Greenflex ML 50 BCA EVA Copolymer Resin,Bio-Circular Attributed,Foam & Footwear Grade

Greenflex ML 50 BCA EVA Copolymer Resin, Bio-Circular Attributed, Foam & Footwear Grade, is a mass-balance-attributed ethylene-vinyl acetate random copolymer intended for crosslinked foam sheeting, injection-molded midsoles, and direct-expansion footwear intermediates. The grade designation places the material in the producer’s foam and footwear portfolio, with the numerical suffix 50 specifying a nominal melt flow rate of 5.0 g/10 min determined under ASTM D1238-23 Procedure A at 190 °C and 2.16 kg. The vinyl acetate comonomer content is approximately 18 wt%, which is within the 15–28 wt% window generally selected for crosslinked midsole and sheet foam because it suppresses polyethylene crystallinity while maintaining sufficient melt strength for bubble stabilization. The BCA descriptor indicates bio-circular attributed feedstock handled under ISCC PLUS mass-balance chain of custody; it does not denote a physical blend of bio-based or recycled polymer that would necessarily shift the molecular weight distribution or comonomer sequence distribution. As a result, the resin is positioned as a drop-in replacement for fossil-based EVA of equivalent melt flow rate and vinyl acetate level in existing foam and footwear processes, with batch-specific certificates of analysis used to confirm that physical properties remain within production tolerances.

Comonomer distribution in the random copolymer is a primary control variable. At 18 wt% vinyl acetate, the polyethylene crystallite length is reduced enough to provide a lower Shore D hardness than low-VA grades, while the polymer remains sufficiently crystalline to resist blocking and surface tack on calender rolls. The melt flow rate of 5.0 g/10 min positions the material for cellular products where rapid mold filling and uniform cell nucleation are required; higher-flow EVA may fill thin sections but can reduce hot melt strength and produce larger cell diameters. The producer’s certificate of analysis should be consulted for density, molecular weight distribution indices, and thermal transitions, because these values are lot- and reactor-dependent.

How Does Bio-Circular Attribution Differ from Bio-Based Content in a Foam-Grade EVA?

Bio-circular attribution operates through mass-balance accounting rather than physical isolation of bio-derived ethylene or vinyl acetate. In practice, the producer may co-process fossil, renewable, and circular feedstocks in the cracker and downstream EVA polymerization line, then allocate the renewable or circular attribute to a defined output fraction. The ISCC PLUS chain-of-custody certification provides the audit trail for that allocation, and certificates of analysis may report attribute-based mass rather than an absolute bio-carbon percentage. Consequently, the polymer backbone of Greenflex ML 50 BCA is chemically equivalent to a fossil-based EVA of the same melt flow rate and vinyl acetate level; the difference appears in scope 3 carbon accounting and in customer-facing sustainability declarations. Analytical confirmation of biogenic carbon, where required, is performed by ASTM D6866-21 Method B using accelerator mass spectrometry. For mass-balance-attributed products, however, the measured ¹⁴C content in a specific pellet may not correspond linearly to the attributed feedstock fraction because of blending and segregation during production. Converters should therefore distinguish between attribute-based claims governed by ISCC PLUS and direct bio-content claims that require physical measurement of the finished article. The BCA designation is best understood as a chain-of-custody feature, not as a predictable shift in Shore hardness, compression set, or tear strength.

Within a typical footwear compounding line, Greenflex ML 50 BCA is first dry-mixed with chemical blowing agents, peroxidic crosslinkers, zinc oxide, and calcium carbonate fillers in a high-intensity mixer before being fluxed in an internal mixer or a twin-screw compounding extruder. The preferred compound discharge window for EVA with 18 wt% vinyl acetate and 5.0 g/10 min melt flow rate lies at 90–110 °C; higher discharge temperatures can initiate premature decomposition of azodicarbonamide blowing agent in the mixer head or create high-torque spikes in a twin-screw extruder. Production-scale internal mixers typically specify rotor speeds of 30–60 rpm and ram pressures of 0.4–0.6 MPa, with dump controlled by torque plateau and compound temperature rather than fixed cycle time. On a twin-screw compounding extruder, a screw configuration with distributive mixing elements and a strand die is used to produce pelletized compound for subsequent sheet calendering or injection molding; a length-to-diameter ratio of at least 28:1 is preferred to ensure dispersion of peroxide and blowing agent without exceeding local melt temperatures above 120 °C. Post-mixing, the compound is usually sheeted on a two-roll mill at roll temperatures of 70–90 °C. Cooling the sheet below 50 °C before cutting or granulating prevents blocking and reduces fines generation. These boundaries are general to EVA foam compounds and should be adjusted using batch-specific data from the producer’s certificate of analysis, because bio-circular feedstock slates can alter low-level trace components that influence scorch and mold fouling.

Foam Expansion and Crosslinking Rate Limits in Midsole Manufacturing

The expansion of EVA foam is governed by matched kinetics of peroxide crosslinking and gas generation. In crosslinked foam sheeting and compression-molded midsoles, the compound is heated to 160–180 °C under 15–20 MPa closure pressure, then opened in a controlled venting sequence to permit cell growth. When the mold opens before sufficient crosslink density has developed, bubble coalescence and cell collapse are observed as gross voids or surface depressions. When the cure is too advanced before venting, the compound has excessive hot strength and the expanding sheet can split, producing internal tears and rejected sole blanks. A typical objective is to reach a torque plate on a moving die rheometer at 170 °C during the blow-gas plasticization stage. In EVA compounds of this melt-flow class, peroxide addition is often held between 0.8 phr and 1.5 phr, with azodicarbonamide loadings of 3–5 phr. Below 0.8 phr peroxide, hot melt strength may be insufficient to support cell walls during venting. Above 1.5 phr, modulus rises but tear strength and elongation can degrade, and the demolding window narrows because of excessive cure. Similar threshold behavior exists for zinc oxide activators: addition above 2.5 phr can accelerate crosslinking disproportionately, shift the rheometer torque curve to shorter times, and cause premature blow-gas release. In practice, mold unloading below 60 °C is recommended to limit post-blow expansion after the part exits the press. Because the BCA resin is a drop-in on the rheological curve, the same accelerator packages and mold release agents should function within normal tolerance; however, full-scale trials should revalidate demold time and part weight because mass-balance feedstocks can change trace components that affect mold fouling and release build-up. Published data for this specific BCA-configured expansion window is limited, so optimum cure times should not be transferred directly from a fossil EVA without comparing moving die rheometer curves between the bio-circular lot and the incumbent control.

When the BCA Grade Replaces Fossil EVA in Injection Molding

When this material is injection-molded into footwear components, the screw plastication and filling phases must be tuned to the 5.0 g/10 min flow value. Barrel temperatures from feed throat to nozzle are typically profiled from 150 °C to 190 °C; nozzle temperatures above 200 °C risk surface degradation, visible yellowing, and premature gas evolution if a blowing agent masterbatch is present. Mold temperatures are normally held at 30–50 °C for rapid skin solidification, though higher temperatures may be used for surface replication on textured midsole sidewalls. Clamp force is calculated from projected area and cavity pressure; for thin-wall foam injection, cavity pressures rarely exceed 40 MPa, and machines with 100–180 t clamp force are sufficient for multi-cavity sole molds. The main difference from structurally similar EVA grades with lower melt flow rates is a shorter filling and packing phase required to avoid overpacking the cavity; overpacking suppresses foam expansion and increases part mass. Screw back pressure should be set between 5 bar and 10 bar to maintain feeding consistency without excessive shear heating. Because this is a bio-circular attributed grade, the injection process should be validated by measuring part mass, Shore hardness, and dimensional shrinkage across at least three injection cycles and comparing them with a fossil EVA control lot.

Control of this material in footwear quality laboratories generally follows the test methods summarized in the matrix below. The methods are referenced as part of incoming resin inspection, compound qualification, and cured foam release testing.

For the European market, the resin should be evaluated for REACH registration under Regulation (EC) No 1907/2006 and for substance restrictions under Directive 2011/65/EU. Compliance with the REACH Candidate List for substances of very high concern is usually confirmed by the compounder or sole manufacturer, not assumed solely from the polymer resin certificate.

Because the BCA version is manufactured under mass-balance allocation, batch-to-batch quality monitoring should not assume that every lot has identical trace organic constituents. Differential scanning calorimetry should show the broad melting endotherm typical of EVA with 18 wt% vinyl acetate, with peak melting near 82–86 °C and a secondary polyethylene shoulder below 110 °C. A narrowing or shift of the melting peak may indicate altered comonomer distribution; if the lot also fails melt flow rate by more than the producer’s tolerance, it should not be blended with existing fossil-EVA inventory without first reoptimizing peroxide and blowing agent levels. Storage below 30 °C in sealed packaging is recommended. Exposure to relative humidity above 60% for extended periods requires pre-drying at 60–80 °C for 2–4 h in a desiccant dryer, not merely a hopper dryer, because surface moisture can produce splay and non-uniform cell nucleation in expanded sections. The grade should not be combined with amine-based antistatic or anti-fog additives in the same compound because amines can interfere with peroxidic cure and cause cure-rate drift; if antistatic function is required, non-amine migratory additives should be screened by rheometer studies at the intended cure temperature.

Compared with high-VA copolymers in the 27–33 wt% range, this grade provides lower blocking, lower tack, and higher flexural stiffness. Compared with low-VA copolymers in the 9–14 wt% range, it offers greater low-temperature flexibility and a lower Shore D hardness. Compared with metallocene polyolefin elastomers used in foam, the EVA grade retains the polar surface energy required for adhesive bonding, printing, and wet ink adhesion, although peroxide cure and compression set remain limitations. The BCA version is differentiated from the fossil ML 50 by feedstock attribution only; no change in molecular weight distribution, melt viscosity, or blowing ratio is implied by the BCA designation. A converter seeking to use this product in a foam/footwear line should therefore focus incoming inspection on the same physical properties that would control a fossil EVA, while maintaining a separate mass-balance ledger for sustainability accounting.