Elevar EB508 EVA Copolymer Resin, 18,5% VA, 0,7 MI, Grado de sacos pesados

Elevate EB508 EVA Copolymer Resin, 18.5% VA, 0.7 MI, Heavy Duty Bags Grade is a high-molecular-weight ethylene-vinyl acetate copolymer with a nominal vinyl acetate comonomer content of 18.5 wt% and a melt mass-flow rate of 0.7 dg/min when measured at 190°C under 2.16 kg load according to ISO 1133-1:2022 or ASTM D1238. The grade is positioned for thick-gauge industrial sack film where high melt strength, impact toughness, and low heat-seal initiation are required. Vinyl acetate content is verified by Fourier transform infrared spectroscopy using ASTM D5594 or ISO 8985, and density by ASTM D1505 at 23°C typically falls between 0.939 g/cm³ and 0.942 g/cm³. The crystalline melt peak recorded by differential scanning calorimetry under ASTM D3418 is commonly 84–88°C, consistent with substantial disruption of polyethylene crystallinity. The product is synthesized by high-pressure free-radical copolymerization, which introduces long-chain branching and a broad molecular weight distribution; these structural features contribute to strain-hardening melt behaviour in blown-film operation.

For heavy-duty bags, EB508 may be extruded as a monolayer or as the sealing layer of a coextruded structure. The 18.5 wt% VA content lowers the seal initiation temperature to the 75–85°C range in 150 µm film tested per ASTM F88, while maintaining cold-temperature flexibility to at least -20°C, as inferred from dynamic mechanical analysis of similar VA copolymers. At 0.7 dg/min, EB508 has higher melt viscosity than general-purpose EVA film grades at 1.5–3.0 dg/min; this raises melt strength and bubble stability in large-diameter, thick-gauge lines but reduces screw throughput by roughly 15–30% at fixed torque compared with higher-MI grades. The material is not a low-temperature heat seal resin for thin packaging, nor is it a high-cling film grade; its VA level and additive system are balanced to reduce blocking at heavy-gauge contact while retaining toughness for loaded sack drop and puncture events.

What Limits the Extrusion Processing Window for EB508 in Heavy-Duty Blown Film?

The processing window is controlled on one side by thermal deacetylation of vinyl acetate and on the other by melt strength thresholds needed to stabilize a thick-gauge bubble. Deacetylation of EVA begins measurably above 210–240°C under non-oxidative thermogravimetric analysis, releasing acetic acid and causing oxidation, crosslinking, and gel formation. Therefore, melt temperature should be kept below 205°C at the die and below 215°C in the metering zone, except for very short residence times. Barrel temperature profiles on a 30:1 L/D single-screw extruder commonly follow a rising sequence of 150–165–175–185–195–200°C from feed throat to die, with the feed throat cooled to 40–60°C to prevent resin bridging. Screw speed should be selected to keep melt temperature measured by an immersion probe at the adapter below 205°C. Adapter and die set temperatures are typically 175–195°C; die temperatures above 210°C may accelerate surface oxidation of acetate moieties and cause smoky off-gas, die lip buildup, and film surface roughness.

Viscosity of EB508 at typical blown-film shear rates between 100 s⁻¹ and 1000 s⁻¹ is substantially higher than that of LLDPE or low-VA EVA at equivalent melt index. Capillary rheometry on comparable grades indicates apparent shear viscosity of 800–1500 Pa·s at 190°C, with pronounced shear thinning at higher output. In a grooved-feed extruder, this translates to die pressures of 280–420 bar at outputs of 90–120 kg/h on a 65 mm line. A melt pump is recommended when upstream pressure fluctuations exceed ±5%, because unstable melt flow through the die gap creates thick-thin gauge bands in sacks. The use of a barrier screw with a Maddock-style mixing section improves melting homogeneity; a general-purpose screw without adequate mixing may produce unmolten high-molecular-weight domains visible as gel-like inclusions. Screen packs of 20/40/60/100 mesh or finer are installed to trap degraded particles, with backpressure monitored to avoid exceeding the extruder thrust bearing rating.

Melt fracture in low-MI EVA can appear as sharkskin at die land shear stresses above approximately 150–200 kPa. When this occurs, die lip temperature is raised in increments of 3–5°C and die land length is maintained at 10–15 times the die gap; a fluoropolymer process aid at the supplier-recommended concentration may also be added. Bubble instability will develop if melt temperature drops below 160°C at the die because melt strength becomes too high and web tension rises. Therefore, the practical lower melt limit for large bubbles is close to 165°C. These two thermal limits create a usable melt temperature range of approximately 165–205°C, which is narrower than that of LDPE-only heavy-duty formulations.

On a production blown-film line with 65 mm screw diameter, 30:1 L/D, and 2.2–2.4 mm die gap, EB508-type heavy-duty grades are usually operated at blow-up ratio 2.0–2.5, frozen-line height 6–10 die diameters, and die temperature 175–195°C. The die gap is wider than used for LLDPE stretch films to reduce shear rate and die lip oxidation, and also to allow draw-down to thick films without excessive orientation. Film thickness in heavy-duty sacks ranges from 100 µm to 250 µm; below 100 µm, the high VA content and low MI produce surface tack that can impair bubble collapse and layflat, while above 250 µm, cooling rate limits production speed and increases blocking risk. Pre-drying is not required when resin is stored below 60% relative humidity, but if condensate has formed on pellets, drying at 55–65°C for 2–4 h to a residual moisture content below 0.05 wt% is required. Purging after shutdown should use fractional-melt LDPE or a commercial purging compound until melt temperature at the die is below 160°C; leaving EB508 in a hot barrel longer than 30 min may generate acetic acid corrosion on brass or copper-alloy instrumentation if internal pH drops.

Mechanical Response and Seal Performance in Filled Industrial Sack Films

For fill-and-drop service, the relevant mechanical properties are dart impact, puncture, tear, and heat-seal integrity. On 150 µm blown film, comparable ethylene-vinyl acetate copolymers with 18–19 wt% VA and 0.6–0.9 dg/min melt index show dart impact values of 700–1200 g per ASTM D1709 Method A, puncture resistance of 55–85 N per ASTM D5748, and normalized Elmendorf tear values that are 20–40% higher in the transverse direction than LLDPE film of equal thickness. Tensile secant modulus at 1% strain is commonly 30–60 MPa per ASTM D638-14, which is lower than LLDPE and high-pressure LDPE film grades. The low modulus contributes to stress distribution around sharp fillers, reducing localized strain at the tip of punctures.

Seal initiation temperature measured on 150 µm film by ASTM F88 at 0.5 MPa seal pressure and 0.5 s dwell typically begins between 75°C and 85°C. Hot tack force measured by ASTM F1921 Method B remains in the 2.5–4.0 N/25 mm range across sealing temperatures from 90°C to 120°C, which is broader than low-VA EVA and LLDPE sealant grades. This hot tack plateau permits sealing through dusty or filled sack top folds and reduces leaker rates after sack drop. The seal-strength plateau at higher temperature is attributable to moderate VA content: enough to accelerate molecular interdiffusion at the seal interface, but not so high that cohesive failure dominates at elevated temperature. For heavy-duty sack closures, a sealant layer containing EB508 is often converted at heat-seal bar temperatures of 100–135°C, with cooling before load stacking to prevent seal creep.

Differences from other products in the ethylene-vinyl acetate family follow a composition-property pattern. At lower vinyl acetate content, such as 9–12 wt%, melt temperature rises, crystallinity increases, tensile modulus and yield stress increase, but seal initiation increases by 15–25°C and low-temperature toughness in filled-drop applications decreases. At higher vinyl acetate content, such as 25–28 wt%, film blocking and coefficient of friction increase substantially, molecular stiffness decreases, and extraction of low-molecular-weight amorphous fractions becomes more likely; such grades are normally reserved for cling film, hot-melt adhesive, and high-cling lamination. EB508 is distinguished by its 0.7 dg/min melt index within the heavy-duty bag segment, because most heavy-duty sack formulations use 1.0–2.5 dg/min LLDPE or EVA. The low MI improves melt strength but makes EB508 less suitable for cast film lines or high-speed extruders with torque limits.

When EB508 Replaces LLDPE or LDPE in Coextruded Heavy-Duty Sack Layers

In coextruded sack films, EB508 is generally placed in the sealant layer or used as a high-toughness modifier. A typical three-layer configuration uses a skin layer containing EB508 at 20–40% of total film thickness, a core of medium-molecular-weight LLDPE or recycled film scrap, and an outer layer of LLDPE or LDPE for stiffness and printability. When EB508 is dry-blended with LLDPE, recommended blend ratios are 20–40 wt% EB508; below 20 wt%, seal initiation remains closer to the LLDPE base, while above 40 wt%, film stiffness may fall below the requirement for tall filled sacks. The difference in seal behaviour is measurable by ASTM F88: a 30 wt% EB508/LLDPE blend on 120 µm film lowers seal initiation by 10–15°C compared with the LLDPE alone. At 50 wt% and above, the blend’s melt elasticity improves bubble stability, but blocking requires addition of synthetic silica antiblock at 2000–6000 ppm.

Direct substitution of LDPE with EB508 in a monolayer sack increases heat-seal strength and puncture resistance, but the lower Young’s modulus and higher elongation at break must be assessed against stack compression and creep. In extended load-holding tests, unmodified EB508 thick films can exhibit creep under sustained stress above 5 MPa at room temperature, whereas LDPE may have secant modulus values 2–4 times higher. For heavy-duty construction bags and resin sacks, thickness compensation of 10–20% or blending with LLDPE is used to maintain dimensional stability. The high VA content also increases oxygen permeability relative to LDPE and LLDPE; therefore, EB508 is not selected for oxygen-sensitive fill materials unless the bag includes a barrier core layer such as metallized film or polyamide.

Regulatory compliance for EB508 is conditional on the additive package and conversion cleanliness. The resin should be accompanied by a REACH registration number under 1907/2006/EC and a RoHS declaration under 2011/65/EU for cadmium, lead, mercury, hexavalent chromium, polybrominated biphenyls, and polybrominated diphenyl ethers. Food-contact suitability for EVA copolymers is referenced in FDA 21 CFR 177.1350; because EB508 may contain antioxidant and processing stabilizers not listed in that citation, food-contact use should be verified for each final package. In storage, EB508 should remain in sealed containers at 5–35°C and below 60% relative humidity. Exposure to strong amines, alkaline residues, or certain transition-metal stearates should be avoided because these species can catalyze deacetylation at elevated melt temperatures, increasing gel formation and diminishing seal strength. The material should not be blended with polypropylene or high-density polyethylene beyond conventional recycling ratios because immiscible domain formation reduces film impact strength and creates delamination in heavy-gauge sacks.

Quality control for EB508 includes pellet size distribution, melt flow rate, density, and vinyl acetate content. The producer’s certificate of analysis should report melt flow rate per ISO 1133-1:2022, density per ASTM D1505, and VA content per ASTM D5594. Gel count testing by film extrusion on a laboratory blower with a 20/40/60 screen pack and visual inspection of 0.5 m² film sections may be used by converters to verify cleanliness. The material’s heavy-duty bag grade designation does not imply a food-contact certification; it indicates targeted rheology and additive content for thick films. Silo or box packaging should be inert plastic or aluminium-lined to avoid metallic contamination; iron debris from conveying systems can catalyze polymer degradation on hot surfaces.

The product should be removed from production at the end of the run by transitioning to a purge grade; extended hold at processing temperatures above 160°C leads to progressive discoloration, gel contamination, and corrosive off-gas. Filtered granulate and edge-trim regrind may be re-extruded at levels up to 20–30 wt% in heavy-duty sacks, provided molecular homogeneity is confirmed by melt flow measurement and gel count inspection, because repeated heat history degrades VA sites and shrinks the usable heat-seal plateau.