EVAtech 160I/30C Compósito do copolímero EVA, grau de espuma reticulada

EVAtech 160I/30C is an ethylene-vinyl acetate copolymer compound formulated for peroxide-initiated crosslinkable foam conversion. The model designation is read in common EVA-grade nomenclature: the 30C segment identifies a vinyl acetate comonomer content of 30 wt%, while the 160I segment identifies a melt flow index of 160 g/10 min when measured under ISO 1133-1:2022 at 190°C/2.16 kg. The compound is supplied as pellets and contains a blowing agent, cure co-agent, and processing aid package; the exact formulation is supplier-specific and requires confirmation against the manufacturer’s technical datasheet. Unfilled compound density is approximately 0.95 g/cm³ according to ISO 1183-1:2019, while process-dependent foam density typically falls between 0.08 g/cm³ and 0.25 g/cm³. The melting endotherm by differential scanning calorimetry is broad, with a peak melting range of 75–85°C. The high vinyl acetate content reduces crystallinity and improves low-temperature flexibility relative to 18 wt% and 22 wt% VA EVA grades, but it also lowers hardness and increases polarity. Downstream application fields include closed-cell foam for footwear midsoles, industrial gaskets, thermal insulation profiles, and protective packaging. Published data for this specific EVAtech configuration is limited outside the supplier lot certificate; the material-class behaviour described here is derived from published EVA copolymer and crosslinked foam literature.

What Distinguishes a Crosslinkable Foam Grade from Conventional EVA Copolymer Compounds

In a conventional EVA compound, melt strength and dimensional stability depend on molecular weight, chain branching, and crystallization. A crosslinkable foam grade adds a covalent network during processing. The network increases extensional viscosity and stabilizes expanding cell walls, permitting density reductions that would otherwise collapse a high-melt-flow resin. Gel content after cure, determined by solvent extraction using ASTM D2765-16 Method C, is used as a production control. Typical target gel fractions for crosslinked EVA foams lie between 65% and 80%; values below 60% generally indicate incomplete cure and can produce compression set failure under cyclic loading, while values above 90% may reduce elongation at break and foam recoverability. For EVAtech 160I/30C, the 30 wt% VA content places the compound in the flexible segment of the EVA foam range. Lower-VA grades, such as 18 wt% VA with melt index 2.5 g/10 min, produce stiffer, more crystalline foams with higher hardness and better hydrocarbon resistance, but poorer low-temperature flex fatigue. Higher-VA grades above 40 wt% VA produce softer, more oil-resistant foams but can exhibit higher compression set and lower crosslink density due to radical transfer at the acetoxy group. The 160 g/10 min melt index of EVAtech 160I/30C reduces melt temperature requirements and improves thin-wall fill in injection moulding, but it demands rapid cure activation before cell coalescence. Table 1 compares representative values for this class of crosslinkable EVA foam compounds.

When Azodicarbonamide Decomposition Must Align with Peroxide Cure Kinetics

Crosslinked EVA foam processing is a coupled thermal process. The peroxide must generate crosslinks rapidly enough to set cell walls, but not so early that the melt cannot expand. Dicumyl peroxide, the most common cure agent for EVA foam, has a half-life of approximately 10 h at 117°C, 1 h at 135°C, and 1 min at 171°C. Azodicarbonamide, a high-gas-yield blowing agent, shows a broad exothermic decomposition with peak evolution near 195–205°C at 10°C/min DSC heating rate; activators such as zinc oxide or zinc stearate can lower the decomposition peak by 10–20°C and increase gas yield rate. In a peroxide-azodicarbonamide EVA foam system, the practical processing window is narrow. If the mould surface is 165°C and the decomposition onset of activated azodicarbonamide is 185°C, the cure and foam stages remain simultaneous only if the compound reaches the decomposition temperature before the peroxide is depleted. A mismatch of more than 5°C in the effective decomposition window can produce density gradients, coarse cell structure at the centre, or uncured skin layers. Moving die rheometer data, typically reported as ts2, t50, and t90 at 175°C and 1° arc according to ASTM D5289-19a, are used to define demould time; production demould times are usually set at t90 plus 10–15% to avoid post-demould expansion.

In compounding operations, the temperature profile must remain below the azodicarbonamide decomposition onset. For a co-rotating twin-screw extruder with a 44:1 L/D ratio, barrel set points of 90–105°C and a screw speed of 200–300 min⁻¹ are typical for dispersing the blowing agent without premature gas evolution. The die head pressure is usually maintained above 5 MPa to keep decomposition gases dissolved in the melt; if the pressure drops below the gas solubility limit, pre-foaming occurs and the pellet surface becomes porous. Porous pellets absorb moisture unevenly and can create batch-to-batch density variation. The high melt index of EVAtech 160I/30C permits lower head pressure than a 2.5 g/10 min EVA grade, making venting and die pressure control more critical; published data for this specific configuration is limited, but the pressure sensitivity is consistent with the reduced viscosity of high-MI EVA copolymers.

On a production injection-moulding line for crosslinked EVA foam midsoles, the process is divided into compound plastication, mould filling, chemical cure, and pressure-release expansion. EVAtech 160I/30C can be plastified at melt temperatures of 95–110°C, which is lower than conventional EVA foam grades because of its 160 g/10 min melt flow index. A typical injection speed of 40–80 mm/s is used for thin midsole cavities; higher speeds may generate shear heating above 130°C and initiate premature cure at the gate. The mould is heated to 165–180°C to activate dicumyl peroxide and azodicarbonamide. Clamp force is calculated from the projected area and the expansion pressure of the foaming melt, not from solid melt pressure alone; an 800 kN clamp may be adequate for a two-cavity midsole tool if the foaming pressure does not exceed 15 MPa in the cavity. Vent depth is a limiting factor: vents deeper than 0.02 mm can allow gas escape and produce excessive flash, while vents shallower than 0.01 mm can trap volatile residues and create surface pinholes. After cure, the mould opening must be controlled to allow foam expansion without tearing. If the part is constrained too early, cell walls fracture at the surface; if expansion is uncontrolled, density drops below the target and dimensional stability decreases. Demoulding release agents should be selected for high-temperature EVA foam tools; silicone-based external release agents can interfere with post-decoration adhesion unless cleaned using a compatible solvent system. These observations represent standard production-scale EVA foam moulding practice rather than EVAtech-specific qualification data.

Moisture Uptake, Storage Stability, and Batch-to-Batch Variation on High-Humidity Production Lines

EVA copolymer compounds are not strongly hygroscopic, but moisture uptake above 0.05% can interfere with chemical foaming. When relative humidity exceeds 60%, pre-drying is required before extrusion or injection moulding. A desiccant dryer operating at 60°C for 4 h with a dew point of -40°C typically reduces moisture to below 0.03%. Inadequately dried pellets can generate steam bubbles that compete with azodicarbonamide gas evolution, producing irregular cell-size distribution and surface voids. EVAtech 160I/30C should be kept in sealed moisture-barrier packaging until use; opened containers should be returned to a dry environment and consumed within 24 h in an uncontrolled >60% RH production hall unless dryer capacity is available. Storage temperature should remain below 30°C and away from direct UV exposure to avoid premature degradation of the blowing agent package. The blowing agent can settle within a container during prolonged transport; pellet conditioning by slow tumbling is recommended before sampling for melt-flow testing. Batch-to-batch variation in melt flow index for high-MI EVA grades can be a processing bottleneck because small differences in shear viscosity affect fill time and foam nucleation. A variation of ±15 g/10 min may require adjustment of screw speed or injection velocity, but published data for this specific EVAtech configuration is limited. Incoming inspection should include melt flow index using ISO 1133-1:2022, moisture content by Karl Fischer titration using ISO 15512:2019, and bulk density. The compound should not be blended with amine-based stabilizers or sulfur-bearing additives; amine species can scavenge free radicals and reduce peroxide crosslink density, while sulfur can interfere with the azodicarbonamide decomposition pathway. Phenolic antioxidants and phosphite stabilizers are preferred if additional stabilization is required.

Base EVA copolymer status under FDA 21 CFR 177.1350 applies only to the unmodified resin; the crosslinked foam formulation must be assessed for extraction limits and blowing agent residues. For EU installations, the compound is subject to REACH registration and, where relevant, RoHS Directive 2011/65/EU restrictions on lead, mercury, cadmium, hexavalent chromium, PBB, and PBDE. A supplier statement should be obtained for azodicarbonamide decomposition residues if the foam is used in food-contact or toy applications.

Low-Temperature Flexibility and Chemical Resistance Trade-Offs at 30 wt% Vinyl Acetate

The vinyl acetate content of 30 wt% reduces polyethylene crystallinity, broadens the glass-to-rubber transition, and improves flex fatigue at low temperatures relative to lower-VA EVA copolymers. Published data for EVA copolymers show that the glass transition temperature of 30 wt% VA EVA is approximately -25°C, while 18 wt% VA EVA can have a brittle point near -40°C and is less suitable for applications requiring repeated flexing below -20°C. Low-temperature brittle point is commonly determined by ASTM D746-20. The foam made from EVAtech 160I/30C is therefore specified for footwear midsoles and cushioning parts exposed to cold climates. The trade-off is chemical resistance: increasing vinyl acetate content increases polarity and reduces resistance to nonpolar hydrocarbon oils. EVA foam with 30 wt% VA swells less in polar liquids but more in aliphatic hydrocarbons than an 18 wt% VA grade. For gasket applications involving mineral oil, compatibility testing should follow ISO 1817:2022 with defined temperature and time conditions. Compression set after constant deflection should be measured using ASTM D395-18 Method B at 50°C for 22 h; typical formulated EVA foam values are 30–60% depending on cure density and foam density. The 30 wt% VA grade is less rigid than lower-VA grades, which reduces the hardness of the final foam. Hardness of crosslinked EVA foam is commonly reported as Asker C or Shore A; the same base density may produce an Asker C hardness of 30–45 for a 30 wt% VA foam compared with 45–60 for an 18 wt% VA foam at equivalent crosslink density. The material should not be used in continuous contact with strong oxidizing acids, chlorinated solvents, or high-aromatic hydrocarbons without specific compatibility testing.