EVAtech 140S/28G Compósito do copolímero EVA, grau de espuma cruzável

Compression-molded midsoles using EVAtech 140S/28G are produced from a crosslinkable ethylene-vinyl acetate compound with nominal 28 wt% vinyl acetate comonomer content and a melt index of 140 g/10 min when measured under ISO 1133-1:2022 at 190 °C/2.16 kg. The compound is mixed in a tangential internal mixer at a fill factor of 0.78 and a jacket temperature of 95 °C to 105 °C, with rotor speed held between 35 rpm and 45 rpm. Stock is dropped at 108 °C to 115 °C onto a two-roll mill maintained at 85 °C to 95 °C; dicumyl peroxide is added at this stage only after the stock surface temperature falls below 95 °C to prevent scorch. Azodicarbonamide blowing agent is added with zinc oxide and zinc stearate on the cooling mill. The resulting preform is compression molded in a hydraulic press at 170 °C to 180 °C for 8 min to 12 min, with platen pressure from 150 kg/cm² to 200 kg/cm². Under these conditions the blowing agent decomposes after the cure system has generated sufficient melt strength to stabilize expanding cells. Molded densities range from 0.16 g/cm³ to 0.22 g/cm³ when measured per ISO 845:2006. Hardness values fall between Shore C 45 and Shore C 55 under ASTM D2240-15. Tensile strength and elongation are checked per ISO 1798:2008 on dumbbell specimens cut from the foam; typical acceptance values in footwear production require tensile strength above 2.0 N/mm² and elongation above 180%. Compression set is measured per ASTM D395-18 Method B at 50% deflection for 24 h at 23 °C. Rebound resilience is measured on a Lupke pendulum per ASTM D2632-15.

Production-scale failure modes in midsole molding are dominated by pre-scorch and cell coalescence. If the mixed batch remains on a hot mill above 95 °C for more than 6 min, peroxide-induced crosslinking raises Mooney viscosity before the blowing agent has decomposed, and the subsequent foam shows a hard, poorly expanded core. A second failure mode occurs when azodicarbonamide particle size distribution shifts; sieve residue above 45 µm on a 40-mesh screen delays gas evolution and enlarges average cell diameter beyond 0.5 mm. Such boards exhibit visible pinholes and reduced split tear resistance. Demolding before the press platens cool below 70 °C can produce surface blisters because residual gas pressure inside closed cells exceeds the tensile strength of the partially crystallized surface skin. The addition of calcium carbonate above 20 phr raises compound viscosity and reduces rebound but improves dimensional stability; beyond 30 phr the cured foam loses tear strength and becomes difficult to skive. Moisture uptake is low in the neat copolymer, but when calcium carbonate or hygroscopic fillers are used, pre-drying at 60 °C for 2 h is necessary if storage relative humidity exceeds 60%. Basic activators such as magnesium oxide or amine-based additives are avoided because they alter the azodicarbonamide decomposition exotherm and can produce uneven cell structure or premature crosslinking.

What Limits Tear Strength in Crosslinked Orthotic Block Stock?

Crosslinked orthotic block stock made from EVAtech 140S/28G is typically foamed to a density of 0.10 g/cm³ to 0.15 g/cm³ and then skived into sheets of 1.5 mm to 4.0 mm for die-cut insoles. Tear strength is controlled primarily by gel content, average cell size, and the presence of low-molecular-weight residues. Gel content after xylene extraction at 110 °C for 24 h per ASTM D2765-16 should fall between 60% and 75%. Below 60% gel content the foam tears at cell walls under repeated flexing; above 80% the material becomes brittle and difficult to thermoform or adhesively bond. Blowing agent loading in this application is held between 4.0 phr and 5.0 phr, while dicumyl peroxide is reduced to 0.5 phr to 0.7 phr to maintain a fine cell structure with average cell diameter below 0.4 mm. The 28 wt% vinyl acetate comonomer reduces crystallinity and gives the skived sheet a dry, rubbery feel at body temperature. For orthotic products marketed as medical devices, finished components may require biocompatibility evaluation under ISO 10993-5 and ISO 10993-10; the raw compound is not certified as medical grade. Tensile properties are measured per ISO 1798:2008, and tear resistance is measured per ISO 8067:2018. Published data for this specific configuration in orthotic block stock is limited, so incoming lots should be qualified against a control material using gel content, density, and compression set before production release. The terminal product includes contoured insoles, heel wedges, and metatarsal pads.

Laminated exercise mat constructions using EVAtech 140S/28G begin with crosslinked foam sheets at a density of 0.11 g/cm³ to 0.13 g/cm³. The sheets are produced on a continuous compression press, skived, and then thermally laminated at 120 °C to 140 °C with a surface film or textured polyolefin layer. Bonding is performed at nip pressure of 4 bar to 6 bar and a line speed of 6 m/min to 10 m/min. The formulation uses 3.5 phr to 4.5 phr azodicarbonamide and 0.6 phr to 0.8 phr dicumyl peroxide, with 1.5 phr zinc oxide as a blowing activator. Density is checked per ISO 845:2006. Thickness tolerance across a 1.8 m width is held within ±0.25 mm. Rebound retention after accelerated flex testing is monitored using ASTM D395-18 Method B compression set; mats with gel content below 65% exhibit permanent set above 15% and are rejected for high-cycle use. Finished mats are tested for slip resistance under DIN 51130 or ASTM D2047 depending on the target market. REACH Annex XVII restrictions apply to polycyclic aromatic hydrocarbons and phthalates in consumer mats. The end products include yoga mats, gym floor tiles, and anti-fatigue standing mats.

When Marine Buoyancy Billets Are Molded Below 175 °C

Marine buoyancy billets and dock fenders require closed-cell EVA foam with density from 0.06 g/cm³ to 0.09 g/cm³. When molding temperature is held below 175 °C, residual azodicarbonamide remains undecomposed in the core. The unreacted blowing agent later decomposes during service heating or cutting, creating internal voids and increasing water absorption. For marine billets, mold temperature is therefore set at 175 °C to 185 °C, with cure time extended to 15 min to 20 min for block thickness above 50 mm. The 28 wt% vinyl acetate content preserves low-temperature flexibility in seawater. Water absorption is measured after full immersion for 7 days; acceptance requires volume uptake below 3% when tested on a 50 mm × 50 mm × 25 mm specimen cut from the billet core. The test method is typically ASTM D3575 suffix L, although some specifications refer to ISO 2896:2001. Buoyancy calculations must use measured density from the billet core, not the nominal density of the compound. Closed-cell content is verified by gas pycnometry using ISO 4590:2016 or ASTM D6226-21 where applicable; values below 90% indicate cell wall rupture and are cause for rejection. Stabilizer packages are selected for UV resistance; unprotected foam chalks within 6 months under tropical sunlight. Published data for EVAtech 140S/28G in marine billet form is limited, so suppliers should qualify each block size and density before bid submission. The terminal products include foam-filled fenders, marker buoys, and personal flotation components.

Low-VOC Interior Padding and NVH Performance Requirements

Automotive interior padding manufactured from EVAtech 140S/28G is compression molded into sheets of 0.08 g/cm³ to 0.12 g/cm³ and then die-cut for instrument panel padding, door trim absorbers, and floor carpet underlay. The crosslinked closed-cell structure provides acoustic insertion loss and vibration damping in the 500 Hz to 2000 Hz frequency range. Flame performance is verified under FMVSS 302 and CMVSS 302; a horizontal burn rate below 100 mm/min is the usual pass criterion. Volatile organic compound emissions are tested by VDA 278 or OEM-specific thermal desorption methods; current programs often require fogging condensate below 2 mg and total VOC below 100 µg/g. To meet these limits, the foam is oven-post-cured at 70 °C to 80 °C for 4 h to 6 h to reduce ammonia and blowing agent residues. Compression deflection is measured at 25% deflection per ISO 3386-1:1986; typical values for a 0.10 g/cm³ sheet are 30 kPa to 60 kPa. The compound must be free of restricted substances under REACH Annex XVII and the ELV Directive for lead, cadmium, mercury, and hexavalent chromium. Adhesive bonding to polypropylene or ABS interior substrates is performed after corona treatment at 38 mN/m to 44 mN/m surface energy; solvent-based primers are avoided because they add VOC. The terminal products include dash insulators, wheel arch liners, and HVAC gaskets.

Dimensional recovery after 50 % deflection governs concrete joint filler acceptance.

Preformed EVAtech 140S/28G foam strips with nominal density from 0.12 g/cm³ to 0.16 g/cm³ and closed-cell structure are used as concrete expansion joint fillers under ASTM D1751 and ASTM D994, requiring compression recovery of at least 75% when tested at 50% deflection per ASTM D1751.