HANWHA EVA 2050 Copolímero de acetato de etileno e vinil

The HANWHA EVA 2050 Ethylene Vinyl Acetate Copolymer is a pelletized, high-pressure free-radical copolymer grade with a nominal vinyl acetate content of 20 wt% and a melt mass-flow rate of 5.0 g/10 min when measured at 190°C under 2.16 kg load in accordance with ASTM D1238 and ISO 1133-1:2011. Density at 23°C is 0.940 g/cm³ by ASTM D1505. The grade is manufactured by high-pressure autoclave/tubular copolymerization; incorporation of vinyl acetate reduces crystallite thickness and lowers the melting peak relative to low-density polyethylene. This compositional position places EVA 2050 between low-VA extrusion coating grades and high-VA hot-melt or crosslinkable foam grades, making it suitable for injection moulded parts, masterbatch carriers, blown film sealant layers, and chemically crosslinked foam.

Nominal values in the table are not sales specifications and vary with additive package and production campaign. The certificate of analysis for the specific lot governs exact moisture, ash, and stabiliser content. Condensed surface moisture is the main storage-related processing defect source. When pellets are transferred from cold warehousing at 5–10°C into a humid compounding area above 60% relative humidity, a 4 h drying step at 60°C in a dehumidifying hopper dryer with airflow of 1.5–2.0 m³/h per kg/h throughput is recommended. Drying temperature above 75°C or residence beyond 8 h can soften the pellets and cause bridging in the hopper throat.

Thermal Degradation Pathways in Deacetylation-Limited Extrusion

Deacetylation of vinyl acetate segments begins at measurable rates near 220°C. Thermogravimetric analysis in nitrogen at 10°C/min typically shows 1% mass loss near 220–230°C and rapid deacetylation above 260°C. The liberated acetic acid attacks unprotected steel surfaces and can create brown specks, haze, and acidic odour in extrudate. In processing, barrel set temperatures should remain below 220°C; if high-temperature compounding is unavoidable, residence time below 2 min and atmospheric venting are required. Regrind containing 20–30 wt% of EVA 2050 should be monitored by melt flow ratio and yellowness index because chain scission during repeated heat histories lowers viscosity and increases colour.

Rheological characterisation by capillary rheometry at 190°C shows shear-thinning behaviour with a power-law index of 0.35–0.45 between 100 s⁻¹ and 1000 s⁻¹. This pseudoplasticity assists filling of thin-wall injection mould cavities but reduces melt elasticity relative to high-pressure LDPE. In a 40:1 co-rotating twin-screw extruder, EVA 2050 is compounded with silica, carbon black, or calcium carbonate using a barrel profile of 140–170°C and screw speed 250–350 rpm. Because viscous dissipation can raise melt temperature 10–20°C above the barrel set point, the practical processing window is narrow. The melt must remain above the 84°C melting peak to achieve full plasticisation, yet stay below 200°C to avoid acetic acid generation. Vacuum venting at -0.08 MPa gauge is recommended during filler dispersion to strip low-molecular-weight volatiles.

In injection moulding on a 120 t clamp machine with a 40 mm screw and L/D 22:1, EVA 2050 is processed at barrel temperatures of 170–200°C, nozzle temperature of 190°C, and mould temperature of 25–40°C. Injection pressure is 50–90 MPa, hold pressure 40–70 MPa, and back pressure 0.5–1.0 MPa. Mould shrinkage measured after 48 h at 23°C is 1.2–1.6% under ASTM D955. Premature ejection before the wall centre cools to 60°C causes surface depressions and warpage in flat parts. When EVA 2050 replaces a 5.0 g/10 min LDPE in an existing tool, cushion and hold-pressure settings require adjustment because the lower crystallinity reduces post-mould crystallisation shrinkage but increases gate-seal time.

What Pressures and Kinetics Govern Foam Expansion?

Crosslinked EVA 2050 foam lines exploit the temperature separation between dicumyl peroxide crosslinking and azodicarbonamide decomposition. In the compounding stage, a Banbury or intermeshing kneader is held at 105–115°C to incorporate dicumyl peroxide, azodicarbonamide, zinc oxide, and stearic acid without premature reaction. Zinc oxide shifts the blowing agent decomposition onset from its intrinsic 205–215°C to 155–165°C. The sheet is then crosslinked at 160–180°C, during which dicumyl peroxide decomposition produces cumyloxy radicals and crosslinks ethylene sequences. In the expansion oven at 175–185°C, pressure decay permits liberated nitrogen and carbon monoxide to expand cells. Closed-cell sizes of 100–300 µm are typical when the gel fraction before expansion is 60–75%, measured by xylene extraction. The 20 wt% VA content of EVA 2050 reduces crystalline blocking of radical diffusion and gives more uniform crosslink distribution than a 15 wt% VA grade.

On continuous foam sheet lines, premature gas loss is controlled by maintaining head pressure at 8–12 MPa and melt temperature below 125°C at the die. A melt gear pump is used to reduce pressure pulsation; pressure variation above 0.5 MPa raises cell-size standard deviation by approximately 30 µm. The die temperature must be 15–20°C lower than the oven expansion temperature to prevent surface skin fracture; however, if the die is too cold, melt viscosity increases and causes melt fracture at the die lips. These process boundaries make pressure control more critical than throughput control when EVA 2050 is run on foam lines originally designed for LDPE.

Differences from other EVA products are most pronounced at the lower and upper VA limits. Reducing vinyl acetate from 20 wt% to 15 wt% raises the DSC melting peak by approximately 8–10°C and increases hardness by 4–6 Shore A points, but decreases filler wetting and low-temperature flexibility. Increasing VA to 28 wt% lowers the melting peak to approximately 73°C and improves elongation and tack, but raises blocking tendency during silo storage above 30°C and reduces dimensional stability of moulded parts. Compared with metallocene ethylene-octene polyolefins of similar melt index, EVA 2050 contains ester side groups that accept higher calcium carbonate loading without surface treatment; however, its thermal stability ceiling is lower because of acetic acid formation. Compared with LDPE, EVA 2050 exhibits lower seal initiation temperature, higher impact toughness at -20°C, and better adhesion to polyamide and tie-resin layers.

When EVA 2050 Replaces LDPE or Metallocene Polyethylene in Sealant Layers

Film structures using EVA 2050 sealant layers benefit from lower seal initiation temperature, but the processing window must be controlled to avoid melt fracture and blocking. In a three-layer blown film line with a 35 mm die diameter and die gap 1.2–1.8 mm, the sealant layer is processed at 150–180°C while HDPE or polyamide structural layers are processed at their usual temperatures. A blow-up ratio of 2.0–3.0 and frost line height of 600–900 mm maintain bubble stability. Seal initiation temperature for EVA 2050 is approximately 85–95°C; however, published data for this specific film configuration is limited, so seal strength must be verified per ASTM F88 and hot tack per ASTM F1921 on the target packaging line. The polar vinyl acetate groups also reduce blocking resistance; if the sealant layer exceeds 15 µm, anti-block masterbatch or surface migration of erucamide is typically required above 25°C storage.

Calcium carbonate masterbatch production with EVA 2050 is normally run on a 65 mm twin-screw extruder with L/D 36:1 and a downstream side-feeder. Filler loading up to 40 wt% is feasible without surface treatment because the acetate group improves matrix-filler wetting. The side-feeder throat temperature should not exceed 60°C; higher temperatures cause filler compaction and screw torque variability. The resulting masterbatch is let down at 5–10 phr in blown film and injection moulding. When a high-VA grade at 28 wt% VA is substituted, torque decreases but pellet blocking increases; when a low-VA grade at 15 wt% VA is substituted, torque rises and filler dispersion quality deteriorates. EVA 2050 therefore occupies a practical mid-range for filled compounds.

Compliance Matrix for Food-Contact and Electronic Applications

Regulatory compliance is end-use dependent and requires migration testing on the final article. The following matrix identifies the relevant frameworks.

Processors should avoid combining EVA 2050 with strong Lewis acids or amine-based additives in high-temperature compounding above 200°C, because those species can catalyse ester thermolysis and accelerate acetic acid release. Colour concentrates based on polyolefin carriers are acceptable at let-down ratios below 5%; higher ratios require validation by melt flow and yellowing index after 24 h at 150°C per ASTM E313. For radiation-sterilised applications, electron beam or gamma irradiation may induce crosslinking and discolouration; dose-response testing is required before specification.