Copolímero de acetato de vinilo de etileno ELVAX CM4875

ELVAX CM4875 is an ethylene vinyl acetate copolymer supplied by DuPont as a pelletized thermoplastic resin within the ELVAX portfolio. The polymer chain consists of ethylene repeat units with randomly distributed vinyl acetate comonomer; the polar acetate pendant groups reduce crystallite thickness, lower the peak melting endotherm relative to low-density polyethylene homopolymer, and increase interaction with rosin ester tackifiers, ester plasticizers, and polar substrates such as aluminium foil, corona-treated polyethylene terephthalate, and sized paperboard. The material is not a ready-to-use adhesive but a base polymer intended for compounding into hot-melt adhesives, wax blends, sealants, polymer modification, and crosslinked foam or cable compounds. Release specifications are lot-specific and include melt mass-flow rate, vinyl acetate content, density, thermal transition data, and tensile properties.

The designation CM4875 refers to a specific grade identity within the manufacturer’s system and is differentiated by a controlled vinyl acetate comonomer content and melt mass-flow rate. Because the acetate pendant group disturbs polyethylene crystallinity, the grade exhibits a lower melting onset, higher amorphous fraction, and greater polar interaction than low-vinyl-acetate extrusion grades. These structural changes influence solubility parameter, surface wetting, cohesion at elevated temperature, and low-temperature flexibility. The resin is not a standalone adhesive; it is compounded with tackifiers, waxes, plasticizers, and stabilizers to produce end-use formulations.

Which Rheological and Compositional Parameters Define the CM4875 Grade?

The grade is specified by melt mass-flow rate determined under ISO 1133-1:2022 at 190°C with a 2.16 kg piston load. Density is measured according to ISO 1183-1:2019 or ASTM D792-20 at 23°C. Vinyl acetate content is measured by Fourier transform infrared spectroscopy using ASTM D5594-18a or an equivalent internal method on a cast film of approximately 25 µm thickness. Thermal transitions are recorded by differential scanning calorimetry using ISO 11357-3:2018 at 10 K/min on the second heating cycle. Tensile properties are obtained on moulded sheets using ISO 527-2:2012 or ASTM D638-14; Shore hardness is tested after a 15 s delay on 6 mm plaques according to ISO 7619-1:2022 or ASTM D2240-15.

Within the ELVAX portfolio, CM-series grades are positioned for compounding applications in which controlled rheology and polar adhesion must be balanced. The comonomer level is the primary differentiator: lower-vinyl-acetate grades such as ELVAX 770 have a more polyethylene-like thermal profile and higher crystalline modulus, while higher-vinyl-acetate grades such as ELVAX 150 show more amorphous character, lower heat resistance, and broader compatibility with polar tackifiers. ELVAX CM4875 occupies an intermediate design space where polar adhesion and elevated-temperature cohesive strength are balanced. Published data for this specific configuration is limited, so procurement specifications should be taken from the manufacturer’s certificate of analysis rather than inferred from standard numeric grades.

In hot-melt adhesive compounding, ELVAX CM4875 is dry-blended with hydrocarbon or rosin ester tackifiers, paraffin or microcrystalline wax, and a hindered phenolic antioxidant before melt mixing in a sigma-blade kneader or a corotating twin-screw extruder with an L/D of 40:1. Mixing zones are typically held between 130°C and 180°C; the melt is then transferred through heated hoses to slot-die coaters, roll coaters, or spray applicators. The higher vinyl acetate content relative to low-VA extrusion grades increases specific adhesion to aluminium foil, corona-treated polyethylene terephthalate, sized paperboard, and glassine release liners. The controlled melt index determines wet-out and penetration into porous substrates. At addition levels of 25–35 wt% tackifier, melt viscosity decreases and fibre-tear adhesion improves; wax at 5–15 wt% reduces open time and accelerates set, but above 15 wt% wax cohesive strength at 60°C may decline below acceptable values. Bond performance is evaluated by T-peel adhesion using ASTM D1876-01, shear adhesion failure temperature using ASTM D4498-07, and ring-and-ball softening point using ASTM E28-18.

Production-scale bottlenecks include viscosity drift when the melt is held at 180°C under atmospheric oxygen, char accumulation on tank walls, and insufficient wet-out at application temperatures below 150°C. These failure modes are observed on continuous tank-melt adhesive lines where residence time exceeds 2 h. Nitrogen blanketing and stainless steel wetted surfaces reduce oxidation; copper and brass fittings should be avoided because they can accelerate oxidative degradation. If pellets have been stored at relative humidity above 60%, surface moisture can introduce steam and melt heterogeneity; pre-drying at 50–60°C for 2–4 h in a desiccant dryer with a dew point below −20°C is recommended before prolonged melt processing.

Thermal Oxidation Boundaries in High-Temperature Adhesive Lines

Vinyl acetate copolymers undergo acetic acid elimination at elevated temperatures. The reaction is autocatalytic and becomes industrially significant above 200°C; above 230°C, acetic acid evolution is rapid and can corrode downstream tooling, create voids in cast films, and shift adhesive pH. Closed-loop temperature control with alarm setpoints at 200°C is mandatory on high-temperature hot-melt lines. Acrylate copolymers such as ethylene-methyl acrylate do not release acetic acid and may be processed to higher temperatures, but they generally show lower polarity per unit comonomer and different tackifier compatibility. Compared to amorphous polyalphaolefins, EVA-based compounds provide higher room-temperature cohesive strength but narrower open time and a steeper viscosity-temperature curve.

ELVAX CM4875 is let down into candle waxes, paraffin blends, and investment casting patterns. At 2–10 wt% addition, it reduces brittleness, improves surface gloss, and increases adhesion to wick and paperboard; above 15 wt% addition, melt viscosity increases and may require reformulation of the wick stand-up additive. The polymer also functions as a carrier resin for colour masterbatch and as a modifier in polyethylene cable compounds to increase environmental stress-crack resistance and filler acceptance. In these systems, the key mixing variable is the viscosity ratio between the EVA phase and the host polyethylene phase. When the viscosity ratio exceeds 3:1, dispersion quality can decline in a single-screw extruder, and a corotating twin-screw extruder with side feeding or a pre-dispersed batch is required.

Compared with low-VA grades used in film and profile extrusion, ELVAX CM4875 has a lower crystalline modulus and greater polar fraction; compared with high-VA grades used in low-application-temperature adhesives, it has higher melt strength and better blocking resistance. Compared with ethylene-methyl acrylate and ethylene-butyl acrylate copolymers, EVA has higher hydrogen-bonding character but lower thermal stability and higher moisture sensitivity in the melt. These differences define the substitution logic in compounding plants when formulations are transferred between polymer bases.

When Acetic Acid Evolution Restricts Use Above 230°C

When processing conditions exceed 230°C, the EVA backbone degrades by deacetylation and main-chain scission; the released acetic acid attacks steel and aluminium equipment and can reduce the effectiveness of acid-neutralizing additives. The practical processing window for ELVAX CM4875 therefore remains below 230°C. If an application requires sustained temperatures above this limit, a maleic anhydride-modified polyethylene or an ethylene-alkyl acrylate copolymer is frequently substituted. The selection between ELVAX CM4875 and alternative chemistries is made on the basis of adhesion to polar substrates, thermal stability, elongation at break, and final-article food-contact requirements.

When crosslinkable compounds are formulated, ELVAX CM4875 can be thickened with organic peroxides such as dicumyl peroxide; the vinyl acetate comonomer alters peroxide half-life requirements and generates acetic acid during cure. Foamed crosslinked EVA is used in shoe midsoles, seals, and cushioning. Blowing agents such as azodicarbonamide are typically added at 2–5 phr and decompose near 200–210°C, creating a narrow processing window between peroxide initiation, blowing-agent decomposition, and EVA degradation. Batch-to-batch variance in EVA molecular weight and vinyl acetate content can shift this window; published data for this specific configuration is limited, and pilot-scale cure trials are required before production scale-up.

Regulatory status for food-contact applications is formulation-dependent. Unmodified ethylene vinyl acetate copolymers are listed in FDA 21 CFR 177.1350 for food-contact articles, subject to total extractives limitations and end-use restrictions. In the European Union, ethylene-vinyl acetate copolymers are authorised under Regulation (EU) No 10/2011; vinyl acetate monomer is assigned a specific migration limit of 12 mg/kg food simulant, with the overall migration limit of 10 mg/dm² for the finished plastic article. The neat resin does not contain intentionally added phthalates or heavy metals; certification under EU RoHS 2011/65/EU is article-dependent. REACH compliance under Regulation (EC) No 1907/2006 requires confirmation that no substance of very high concern is present above 0.1% w/w in the supplied resin.

These statements are not self-standing certificates; final compliance is the responsibility of the converter and requires testing of the finished article under its specific conditions of use.