Greenflex MP 35 BCA EVA Copolymer Resin,Bio-Circular Attributed,High Elasticity Grade

In high-volume footwear midsole moulding, the melt strength of an ethylene-vinyl acetate copolymer is the primary determinant of cell stability during pressure release after injection. If the supplier’s MP nomenclature follows the convention where the two-digit suffix denotes nominal vinyl acetate mass fraction, Greenflex MP 35 BCA is positioned at 35 wt% vinyl acetate; the certificate of analysis must be consulted because a variation of ±1.5 wt% shifts the crystalline melting point, melt viscosity, and gas solubility in foam. The bio-circular attributed content is allocated through a mass-balance chain of custody, typically under ISCC PLUS certification, and does not alter the comonomer structure or the melt rheology relative to the fossil-based equivalent. Because the pellets can absorb surface moisture after warehouse storage below 10°C and subsequent exposure to a 25°C, 60% RH production hall, a desiccant hopper dryer set at 55°C for 3 h is specified when the ambient dew point exceeds 10°C; surface moisture is reduced below 0.05 wt% before the material enters the screw.

The plastification unit should be a reciprocating screw injection machine with an L/D ratio of at least 20:1 and a compression ratio of 2.2:1 to 2.8:1. Barrel zone settings from 170°C to 185°C are used for high-vinyl-acetate EVA grades, with the melt temperature checked by a needle pyrometer at 180-200°C. Azodicarbonamide or 4,4'-oxybis(benzenesulfonyl hydrazide) is introduced as a dry blend or masterbatch at 0.5-2.5 wt%, with zinc oxide or zinc stearate activator at 0.1-0.4 phr to lower the azodicarbonamide decomposition onset to the 155-180°C window. Premature blowing agent decomposition in the barrel causes screw slip and gas venting from the feed throat; the remedy is to reduce the first barrel zone to 140°C or to use a gas-purged feed throat. Dicumyl peroxide at 0.5-1.0 phr is incorporated when compression set resistance per ISO 815-1 is required; the peroxide is added as a pre-dispersed powder masterbatch at 40-50 wt% active content to avoid localized over-cure near solid granules.

The mould is filled to 60-80% of the cavity volume, and the clamp force must exceed the gas pressure generated during azodicarbonamide decomposition; for a 2-cavity midsole mould on a 150 t clamp press, the available clamp margin is typically 15-25% above the peak cavity pressure. After a short cooling hold, the press opens to a controlled daylight gap of 10-20 mm to permit free foam expansion; a second closing step may be used to shape the sidewall. Demoulding before surface solidification produces split tears at the parting line and voids at the gate. Shrinkage after demoulding is measured linearly and typically stabilises at 2-3% for expanded densities between 0.18 g/cm³ and 0.30 g/cm³. Finished components are stabilised at 40°C for 24 h before hardness is tested per ASTM D2240 and tear strength per ASTM D624; density is measured by water displacement per ISO 1183-1:2019. Published lot-specific data for this bio-circular grade in microcellular injection is limited; the stated window must be validated on the target press because clamp force, nozzle tip geometry, and hot runner balance influence cell uniformity more than the resin MFR alone.

Does High-Vinyl-Acetate EVA Broaden the Peroxide Cure Window in Thick Slabstock?

Thick-section slabstock production of cross-linked EVA foam represents a process conflict between cure exotherm and thermal conductivity. The core of a 30 mm slab lags the surface by several minutes when the platen is held at 170°C; the peroxide selected for cure at 160-170°C begins decomposing at 130-140°C while the core is still warming. Dicumyl peroxide exhibits a 1 h half-life at approximately 135°C and a 1 min half-life at approximately 171°C. If the oven set point is raised to accelerate core heating, the surface can reach full cure before the center has reached 150°C, producing a hard skin, unexpanded core, and post-cure shrinkage. The cure system is therefore staged: a first oven or press stage holds the slab at 120-125°C to equalise temperature without significant cure, followed by a second stage at 160-170°C for final expansion and crosslinking. Moving die rheometer data per ASTM D5289 are used to define ts2 and tc90; for a peroxide-EVA slabstock formulation, ts2 at 160°C should exceed 2 min and tc90 should fall between 8 min and 12 min in the unexpanded compound. Published data for this specific bio-circular grade in slabstock is limited; the rheometer cure must be re-run after every change in blowing agent masterbatch source.

Blowing agent decomposition must be timed to coincide with the thermoplastic phase melting and before crosslinking advances. Azodicarbonamide activated with zinc oxide decomposes between 155°C and 180°C, which matches the cure stage. If the blowing agent releases gas too early in the preheating stage, the slab expands before peroxide crosslinks begin, causing cell collapse. If it releases too late, crosslinked networks restrict bubble growth and the foam density remains above target. A gradient in cell size exceeding 50% between skin and core is typically traceable to a cure rate mismatch. The exotherm from peroxide decomposition further complicates heat transfer; local core temperatures can overshoot the platen set point by 10-15°C in slabs above 25 mm, causing accelerated deacetylation and acetic acid release. Stainless steel press frames and exhaust extraction are specified because the acid vapour accelerates corrosion on plain carbon steel tooling.

After the cure stage, the slab is cooled gradually at 5-10°C/min. Rapid cooling produces skin-core density differential and post-cure shrinkage of the large faces. Dimensional stability is checked after 72 h at 23°C and 50% RH. The key laboratory values for release are density per ISO 845, compression set per ISO 815-1 after 24 h at 70°C, and split tear strength per ASTM D624. The high vinyl acetate content of Greenflex MP 35 BCA favours lower Shore A hardness and higher rebound resilience when tested per ISO 868 and ISO 8307, but the final compound must remain above the minimum tensile strength required for sheeting; the balance is adjusted with calcium carbonate filler at 5-20 wt% and with crosslinker dose.

When a high-vinyl-acetate EVA is selected for monolayer photovoltaic encapsulant film, the first lot verification is gel content after lamination, not melt flow. Calendered or cast film with a thickness of 0.4-0.6 mm is laid up between glass and backsheet in a vacuum laminator. The vacuum is pulled to below 30 mbar before the membrane applies atmospheric pressure; the module is then heated at 145-155°C for 12-18 min. Peroxide-initiated crosslinking is monitored by gel content per ASTM D2765 or ISO 10147; film removed after lamination should exceed 70% gel content. A value below 65% indicates under-cure or inhibitor interference from antioxidant or masterbatch additives. A value above 90% may indicate excessive crosslink density and can raise film shrinkage during lamination, increasing the risk of busbar misalignment. The high elastic recovery of this grade may reduce microcrack incidence during lamination and mechanical load testing, but published comparative data for this specific formulation is limited; module-makers must run their own cell crack analysis according to electroluminescence or thermography after IEC 61215 static load testing.

Damp heat exposure per IEC 61215 at 85°C and 85% RH for 1000 h is the most severe test for EVA degradation. Hydrolytic and thermal deacetylation can release acetic acid, which attacks tin-lead solder coatings and silver busbars. Supplier control limits for EVA encapsulants often flag an aqueous extract pH below 4.5 after damp heat; ion chromatography is used to quantify acetate. The bio-circular mass balance attribution under ISCC PLUS does not change the deacetylation chemistry, and the same stabilization package limits apply as for fossil EVA. If the grade is used in an encapsulant film that will be claimed as bio-circular, the mass balance certificate must cover the entire film converting step and the module lamination step; mixing fossil and bio-attributed pellets without documented allocation breaks the claim. The lamination window must be re-validated when the vinyl acetate content differs by more than ±1.5 wt% from the qualified lot because the melting point and peroxide solubility shift.

Optical haze and adhesion to glass are controlled by the additive package, not by the bio-circular attribution. Film producers should measure peel strength to glass after lamination and after damp heat; a typical acceptance criterion is retention of at least 60% of initial peel strength after 1000 h damp heat, but module-makers set exact limits. UV preconditioning per IEC 61215 MQT 10 is followed by yellowness index measurement per ASTM E313; a ΔYI below 2.0 after 60 kWh/m² UV dose is often targeted for clear encapsulants. The high-vinyl-acetate EVA generally shows better low-temperature impact absorption than lower-VA encapsulants, but published data for this specific bio-circular grade in module encapsulants is limited; pilot line lamination is mandatory before series production.

Automotive Interior Foam Skins and Fogging Control Limits

Roll-fed thermoforming of EVA foam sheet in automotive interior manufacture imposes simultaneous limits on grain retention, edge thinning, and condensable emissions. Sheets of 1.0-3.0 mm thickness are heated to a surface temperature of 120-160°C before vacuum forming. High-vinyl-acetate EVA provides deeper grain reproduction at lower surface temperatures than low-VA grades, but the lower melt strength may increase edge thinning if the sheet is overheated above 160°C. The heater bank is zoned so that corners and deep cavities receive more radiant energy than flat fields; surface temperature is checked with an infrared pyrometer across the sheet to maintain a spread below ±5°C. During forming, vacuum is applied within 1-2 s of sheet removal from the oven; a delay causes cooling below the forming window and spring-back. Mould temperature is held at 20-40°C for grain definition; higher mould temperatures reduce shrinkage but degrade grain sharpness.

Fogging tests per ISO 6452 or SAE J1756 measure condensable emissions from the formed skin. Many OEM specifications require the reflectometric fogging value to remain below 2 mg of condensate, but the exact limit is part-specific and may be lower for instrument-panel surfaces. Volatile organic compound and semi-volatile organic compound emissions are analysed by VDA 278 after applying the foam skin to a carrier. High-vinyl-acetate EVA can outgas acetic acid and low-molecular-weight oxidation products if the thermoforming line is operated above the stabilizer system’s durability limit; exhaust extraction across the heating tunnel at a face velocity of 0.5 m/s is specified, and the oven temperature is reduced rather than extending residence time. The bio-circular mass balance documentation must be retained through sheet extrusion, thermoforming, and lamination if the part carries an ISCC PLUS claim; physical mixing of bio-attributed and fossil EVA sheet without allocation records breaks chain of custody.

Odor examinations are performed by a trained panel according to VDA 270 or OEM-specific variants; a score worse than 3 at 80°C is typically rejected for interior materials, but acceptance is driven by the automotive manufacturer. Because the grade is a high-elasticity EVA, flexible foam skins show lower crack initiation at 0°C than stiffer low-VA grades; cold flex testing can be run per ASTM D747 or as a simple mandrel bend after 4 h at -20°C. The final assembly must be validated for scratch and mar performance per GMW14688 or the equivalent OEM method, because high-VA EVA is softer and may exhibit higher surface friction. Published data for this specific bio-circular formulation in thermoformed automotive skins is limited; the fogging and odor performance must be established on the actual sheet line with the final embossing and UV coating, if applied.

Downstream of pelletising, masterbatch producers often re-extrude EVA at high filler loadings to deliver chemical blowing agent concentrates that are diluted into footwear, packaging foam, or cross-linked sheet. Greenflex MP 35 BCA is used as a carrier when the high vinyl acetate content improves filler wetting and when the end product requires a soft hand. A co-rotating twin-screw extruder with L/D of 40:1 is configured with side feeding at zone 6 for calcium carbonate or zinc oxide and with a vacuum vent at -0.08 MPa to remove moisture and low-molecular-weight volatiles. The melt temperature at the die is held between 140°C and 170°C; higher temperatures reduce viscosity but increase the risk of premature azodicarbonamide decomposition. Screw speed is set to achieve a specific mechanical energy input between 0.15 kWh/kg and 0.25 kWh/kg, because shear heating from high speed can override the barrel settings and raise the melt temperature by 10-20°C.

The high elasticity of the carrier resin influences strand pelletizing. The water bath is operated at 30-40°C; too cold a bath produces rigid strand surfaces that shatter at the cutter, while too warm a bath allows strand stretching and non-uniform pellet geometry. A pelletizer equipped with a 6-blade rotor and a bed knife gap of 0.1-0.3 mm is used to reduce tailing. Melt filtration through a mesh pack of 60/80/100 is specified when the masterbatch is intended for film or thin foam; pressure upstream of the filter is monitored, and a rise above 150 bar triggers screen replacement. Quality control includes MFR per ISO 1133-1:2022 at 190°C/2.16 kg, ash content per ISO 3451-1, and thermal stability by thermogravimetric analysis to confirm the blowing agent gas yield has not been depleted during compounding.

Masterbatch dilution ratios are governed by the end foam density. A 50 wt% azodicarbonamide masterbatch is typically let down at 1-5 phr in the final injection or calendering compound; the exact ratio must be recalculated when the resin MFR shifts because viscosity influences gas diffusion and cell size. Bio-circular attributed lots must be stored in a separated silo or documented mass-balance tank; blending with fossil feedstock is allowed under mass balance only if the bookkeeping is maintained. The carrier resin does not make the final foam bio-circular unless the downstream converter also holds an ISCC PLUS or equivalent chain-of-custody certificate. Published data for this specific grade as a high-filler carrier is limited; compounding scale-up should proceed from a torque rheometer to a pilot twin-screw line before factory-scale production.

When Low-Durometer EVA Profiles Replace Plasticized PVC in Closure Seals

Extruded solid profiles from high-vinyl-acetate EVA find replacement openings in closure seals where plasticized PVC migration is undesirable. The high comonomer content shifts Shore A hardness into the 40-70 range without the use of a liquid plasticizer. Extrusion is performed on a single-screw extruder with L/D of 24:1 or 30:1 and a barrier screw; barrel zone settings from 150°C to 170°C are used for high-VA EVA. A melt pump between the die and the screw stabilizes output because the high-VA grade displays stronger temperature-viscosity sensitivity than low-VA EVA; the melt temperature is kept below 180°C to limit acetic acid formation. The die land length is increased relative to PVC tooling because EVA exhibits less die swell and requires a higher draw-down ratio; draw-down ratios of 1.2:1 to 1.6:1 are common, but the exact value is determined by the profile wall thickness and haul-off speed.

Compression set is the primary fitness-for-use parameter for closure seals. Testing is carried out per ISO 815-1 or ASTM D395 for 24 h at 70°C; a compression set below 35% is typically required for dynamic sealing faces, while static gaskets may tolerate 45%. The high-elasticity grade is formulated with a peroxide crosslinker when the compression set must remain below 30%; however, crosslinking reduces the possibility of downstream welding into corner joints. Operational boundaries include continuous service above 70°C, where compression set and creep increase rapidly, and contact with aromatic solvents, ketones, or chlorinated solvents, which swell the high-VA copolymer. If the seal is intended for repeated food contact, compliance is assessed under FDA 21 CFR 177.1350 and EU Regulation 10/2011 on the finished profile; the bio-circular mass balance allocation does not alter migration behaviour, and migration testing must be performed on the final product with the actual additives and colourants.

The surface friction of EVA profiles is higher than plasticized PVC; silicone or water-based coatings are applied to the extrusion line to reduce insertion force. Coating adhesion is tested by tape pull after 24 h conditioning at 23°C and 50% RH. Hardness is checked per ISO 868 or ASTM D2240 after the profile has been conditioned for 1 h; hardness drift of more than 3 Shore A points between production samples indicates batch-to-batch vinyl acetate variation or incorrect let-down of the masterbatch. Published data for this specific bio-circular grade in low-durometer profile extrusion is limited; the specified hardness, compression set, and food-contact migration limits are compound-dependent and must be verified on the production extruder with the final formulation.