HANWHA EVA 2315 Copolímero de acetato de vinilo de etileno

HANWHA EVA 2315 Ethylene Vinyl Acetate Copolymer is a random ethylene–vinyl acetate copolymer produced by Hanwha Chemical Corporation with a nominal vinyl acetate content of 23 wt% and a melt index of 1.5 g/10 min measured at 190 °C under a 2.16 kg load in accordance with ASTM D1238-20 or ISO 1133-1:2022. The resin is supplied as translucent pellets with CAS Registry Number 24937-78-8. Incorporation of 23 wt% vinyl acetate randomly distributed along the polyethylene backbone reduces the crystalline weight fraction to approximately 15–20%. The remaining crystalline domains are smaller and less perfect than those in low-density polyethylene, which lowers the differential scanning calorimetry melting peak to approximately 68 °C when tested under ASTM D3418-21 and the Vicat softening point to approximately 58 °C under ASTM D1525-17e1. The melt index of 1.5 g/10 min is lower than that of Hanwha EVA 2328, which has the same nominal vinyl acetate content but a melt index of 2.8 g/10 min. This difference reflects higher average molecular weight in EVA 2315 and directly affects melt strength, shear viscosity, elongational deformation behavior, and foam cell stability. The product is therefore positioned for applications in which the polymer must sustain extensional deformation during expansion, coating, or lamination rather than cases requiring maximum mold-fill speed.

Why Does 23 wt% Vinyl Acetate Content Shift the Low-Temperature Flexibility and Adhesion Boundary?

At 23 wt% vinyl acetate, the Shore A hardness of EVA 2315 is published as 94 under ASTM D2240-15 or ISO 868:2003, compared with 96 for an 18 wt% vinyl acetate grade such as Hanwha EVA 1828. Tensile strength at break is approximately 18 MPa and elongation at break is approximately 780% when measured under ASTM D638-14 or ISO 527-2:2012. The polar acetate side groups increase the surface energy of the copolymer and improve adhesion to polar substrates such as polyurethane, polyester fabric, epoxy-coated metal, and glass. The reduction in crystallinity is the principal contributor to low-temperature flexibility; the amorphous phase retains segmental motion below −25 °C, but the absence of a continuous crystalline network is what prevents low-temperature embrittlement in flexing components. In practice, this property is exploited in footwear sole components, cable compounds, foam interlayers, and impact-modification layers. The grade is not selected for elevated-temperature load-bearing applications because the Vicat softening point of 58 °C and melting peak near 68 °C define the upper service temperature for dimensional stability.

The following table consolidates manufacturer-published typical values for EVA 2315. These values are engineering references and are not lot-release specification limits unless stated on the certificate of analysis.

A Processing Ceiling Imposed by Deacetylation Kinetics at High Melt Temperature

Barrel temperature profiles for EVA 2315 are generally set from 130 °C in the feed zone to 170–185 °C at the die for single-screw extrusion. A polyolefin screw with 24:1 to 30:1 L/D and a compression ratio of 2.5:1 to 3.5:1 is used with a screen pack of 40/60/80 mesh. The die melt temperature should remain below 210 °C. Above this boundary, the deacetylation rate accelerates, releasing acetic acid at detectable levels and creating corrosive condensate on downstream equipment. For injection molding, melt temperature is typically 160–190 °C and mold temperature is held at 20–40 °C. Because EVA 2315 has a low melt index, injection pressure requirements are higher than for an equivalent-flow EVA 2328 part, and clamp force calculations should use a cavity pressure factor of 300–400 bar rather than the lower factors common for higher-flow grades. Shot-to-shot variation should be monitored by cushion position, because the higher viscosity of EVA 2315 increases recovery torque and can widen residence-time distribution in the screw front zone if screw speed is not reduced.

Foam expansion is the most sensitive processing route for EVA 2315. The 1.5 g/10 min melt index provides high melt strength, which lowers the probability of cell wall rupture when gas pressure is released. Azodicarbonamide-based chemical blowing agents are activated between 160 °C and 185 °C in the presence of ZnO and zinc stearate kickers. The blowing agent decomposition exotherm produces a local temperature increase of 10–15 °C; therefore, production-scale batch mixers are operated 5–10 °C below the target final expansion temperature. On two-roll mills and compression presses, the foaming plateau is usually narrower than ±5 °C, and deviations outside this range produce either under-expanded plaques or cell coalescence.

The expansion reaction sequence in EVA 2315 foam is typically characterized by two simultaneous rate processes: peroxide-induced crosslinking and azodicarbonamide decomposition. The apparent activation energy of dicumyl peroxide decomposition in polyolefin melts is approximately 170 kJ/mol; the azodicarbonamide decomposition, when activated by ZnO and zinc stearate, exhibits peak gas evolution near 175 °C. If crosslinking lags gas evolution by more than 20–30 s at the press plateau, the expanding gas escapes through the uncrosslinked melt and foam density increases. The low melt index of EVA 2315 retards bubble growth and maintains biaxial extensional stresses high enough to resist cell wall thinning. Process records from production-scale compression foaming lines show that a press plateau of 7–10 min at 160–170 °C is typically required to complete the peroxide cure before opening the press. Shorter cycles produce surface blisters and internal splits. This is a critical threshold risk because the difference between controlled expansion and open-cell collapse is no wider than ±5 °C in stock temperature when stock thickness exceeds 10 mm. Published data for this specific configuration is limited to equipment manufacturer technical bulletins and internal process records; no universal foaming recipe should be transferred without pilot verification.

In extruded sheet production, EVA 2315 is processed at die temperatures of 175–185 °C and polished roll temperatures of 50–70 °C. The sheet is used for thermoformed interior trim, protective packaging, and foam-laminated structures. Because the 23 wt% vinyl acetate content increases surface tack relative to EVA 1828, an anti-block masterbatch is commonly added at 0.5–2.0 wt% to prevent film-to-film blocking on reel winding. Thickness control in cast sheet requires die lip adjustment to compensate for the higher melt elasticity of EVA 2315; edge bead thickness should be monitored at ±0.05 mm across the web. Published data for this specific configuration is limited, and the suitable anti-block type must be confirmed for food-contact status if the final sheet is intended for primary packaging.

In footwear midsole production, EVA 2315 is used as a high-molecular-weight fraction in blends with EVA 2328 or metallocene-catalyzed polyolefin elastomers. A typical loading of 10–30 phr of EVA 2315 raises compound low-shear viscosity and reduces cell coalescence during depressurization. Internal mixer processing is performed at a fill factor of 0.75–0.85 with a first-stage drop temperature of 105–110 °C; the chemical blowing agent and dicumyl peroxide are added in a second stage below 90 °C to prevent premature decomposition. Dicumyl peroxide is used at 0.6–0.9 phr to generate a crosslink network that stabilizes the expanded cell walls after gas evolution. The compounded sheet Mooney viscosity is held within ±3 MU of the qualified reference, and foam density is controlled within ±0.01 g/cm³ across production lots. Failure modes observed on expansion presses include visible gas burn marks when peroxide kickers exceed the specified range and non-uniform cell size distribution when the mill roll temperature drops below 80 °C.

When Low Melt Index Is Preferred Over Higher-Flow EVA Grades in Hot-Melt Adhesive Systems

In hot-melt adhesive formulations, EVA 2315 is compounded with C5 aliphatic or rosin ester tackifying resins at 30–60 phr and paraffinic or microcrystalline waxes at 5–20 phr. The 1.5 g/10 min melt index produces a higher Brookfield viscosity at 180 °C than EVA 2328, reducing penetration into porous paper and nonwoven substrates while increasing cohesive strength. Shear adhesion failure temperature is commonly evaluated under ASTM D4498 or equivalent internal methods; final values are formulation-specific and cannot be predicted from the base polymer alone. Polar modifying resins such as sucrose acetate isobutyrate may be added at 5–15 phr to increase adhesion to polyester and polyamide films. Formulators must monitor viscosity drift over 72 h at 180 °C because prolonged heating of high-vinyl-acetate copolymers can cause deacetylation, a reduction in pH, and char formation on hot-melt tank walls. Published data for this specific configuration is limited; open time and set speed must be validated on the target application equipment because substrate temperature and coat weight dominate the final bond performance.

The adjacent grade comparison in the table below is derived from manufacturer-published nominal values. The identical vinyl acetate content of EVA 2315 and EVA 2328 does not imply interchangeability, because the melt index difference changes shear stress in the sprue and cavity, melt strength in foam expansion, and final part shrinkage.

Because EVA 2315 is a polyolefin copolymer, it is insoluble in water and chemically stable under ambient storage below 40 °C and below 60% relative humidity. Pre-drying is recommended at 60 °C for 2 h in a dehumidified-air hopper dryer when storage humidity exceeds 60%; drying above 70 °C may cause pellet agglomeration. The polymer should not be processed in equipment that has been in contact with strong oxidizing acids or high-temperature organic peroxides beyond the controlled crosslinking levels used in foaming. Pellets should be stored in sealed original packaging away from direct sunlight. Silo storage should use stainless steel or aluminium and avoid copper-bearing alloys, because trace transition metal ions can accelerate deacetylation at processing temperatures. Conveying air must be dried to −20 °C dew point or below to prevent moisture pickup. During purging, a suitable LDPE or lower-vinyl-acetate EVA purge grade should be used before shutdown to displace EVA 2315 from the barrel. Smoke and fumes released during overheating contain acetic acid and olefinic fragments; local exhaust ventilation should maintain workplace air concentrations below the applicable occupational exposure limit.

For food-contact evaluation, EVA copolymers may be evaluated under 21 CFR 177.1350 when comonomer content and extractive limits are satisfied; the final article must be assessed with additives and colorants. Under REACH, the polymer is evaluated under the polymer exemption of Article 2(9) when the monomer components are registered; downstream users must verify residual vinyl acetate monomer against workplace exposure limits. No RoHS heavy metal restrictions are expected from the base resin, but pigment concentrates and compounding additives may alter the final article classification.

When EVA 2315 is compounded at 5–20 wt% into high-density polyethylene or linear low-density polyethylene, the copolymer increases the amorphous phase fraction and improves environmental stress crack resistance and notched impact strength as measured under ISO 180:2020. The penalty is a reduction in flexural modulus; the magnitude is grade-dependent and must be measured on the final compound rather than predicted from the base polymer values. Twin-screw compounding is carried out on a 32:1 L/D corotating extruder with a melt temperature of 180–200 °C at the die. When mineral fillers are present, side-feeding is recommended to minimize filler attrition and to maintain residence time below the deacetylation threshold. The lower melt index of EVA 2315 relative to EVA 2328 requires higher specific energy input and may reduce throughput by 5–15% on a given screw configuration; this throughput loss is accepted where improved impact toughness and melt strength justify the operating cost.