EVAtech 150I/15A Composto do copolímero EVA, grau de espuma reticulada

EVAtech 150I/15A is an ethylene-vinyl acetate copolymer compound supplied in pellet or sheet form and classified as a crosslinkable foam grade. The alphanumeric designation is not a direct ISO 1133-1 or ASTM D1238 melt-flow index; in commercial practice, the 15A field typically corresponds to a nominal vinyl acetate comonomer content of approximately 15 wt%, while the 150I field identifies an internal grade modifier or compounding sequence rather than a melt index of 150 g/10 min. The supplier certificate of analysis remains the binding specification. The material contains a peroxide- or radiation-responsive crosslinking system and a chemical blowing-agent package intended for closed-cell foam expansion. It is processable on Banbury internal mixers, two-roll mills, and low-shear single-screw or twin-screw extruders with L/D ratios from 24:1 to 32:1. The thermal processing window is narrower than that of unmodified EVA; barrel or roll temperatures above 110°C produce scorch, while insufficient blowing-agent decomposition leaves high-density unexpanded regions.

What Are the Critical Incoming Material Specifications?

Incoming inspection for EVAtech 150I/15A should verify vinyl acetate content, melt flow rate, moisture, ash, and thermal transitions before direct compounding or foam expansion. Vinyl acetate content controls polarity, gas permeability, and peroxide crosslinking efficiency; a deviation of ±1 wt% shifts the optimum peroxide dosage and compression set, particularly for density targets below 0.20 g/cm³. Melt flow rate is determined by ISO 1133-1:2022 at 190°C/2.16 kg and should be compared with the batch certificate; the 150I field is not an MFR value. Residual moisture above 0.10 wt% causes surface pitting and irregular cell coalescence; pre-drying at 60°C for 4 h is applied when storage relative humidity exceeds 60%. Ash content by ASTM D2584-18 is used to detect filler excursions or crosslinking-agent agglomerates.

On a 40:1 L/D co-rotating twin-screw extruder with segmented screw elements, the compound is fed in the first barrel section; liquid peroxide and processing aids are injected downstream into the melt seal to prevent localized shear-induced decomposition. Dicumyl peroxide exhibits a 1 h half-life at approximately 135°C and a 1 min half-life near 171°C. Barrel zones above 120°C reduce scorch safety, and the die head is typically maintained at or below 105°C. The blowing agent is added as a pre-dispersed masterbatch or through side-stuffing after peroxide distribution. Premature crosslinking appears as rising melt pressure, motor torque, and surface shark-skin on the sheet; scorched compound cannot be reworked. On a two-roll mill, the compound is processed at 95–110°C with a friction ratio of 1.1:1 to 1.2:1. Sheet thickness is held to ±0.2 mm to support uniform heat transfer during subsequent expansion.

Cure State, Blowing-Agent Decomposition, and Cell Morphology Control

The expansion of EVAtech 150I/15A depends on the overlap between peroxide decomposition and chemical blowing-agent gas yield. Azodicarbonamide decomposition in EVA foam compounds commonly falls in the 195–215°C range, but the actual onset is influenced by zinc oxide or zinc stearate activators. In compression-molded sheet expansion, the cure cycle is typically 160–175°C under 15–20 MPa platen pressure for 8–15 min, followed by controlled pressure release to permit cell growth. Gel content, determined by ASTM D2765-16, should reach 60–85 wt% after cure; values below 55 wt% can produce cell-wall rupture and coarse cell structures. Closed-cell content measured by ISO 4590:2016 is commonly above 85% for crosslinked EVA foams at densities from 0.10 g/cm³ to 0.25 g/cm³. Compression set per ISO 815-1:2014 at 50°C for 22 h remains below 35% at 0.15 g/cm³ for this class; non-crosslinked EVA foam of equivalent density can exceed 50% under the same conditions. Tensile elongation at break per ISO 37:2017 commonly falls in the 150–300% range for crosslinked EVA foams at 0.15 g/cm³, but published data for this specific configuration is limited.

EVAtech 150I/15A differs from general-purpose EVA film and extrusion grades in melt-state extension behavior and cure response. Unmodified EVA film grades often have MFR values from 2.0 g/10 min to 20.0 g/10 min, narrow molecular weight distribution, and no peroxide or blowing-agent residue; this foam compound is formulated with a broader molecular weight distribution and a reactivity package that increases extensional viscosity as crosslinking initiates. Compared with LDPE foam compounds, the 15 wt% vinyl acetate content reduces crystallinity and improves low-temperature flexibility, but lowers the upper service temperature and increases polar-solvent sensitivity. Compared with metallocene POE foam grades, EVA typically provides higher green strength and established compression-molding behavior; POE can provide lower residual odor and improved ageing behavior but may require higher peroxide dosage. The substitution decision should be made using compression set data per ISO 815-1:2014, tensile property data per ISO 37:2017, and density data per ISO 845:2009, not by hardness or visual cell structure alone.

When Evaluating Substitution for LDPE or POE Foam in Cushioning and Sealing Lines

Comparison of EVAtech 150I/15A with non-crosslinked EVA, LDPE, and POE foam grades requires separating class-level published data from lot-specific certificate values. The table below provides representative property ranges for foam classes, not guaranteed product specifications.

When EVAtech 150I/15A replaces LDPE foam in a sealing or cushioning line, the higher polarity of EVA requires revalidation of adhesive compatibility, moisture absorption, and compression stress relaxation. When it replaces POE foam, lower peroxide dosage may be required because of the vinyl acetate radical-scavenging behavior; this must be confirmed by moving-die rheometer torque differences and gel content measurements. Non-crosslinked EVA foam is not a direct drop-in replacement where compression set below 35% after 22 h at 50°C is required.

Thermal Degradation, Shrinkage, and Post-Expansion Dimensional Stability

After expansion, crosslinked EVA foam retains viscoelastic stress and trapped gas that diffuses gradually from closed cells. If the compound is not adequately crosslinked, cell walls undergo viscous flow during cooling, producing gauge variation and shrinkage. Shrinkage after demolding is typically controlled by holding the foam at 60–80°C for 4–24 h in forced-air ovens, followed by dimensional change measurement per ASTM D3574-17. Thermal degradation onset measured by thermogravimetric analysis per ISO 11358-1:2022 occurs above 300°C under nitrogen for EVA, but oxidative decomposition starts lower. The crosslinked network raises the onset of viscous flow and reduces compression set after ageing at 70°C for 22 h. Residual blowing-agent decomposition products, particularly cyanuric acid from azodicarbonamide, can bloom on the foam surface if cure is incomplete; this is detected by FTIR-ATR or visual inspection under 10× magnification. Published data for EVAtech 150I/15A-specific degradation kinetics is limited; the above values are class ranges for 15 wt% vinyl acetate crosslinked EVA foam.

Storage stability of the unexpanded compound is influenced by humidity and temperature. The material should be stored below 30°C and 60% RH in closed packaging; moisture pickup above the 0.10 wt% threshold increases melt-phase void formation. Peroxide-containing compounds have finite shelf life; typical storage stability for dialkyl peroxide masterbatches is 6–12 months at 20–25°C, but the exact shelf life for EVAtech 150I/15A should be taken from the manufacturer's technical data sheet.

When fillers such as calcium carbonate or fumed silica are added, the compound's melt viscosity increases and the expansion ratio decreases. Addition of 5–20 phr calcium carbonate can raise density by 0.03–0.10 g/cm³ and reduce tensile elongation; these effects are measured by ISO 1183-1:2019 and ISO 37:2017. Blowing-agent levels must be re-optimized when filler loading exceeds 10 phr because nucleating effects increase cell count but reduce cell size. EVA-compatible color masterbatches are incorporated at 1–3 wt%; high-acid or amine-functional carrier resins should be avoided because they can alter peroxide cure kinetics and final crosslink density.

In industrial foam manufacture, EVAtech 150I/15A is used in compression-molded footwear midsoles, orthopedic insoles, gaskets, buoyancy aids, and anti-vibration padding. For footwear, expanded density and Asker C hardness are measured by ISO 845:2009 and JIS K 7312:1996; hardness values for this class are commonly 45–60 Asker C after expansion to 0.15–0.20 g/cm³. For gaskets, compression force deflection at 25% strain is screened by ISO 3386-1:2014, and compression set at 70°C for 22 h is evaluated by ISO 815-1:2014. Thermal insulation applications require thermal conductivity measurements by ISO 8302:1991; published data for EVAtech 150I/15A in this configuration is limited. The compound is colored with EVA-compatible masterbatches; amine-based additives and high-pH fillers should be avoided because they can interfere with peroxide decomposition and alter final cure state. Compliance documentation should be confirmed under EC No 1907/2006 (REACH) and RoHS recast 2011/65/EU before use in regulated applications.