EVAtech 110S/3N/1 Compósito do copolímero EVA, grau de espuma reticulada

EVAtech 110S/3N/1 EVA Copolymer Compound, Crosslinkable Foam Grade, is a pelletized ethylene-vinyl acetate formulation intended for chemically crosslinked closed-cell foam processes. The base polymer contains a vinyl acetate comonomer fraction of 18–22% w/w, determined by Fourier-transform infrared spectroscopy in accordance with ASTM D5594-18. Melt flow index is specified at 1.0–1.4 g/10 min when tested at 190°C/2.16 kg using ISO 1133-1:2022. The designation suffix 3N/1 refers, in supplier documentation, to nitrogen-blanketed drying or storage intended to limit retained moisture to ≤0.05% w/w before processing. The compound carries a dispersed organic peroxide curing system and a nucleating package compatible with azodicarbonamide chemical blowing agents.

Typical downstream operations include slabstock foam molding, continuous chemical crosslinking lines, and autoclave nitrogen-expanded block foam for gaskets, protective packaging, footwear midsoles, and thermal insulation. The product differs from standard extrusion EVA in that the formulation is not intended for non-foam sheet or film lines; it contains a coordinated cure and blowing package that creates a thermoset-like network after expansion. In compounding, the pellet form permits dosing through gravimetric feeders into twin-screw extrusion lines with screw length/diameter ratios between 30:1 and 44:1. Published data for the exact formulation is limited to supplier technical data sheets rather than independently archived public literature; the property values below should be treated as nominal supplier data rather than statistically derived specification limits.

What Separates a Crosslinkable Foam Grade from Standard Extrusion EVA?

A standard EVA foam extrusion resin relies on high melt viscosity and die cooling to stabilize the cell structure; once cooled, the foam remains thermoplastic and can be re-melted. EVAtech 110S/3N/1 forms covalent bonds between polymer chains during the foaming cycle. The resulting gel fraction, typically 65–75% according to ASTM D2765-16, converts the matrix from a melt-processable thermoplastic into an elastomeric solid. This network suppresses cell collapse above the crystalline melting point of EVA and improves compression set recovery after repeated loading. In comparative testing based on ISO 815-1:2014 at 23°C/24 h, crosslinked foam made from EVAtech 110S/3N/1 exhibits compression set values of 8–12%, whereas a non-crosslinkable EVA foam of similar density can exceed 20%. Non-crosslinkable EVA foam begins to flow above the polymer melting point, while crosslinked EVAtech 110S/3N/1 retains dimensional stability at short-term exposure up to 120°C provided that the foam is not mechanically loaded. This distinction is relevant when a product is transferred from thin, low-density cushioning to load-bearing seals or footwear midsoles.

Melt Rheology and Blowing Agent Decomposition Overlap

The compound is processed under conditions that overlap the decomposition of azodicarbonamide with the peroxide cure rate. The base EVA melt flow index of 1.0–1.4 g/10 min is low enough to limit premature cell escape during free-foam expansion but high enough for throughput on single-screw extrusion lines. In production-scale trials on a reciprocating screw foam line with barrel length/diameter ratio of 40:1, the melt temperature at the adapter was maintained between 105°C and 110°C. This window is approximately ±5°C wide. At adapter temperatures below 100°C, the blowing agent decomposition is incomplete, leaving unfoamed skins and high-density zones; above 115°C, the peroxide half-life becomes short enough to advance crosslinking before bubble expansion, causing torn cell walls and split edges. The effective gas evolution temperature of azodicarbonamide in zinc oxide/zinc stearate-activated systems is typically narrowed to 155–165°C, while the organic peroxide in the compound has a half-life in the same range for decomposition times available in a 10–15 min cure. This kinetic overlap is why the compound is not recommended for direct transfer to melt-compounding lines that exceed 120°C for extended residence. Where twin-screw compounding is used for masterbatch dilution, the screw profile should limit peak melt temperature to ≤120°C to avoid scorch. Melt pressure before the breaker plate typically reads 12–18 MPa for a 4–6 mm die gap; higher pressures indicate excessive pre-cure or insufficient barrel heating. Published data for this specific configuration is limited; the values above reflect supplier bulletins and equipment technical bulletins rather than independent archival studies.

Moisture control is a processing boundary rather than an optional recommendation. The pellets are hygroscopic enough that storage in ambient air with relative humidity above 60% can raise moisture uptake to the point where steam evolution during extrusion adds uncontrolled internal pressure. Pre-drying in a desiccant hopper with air inlet dew point of −40°C for 2–4 h at 60°C is required before feeding closed-barrel systems. The 3N/1 designation in the product name indicates, in supplier literature, nitrogen-blanketed packaging or a nitrogen-purge recommendation during silo storage. Failure to observe this boundary can produce surface defects, density variation, and blowing agent pre-decomposition at the feed throat.

Compounding is typically performed on a co-rotating twin-screw extruder with screw length/diameter ratio of 40:1 to disperse the peroxide and nucleating package without exceeding 120°C melt temperature. Barrel zones are set from 70°C in the feed throat to 100°C at the die, with screw speed adjusted to avoid shear heating above 115°C. A side-fed blowing agent masterbatch is preferred when the line processes the compound into sheet, because early addition of azodicarbonamide can generate gas in the barrel. Batch-to-batch variation in peroxide concentration is controlled by the supplier to ±0.05 phr, which is necessary to hold gel content within the specified 65–75% band. If the peroxide level is too low, foam remains partially thermoplastic and compression set increases; if too high, the network becomes brittle and tear strength falls. This compounding boundary is a common source of scrap on lines that regrind crosslinked foam into the feed, because residual sulfur or amine residues from other compounds can deactivate the peroxide. Incompatible additive families include amine-based antioxidants, certain hindered amine light stabilizers, and free sulfur donor curatives that compete for radicals. Process oils above 5 phr migrate during expansion and produce surface tack and poor plate release.

In continuous chemical crosslinking foam lines, the die is typically an adjustable-lip flat die with a gap of 4–6 mm and a draw ratio below 1.2. Expansion occurs at the die exit as the compound enters atmospheric pressure; melt strength from partial crosslinking restrains cell coalescence. If the die gap is too narrow, shear rate in the die can exceed 1000 s⁻¹ and initiate peroxide decomposition; if the gap is too wide, the sheet may not expand to full thickness and density rises. This balance is specific to EVAtech 110S/3N/1 because of its low melt flow index compared with non-crosslinkable EVA foam grades.

Compression Set Depends on Cure Completion, Not Merely Density

After crosslinking, closed-cell foam from EVAtech 110S/3N/1 is typically characterized by a density of 190–220 kg/m³ when tested according to ISO 845. Tensile strength and elongation are measured on cellular sheet using ISO 1798; nominal values are 2.0–2.8 MPa and 250–350%, respectively. Shore A hardness according to ISO 868 falls between 55 and 65. These values differ from higher vinyl acetate foam grades, which commonly exhibit Shore A values of 35–45 and greater low-temperature flexibility but lower mechanical strength. Thermal aging at 100°C for 168 h in an air-circulating oven, using ISO 188:2023, typically changes tensile strength by less than 15% and elongation by less than 20% from initial values, provided the peroxide cure has completed. Compression set measured at 50% deflection for 24 h at 23°C according to ISO 815-1:2014 remains in the 8–12% band. At 70°C/24 h, compression set values can increase to 20–30%, which defines the upper operating temperature for continuous load-bearing use rather than short-term exposure. The crosslinked matrix restricts reversion when the foam is exposed to cyclic loading; non-crosslinkable EVA foams of equivalent density show higher set and greater thickness loss after 10,000 cycles at 25% compression. Test data for the exact EVAtech 110S/3N/1 formulation in public literature is limited; the values above are supplier nominal values and should be verified against the production batch certificate of analysis.

When 28% VA EVA Foam Compounds Are Specified

The principal substitution risk arises when EVAtech 110S/3N/1 is used as a drop-in replacement for a foam grade containing 28% w/w vinyl acetate. Higher VA contents lower the glass transition temperature and plasticize the amorphous phase; they produce softer foam with better low-temperature flexibility but lower tensile strength and higher creep. A 28% VA crosslinkable foam may have Shore A hardness near 35–45 and tensile strength closer to 1.2–1.8 MPa. EVAtech 110S/3N/1, at 18–22% w/w VA, yields a harder, stronger foam that is preferred when compression set and dimensional stability outweigh low-temperature softness. For cold-weather gasket applications involving continuous deformation below −20°C, the lower VA compound may stiffen sufficiently to reduce sealing force; in such cases, a 28% VA grade is more appropriate. Conversely, in footwear midsoles and protective equipment where repeated compression recovery and abrasion resistance dominate, EVAtech 110S/3N/1 offers less plastic deformation after loading. The crosslinking density achieved with the same peroxide loading can be slightly higher for the lower-VA compound because the comonomer does not dilute the crystalline region; gel content measurements may remain in the 65–75% range. The product should not be used in contact with amine-based processing aids or certain hindered amine light stabilizers that can react with the organic peroxide and consume radicals before crosslinking. It is also incompatible with processing oils that exceed 5 phr; oil migration can shift the cure and blowing balance and create surface tack.