Elvax 360 EVA Copolymer Resin,Footwear & Adhesives Grade

Among ethylene vinyl acetate copolymers supplied for footwear compounding and hot-melt adhesive manufacture, Elvax 360 EVA Copolymer Resin is specified where a 25 wt% vinyl acetate content must be combined with a relatively low melt flow rate. The grade is supplied as a pelletized copolymer and is described in commerce as a footwear and adhesives grade; its nominal vinyl acetate content is 25 wt%, and its melt index according to ASTM D1238-20, Procedure A at 190°C and 2.16 kg is 2.0 g/10 min. Density determined under ASTM D792 is approximately 0.95 g/cm3. The 25 wt% vinyl acetate segment reduces crystalline order relative to EVA grades with 18 wt% or 12 wt% vinyl acetate, which increases polarity, low-temperature flexibility, and compatibility with rosin ester and hydrocarbon tackifiers. Because the melt index is lower than high-flow grades such as Elvax 350 at 19 g/10 min, the resin contributes longer chain entanglement and higher melt viscosity during adhesive application and foam molding. The product is not characterized by a single fixed set of application properties; final tensile, tear, compression set, and peel values depend on compound formulation, crosslink density, foam density, substrate selection, and thermal history.

When a 25 wt% Vinyl Acetate Copolymer with a 2.0 dg/min Melt Index Replaces High-Flow EVA in Hot-Melt Assembly

In hot-melt adhesive manufacturing, the lower melt index of Elvax 360 relative to Elvax 350 shifts the balance between open time, wet-out, and cohesive strength. The melt index difference—2.0 g/10 min versus 19 g/10 min under ASTM D1238—corresponds to higher viscosity at equal temperature. On production-scale hot-melt batch mixers with sigma blades or helical dispersion blades, the resin is typically compounded with tackifier, wax, and antioxidant at temperatures between 150°C and 180°C. In formulations containing 18 wt% to 35 wt% EVA, the use of Elvax 360 requires longer incorporation time and higher torque than a high-flow grade; however, the resulting adhesive generally provides greater resistance to cohesive failure and improved high-temperature shear strength. The tackifier loading is frequently set between 40 phr and 60 phr for a C5/C9 hydrocarbon resin with a ring-and-ball softening point of 95°C to 110°C; wax addition is maintained between 10 wt% and 25 wt% of the total formulation to reduce melt viscosity and open time. Formulation-specific data are required because adhesive performance is measured under ASTM D4498 for high-temperature shear, ASTM D1876 for T-peel, and ISO 11339 for flexible adherend T-peel; published data for this specific grade in a defined adhesive system is limited. The resin should not be held above 230°C for prolonged periods because thermal decomposition of the vinyl acetate comonomer releases acetic acid and reduces adhesion.

A laboratory evaluation sequence for hot-melt adhesives based on Elvax 360 typically includes melt mixing in a 200 g electrically heated sigma-blade mixer, application through a heated slot die at a controlled coating weight of 50-150 g/m2, and bonding to corona-treated polyolefin film. Initial T-peel strength measured under ASTM D1876 may be recorded after 24 hours of conditioning at 23°C and 50% RH; full property development is substrate-dependent. On high-speed packaging lines, open time and wet-out are checked against a reference adhesive based on a higher-flow EVA before changing to Elvax 360.

What Distinguishes Elvax 360 from Elvax 350 and Elvax 260 in Compounded Systems?

The selection of a specific EVA grade in footwear and adhesive compounds is driven primarily by vinyl acetate content and melt index. Table 1 compares four grades that are frequently evaluated against Elvax 360 in these applications. The values are nominal manufacturer-published values; incoming resin shipments are controlled by ASTM D1238 melt index and by supplier certificate of analysis for vinyl acetate content.

At equal vinyl acetate content, the difference between Elvax 360 and Elvax 350 is melt viscosity. At equal melt index range, the difference between Elvax 360 and Elvax 460 is vinyl acetate content; the 25 wt% VA grade has lower crystalline melting point and greater polarity than an 18 wt% VA grade. Compared with Elvax 260, the 28 wt% VA product provides higher adhesion to polar substrates but may require greater antioxidant stabilization due to increased amorphous phase. Peak melting point by differential scanning calorimetry under ASTM D3418 for Elvax 360 is approximately 76°C; lower VA grades display higher crystalline melting points. In adhesive compounding, the higher VA content of Elvax 260 improves low-temperature flexibility but usually reduces high-temperature shear resistance when compared at equivalent melt index. Rheological acceptance of Elvax 360 is not fully captured by melt index alone; capillary rheometry under ASTM D3835 at shear rates from 10 s−1 to 1,000 s−1 is used when hot-melt line pressure drop and die wall shear stress are limiting. Lot-to-lot variation is assessed by melt index under ISO 1133-1:2022; the supplier’s certificate of analysis reports melt index, vinyl acetate content, and density. Out-of-specification batches with higher melt index can reduce cohesive strength in adhesives and lower melt strength in foaming; lower melt index can increase mixer torque and injection pressure.

Compounding Parameters That Control Foam Density and Crosslink Uniformity

Because midsole foaming compounds rely on simultaneous decomposition of a chemical blowing agent and peroxide-induced crosslinking, the viscosity of the EVA base resin controls both dispersion and cell nucleation. Elvax 360 is compounded in an internal mixer or continuous twin-screw compounder with a length-to-diameter ratio not lower than 40:1. The lower melt index of 2.0 g/10 min, compared with 19 g/10 min for Elvax 350, provides higher elongational viscosity at the blowing temperature, which helps maintain cell walls during azodicarbonamide decomposition. Dicumyl peroxide crosslinking is used to set the foam structure; the peroxide addition is constrained by the half-life at the press cure temperature and by scorch in the mixer. Typical batch mixing equipment drops compound at a temperature below 110°C to avoid premature peroxide decomposition. Azodicarbonamide expansion levels are commonly set between 2 phr and 5 phr, while dicumyl peroxide is used between 0.5 phr and 1.0 phr; zinc stearate and calcium carbonate are added as nucleating and release aids. Calcium carbonate at 5-15 phr increases hardness and modifies expansion ratio, while zinc stearate at 0.5-1.5 phr functions as release agent and activator. Foam density is controlled between 0.15 g/cm3 and 0.30 g/cm3 for many midsole constructions, with density measurement under ISO 845 or ASTM D3575. Compression set is evaluated under ASTM D395 method B at 50°C or 23°C after prescribed recovery times. The use of Elvax 360 rather than a higher-flow grade can improve compression set and resilience at equal density, but only when the compound is homogeneously crosslinked; residual unreacted peroxide or incomplete blowing agent decomposition introduces density gradients that are detectable in ASTM D3574 fatigue flex tests. Published data for this specific grade in a fixed footwear formulation is limited.

On reciprocating screw injection molding machines used for EVA foam, barrel setpoints are typically maintained between 70°C and 95°C to prevent premature gas evolution, while the mold is held at 160°C to 180°C to trigger blowing agent decomposition and crosslinking. The lower melt index of Elvax 360 may require screw backpressure adjustment to achieve shot-to-shot consistency and to avoid gas pockets during cavity filling. Molds with hot runner or cold runner systems are set to avoid premature foaming before full cavity filling.

Tensile, Tear, and Hardness Benchmarks in Crosslinked Foam Systems Are Compound-Dependent

In crosslinked foam systems, final mechanical properties are not directly assignable to the EVA base resin alone; they are determined by the ratio of Elvax 360 to other EVA grades, the type and loading of blowing agent, the peroxide level, and the expansion ratio. Tensile strength under ASTM D638, trouser tear strength under ASTM D624, and hardness under ASTM D2240 are used to compare production lots. Many midsole specifications define acceptance limits using Shore Asker C hardness for compression behavior, but the numeric limits are set by the footwear brand and are compound-dependent. When Elvax 360 is used as the high-molecular-weight component in a blend with a higher-flow EVA, the formulation is adjusted to maintain the same expandable melt viscosity at the blowing temperature. Laboratory trials with a torque rheometer and a heated hydraulic press are required to establish the relationship between melt index, crosslink density, and cell size.

In hot-melt adhesive finishing operations, application temperature is selected at the melt tank and hose/nozzle system to maintain viscosity below 5,000 mPa·s for wheel or slot-die coating; when Elvax 360 is used, the operating temperature may be raised by 5-10°C relative to a 19 g/10 min grade to achieve equivalent flow. Equipment with nitrogen-blanketed tanks and recirculation lines reduces exposure to oxygen at temperatures above 150°C. Cohesive strength and T-peel on treated polyethylene or polypropylene substrates depend on substrate surface energy measured by ASTM D2578 for dyne level, and on adhesive thickness measured under ASTM D883. Long-term open time and thermal stability are evaluated in production by viscosity drift over an 8-hour holding period; a drift greater than 10% may indicate polymer degradation or wax phase separation. Published data for this specific grade in such a multi-component system is limited.

Thermal Degradation and Acetic Acid Release During Extended Melt Holding

At melt temperatures above 230°C, the vinyl acetate segments in EVA can undergo thermal deacetylation, releasing acetic acid and forming unsaturation. Corrosion-resistant hot-melt equipment and ventilation are used to handle acidic volatiles. Thermogravimetric analysis under ASTM E1131 or ISO 11358 can be used to compare degradation onset between lots; the onset temperature is formulation and atmosphere dependent. Because the resin contains 25 wt% vinyl acetate, the degradation pathway is more pronounced than in EVA grades with 12 wt% or 15 wt% VA; higher VA grades may exhibit lower thermal stability if not stabilized. The processor should avoid direct flame impingement on the melt, maintain melt temperature below 230°C, and minimize hold time in high-temperature reservoirs to less than 4-6 hours under normal atmospheric conditions unless process-specific data support longer residence. In nitrogen-blanketed systems, residence time limits can be extended, but published data for this specific grade under all equipment configurations are limited.

Because surface condensation on cold pellets is a more common source of moisture-related defects than bulk moisture absorption, pellets stored below 10°C and exposed to ambient air above 60% RH should be equalized in closed containers before feeding. If drying is applied, desiccant air at a temperature below 50°C for 2-4 hours is used to prevent pellet agglomeration. Higher drying temperatures can soften the pellets and cause bridging in hoppers.

Regulatory status depends on the finished article and use condition. For food-contact adhesive applications, the resin may be evaluated under 21 CFR 177.1350 for ethylene-vinyl acetate copolymers and under 21 CFR 175.105 for adhesives. Compliance under EU Regulation 10/2011 is determined on the final plastic article or adhesive layer, not solely on the base resin. A REACH registration under Regulation (EC) No 1907/2006 is maintained by the supplier for relevant registration obligations. RoHS 2011/65/EU applies to electrical and electronic equipment articles; a polymer resin shipment is not a finished RoHS article. These statements are not a substitute for supplier food-contact, medical-use, or electrical-equipment certification.