HANWHA EVA 2250 Copolímero de acetato de vinilo de etileno

Hanwha EVA 2250 is an ethylene vinyl acetate copolymer supplied by Hanwha Solutions as a pelletized resin for melt-extrusion and injection-molding operations. The grade designation encodes a nominal vinyl acetate content of 22.5 wt% and a nominal melt mass-flow rate of 5.0 g/10 min when determined at 190 °C under a 2.16 kg piston load in accordance with ASTM D1238. The polymer is produced in a high-pressure ethylene copolymerization process in which vinyl acetate insertion disrupts polyethylene crystallinity, producing a semicrystalline resin with a density near 0.94 g/cm³ when measured by ISO 1183-1:2019 or ASTM D1505. Differential scanning calorimetry under ISO 11357-3 typically resolves a broad melting endotherm with a peak near 84 °C, although the exact peak temperature varies with cooling rate and comonomer distribution. The material combines lower flexural modulus and higher elongation than low-density polyethylene with polar adhesion to fillers, cellulosic substrates, and polyurethane coatings. It is therefore positioned between lower-vinyl-acetate stiffness grades and higher-vinyl-acetate elastomeric grades in the Hanwha EVA portfolio.

Thermal and Rheological Measurements That Define the Grade

Lot-to-lot verification should rely on the resin certificate of analysis, because narrow property ranges are controlled during polymerization and subsequent pelletization. The following table lists commonly applied test methods and representative target values for a 22.5 wt% vinyl acetate EVA with a melt flow rate near 5.0 g/10 min. The values are not a substitute for Hanwha Solutions lot-specific data and should be confirmed against the stated standards.

The melt flow rate of 5.0 g/10 min places EVA 2250 in a medium-flow region suited to both single-screw extrusion and injection molding without plasticizer addition to achieve processable viscosity. The melt is pseudoplastic, and branched EVA melts of this composition class commonly exhibit a power-law index of approximately 0.35 to 0.45 across shear rates from 10 s⁻¹ to 1000 s⁻¹; this range should be confirmed on the specific lot by capillary rheometry. The reduced crystallinity also lowers melt elasticity compared with high-density polyethylene, which reduces die swell and improves draw-down control in thin film and coating lines. Because secondary crystallization can continue for several hours after molding, mechanical comparison testing should be preceded by conditioning at 23 °C and 50% relative humidity for at least 40 h according to ISO 291 or ASTM D618.

When Thermal Deacetylation Limits Melt Temperature and Residence Time

The acetate ester side group is the primary thermal vulnerability of EVA copolymers. Under thermogravimetric analysis at 10 °C/min in inert atmosphere, acetic acid elimination becomes detectable near 200 °C and accelerates above 250 °C; the onset shifts lower in the presence of oxygen, copper ions, or acidic residues. Melt processing should therefore avoid melt temperatures above 220 °C, and hot-runner injection tools should limit residence time at such temperatures to less than 5–10 min to avoid yellowing, gel formation, and loss of adhesion. On a single-screw extruder with a 30:1 L/D ratio, a barrel profile from 150 °C at the feed throat to 180–200 °C at the die is suitable for film and sheet lines. Screws with a compression ratio of 2.5:1 to 3.0:1 and a barrier section improve melting uniformity because the high-comonomer resin softens more readily than linear low-density polyethylene. Downstream pressure at the breaker plate should be monitored; sustained melt pressure above 300 bar may indicate unmelts or gel accumulation causing output instability. If acetic acid is liberated during a machine fault or purge, stainless-steel downstream equipment and local exhaust ventilation are required because the acid can corrode carbon steel and copper alloys.

Drying and storage conditions are not severe for EVA 2250, but surface moisture after humid storage can generate splay in cast film and reduce foaming uniformity. If pellets have been exposed to relative humidity above 60%, a desiccant-bed dryer set at 60 °C for 4 h is recommended before processing. Drying temperatures above 70 °C should be avoided because pellet surface tack can initiate hopper bridging. The resin should be stored indoors below 35 °C, away from ultraviolet light and oxidizing agents; photooxidative chain scission at the acetate group can shift the melt flow index and reduce heat-seal strength. Processors should not combine EVA 2250 with amine-based additives when a peroxide cure is planned later, because amine radicals consume peroxide and retard crosslinking.

What Are the Practical Differences Between EVA 2250 and Lower Vinyl Acetate Copolymers?

Lower-vinyl-acetate copolymers in the 12–18 wt% range retain greater polyethylene crystallinity and therefore exhibit higher flexural modulus, higher tensile strength, and better dimensional stability, but lower clarity, lower adhesion to polar surfaces, and reduced low-temperature impact resistance. EVA 2250 at 22.5 wt% vinyl acetate reduces crystalline sequence length sufficiently to shift behavior toward elastomeric response: elongation at break rises, Shore hardness decreases, and the material remains flexible below -40 °C. The property change is not linear with vinyl acetate content. The largest changes often occur between 15 wt% and 25 wt% vinyl acetate because crystalline lamellae are disrupted beyond a threshold where secondary crystallization can no longer restore stiffness. A converter choosing between an 18 wt% vinyl acetate grade and EVA 2250 can expect the higher-vinyl-acetate material to accept higher filler loadings, produce softer foam, and bond more reliably to polyurethane cements, but it will exhibit greater creep under load and lower resistance to hydrocarbon solvents. These trade-offs should be evaluated with ISO 527-2 for tensile properties, ISO 178 for flexural modulus, ASTM D2240 for durometer, and ASTM D1693 for environmental stress-crack resistance.

Film Casting, Foam Expansion, and Injection-Molded Footwear Components

In cast film and sheet extrusion, EVA 2250 is usually processed at chill-roll temperatures between 10 °C and 25 °C. The low crystallinity reduces blocking and permits high-clarity sheet when appropriate antiblock is included. Heat-seal initiation temperature is lower than that of low-density polyethylene, and peel strength on heat-sealed films should be measured according to ASTM F88 when sealing jaws are being optimized. In chemically cross-linked foam, the resin can be compounded with azodicarbonamide blowing agent and dicumyl peroxide crosslinking agent on a two-roll mill or internal mixer at temperatures below 110 °C to prevent premature cure. The compounded sheet is then expanded in a press or continuous foaming oven at 160–190 °C. Cure and expansion must be balanced: premature gas release before sufficient gelation produces cell collapse, while excessive crosslinking restricts expansion and increases foam density. Zinc oxide or other acid acceptors can shift azodicarbonamide decomposition downward from its unactivated onset near 205 °C, keeping expansion closer to the EVA processing window. A continuous foaming line often requires a zoned oven and belt-speed control so that the compound reaches gelation before full blowing-agent decomposition. On production-scale equipment, cure is characterized by moving-die rheometry at 180 °C, and foam density is measured according to ISO 845. For injection-molded foam components such as midsoles, the melt is injected at reduced shot size so that foaming fills the cavity; vents must be machined to allow gas escape, and clamp force must resist mold opening from internal blowing pressure. Published data for EVA 2250-specific foaming formulations is limited, so the resin manufacturer’s technical service recommendations should be used for initial formulation work.

Hot-melt adhesive and wax-blend operations use the 5.0 g/10 min melt flow index to balance wet-out and cohesive strength. On a twin-screw extruder with 40:1 L/D, tackifier dispersion can be conducted at 120–170 °C, but a temperature gradient after the feed zone prevents low-melting tackifier from forming a separate liquid phase that reduces shear. EVA 2250 has a polar acetate group, so its molten surface wets paper and boardstock with a lower contact angle than metallocene polyethylene; the practical result is faster fiber-tear adhesion in hot-melt bonding. However, head-space extraction is required when melt temperatures exceed 200 °C because acetic acid and oligomeric fractions are volatile at those temperatures. The resin should not be held over copper or copper-alloy hot-melt tank surfaces for extended periods because heat plus liberated acetic acid accelerates corrosion.

How Does EVA 2250 Compare with Ethylene Methyl Acrylate and Metallocene Polyethylene?

Ethylene methyl acrylate and ethylene butyl acrylate copolymers provide polarity without the acetic acid elimination pathway. They can be processed at higher temperatures with less risk of acid-catalyzed degradation, but they often exhibit higher surface tack and different mechanical strength at equivalent comonomer content. EVA 2250 provides a different adhesion-to-cost position in packaging and footwear compounds, but comparative selection depends on service temperature and ultraviolet exposure. Metallocene linear low-density polyethylene offers higher puncture resistance and better organoleptic properties, but it lacks the polar adhesion and filler-carrying capacity of EVA 2250. Where a converter requires low-temperature flexibility plus adhesion to paper, polyethylene fiber, or polyurethane coatings, EVA 2250 is commonly evaluated first; where sustained service above 150 °C is required, polyamide-based systems or crosslinked hydrocarbon elastomers are more appropriate. These differences are quantified by ISO 527-2 tensile modulus, ASTM D1003 haze, ASTM D1693 environmental stress-crack resistance, and ISO 1133-1:2022 melt mass-flow rate.

Regulatory Evaluation Methods and Operational Boundaries

EVA copolymers may be evaluated for food-contact articles under FDA 21 CFR 177.1350 when the finished article meets the extractables limitations specified in that section. The converter, not the resin supplier, is responsible for end-use compliance. For European Union applications, overall migration testing should be performed on the finished article according to the applicable parts of EN 1186-1 and the relevant annexes of Commission Regulation EU 10/2011. No specific compliance should be inferred without a letter of guarantee from Hanwha Solutions for the purchased lot. The product is not recommended for continuous load-bearing service above 80 °C, because creep and compression set increase as crystallinity declines. Strong acids, strong bases, and ketone-containing cleaning solvents should be avoided because they attack the acetate group or swell the amorphous phase. Pro-oxidant masterbatches intended for degradable polyolefin films should not be blended with EVA 2250 unless accelerated aging is an explicit performance requirement.