HANWHA EVA 1826 Copolímero de acetato de vinilo de etileno

Hanwha EVA 1826 is a pelletized ethylene vinyl acetate copolymer produced by Hanwha Chemical Corporation. The grade designation 1826 encodes a nominal vinyl acetate content of 18 wt% and a nominal melt index of 2.6 g/10 min as measured by ASTM D1238-20 at 190 °C with a 2.16 kg load. Pellet density is approximately 0.940 g/cm³ when determined in accordance with ASTM D1505-18 or ISO 1183-1:2019. This grade occupies a medium-flow, medium-polarity position between low-VA film grades and higher-VA adhesive or encapsulant grades. The polar acetate side groups disrupt ethylene chain crystallinity, lowering the melting point and increasing adhesion to polar surfaces compared with LDPE homopolymer. In contrast to EVA grades containing 28 wt% or 33 wt% vinyl acetate, HANWHA EVA 1826 retains more crystalline structure, higher modulus, lower surface tack, and better creep resistance at elevated temperatures. It is specified for injection moulding, compounding, foam extrusion, masterbatch carrier resin, and hot-melt adhesive modification.

The tabulated values are representative of published technical data and are not batch release limits. Mechanical values depend on specimen preparation, conditioning at 23 °C and 50% RH for 48 h, and test speed. Current lot certification should be obtained for any specification-bound application.

Why Does 18 wt% Vinyl Acetate Content Change Crystallinity, Adhesion, and Low-Temperature Flexibility Relative to LDPE and Higher-VA EVA Grades?

The incorporation of 18 wt% vinyl acetate into the polyethylene chain introduces a random distribution of polar acetate groups. These groups reduce the length of crystallizable ethylene sequences, lower the melting point, and suppress crystallinity to a level that improves environmental stress crack resistance and low-temperature brittleness relative to LDPE homopolymer. The glass transition of EVA remains below -20 °C, so EVA 1826 maintains flexibility at refrigerator temperatures; however, the crystalline fraction still provides enough chain-network integrity to resist creep at 60 °C. Compared with EVA grades containing 28 wt% or 33 wt% vinyl acetate, EVA 1826 has higher room-temperature modulus, lower surface tack, and less compatibility with highly polar rosin ester tackifiers. It also has lower gas solubility for CO₂ and N₂, which reduces expansion efficiency in direct-gas foaming but improves dimensional stability after expansion. The melt index of 2.6 g/10 min places EVA 1826 above low-flow blow-moulding grades and below high-flow injection grades; this flow position favors injection moulding, medium-speed profile extrusion, and continuous compounding where melt temperature must be controlled below 210 °C.

On production-scale twin-screw compounding lines with L/D ratios between 48:1 and 52:1, EVA 1826 is processed at barrel set temperatures of 150 °C to 190 °C. Viscous dissipation at screw speeds above 350 rpm can increase actual melt temperature to 200–215 °C even when the final barrel zone is set below 190 °C. The acetate ester begins measurable thermal deacetylation in this upper range; acetic acid is detectable in vacuum vent condensate, and long residence times above 220 °C generate discoloration and crosslinked gel particles. Continuous extrusion should therefore maintain melt temperature at 160–205 °C and limit residence time above 210 °C to less than 8 min. Devolatilization sections should operate at 80–95 kPa differential pressure to remove acetic acid and moisture. Hopper drying at 60–70 °C for 2–4 h is recommended when ambient relative humidity exceeds 60% to prevent surface pitting and feed throat surging. The resin should not be processed in direct contact with strong alkali, primary amines, copper-based stabilizers, or bronze melt-path components where prolonged high-temperature residence is anticipated. Localized alkalinity accelerates acetate group loss. On injection moulding machines with clamp force between 80 tonnes and 180 tonnes, the grade runs at melt temperatures of 170–195 °C, mould temperatures of 20–40 °C, injection pressure of 50–80 MPa, holding pressure of 30–50 MPa, and cooling time of 15–30 s for wall thicknesses of 2–4 mm. Rapid cooling reduces crystallinity and increases flexibility but can increase post-mould shrinkage; draft angles of 1.5–2.5° and polished or PTFE-coated cavity surfaces reduce release forces caused by the polar acetate group.

When EVA 1826 Is Substituted into Hot-Melt Adhesive Formulations Instead of EVA 2825

Hot-melt adhesive formulations based on EVA, hydrocarbon tackifier, and paraffin wax respond to VA content and melt index through changes in open time, cohesive strength, and adhesion to corrugated board. Substituting EVA 1826 for EVA 2825 reduces polar interaction with uncoated paper and decreases low-temperature peel, but improves creep resistance at 60 °C because the higher crystalline fraction acts as a physical network. The lower VA content also reduces compatibility with fully esterified rosin esters and may require a higher hydrocarbon resin loading to maintain wet-out on recycled board. In continuous hot-melt mixing at 160–180 °C, EVA 1826 disperses more slowly in paraffin wax than a 28 wt% VA grade of equivalent melt index; pre-wetting the resin with a portion of the tackifier at 150 °C for 10 min minimizes phase separation and visual haze. Formulations containing 30–40 phr EVA 1826, 40–50 phr C5/C9 hydrocarbon resin, and 20–30 phr paraffin wax typically produce ring-and-ball softening points between 85 °C and 105 °C; exact values depend on resin softening point, oil content, and wax melt distribution. Viscosity at 180 °C is measured with a Brookfield Thermosel spindle 27; application viscosity for case and carton sealing is generally kept between 500 mPa·s and 2000 mPa·s. Heat-fail temperature is evaluated by ASTM D4498, and T-peel adhesion is evaluated by ASTM D1876. Because EVA 1826 has lower VA content than EVA 2825, the tacky window is typically shortened by 10–20% under identical formulation conditions, while elevated-temperature creep resistance improves. Published product-specific data for this formulation space is limited; laboratory-scale viscosity and peel testing are required before converting a production line from EVA 2825 to EVA 1826.

Chemically foamed EVA sheet for footwear midsoles is one of the most demanding applications for EVA 1826. In a typical batch mixing route, EVA 1826 is compounded on a tangential Banbury or intermeshing internal mixer at fill factors of 0.75–0.85 and discharged at 95–105 °C. The formulation includes an azodicarbonamide-bearing masterbatch at 15–20 phr, corresponding to 3–5 phr active azodicarbonamide, dicumyl peroxide at 0.8–1.5 phr, zinc oxide at 0.5–1.0 phr, zinc stearate at 0.5–1.0 phr, and calcium carbonate at 5–15 phr. The matched batch is sheeted on a two-roll mill at 90–105 °C and converted into preforms. Vulcanization and foam expansion are carried out in multi-daylight hydraulic presses at 165–175 °C. Cure rheology measured by an oscillating disc rheometer at 170 °C should reach 90% of maximum torque within 8–12 min; shorter cycles leave under-cured cell walls and higher compression set. At a target foam density of 0.15–0.20 g/cm³, EVA 1826 provides faster cavity filling than lower-MI EVA 1315 but may produce slightly larger cell diameter and lower split tear resistance in thick sections. To improve melt strength and gas retention, processors often blend EVA 1826 with 10–20% EVA 1315 or LDPE. Physical properties after expansion are assessed by density per ISO 845, cell size distribution per ASTM D3576, compression set per ISO 1856:2018 after 50% compression for 6 h at 23 °C, and rebound resilience per ISO 8307. Compression set values of 35–55% and rebound resilience of 40–50% are common for EVA 1826-based foam at 0.18 g/cm³; higher-VA grades such as EVA 2825 reduce hardness and increase rebound, while lower-VA grades such as EVA 1315 increase modulus but may crack under high elongation in the expanded state.

In coextruded film and seal-layer applications, EVA 1826 is typically used as a blend partner with LDPE at 10–20 wt% addition. The VA comonomer lowers heat-seal initiation temperature by approximately 5–10 °C and improves dart impact strength as measured by ASTM D1709. Environmental stress crack resistance, measured by ASTM D1693, is also improved relative to unmodified LDPE. Compared with EVA 2825, the 18 wt% VA grade generates a less tacky seal layer, reducing blocking during roll winding and slitting, but the low-temperature seal strength under frost conditions is inferior. EVA 1826 is not a photovoltaic encapsulant grade; it has higher crystalline haze and lower crosslinked optical coupling than EVA 2825 or EVA 2843, and should not be substituted directly in solar module lamination lines. For packaging applications, hot-tack and seal strength should be evaluated by ASTM F88 and internal hot-tack tests at the intended line speed and seal jaw temperature because the narrow high-speed window is structure-dependent.

Thermal Degradation Pathways During High-Temperature Processing

The primary thermal degradation route for EVA is acetic acid elimination from the vinyl acetate units, leaving conjugated double bonds along the polyethylene backbone. This deacetylation reaction accelerates above 220 °C and is autocatalytic because the generated acetic acid promotes further ester cleavage. Moisture, residual alcohols, and certain transition metal ions accelerate the process, whereas phenolic antioxidants and phosphite stabilizers primarily retard oxidative chain scission rather than deacetylation. Therefore, thermal residence time and melt temperature remain the key control variables. The acetic acid liberated during processing is corrosive to carbon steel tooling; downstream vent ports, die lips, and take-off equipment should be fabricated from 316L stainless steel or hard chrome-plated surfaces. Nitrogen blanketing of drying hoppers is not required below 70 °C, but closed vacuum vent lines should be monitored for acetic acid adsorption and pH change. Published kinetic data specific to HANWHA EVA 1826 is limited; general EVA degradation studies indicate deacetylation rates increase sharply above 210 °C, and the reaction rate approximately doubles for every 10–15 °C increase in this region. Operators should set high-temperature alarms at 215 °C on melt thermocouples and initiate automatic screw-speed reduction when the alarm threshold is exceeded to prevent gel formation and lot rejection.

Regulatory compliance for EVA 1826 generally falls within the manufacturer’s REACH registration dossier and the applicable provisions of 21 CFR 177.1350 for ethylene-vinyl acetate copolymers used as indirect food-contact components. End-use migration testing under the intended conditions of use remains necessary because the regulation includes total extractives limitations and additive restrictions. RoHS 2011/65/EU compliance is typically declared for lead, cadmium, mercury, hexavalent chromium, PBB, and PBDE in the unpigmented base resin; however, color concentrates and flame-retardant masterbatches must be evaluated separately. The resin is not intended for implantable medical devices or for applications requiring UL 94 V-0 flame performance without a separate flame-retardant system. No ISO 10993 biocompatibility statement should be inferred for the neat resin without additional testing. For incoming material release, lot certificates should confirm nominal VA content by the supplier’s calibrated method, melt index by ISO 1133-1:2022, and density by ISO 1183-1:2019. Storage below 40 °C in sealed containers away from direct sunlight is recommended, and opened bags should be consumed within 8 h or resealed to prevent dust pickup and moisture condensation. In masterbatch carrier applications, EVA 1826 can accept high calcium carbonate filler loadings in twin-screw compounding, but its lower VA content means that pigment wetting and polar wax dispersion are less effective than in EVA 2825 or EVA 3343; the grade is therefore selected when higher stiffness and lower surface tack of the final compound are desired.