Copolímero de acetato de vinilo de etileno ELVAX 660

ELVAX 660 Ethylene Vinyl Acetate Copolymer is a low-vinyl acetate EVA grade with a nominal vinyl acetate content of 12 wt% and a melt index of 2.5 dg/min when measured under ASTM D1238 at 190 °C with a 2.16 kg load. Density is reported at 0.933 g/cm³ under ASTM D792. The copolymer is profile-extruded, injection-molded, calendered, and compounded for flexible automotive interior parts, appliance bumpers, gaskets, tubing, footwear components, and as a polymeric binder in wax-based hot-melt systems. Its position between LDPE and higher-VA EVA grades produces a distinct balance of semicrystalline stiffness, low-temperature flexibility, stress-crack resistance, and moderate polarity.

What Distinguishes ELVAX 660 from LDPE and Higher Vinyl Acetate Copolymers?

The vinyl acetate monomer randomizes ethylene sequences and reduces crystalline order. At 12 wt% VA, total crystallinity remains sufficient to retain a peak melting endotherm near 95–98 °C under ASTM D3418, whereas a 25–28 wt% VA adhesive-grade EVA typically shows a melting range below 85 °C and much lower tensile modulus. The lower crystallinity of high-VA grades increases segmental mobility and tackifier compatibility but reduces creep resistance at elevated service temperature. In contrast, ELVAX 660 retains a Vicat softening point high enough for semi-structural profiles, while the VA comonomer provides improved environmental stress crack resistance compared with LDPE homopolymer grades. The difference is also rheological: ELVAX 660 has higher melt viscosity than high-VA grades with comparable melt index because the lower comonomer content preserves longer ethylene sequence lengths and higher chain entanglement density.

These differences translate directly into equipment behavior. In a single-screw extruder with a 24:1 L/D barrier screw, ELVAX 660 reaches stable melt pressure at 170–200 °C with specific output in the range 0.8–1.4 kg/h/rpm depending on screw design; published data for this specific configuration is limited. If the same screw is used with high-VA EVA, melt temperature must be reduced by 10–20 °C to prevent viscosity drop and surging. Compared with LDPE, ELVAX 660 requires a slightly lower die temperature and has a narrower melt fracture threshold at high shear rates.

Profile extrusion of ELVAX 660 on a 40:1 L/D single-screw line typically starts with a barrel profile of 150–170 °C in the feed throat zone, 175–190 °C in the compression zone, 190–205 °C in the metering zone, and 195–210 °C at the die. A screen pack of 60/100/60 mesh is used to increase back pressure and eliminate gels. Melt temperature measured with an immersion thermocouple should remain below 220 °C. Pellets stored below dew point should be dried at 60–70 °C for 2 h to remove surface condensation before processing; EVA hydrolysis is not a principal risk, but moisture splay and melt-pressure fluctuations are observed at relative humidity above 60 %. Injection molding conditions for thick-wall seals include a rear zone of 160–180 °C, middle zone 180–195 °C, front zone 190–205 °C, and nozzle 195–205 °C, with mold temperature controlled at 20–40 °C to balance cycle time and surface replication. Clamp force requirements are lower than for HDPE of equivalent melt index because of reduced injection pressure.

When ELVAX 660 Is Melt-Blended into Wax and Hot-Melt Formulations

In wax-based hot-melt systems, ELVAX 660 functions as a polymeric backbone that raises cohesive strength and high-temperature creep resistance without producing the high melt viscosity of a 25–28 wt% VA EVA at equal loading. It is mixed in a swept-surface kettle or double-planetary mixer at 150–180 °C with paraffin wax, microcrystalline wax, and rosin ester or hydrocarbon tackifier. The 12 wt% VA content provides sufficient polarity to wet polar surfaces such as corona-treated polyethylene and coated paperboard, while retaining solubility in low-polarity waxes. In a typical 100-part formulation containing 30 parts ELVAX 660, 40 parts paraffin wax, and 30 parts rosin ester, melt viscosity at 180 °C is controlled by both the polymer melt index and the resin-to-wax ratio; higher-VA EVA grades reduce mix viscosity at equivalent loading but lower peel adhesion on nonpolar substrates. High-shear dispersion is not required in wax blending, but dead spots in the kettle must be eliminated because localized wall temperatures above 200 °C accelerate vinyl acetate deacetylation and can generate acetic acid.

Compounded profiles containing calcium carbonate, talc, or carbon black are prepared on a co-rotating twin-screw extruder with an L/D ratio of 40:1 and a side feeder downstream of the polymer melt seal. A typical filler loading of 20–30 wt% calcium carbonate lowers elongation at break from above 700 % to the 300–450 % range when tested under ASTM D638 at 50 mm/min; the reduction is approximately linear with filler volume fraction up to 30 wt%. Carbon black at 2–5 wt% is dispersed in the first mixing zone at screw speeds of 200–350 rpm and specific energy input of 0.15–0.25 kWh/kg. For chemical foaming, azodicarbonamide decomposition at 195–215 °C is matched to the ELVAX 660 melt temperature plateau; the low melt index of 2.5 dg/min provides sufficient melt strength to stabilize cell walls and limit coalescence in profiles with density reductions of 20–40 %.

The Acetic Acid Release Boundary Narrows Above 220 °C

EVA deacetylation begins to evolve acetic acid at measurable rates when melt temperature exceeds 220 °C and accelerates rapidly above 230 °C. Reported activation energies for EVA deacetylation in inert atmosphere are in the range 170–200 kJ/mol; published data for this specific configuration is limited. The practical consequence on a production line is that a 10 °C increase in melt temperature from 220 °C to 230 °C can shorten the safe residence time by a factor of roughly 2–3. Corrosion-resistant downstream equipment, venting, and strict residence-time control are required for extrusion. Avoid combination with amine-based additives that can catalyze deacetylation or cause premature crosslinking. Stabilization with phenolic antioxidants and a secondary phosphite at total loading of 0.1–0.3 wt% is common for extended heat histories.

In coextruded flexible packaging structures, ELVAX 660 is evaluated as an alternative sealant layer to LDPE and acid-modified ethylene copolymers. The presence of 12 wt% VA reduces the minimum seal initiation temperature by approximately 10–20 °C relative to LDPE of similar density, and broadens the hot-tack window on form-fill-seal lines at sealing pressures of 0.3–0.6 MPa. Heat seal strength measured under ASTM F88 is sensitive to seal-bar temperature, dwell time, and corona treatment level. At equivalent VA content, ELVAX 660 provides a lower seal-through-contamination threshold than ethylene-octene plastomers but a narrower low-temperature flexibility window than a 15–18 wt% VA EVA grade. Testing on a horizontal form-fill-seal machine at 60 packages/min typically shows stable seal transfer when the seal bar temperature is maintained at 110–130 °C.

Regulatory Status Shifts When Additives and Fillers Enter the Compound

ELVAX 660 is typically compliant with FDA 21 CFR 177.1350 for ethylene-vinyl acetate copolymers in food-contact applications, subject to end-use extraction limits and use conditions defined by the finished article. Under EU food-contact regulations, it is evaluated under Regulation (EU) No 10/2011 with an overall migration limit of 10 mg/dm² or 60 mg/kg for the final article. REACH registration is maintained by the manufacturer, and RoHS Directive 2011/65/EU is not triggered for the polymer itself but applies to any pigments, stabilizers, or flame retardants added during compounding. Electrical insulation compounds require testing to the relevant IEC or ASTM harness standards; EVA at 12 wt% VA is not inherently flame retardant and must be formulated with mineral fillers or halogen-free flame retardants to achieve pass rates under IEC 60332-1 or UL 94.

Wire and cable jacketing compounds based on ELVAX 660 are prepared with aluminum trihydrate or magnesium dihydrate fillers at loadings of 50–65 phr, crosslinked with organic peroxides in a continuous vulcanization line, and extruded on a 20:1 L/D single-screw or twin-screw line with melt filtration. The peroxide cure is initiated at 170–190 °C and completed in a heated catenary tube; tensile strength after crosslinking is measured under IEC 60811-501 and heat ageing under IEC 60811-401. Lower VA content reduces polarity-driven moisture absorption but also reduces filler wetting compared with 18 wt% VA EVA; silane coupling agents are therefore added at 0.5–1.0 wt% to maintain elongation and hot-set performance. Published data for this specific configuration is limited; plant trials are required to confirm die build-up and cure speed.