LG EVA 28150 Copolímero de acetato de vinilo de etileno

LG EVA 28150 is an ethylene-vinyl acetate copolymer supplied as free-flowing pellets for hot-melt adhesive compounding, wax modification, and polyolefin blend adjustment. The product designation is commonly parsed as 28 wt% vinyl acetate comonomer and 150 g/10 min melt flow rate, measured under ASTM D1238 or ISO 1133-1:2022 at 190 °C with 2.16 kg load. The vinyl acetate content is expressed on a weight basis rather than a mole basis; a 28 wt% acetate level corresponds to a lower mole fraction of comonomer and therefore produces a specific combination of crystalline disruption, melt rheology, and surface polarity. The copolymer is intended for low-to-moderate-temperature melt processing and is not positioned as a load-bearing structural grade. Major application areas include packaging hot melts, bookbinding adhesives, adhesive sticks, wax-based coating modification, and selected polyolefin compatibilisation. Because this product combines high vinyl acetate content with a high melt flow index, it differs substantially from low-vinyl-acetate extrusion grades in modulus, melting point, thermal stability, and substrate wetting behaviour.

The following table presents class-typical physical property ranges for high-vinyl-acetate EVA copolymers with nominal melt flow rates near 150 g/10 min. These values are drawn from public polymer reference data and typical supplier technical literature for this product class; they are not a guaranteed release specification. Exact values for LG EVA 28150 must be taken from the manufacturer’s certificate of analysis and current product datasheet.

At 28 wt% vinyl acetate, the polyethylene crystal lattice is disrupted to such an extent that the melting endotherm is broad and shifted down to between 68 °C and 82 °C under ISO 11357-3. The degree of crystallinity inferred from melt enthalpy is frequently only 15–25%, compared with 35–50% for low-density polyethylene. This reduction in crystallinity lowers the modulus, yield point, and heat seal initiation temperature, while increasing optical clarity, flexibility, and the diffusion coefficient of gases and moisture. For the compounder, heating the material above 90–100 °C is usually sufficient to obtain a low-viscosity melt that can wet paper, aluminium, and corona-treated polyester; for LDPE, comparable melt wetting requires a considerably higher temperature. The product is therefore used where low-temperature application and rapid surface coverage are more important than creep resistance or load-bearing capacity.

What separates a 28 wt% vinyl acetate grade from low-VA extrusion copolymers?

The principal difference is a shift from semicrystalline rigidity to amorphous rubber-like behaviour. A low-vinyl-acetate EVA with 18 wt% comonomer retains a tensile modulus in the region of 40–70 MPa under ISO 527-2, whereas the 28 wt% high-melt-flow product typically falls below 20 MPa. The higher vinyl acetate content also increases the copolymer density to 0.945–0.957 g/cm³, raises the permeability to oxygen and water vapour, and reduces resistance to hydrocarbon oils. In hot-melt adhesives, these changes are directionally favourable for adhesion to polar substrates because the vinyl acetate carbonyl groups interact with hydroxy and ester functionality present in paper, rosin esters, and corona-treated films. In moulded or extruded parts, however, the same changes reduce temperature resistance and increase the risk of surface tackiness at ambient temperature.

In compounding practice, the difference in melt flow rate is often more important than the difference in vinyl acetate content alone. The high melt flow rate of LG EVA 28150 allows it to be incorporated into a heated mixer at relatively low torque and to distribute itself around wax and tackifier particles quickly. However, this same low viscosity reduces the ability of the melt to build pressure in a single-screw extruder or to form a stable bubble in blown-film extrusion. Production experience on a 40:1 L/D co-rotating twin-screw extruder at screw speeds of 200–300 rpm shows that the material melts early in the screw and can be conveyed with low specific mechanical energy input; the limiting factor is not plastication but the need to keep the melt temperature below the deacetylation threshold. In open mixer operations, the product can adhere to cold metal surfaces if condensation is present, and cleaning cycles with warm solvent or polymer purging are often required.

Thermal degradation boundary and acetic acid release

The most severe processing limitation is thermal deacetylation of the vinyl acetate units. Under inert gas, thermogravimetric analysis of high-vinyl-acetate EVA at a heating rate of 10 °C/min generally shows initial mass loss between 220 °C and 250 °C, but in melt processing the practical ceiling is lower because shear and dissolved oxygen accelerate degradation. At melt temperatures above 200 °C, acetic acid is evolved as a gas and the melt becomes acidic. This causes a characteristic pungent odour, gel formation, discoloration from light amber to brown, and pressure fluctuation at the die. Stainless steel construction is recommended for mixing tanks, vent lines, and condensation traps because the acidic condensate corrodes carbon steel. The most reliable processing window on continuous compounding lines is 150–180 °C at the melt thermocouple, with atmospheric venting before vacuum devolatilisation at −0.06 MPa to −0.08 MPa gauge. Pre-drying is necessary at 70–80 °C for 2–4 h when pellets have been stored at relative humidity above 60%. Dried moisture content should be below 0.05 wt% as measured by Karl Fischer titration before feeding to a melt pump or extruder.

The high vinyl acetate content also means that the polymer should not be mixed with strongly acidic additives, certain Lewis acids, or materials that release free radicals at melt temperature, because these accelerate deacetylation and gel formation. The product is unlikely to be adequately stabilised for repeated high-temperature regrind cycles; regrind addition should be limited to 10–20 wt% unless thermal stability trials demonstrate otherwise. Long residence times above 180 °C, even with a nitrogen blanket, shift the molecular weight distribution and increase the amount of acetic acid trapped in the melt. Vacuum venting and wiped-film devolatilisation are preferred when low-volatile adhesive compounds are specified.

When a 150 g/10 min melt flow rate dictates hot-melt rheology

A melt flow rate of 150 g/10 min places this material in the low-viscosity region of EVA grades. In hot-melt adhesive compounding, the final application viscosity at 180 °C is usually adjusted with wax and tackifier to between 500 mPa·s and 5,000 mPa·s as measured by ASTM D3236. The EVA contributes to cohesive strength and substrate adhesion, but its low molecular weight means that it cannot provide high peel strength at elevated temperatures. For packaging adhesives, opening time and set speed are controlled by the wax phase and by the crystallisation rate of the formulation; the EVA mainly provides flexibility, shock resistance, and adhesion to paper and board. In bookbinding, the product can be formulated into side-glue and spine-glue systems where moderate open time and good flexibility at low temperature are required. In adhesive sticks, the high melt flow permits a smooth application but requires sufficient wax content to avoid tackiness at room temperature.

The same rheological character limits other conversion routes. The melt strength is too low for blown-film extrusion; attempts to run the pure product on a conventional film tower generally produce bubble instability above linear speeds of 5–10 m/min. In flat-die coating, the low viscosity can allow wetting on lightweight substrates, but edge neck-in and die drool increase unless the die gap is kept below 200–300 μm and the air gap is minimised. Injection moulding is technically possible but seldom used because the product is too soft for structural parts; when used as an impact modifier or adhesion promoter in polyolefin compounds, addition levels of 5–15 wt% are more typical. Above 20 wt%, the final compound may lose heat deflection temperature and may require reformulation of the stabiliser package to account for the EVA phase.

Regulatory compliance must be assessed on the finished article rather than on the base polymer alone. Ethylene-vinyl acetate copolymers may fall under 21 CFR 177.1350 in food-contact applications, subject to the end-use temperature and food-type limitations in the regulation. In Europe, plastic food-contact materials are controlled under Commission Regulation (EU) No 10/2011; the specific migration of vinyl acetate and the overall migration of the finished material must be measured. The base resin is outside the scope of RoHS 2011/65/EU restrictions, but the final compound may include additives that are restricted, such as certain phthalates or heat stabilisers. Thermal decomposition products of the copolymer include acetic acid and carbon monoxide; local exhaust ventilation is required in melt processing, and occupational exposure limits for acetic acid should be verified for the production area. If replacing a lower-VA EVA with LG EVA 28150 in an existing hot-melt formulation, the wax content often must be reduced by 3–8 wt% to maintain equivalent melt viscosity, and the tackifier may need to be shifted toward a lower softening point to avoid phase separation. These adjustments are formulation-specific and must be confirmed by pilot-scale coating trials on the actual substrate line.