EVATHENE UE3302 EVA resina de copolímero, 33% VA, espuma e calçado grau

EVATHENE UE3302 is an ethylene-vinyl acetate copolymer resin positioned in the foam and footwear grade segment; the grade designation encodes a nominal vinyl acetate content of 33 wt%. On a molar basis, that comonomer loading corresponds to approximately 13.8 mol% vinyl acetate, calculated from the 86 g/mol vinyl acetate repeat unit and the 28 g/mol ethylene repeat unit. The polymer is supplied as pellets and is characterized by density, melt flow rate, and vinyl acetate content. Density is class-typical for EVA copolymers of this composition, near 0.95 g/cm³ when tested under ASTM D792-20. Melt flow rate is determined under ASTM D1238-20 at 190°C/2.16 kg; foam and footwear grades are generally selected from the low-melt-flow portion of the series because melt strength during gas expansion is process-critical. Exact lot-specific melt flow rate, tensile properties, and hardness are supplier-controlled and should be obtained from the certificate of analysis; published data for this specific configuration is limited. The resin differs from general-purpose EVA grades by the combination of 33 wt% vinyl acetate and a rheological package intended for chemical blowing-agent expansion, rather than for thin-gauge film or high-speed injection molding. The product is used in chemically crosslinked foam sheets, compression-molded midsoles, and injection-molded footwear components where cell uniformity, Shore hardness reduction, and low-temperature flexibility are specified.

What Distinguishes a 33% VA Foam and Footwear Grade From General-Purpose EVA?

Vinyl acetate content directly controls crystallinity, melting behavior, hardness, and polar interaction in EVA copolymers. Representative differential scanning calorimetry data reported for EVA copolymers show a crystalline melting endotherm near 86°C at 18 wt% vinyl acetate, falling to approximately 62°C at 33 wt% and near 50°C at 40 wt% when tested under ASTM D3418-21. The corresponding reduction in crystalline fraction lowers Shore hardness from roughly 90–95 Shore A for 18 wt% VA grades to 65–75 Shore A for 33 wt% VA grades when measured on compression-molded plaques under ASTM D2240-15. Consequently, EVATHENE UE3302 provides a softer, more rubber-like response than low-VA extrusion-coating or general-purpose grades at equivalent melt flow rate.

Low-temperature flexibility is also improved because vinyl acetate units disrupt polyethylene crystallinity and reduce the low-temperature modulus plateau. Brittleness temperature testing under ASTM D746-20 commonly places 33 wt% VA EVA compounds at or below -40°C, whereas lower-VA grades may become brittle nearer -20°C, though exact values depend on plasticizer and filler loading. The polar acetate group increases surface energy and adhesion to polyurethane, polyester fabric, and polyether blockamide substrates. Adhesion is frequently evaluated by 180° peel testing under ASTM D903-98; higher VA content reduces the need for corona treatment or solvent primers relative to 18 wt% VA grades. At 40 wt% VA, surface tack and pellet blocking become more pronounced, while melt strength declines and gas retention during expansion becomes less stable. EVATHENE UE3302 occupies an intermediate position where polar adhesion and expansion stability overlap.

In crosslinked EVA foam production, EVATHENE UE3302 is first fluxed in an internal mixer or low-shear compounding extruder. The polymer is mixed at 105–115°C before filler addition; calcium carbonate is commonly added at 10–25 phr to reduce cost and improve cell nucleation. The blowing agent and peroxide crosslinking agent are added below 110°C to avoid premature decomposition. Azodicarbonamide decomposes near 200–210°C, with a published gas yield near 220 mL/g, while dicumyl peroxide undergoes thermally triggered decomposition at higher temperatures, allowing the compound to be shaped before crosslinking. The sheeted compound is passed through a two-roll mill at 90–100°C and then transferred to a hydraulic press or continuous foaming oven. Cell-size control is evaluated by sectioning the foam and measuring cell diameter by optical microscopy; no accepted ASTM method exists for visual cell-size rating, so internal pass/fail criteria are used.

Batch-to-batch variation in melt flow rate is the primary rheological variable observed on production lines; small shifts can alter die pressure and cell growth unless the formulation is adjusted. Quantitative correlations between UE3302 lot melt flow rate and foam density are not fully published; processors routinely cross-check incoming melt flow rate against internal reference lots before changing setpoints. Unlike hygroscopic polymers such as polyamide, EVA does not require aggressive drying. Surface moisture from condensation at relative humidity above 60% is the main source of water-related surface defects.

Rheological Constraints in Continuous Sheet Foam Extrusion

For continuous sheet foam, EVATHENE UE3302 is processed on single-screw extruders with L/D 25:1 to 30:1 and a barrier screw configuration. Temperature profiles from feed to metering are typically held at 130–170°C, with the die maintained near 180°C to balance melt strength against premature blowing-agent decomposition. The melt temperature must remain below 210°C because vinyl acetate groups begin significant deacetylation near 230°C, releasing acetic acid and forming gel specks. A processing excursion of 5°C or more above the established upper limit can produce visible yellowing and equipment corrosion.

At equivalent melt flow rate, the 33 wt% VA grade exhibits lower zero-shear viscosity than 18 wt% VA material because reduced crystallinity weakens the physical network in the melt. This lowers specific energy input during mixing but narrows the operating window for gas retention. Die pressure is monitored as a real-time indicator of viscosity; a die pressure drop of more than 10% across a run typically signals feed or temperature drift. Foam density in continuous sheet is controlled by die gap, haul-off speed, and blowing-agent loading. Typical die gaps for EVA foam sheet range from 0.5 mm to 1.5 mm, but published data for UE3302-specific tooling is limited.

Compression-molded midsole production uses hydraulic presses with 150–300 tonnes clamp force and multi-cavity molds. The compound is cut into preforms and loaded at 90–100°C, then cured and expanded at 170–190°C under pressure. Mold venting is critical; trapped gas from azodicarbonamide can cause split lines in thick sections. Wall sections above 20 mm may require dual-step curing to avoid core blowout. Injection molding of 33 wt% VA EVA footwear shells uses melt temperatures of 180–190°C and mold temperatures of 20–40°C. Because of low crystallinity, cooling time is longer than for lower VA grades, and ejection can be more sensitive to surface tack.

When 33% VA EVA Replaces Lower Vinyl Acetate Copolymers in Sole Compounds

Replacement of an 18 wt% VA grade with EVATHENE UE3302 in a sole compound lowers hardness and increases elongation but also reduces thermal resistance and may increase compression set unless crosslink density is adjusted. The following table compares representative copolymer-class properties measured on compression-molded plaques, not guaranteed lot values for any specific EVATHENE grade.

Because UE3302 is supplied as a foam and footwear grade, formulations that replace 18 wt% VA grades may require a higher peroxide loading to maintain compression set resistance. Compression set is measured under ASTM D395-18 at 23°C or 70°C. As vinyl acetate content increases, the unvulcanized polymer is softer and the crosslink network must carry a larger share of the recovery force. A direct substitution based only on melt flow rate is therefore inadequate; the higher vinyl acetate content also lowers the melting point, so extruder and mold temperatures may be reduced by 5–10°C to avoid premature blowing-agent decomposition and surface stickiness.

Surface moisture rather than internal moisture governs hopper handling of EVATHENE UE3302. When warehouse relative humidity exceeds 60%, pellet surface condensation can produce voids or surface defects in molded parts; a desiccant or hot-air hopper dryer set at 70°C for 2–3 h is sufficient. The resin should not be exposed to strong oxidizing acids or strong bases because hydrolysis of the acetate group releases acetic acid. Processing equipment should be constructed with corrosion-resistant venting hardware because deacetylation products at elevated temperatures are acidic. For regulatory documentation, neat resin information is typically aligned with EU REACH Regulation (EC) No 1907/2006 and EU RoHS Directive 2011/65/EU; the presence of substances of very high concern must be confirmed with the supplier safety data sheet. Food-contact use is not implied by the foam and footwear grade designation. If an EVA copolymer is considered for food-contact articles, compliance with 21 CFR 177.1350 must be evaluated for the specific formulation, including blowing-agent residues and crosslinking byproducts.