Braskem América SVT2180 EVA Copolímero Resina, Bio-Circular Atribuído (≥80% Bio-Carbono), Grado de espuma reticulada

Braskem America SVT2180 is an ethylene-vinyl acetate copolymer resin classified as a crosslinkable foam grade, supplied with a bio-circular attributed biogenic carbon allocation of at least 80%. The material is intended for chemically crosslinked closed-cell foam processing rather than unmodified film extrusion or rigid injection molding. In practice, the resin is compounded with organic peroxide cure agents, chemical blowing agents, zinc oxide activators, and processing aids before expansion in compression molding, injection foaming, or autoclave foaming lines. The bio-circular attribution is a mass-balance chain-of-custody designation, not a claim of biodegradability or compostability. Direct analytical verification of biogenic carbon may be carried out using ASTM D6866-21 or ISO 16620-2:2019; those methods answer a different question than a mass-balance certificate such as ISCC PLUS. The grade is used in footwear midsoles, insoles, sports mats, cushion packaging, thermal insulation, gaskets, and impact-protection components. The exact melt flow rate, vinyl acetate content, and density for SVT2180 must be obtained from the producer’s certificate of analysis or technical data sheet; published data for this specific configuration are limited in this document.

For crosslinkable EVA foam grades of this class, class-level process-control values typically include a melt mass-flow rate in the range 1.5–4.0 g/10 min at 190°C/2.16 kg under ASTM D1238-20, a vinyl acetate content of 15–28 wt%, and a base-resin density of 0.935–0.950 g/cm³ under ASTM D1505-10. These ranges are not a substitute for the SVT2180 product specification. Vinyl acetate content controls crystalline melting point depression, low-temperature flexibility, and compatibility with peroxide cure systems. Higher vinyl acetate content generally improves softness and filler acceptance but lowers upper service temperature and can increase compression set if the cure network is underdeveloped. Melt mass-flow rate controls mixing torque and melt strength during gas expansion; values above the foam-grade band may cause cell rupture, while excessively low values can reduce blowing-agent dispersion and increase mold-fill pressure.

What Distinguishes SVT2180 from Conventional Fossil EVA Foam Resins?

The principal difference is feedstock attribution rather than a necessary change in polymer backbone chemistry. Conventional EVA foam resins are manufactured from fossil naphtha, whereas SVT2180 carries bio-circular attribution through a mass-balance framework that assigns renewable biogenic carbon to the resin output. If the producer maintains equivalent vinyl acetate content and melt flow rate, the peroxide cure response and blowing-agent expansion behavior are expected to be comparable to a fossil reference grade. The physical and rheological behavior remains governed by the same structural variables: vinyl acetate weight fraction, melt mass-flow rate, molecular weight distribution, and long-chain branching.

Compared with high-VA hot-melt EVA grades, which often exhibit melt flow rates above 25 g/10 min, crosslinkable foam grades are normally controlled below 6 g/10 min to retain melt strength during gas expansion. Compared with low-density polyethylene foam resins, the vinyl acetate units in SVT2180 reduce crystallinity and increase chain flexibility, which supports the formation of softer closed-cell foam with higher elongation. Compared with bio-based polyurethane foams, EVA foam is thermoplastic before crosslinking and uses a different cure chemistry based on organic peroxide decomposition rather than isocyanate-polyol addition. The bio-circular version should not be confused with physically bio-based EVA that may show a direct 14C measurement corresponding to the claimed percentage. In mass-balance attribution, the renewable carbon allocation may be concentrated in a portion of the output stream while the final polymer remains structurally equivalent to fossil EVA.

On injection foaming lines, a reciprocating screw with a compression ratio of 2.5:1–3.0:1 and L/D ratio of 20:1–24:1 is commonly used for EVA foam compounds. The feed and compression zones are held below 120°C to prevent premature blowing-agent decomposition, while the nozzle temperature may be allowed to reach 160–180°C only at the point of injection. Clamp force must be sufficient to resist mold breathing during gas expansion; insufficient clamp tonnage produces flash, density gradients, and dimensional variation. Observed production-line failure modes include gas blowholes at knit lines, silver streaks from moisture or volatiles, and plate-out on mold surfaces from blowing-agent residues. The use of SVT2180 does not eliminate these failure modes because the bio-circular feedstock does not alter the underlying peroxide-cure physics. Qualification of SVT2180 as a replacement for a fossil EVA foam grade requires comparison of the certificate of analysis, rheometer cure curve, and blown foam density against the reference material under the same machine settings. Published data for this specific substitution on a named injection foam platform are limited.

Crosslinkable Foam Processing Window and Thermal Thresholds

In production-scale crosslinking of EVA foam, the thermal decomposition of the organic peroxide and the gas-yielding reaction of the blowing agent must be synchronized with the compound’s melt viscosity profile. Dicumyl peroxide, a common cure agent, has a half-life of approximately 10 h at 117°C, 1 h at 135°C, and 1 min at 171°C. Azodicarbonamide, the dominant chemical blowing agent for EVA sheet and molded foam, decomposes exothermically in the range of 195–215°C when activated with zinc oxide or zinc stearate, releasing roughly 220 mL/g of gas at standard temperature and pressure. These two reactions are not independent. If the viscous melt crosslinks too early, the expanding gas cannot nucleate and grow into uniform closed cells, producing cracked foam or dense skin layers. If the blowing agent decomposes before sufficient network formation, cell walls rupture and the foam collapses.

Actual processing therefore uses staged temperatures. An internal mixer with tangential rotors and a fill factor of 0.70–0.80 is typically dropped at 105–115°C to avoid blowing-agent decomposition during mixing. A two-roll mill is then operated at 70–80°C with a friction ratio of 1.15–1.25. The compounded sheet is expanded in a hydraulic compression press at 150–180°C. Mold pressure is not arbitrary because it must keep gas in solution until the cure network has sufficient melt strength to support expanding cells. Surface scorching, plate-out, and delamination occur when the cure temperature overshoots the blowing-agent induction period or when mold-release chemistry interacts with acetic acid released from EVA degradation. The order of addition on the mill or internal mixer also controls scorch: fillers, zinc oxide, and stearic acid are dispersed before dicumyl peroxide; adding peroxide above 105°C can generate scorch particles that later appear as hard specks in the foam. Published SVT2180-specific cure kinetics are limited; the producer should be consulted for recommended peroxide and blowing-agent concentrations.

If the Foam Density Must Drop Below 0.15 g/cm³, What Changes in Formulation?

Low-density EVA foam below 0.15 g/cm³ is produced by increasing chemical blowing-agent loading and reducing filler content, but the response is not linear. Azodicarbonamide is typically used at 2.0–6.0 phr in crosslinked EVA foam; dicumyl peroxide is held between 0.7 phr and 1.2 phr, and zinc oxide at 1.0–3.0 phr functions as a blowing-agent activator. Increasing azodicarbonamide above the upper limit without increasing crosslink density leads to cell coalescence, coarse cell-size distribution, and reduced tear strength. Calcium carbonate filler raises foam density and reduces rebound but improves dimensional stability and tear resistance. Moving below 0.15 g/cm³ therefore forces a trade-off between density and mechanical robustness. Crosslink density is controlled through gel content or rheometer torque; compression set after 22 h at 70°C under 50% deflection per ASTM D395-18 is a practical production control. If compression set exceeds the target, the network is often undercured. The remedy is not always additional peroxide; it may require a co-agent such as triallyl cyanurate or trimethylolpropane trimethacrylate to increase crosslink efficiency without increasing scorch. A higher vinyl acetate EVA grade shifts the rubber plateau to lower temperature and improves low-temperature flexibility, but it can also reduce heat resistance and increase compression set at the same cure level. The exact vinyl acetate content of SVT2180 must be confirmed from the producer’s certificate of analysis because it controls both the glass transition region and compatibility with the peroxide cure system.

Compliance Must Address Biogenic Carbon, Foam Mechanics, and Food-Contact Boundaries.

Regulatory treatment of SVT2180 requires separating the bio-circular feedstock documentation from the finished article requirements. The bio-carbon attribution is supported by chain-of-custody certification under ISCC PLUS or a comparable mass-balance framework; analytical verification of biogenic carbon may be performed by ASTM D6866-21 or ISO 16620-2:2019. The base polymer falls within the olefin polymer family and, when unmodified and meeting extraction limits, may be assessed against FDA 21 CFR 177.1520. However, foam formulations containing peroxide decomposition residues, blowing-agent by-products, or colorants must be evaluated on the finished article. European users should assess the grade under REACH 1907/2006 and, for food contact, under EU 10/2011 with migration testing appropriate to the foam density and surface area.

Storage prior to blending is governed by moisture uptake and contamination rather than extensive drying. EVA is less hygroscopic than polyamide or polyurethane, but when ambient relative humidity exceeds 60%, surface moisture or pellet condensation can create steam during expansion and cause cell-size irregularities. A conditioned drying step at 60°C for 2–4 h is applied only when incoming moisture above 0.1% by Karl Fischer titration is confirmed. The resin must not be processed above 230°C for extended periods because EVA begins to liberate acetic acid through deacetylation. This release causes corrosion on steel tooling, crosslink interference, odor in the finished foam, and surface deposits on molds. Amine-based additives are generally incompatible with peroxide-cured EVA foam because they scavenge free radicals, producing retarded cure rates and nonuniform crosslink density. Continuous service of EVA foam is generally limited to temperatures below 80°C; published data for SVT2180 in long-term high-temperature load-bearing applications are limited, so accelerated heat-aging evaluation per ASTM D3045 or a comparable practice is required before acceptance.