers. The glass transition temperature is broad and commonly observed between -30 °C and -15 °C. These thermal transitions explain the lower processing temperature and softer low-temperature response. The polar acetate group increases the surface energy of the melt, improving wetting of metal oxides and hydroxyl-bearing substrates. In hot-melt adhesive formulations, this polarity supports peel adhesion to polyethylene terephthalate and corrugated board without the higher plasticizer loadings required by some ethylene-ethyl acrylate copolymers.

Peel adhesion is substrate-specific. On aluminium or polyester, ASTM D903 or ISO 11339 is commonly used depending on joint geometry. The measured force is controlled by formulation variables, including tackifier, wax, processing temperature, and coating weight, rather than by the polymer alone. Published data for the neat resin isolated from formulated adhesive compounds are limited for this specific configuration.

Thermogravimetric analysis of EVA copolymers under nitrogen shows a two-stage mass loss: acetic acid elimination followed by hydrocarbon backbone degradation. Screening should be conducted at 10 °C/min under nitrogen using ASTM E2550 or ISO 11358-1. The onset temperature is influenced by heating rate and metal contamination, and apparent activation energies for acetic acid elimination are not single-valued material constants. These thermal data support the upper processing limit but do not replace production-scale monitoring.

Capillary rheometry under ISO 11443 is preferred over melt-flow index for die and nozzle design because the melt-flow index is a single-point parameter. At 180 °C, the material is expected to show shear-thinning behaviour; the apparent viscosity at 100 s⁻¹ may be one order of magnitude lower than at 10 s⁻¹. Exact viscosity curves for EVAtech EVA 140S/28G are not available in multi-lot public reports, so vendor capillary rheometry data should be used for sizing gear pumps, screen packs, and slot dies.

In hot-melt adhesive compounding lines using L/D 25:1 to 36:1 twin-screw extruders, the high melt-flow index reduces melt pressure at constant screw speed when compared with 6 g/10 min EVA. The resin is introduced at the feed throat with pre-dried regrind when the storage environment exceeds 60 % relative humidity. A vented barrel with reduced pressure is applied when melt temperatures above 180 °C are maintained for more than a few minutes; EVA releases acetic acid under severe thermal stress, and the vapour is corrosive to carbon steel downstream surfaces. The molten material is filtered through screen packs of 100 µm to 250 µm and delivered to slot dies or spray nozzles. Brookfield viscosity of finished hot-melt formulations is monitored using ASTM D3236-88 with an SC4-27 spindle at 180 °C; the target viscosity depends on coating line speed and substrate porosity. Equipment set points for this class are commonly 160 °C to 190 °C, while sustained operation above 200 °C is avoided because degradation rate increases sharply. Hot-melt tanks with nitrogen blanketing and tight temperature control limit viscosity drift and char formation. Batch-to-batch variation is monitored by in-line melt pressure transducers; a pressure deviation greater than ±5 % at constant screw speed may indicate a lot shift or feed hopper bridging.

In polymer modification, the grade is added to polyolefin compounds to increase filler wetting and stress-cracking resistance. In low-shear internal mixers, the lower melt viscosity permits shorter cycle times and reduced heat history when compared with a 25 wt% VA, 10 g/10 min EVA. Dispersion of calcium carbonate, magnesium hydroxide, and carbon black is improved when the copolymer is blended under controlled shear at melt temperatures below the acetic acid elimination threshold. The specific mixing torque reduction should be measured on the target mixer; published torque values for this exact grade are limited.

When a 140 g/10 min Melt Flow Index Is Substituted for Low-MI Structural EVA

Substitution of EVAtech EVA 140S/28G into a film or profile extrusion line designed for 3 g/10 min to 10 g/10 min EVA changes pressure consumption, melt strength, and cooling behaviour. Screw torque and die pressure drop decline because the high melt-flow index reduces apparent viscosity. In blown film, the bubble may show reduced stability at high blow-up ratios because melt strength is lower; machine-direction draw should be limited and air ring pressure reduced. In thick-wall profile extrusion, the high-flow material may sag before solidification unless haul-off speed and water bath temperature are adjusted. The grade is not a drop-in replacement for structural EVA where the part must retain high cohesive strength or dimensional stability under load. The table below gives directional property contrasts for substitution at constant vinyl acetate content.

Tensile and elongation values in the table are class-typical and not lot-specific. Before substituting the grade, the operational window should be confirmed on the target line because high-flow EVA can cause seal-bar contamination in form-fill-seal operations if the melt temperature is too high. The resin should not be melt-blended with readily oxidizing agents or with materials that generate strong acids; acetic acid released during degradation is corrosive to downstream carbon steel surfaces.

Compliance and Test Method Matrix

Regulatory evaluation is formulation-dependent. Food-contact adhesives containing the polymer are evaluated under 21 CFR 175.105; the polymer itself may fall under 21 CFR 177.1350 when used in certain food-contact articles, but migration testing is required on the finished article. Low-voltage electrical and electronic applications are assessed under RoHS Directive 2011/65/EU, and EU supply chains require registration and safety data under REACH. The following matrix lists typical test methods used to verify the grade.

Wax blending and coating lines use the same balance of flow and polarity. Paraffin and microcrystalline wax formulations are modified with 28 wt% VA EVA to increase viscosity, extend open time, and reduce surface brittleness. In wax coating lines, the high-flow grade permits addition at 150 °C to 170 °C without pre-dispersion when a high-shear impeller is used. Compared with 18 wt% VA EVA, lower crystallinity reduces haze in thin coatings but also lowers blocking resistance; paraffin type and congealing point must therefore be selected using the vendor congealing point method. Compared with 33 wt% VA EVA, the 28 wt% resin is less polar for metal-foil adhesion but offers better smear resistance. Production-scale wax coating lines using slot-die heads have reported lower charge pressure relative to lower-flow EVA; quantitative pressure data for this specific grade are limited in public literature.