Copolímero de acetato de vinilo de etileno CERTENE EDI-240 (Muehlstein)

Supplied through Muehlstein, CERTENE EDI-240 is an ethylene-vinyl acetate copolymer pellet grade. The EDI-240 nomenclature is consistent with a nominal vinyl acetate comonomer content of 24 wt% and a nominal melt flow index of 2.0 g/10 min when measured at 190 °C under a 2.16 kg load in accordance with ASTM D1238-20 or ISO 1133-1:2022. The copolymer is produced by high-pressure radical copolymerization, which gives a random comonomer distribution and lowers crystallinity relative to low-density polyethylene homopolymer. Lot-specific values for vinyl acetate content, melt flow index, density, additive package, and moisture are recorded on the certificate of analysis supplied by Muehlstein and control the actual processing window.

Because the vinyl acetate side groups interrupt the polyethylene crystal lattice, density is typically reported near 0.94 g/cm³ under ASTM D1505. The material is intended for extrusion, coextrusion, injection molding, and high-shear compounding. Typical fabrication routes include sealant webs in flexible packaging, chemically blown or crosslinked foam, footwear midsoles, and filled wire-and-cable compounds. The resin is not a single-site ethylene-octene plastomer; its acetate functionality provides higher polarity, lower heat-seal initiation temperature, and a different thermal-degradation envelope.

Processors should not infer a universal processing window from the melt index alone. Incoming inspection under ASTM D1238-20 is required where film gauge, foam density, or injection-part weight are critical. Lot-to-lot melt-flow variation in the range of ±0.2 g/10 min can be acceptable for general extrusion but may require throughput or temperature adjustment on lines operating at narrow tolerance.

How Does a 24 wt% Vinyl Acetate Content Affect Thermal and Mechanical Performance?

The reduction in crystallinity produces a broad melting endotherm under ASTM D3418-21. Representative values for ethylene-vinyl acetate copolymers containing 24 wt% vinyl acetate center near 76 °C, while the Vicat softening temperature under ASTM D1525 with a 10 N load is commonly reported near 54 °C. These values restrict continuous load-bearing service. A film, foam part, or molded component held above 50 °C can exhibit blocking, creep, and loss of dimensional recovery. The thermal ceiling is lower than that of 12–18 wt% vinyl acetate grades, which generally retain useful stiffness at higher service temperatures.

At the same time, the polar acetate group improves surface wetting on polar substrates. In coextruded blown film, adhesion to polyamide, ethylene-vinyl alcohol, ionomer, and coated paper is improved compared with a low-density polyethylene sealant when tested on laboratory coextrusion lines using a die gap of 2.0 mm and a blow-up ratio of 2.0:1–2.5:1. Adhesion is not a single bulk property; it depends on interfacial melt temperature, line speed, air-gap residence time, and the polarity of the adjacent layer.

Thermal degradation is the principal process limitation. Above approximately 210 °C, the acetate group undergoes acetic acid elimination. The field indicators are acetic odor, yellowing, gel formation, die-lip carbonization, and reduced film clarity. Long residence time at elevated temperature or high-shear zones with poor temperature control can initiate degradation even when the barrel set point is below 210 °C. Unvented equipment, oversized screw channels, or high screw speed can push actual melt temperature outside the safe range.

The lower melting point is advantageous in sealant layers. Heat-seal initiation for EVA copolymers in this composition range commonly falls between 85 °C and 100 °C on heated-bar equipment with jaw pressure of 0.3–0.5 MPa and dwell time of 0.5–1.0 s. This permits coextruded structures to seal below the deformation temperature of oriented outer layers. The actual seal window must be established on the target packaging line because film thickness, heat-transfer rate, and contaminant levels shift the curve.

Comparative Property Trends Across Low, Mid, and High Vinyl Acetate EVA Grades

Within ethylene-vinyl acetate copolymers, the 24 wt% vinyl acetate grade occupies an intermediate position. Lower-vinyl-acetate grades with 12–18 wt% comonomer show higher crystallinity, higher melt point, higher tensile strength, and lower surface tack. Higher-vinyl-acetate grades with 28–33 wt% comonomer show lower melt point, higher elongation, greater polarity, and more rubber-like behavior, but they are more difficult to pelletize, more prone to blocking, and less thermally stable. The values in the following tables are representative of unfilled ethylene-vinyl acetate copolymers and are not a substitute for the lot certificate of analysis for EDI-240.

The table below summarizes the general property shift relative to low- and high-vinyl-acetate EVA copolymers. These ranges are drawn from published polymer-science data for unfilled resins and are affected by molecular weight, additive package, and test specimen preparation.

Film structures specifying EDI-240 as a sealant benefit from reduced seal initiation, but the lower melt temperature must be considered when the same line runs polyamide or polyester outer layers. Blow-up ratio, frost-line height, and collapsing-frame tension require re-setting when changing from a low-vinyl-acetate sealant or LDPE sealant to this grade. Failure to adjust these parameters can produce bubble instability, gauge variation, blocking at the nip, and width variation in finished reels.

In foam processing, the grade accepts chemical blowing agents such as azodicarbonamide at 2.0–4.0 phr. Compression molding or continuous vulcanization lines must control mold temperature within ±2 °C because the decomposition of azodicarbonamide and the melt viscosity of the EVA matrix are both temperature-sensitive. Free-foam density is typically in the range of 0.08–0.20 g/cm³, depending on mold fill ratio, gas loss, and blowing-agent efficiency. Crosslinked molded foams commonly use dicumyl peroxide at 0.5–1.0 phr; cure behavior is monitored on a moving-die rheometer at 175 °C to avoid scorch during injection or transfer molding.

In wire-and-cable compounding, mineral filler loadings of 60–70 wt% are processed on co-rotating twin-screw extruders with L/D 40:1, side feeding, and controlled barrel venting. Melt temperature must be kept below 210 °C at the die. When magnesium hydroxide or aluminum trihydrate is used, vent vacuum should be maintained at −0.08 MPa gauge or better to remove moisture and volatile by-products. Torque above approximately 85% of drive capacity indicates overfeeding or insufficient screw-dispersive capacity and may lead to melt-temperature rise and resin degradation.

On a single-screw blown-film extruder with L/D ≥ 24:1 and a barrier screw, a rising barrel profile from 120 °C at the feed zone to 190 °C at the adapter is used. Die temperatures are maintained between 190 °C and 205 °C. If melt temperature exceeds 210 °C, acetic acid evolution and die-lip carbonization become likely. Screw speed, backpressure, and screen-pack resistance should be configured so that measured melt temperature remains below 210 °C. Purging with a low-melt-index LDPE before shutdown reduces oxidized EVA deposits in the die and adapter.

Moisture uptake above 0.05 wt% can generate surface defects, bubbles, and loss of film clarity. At ambient relative humidity above 55% RH, pre-drying is recommended at 60–65 °C for 3–4 h in a desiccant dryer. Drying temperatures above 70 °C should be avoided because pellet agglomeration can occur in the hopper or dryer bed. Injection molding uses barrel temperatures of 140 °C to 190 °C and mold temperatures of 20–35 °C. Gate blush, sink marks, and weld-line weakness are common when mold temperature is below 15 °C or when injection speed is excessive for wall thickness.

Compared with an ethylene-methyl acrylate copolymer of similar comonomer content, EVA offers higher polarity at equivalent melt index but has a lower thermal-degradation threshold because the acetate group can eliminate acetic acid. Compared with a single-site ethylene-octene polyolefin elastomer, EDI-240 provides better adhesion to polar substrates but lower thermal stability and lower ultraviolet resistance. These differences affect material selection in coextruded sealant, tie-layer, and adhesive applications.

Regulatory support for this EVA grade is typically limited to food-contact statements under FDA 21 CFR 177.1350 when the resin is used in repeat-use food-contact articles under specified conditions, but the converter must verify end-use migration limits. For European articles, compliance is assessed under EU Regulation 10/2011 using food simulants. The supplier can provide a Declaration of Compliance only when the specific lot, final thickness, temperature, and food type fall within the intended-use scope. Industrial requirements such as REACH and RoHS Directive 2011/65/EU are generally addressed in the supplier’s regulatory documentation, not by the grade designation alone.

Pellets should be stored in unopened bags at temperatures below 35 °C and away from direct sunlight. EVA copolymers are susceptible to oxidative degradation over extended storage. Condensation from temperature swings can raise pellet moisture and require drying. The material should not be exposed to copper, copper alloys, or strong oxidizing agents because metal ions can accelerate thermo-oxidative breakdown. In silos, surface tack and low melt point can cause pellet bridging at wall temperatures above 40 °C; mass-flow bins and first-in, first-out inventory management are preferable.

Avoid compounding with amine-based antistatic or stabilizer additives that can react with residual acetic acid and cause premature crosslinking, discoloration, or plate-out on die surfaces. Recycling of post-industrial scrap is possible when the scrap is screened for melt flow index and vinyl acetate content by ASTM D5594-18 or equivalent FT-IR methods. Batch-to-batch variation in scrap can shift the melt index beyond the processing tolerance of the line. When regrind is used above 20 wt%, gel count, color shift, and melt pressure should be monitored at regular intervals.