Greenflex ML 50 BCA EVA Copolymer Resin, Bio-Circular Atribuído, Espuma e Grado de Calçados

Greenflex ML 50 BCA is processed as a primary ethylene-vinyl acetate copolymer resin with a nominal vinyl acetate content of 50 wt% and an ISCC PLUS mass-balance bio-circular attribution. The bio-circular certification does not alter melt viscosity, curing kinetics, foam density, or compression set; it is a chain-of-custody mechanism that allows downstream converters to allocate renewable feedstocks to foam and footwear compounds. The high vinyl acetate repeat unit suppresses polyethylene crystallinity, producing a low crystalline melting range, high filler acceptance, and limited melt strength compared with lower-VA EVA grades. Downstream manufacturers making biobased carbon content claims on finished articles must verify the specific batch allocation and, if required, test the final foam independently against ASTM D6866-22 or ISO 16620-2:2019. Process windows valid for fossil-based high-VA EVA may be used as preliminary starting points, but each compound must be revalidated under production-scale conditions.

Closed-loop injection-foam midsole production with Greenflex ML 50 BCA normally begins in a co-rotating twin-screw compounder with an L/D ratio of 44:1 to 52:1. Field records from multi-cavity midsole lines indicate that the resin is charged at 100 phr as the base polymer, while lower-VA EVA grades of 18-22 wt% vinyl acetate are introduced at 10-25 phr to adjust hardness without eliminating rebound. Azodicarbonamide is metered at 2.2-3.5 phr, dicumyl peroxide at 0.5-0.8 phr, zinc oxide at 1.0-1.5 phr, and zinc stearate at 0.5-1.0 phr. Calcium carbonate may occupy 5-15 phr to reduce raw-material cost, but at equivalent foaming conditions it raises density by approximately 0.02-0.05 g/cm³. The compound is pelletized below 95°C to prevent premature peroxide decomposition. Injection molding is conducted on multi-cavity tools with clamp force between 250 t and 450 t, barrel temperature profile 85-100°C, and mold temperature 165-180°C. Cavity gas pressure and venting are the primary control variables because azodicarbonamide decomposition releases gas at a rate that must match the evolving polymer cross-linking network. Midsoles are typically controlled at a density of 0.18-0.25 g/cm³ according to ASTM D3575-14 Test A, and compression set is checked by ASTM D3575-14 Test D after 6 h at 50°C with 50% compression. Compliance screening for European footwear includes REACH EC 1907/2006 Annex XVII restricted PAHs, phthalates, and short-chain chlorinated paraffins, as well as AfPS GS 2019:01 PAK limits where German market testing is required. Terminal product types include performance running shoe midsoles, basketball midsoles, walking shoe midsoles, and injection-molded EVA shell midsoles for casual footwear.

What Compression Press Parameters Govern Low-Density Sandal Sheet Foam?

Low-density sandal sheet foam is converted in multi-daylight compression presses rather than injection machinery because sheet thickness of 40-60 mm exceeds the flow-length capability of most injection tools. Greenflex ML 50 BCA is useable as a 100 phr base resin; azodicarbonamide loading is increased to 2.5-4.0 phr to target a final density of 0.12-0.18 g/cm³. Dicumyl peroxide is held at 0.5-0.7 phr because higher peroxide levels raise cross-link density too early and trap gas, producing split sheets. The production sequence includes internal mixing at 100-110°C, two-roll sheeting at 80-90°C, pre-forming into billets, and compression molding at 170-185°C under platen pressure of 150-200 kg/cm². The critical process conflict is heat transfer through the thick pre-form: if the billet center remains below the azodicarbonamide decomposition onset for too long, the sheet develops a dense skin and an under-foamed core. Press cycles are therefore extended to 12-20 min depending on billet thickness, and post-cure cooling is staged under pressure to control shrinkage. Density is verified by ASTM D3575-14 Test A; compression set is measured by ISO 1856:2018 at 50% deflection for 6 h at 40°C. Tear resistance is screened using ASTM D3575-14 Test F, with split-prone compounds rejected below 2.0 kN/m. Compliance for sandals and slides includes REACH EC 1907/2006, RoHS 2011/65/EU for exported components containing electrical elements, and California Proposition 65 phthalate thresholds. Terminal product types include single-density sandal sheet, two-layer slide soles, contoured comfort sandals, and die-cut sandal footbeds.

Footbed Laminates, Orthotic Inserts, and Direct-Press Insoles

Footbed-grade foam compounds based on Greenflex ML 50 BCA are processed at lower thickness, typically 2-6 mm, and are laminated to polyester or nylon face fabrics in a separate hot-press or roll-laminating step. The base resin is charged at 100 phr and is frequently modified with 10-20 phr of ethylene-octene polyolefin elastomer to reduce compression set after repeated wear. Azodicarbonamide loading is reduced to 1.5-2.5 phr to yield a density of 0.15-0.20 g/cm³; dicumyl peroxide is set at 0.6-0.9 phr to maintain cell-wall strength during lamination at 120-140°C. The foam sheet is produced by compression molding or continuous calendar foaming, then skived to uniform thickness before lamination. Solvent-free polyurethane dispersion adhesives are applied at 15-30 g/m² dry coat weight and activated at 70-90°C under 1-3 bar nip pressure. Process control is concentrated on surface energy and cell collapse: if the foam surface exceeds 140°C during lamination, closed cells collapse and the sheet loses cushioning. Compliance for skin-contact and orthotic applications includes REACH EC 1907/2006, ISO 10993-5:2009 and ISO 10993-10:2010 where the finished device is classified as a medical device, and ISO 1856:2018 compression set for the foam component. Substance restrictions for the German and EU markets include AfPS GS 2019:01 PAK and the EU Toy Safety Directive 2009/48/EC if products are marketed for children. Terminal product types include removable sockliners, full-length orthotic shells, 3/4-length arch supports, heel cups, and direct-press casual footbeds.

Impact-absorbent mat foam and protective sports padding are produced from the same high-VA EVA base but with lower cross-link density and higher blowing-agent loading than footwear midsoles. Greenflex ML 50 BCA is charged at 100 phr; azodicarbonamide is metered at 3.0-5.0 phr to reach a density of 0.10-0.15 g/cm³. Dicumyl peroxide is reduced to 0.4-0.6 phr because a harder cross-linked network reduces impact-energy absorption. Zinc oxide at 1.5-2.5 phr and zinc stearate at 0.5-1.0 phr are added as activators. The production route is slab compression molding in large high-pressure presses, followed by waterjet or die cutting into sheet, tile, or shaped padding. Mold temperature is controlled between 165°C and 175°C; the slab is cooled under pressure for 20-30 min to avoid post-demold expansion and bowing. Field data from thick-slab lines indicate that center density can remain 0.02-0.04 g/cm³ higher than edge density when pre-form thickness exceeds 80 mm. Impact-attenuation testing is conducted by the downstream converter according to EN 1177:2018 where playground surfacing claims are made, or by product-specific standards for sports flooring and protective padding. Density and compression set are screened by ASTM D3575-14 Test A and ASTM D3575-14 Test D. Compliance includes REACH EC 1907/2006, RoHS 2011/65/EU, and California Proposition 65 phthalate restrictions. Terminal product types include gym mats, martial arts landing mats, wall padding, and die-cut protective knee and elbow pads.

When EVA/Rubber Blends Are Considered for Casual Footwear Outsoles

High-VA EVA is blended with styrene-butadiene rubber or natural rubber only where the outsole must retain a foam-like low density while offering higher abrasion resistance than pure EVA foam. Greenflex ML 50 BCA is used at 30-50 phr in such blends; the balance consists of SBR 1502 or SVR 3L natural rubber at 50-70 phr, zinc oxide 3-5 phr, stearic acid 1-2 phr, silica 20-30 phr, azodicarbonamide 1.5-2.5 phr, and dicumyl peroxide 0.4-0.8 phr. Internal mixing is performed at 70-90°C with a two-wing rotor; the batch is then sheeted on a two-roll mill at 50-60°C. Final compression molding is run at 160-175°C for 8-14 min. The main process conflict is phase morphology: at Greenflex ML 50 BCA loadings above 50 phr, the compound loses hot tear strength and may stick to mill rolls; below 30 phr, the density advantage disappears. Abrasion resistance is tested according to ISO 20871:2018 for footwear sole abrasion or ASTM D5963-04(2019) for rubber property abrasion; values for foamed EVA/rubber blends are higher than solid vulcanizates and must be interpreted only within the same density range. Compliance includes REACH EC 1907/2006, RoHS 2011/65/EU for restricted substances, and ASTM D6866-22 only if a biobased carbon claim is required independent of mass-balance certification. Terminal product types include casual shoe outsoles, slipper outsoles, children’s soft-soled footwear, and lightweight outdoor sandal outsoles.

Thermoforming EVA Internal Shoe Stiffeners Requires Controlled Cell Collapse

Internal shoe stiffeners made from EVA foam sheet require the opposite direction of density control: the converter starts from a higher-density closed-cell sheet and uses heat and pressure to collapse selected regions into a stiff thermoplastic structure. Greenflex ML 50 BCA is charged at 100 phr, with azodicarbonamide reduced to 0.5-1.2 phr to produce a base sheet density of 0.35-0.55 g/cm³. Dicumyl peroxide is set at 0.3-0.6 phr; higher peroxide levels produce a thermoset network that resists the subsequent thermoforming step. The production route is continuous sheet extrusion or calendering at 95-115°C, followed by vacuum or pressure thermoforming at 90-110°C. Heated aluminum tools with polished cavity surfaces are used to densify the edge of the counter or toe puff while preserving a cushioned center. The main process limitation is hot tear at the transition zone between dense and cellular regions; tool temperature differentials greater than 15°C across one part have been observed to generate local tearing in field trials. Compliance for shoe stiffeners includes REACH EC 1907/2006, RoHS 2011/65/EU, and ISO 20871:2018 where wear resistance of the stiffener is claimed. Tensile strength and elongation can be screened with ASTM D3575-14 Test E; hot tear should be evaluated on line by the converter using the same cellular-foam test protocol. Published data for this specific bio-circular attributed grade in thermoformed internal stiffeners is limited; processors should validate tensile strength, cell collapse behavior, and shape retention under their own tooling conditions. Terminal product types include thermoformed toe puffs, heel counters, arch stiffeners, and internal heel stabilizer components for safety and casual footwear.