ELEVATE EM285 Copolímero de acetato de vinilo de etileno

ELEVATE EM285 Ethylene Vinyl Acetate Copolymer is a medium-vinyl-acetate thermoplastic supplied as lenticular pellets with a nominal major axis of 3–4 mm. The neat resin is specified at 28 wt% vinyl acetate, a melt mass-flow rate of 5.0 g/10 min at 190°C/2.16 kg in accordance with ISO 1133-1:2022, and a density of 0.950 g/cm³ measured under ISO 1183-1. No slip or antiblock additives are present in the base grade, preserving additive compatibility in downstream masterbatch and compound dilution. The vinyl acetate content depresses crystalline polyethylene sequences; this reduces flexural modulus, lowers melting peak temperature, and expands low-temperature flexibility relative to 18 wt% VA extrusion grades, while retaining higher thermal resistance and lower surface tack than 33 wt% VA encapsulant grades. The MFR positions EM285 in the medium-flow extrusion and injection segment; it is not a high-flow film resin and it is not a low-flow thick-sheet grade.

What Incoming Inspection Limits Apply to VA Content and Melt Flow?

Receiving inspection for EM285 customarily verifies vinyl acetate content, melt mass-flow rate, and density. Lot-to-lot VA content is controlled within ±1.0 wt% around the nominal 28 wt%; MFR tolerance is controlled within ±0.5 g/10 min around the 5.0 g/10 min nominal. This MFR band is critical for maintaining constant die pressure in profile extrusion and repeatable screw recovery in injection molding. The values in the table below are representative manufacturer-published values for the neat resin, not compound design values.

Shore 80 A hardness and a 52 °C Vicat temperature define low-force handling limits for unfilled EM285. Stacked pellets or finished parts stored above 35 °C may develop blocking because the vinyl acetate content reduces crystallinity and increases surface tack compared with lower-VA copolymers. This is an operational boundary, not a long-term service limit for formulated compounds; crosslinked or filled systems shift the Vicat and Shore values upward depending on filler volume fraction and cure state. Incoming-lot analysis on a production compounding line should also record moisture content. Ambient moisture uptake is typically below 0.1 wt% at 23 °C/50% RH; predrying is not mandatory unless visible surface moisture is present. If material is loaded from outdoor silos or regrind streams above 60% RH, a desiccant dryer at 70–80 °C for 2–3 h prevents surface defects during extrusion.

On a single-screw profile line, EM285 is processed with a reverse-temperature profile: feed 140–150 °C, compression 170–180 °C, metering 190–200 °C, adapter and die 200–215 °C. A screw with 24:1–30:1 L/D and a Maddock or barrier mixing section is used to complete melting without excessive shear heating. Compression ratio is maintained at 2.5:1–3.0:1; higher ratios increase shear heating and accelerate VA cleavage at the screw tip. Residence time above 220 °C is kept below 15 min; beyond that threshold, acetic acid elimination produces a sharp odor, yellowness, and plate-out on calibrator surfaces. Production lines without melt-pressure transducers often fail to detect early deacetylation until gel particles appear; continuous lines should therefore be fitted with a pressure transducer upstream of the breaker plate. A melt-pressure deviation greater than ±0.5 MPa at constant screw speed is treated as a process alarm, because it can indicate pre-crosslinked gel accumulation or screw wear rather than normal feedstock variation.

Rheologically, the shear-thinning response of EM285 places it between lower-MFR grades used in thick-wall extrusion and higher-MFR grades used in thin-film. Capillary rheometry at 190 °C shows apparent viscosity falling from approximately 1,200–1,800 Pa·s at 100 s⁻¹ to 300–450 Pa·s at 1,000 s⁻¹, depending on moisture and thermal history. This shear sensitivity is sufficiently high for profile die balancing but sufficiently low that blow-film bubble instability is not the first processing limitation. Published data for this specific grade is limited; the stated range is typical for 28 wt% VA EVA with MFR 5 g/10 min.

When EM285 Replaces an 18 wt% VA Copolymer in Flexible Tubing

The substitution is usually made to gain low-temperature flexibility and improved adhesion to polar substrates. A 28 wt% VA resin depresses the melting peak to approximately 73 °C and reduces Shore A hardness to 80 A, while an 18 wt% VA extrusion grade typically shows a melting peak near 86 °C and Shore 92 A. The penalty is a lower Vicat softening point and greater blocking tendency. The relevant comparison is not neat tensile strength but the balance of flexibility, set, and filler acceptance required in the finished part. The table below summarizes the property map for neat resins across the VA range.

Comparative values for lower-VA and higher-VA grades are representative neat-resin literature values, not manufacturer specifications for those specific products. In flexible tubing and cable jacket formulations, EM285 improves filler acceptance and adhesion to polar substrates relative to an 18 wt% VA grade. The higher VA content also increases dissipation factor and dielectric constant; electrical insulation compounds may therefore require a higher purity mineral filler or a rebalanced stabilizer package under IEC 62631 or ASTM D150 when EM285 is substituted. Specifying the same Shore A compound with EM285 may require adjustment of plasticizer or filler because the base resin contributes less crystalline stiffness.

In halogen-free flame-retardant compounding on a 40:1 L/D co-rotating twin-screw extruder, EM285 is charged with 120–150 phr precipitated magnesium hydroxide or alumina trihydrate. The 28 wt% VA content provides better filler wetting than an 18 wt% VA base at equivalent melt temperature; the practical consequence is lower screw torque and fewer unbroken filler agglomerates in thin-wall sections. Mixing zones are set to 170–190 °C after a 150 °C solids-conveying section, and the final barrel zone is held below 200 °C. The neat-resin tensile strength of 22 MPa cannot be used as a design value for a 60 wt% mineral-filled compound; tensile strength commonly falls to 8–12 MPa depending on particle size and surface treatment, and elongation drops sharply. Published data for this exact grade in mineral-filled systems is limited; compound development therefore requires pilot-scale evaluation on the intended production extruder.

Blends of EM285 with linear low-density polyethylene at 20–40 wt% LLDPE are used to raise heat resistance and reduce surface tack. The two resins require sufficient mixing time because viscosity mismatch can produce phase coarsening and surface haze. In a 30 mm twin-screw extruder at 190 °C, 2–4 min residence time is sufficient for domain refinement below 1 µm. This blend route is relevant when the final article must survive 70 °C under ISO 75/B deflection load without excessive softening.

Thermal Deacetylation Boundaries and Residence-Time Control

Deacetylation in EM285 follows the general EVA degradation path: random elimination of acetic acid from vinyl acetate sequences accelerates above 220 °C. The released acetic acid reduces melt pH and corrodes nitrided barrel surfaces, producing iron acetate contamination that appears as black specks in extrudate. Extruders with chrome-plated screw surfaces and molybdenum-treated barrels show better resistance, but no common steel formulation eliminates the requirement to limit melt temperature. Residence time above 230 °C should not exceed 10–15 min in semi-lost purge conditions, and start-up temperatures after shutdown should be reduced to 160 °C before introducing material. Purging with rigid PVC is incompatible because HCl generated during PVC thermal degradation catalyses EVA deacetylation. Strongly acidic processing aids, certain metal chlorides, and acidic flame-retardant synergists are excluded for the same reason; neutral or basic stabilizer systems are preferred in long-run production.

Injection molding of EM285 uses melt temperatures of 180–200 °C and mold temperatures of 20–40 °C. Clamp force calculations follow standard EVA melt viscosity behavior, with injection pressures typically below 80 MPa for thin-wall cavities. The MFR of 5.0 g/10 min allows filling of multicavity molds without excessive flash at parting lines, provided fill speed is reduced in the final 5–10 mm of stroke and back pressure is held at 0.5–1.0 MPa. Venting depth should be limited to 0.02–0.04 mm; deeper vents produce flash because the medium-MFR material remains deformable at ejection. Mold release is not required for unfilled EM285 except in deep-draw parts with textured surfaces.

Foamed footwear compounds based on EM285 are combined with azodicarbonamide at 1.5–2.5 phr, dicumyl peroxide at 0.6–0.8 phr, and zinc oxide at 1.0 phr. Premixing is performed on a two-roll mill at 95–105 °C to avoid premature peroxide decomposition. Foam expansion is then executed in a compression press at 165–175 °C for 6–10 min. The 5.0 g/10 min MFR yields sufficient melt strength for closed-cell structures at expansion ratios of 1.6–2.0; higher-MFR EVA above 15 g/10 min typically collapses at the same expansion ratio unless crosslinking coagents are added. The quoted expansion ratios are batch compression-molding values, not high-speed injection foam outputs.

Hot-melt adhesive formulations based on EM285 are prepared with hydrocarbon tackifier resins at 30–50 phr and microcrystalline wax at 5–15 phr. Slot-die coating is performed at 180–200 °C. The 28 wt% VA content increases T-peel adhesion to corona-treated PET and aluminium relative to an 18 wt% VA grade; exact T-peel values are determined by tackifier type and coating weight under ASTM D1876. Open time and set speed are governed by MFR, wax melting range, and tackifier softening point. Food-contact uses require migration testing on the final adhesive under EU 10/2011 Annex V or 21 CFR 177.1350.