LG EVA 28025 resina de copolímero EVA,28% VA,25 MI,Grado adesivo de fusão quente

LG EVA 28025 is a pelletized ethylene-vinyl acetate copolymer resin supplied by LG Chem and designated as a hot melt adhesive grade. The product designation identifies two primary specification points: a vinyl acetate comonomer content of 28 wt% and a melt index of 25 g/10 min measured at 190°C under 2.16 kg load following ASTM D1238-20 or ISO 1133-1:2022. Nominal density is 0.95 g/cm³ at 23°C per ASTM D792-20; vinyl acetate content is determined by Fourier transform infrared spectroscopy according to ASTM D5594-18a. The ethylene-vinyl acetate copolymer identity corresponds to CAS 24937-78-8. The material is not a finished adhesive; it is a base polymer for compounding with tackifiers, waxes, and antioxidants before application. As a hot melt adhesive base, it provides polar adhesion to cellulose, aluminium foil, paperboard, wood fiber, and surface-oxidized metals, while the 25 g/10 min melt index supports low-viscosity handling in high-speed application equipment.

Within the ethylene-vinyl acetate copolymer family, vinyl acetate content is the primary regulator of crystallinity and polarity. At 28 wt% VA, the polyethylene crystalline lattice is disrupted sufficiently to lower the softening range and increase low-temperature flexibility relative to low-VA grades. The carbonyl groups of the vinyl acetate units provide dipolar and hydrogen-bond-acceptor interactions at the adhesive interface, increasing peel adhesion to polar substrates. The 25 g/10 min melt index is a single-point inverse viscosity indicator and does not define the complete shear-thinning curve. Capillary rheometry according to ASTM D3835 or ISO 11443 is needed to generate viscosity data for gear-pump sizing and nozzle pressure-drop calculations. The grade occupies a middle position between low-VA EVA used in heat-resistant packaging and high-VA EVA used for low-temperature film and flexible packaging applications.

Why 28 wt% Vinyl Acetate Shifts Adhesion, Flexibility, and Thermal Response

The 28 wt% VA level is high enough to create a measurable polar surface contribution but low enough to retain compatibility with paraffin wax and hydrocarbon tackifiers in conventional hot melt formulations. If VA is increased above approximately 33 wt%, formulation compatibility with nonpolar waxes declines and tackifier selection must shift toward polar rosin esters or terpene phenolics. At VA below 18–19 wt%, adhesion to polar substrates is lower and the polymer is more crystalline. The 28 wt% grade therefore provides a balance for packaging and bookbinding formulations where both wet-out and cold-flex are required. Published mechanical property data for EVA copolymers in this VA range indicate tensile strength values generally between 10 MPa and 20 MPa and elongation at break above 600%; however, these are literature-class values and must not replace the grade-specific supplier datasheet. Hardness, tensile strength, and elongation are controlled by the supplier and are reported in the certificate of analysis.

Thermal behaviour of the base polymer influences hot melt set speed and heat resistance. The crystalline melting peak is suppressed relative to low-VA EVA; differential scanning calorimetry of 28 wt% VA grades generally shows a broad melting endotherm in the 65°C to 80°C range, depending on thermal history. A broad melting endotherm contributes to a wide softening range and allows the adhesive film to remain flexible after solidification but lowers upper service temperature under load. The base resin alone is not formulated for load-bearing conditions above 60°C.

Table 1 summarizes the nominal base resin characteristics relevant to incoming inspection. Values are nominal, not specification limits; the supplier certificate of analysis is the governing document.

These values form the minimum incoming QC profile for hot melt compounders. Melt index should be rechecked after drying because thermal history and moisture can shift flow. Vinyl acetate content should be checked by FTIR when blending with other EVA grades to maintain final adhesive polarity. Density is used for weight-to-volume conversion in continuous gravimetric feed systems. Absence of these QC steps can produce lot-to-lot viscosity shifts in the final adhesive.

Tackifier compatibility with 28 wt% VA EVA is governed by polarity match. Rosin ester tackifiers are commonly used in packaging and bookbinding because their polar ester groups interact with the vinyl acetate carbonyls. Hydrocarbon tackifiers may reduce viscosity and improve wet-out but can lower final adhesion if used above the compatibility limit. Paraffin wax reduces melt viscosity and sets fast but can bloom on the adhesive surface if wax concentration is too high or VA content exceeds polarity compatibility. Fischer-Tropsch wax provides higher heat resistance than paraffin wax but may require a higher processing temperature. The correct tackifier/wax ratio is formulation-specific and is validated by peel, shear, and hot tack testing using ASTM D1876 for T-peel, ASTM D3163 or ASTM D1002 for shear, and ASTM D4498 for heat fail temperature.

Open time and set speed are not fixed by the base polymer alone. The 25 g/10 min melt index contributes to short open time and rapid set compared with lower MI grades, but wax type and concentration dominate. For manual assembly, tackifiers with higher softening points and lower wax content extend open time. For high-speed carton sealing, the formulation typically contains enough wax to define a fast set point. These values are measured in production trials; published data for this specific configuration is limited.

Processing Boundaries in Hot Melt Compounding

Thermal processing of EVA requires strict temperature control because vinyl acetate units degrade by deacetylation. The degradation reaction releases acetic acid and creates unsaturation along the polymer chain. In bulk hot melt tanks, the melt temperature is typically maintained at 160–180°C; excursions above 200°C for more than a short period accelerate viscosity drift, colour change, and char formation. Contact surfaces in tanks, pumps, hoses, and application heads are preferably 316 stainless steel because acetic acid is corrosive to carbon steel. Nitrogen blanketing is used in continuous operations to limit oxidative degradation. Dead-leg fittings and stagnant zones should be eliminated because char formed in stagnant hot melt can slough into the adhesive stream and plug nozzles.

For compounding, a jacketed sigma-blade mixer with a working capacity of 50–200 L and blade speeds of 20–40 rpm is common for batch hot melt production. Alternatively, a corotating twin-screw extruder with L/D 40 and a temperature profile from 120°C to 160°C is used when high filler loading or continuous pelletization is required. The base resin is melted first in the mixer before tackifier and wax addition; loading hot tackifier into unmelted polymer can cause non-uniform plasticization and local overheating.

Moisture uptake is low, but condensation on cold pellets can introduce surface moisture. When bags are opened in humid conditions or pellets are brought into a warm production area from cold storage, drying at 60–70°C for 2–3 hours in a desiccant or hot-air dryer is recommended. Drying above 80°C risks pellet blocking and pre-thermal degradation. Surface moisture produces bubbles in slot die coatings and can cause intermittent flow from hot melt guns.

Because the melt index is a single-point test, it should not be used alone to set gear pump speed. A Brookfield viscometer at 180°C with a Thermosel spindle is used for QC of formulated hot melt; viscosity drift from the established control band indicates degradation or batch segregation. Capillary rheometry per ASTM D3835 provides the shear viscosity curve from 100 s⁻¹ to 10,000 s⁻¹, covering the shear rates encountered in nozzle and slot-die application. The absence of such data for a specific formulation should be noted in the purchase specification and resolved before high-speed production.

During compounding, hindered phenolic antioxidant is typically added at 0.5–1.0 wt% of total formulation to protect the molten adhesive during hold times at temperature. The antioxidant package should be validated by accelerated ageing, such as 72 h at 180°C with periodic viscosity measurement. The base resin alone is not stabilized for prolonged hot melt residence. Application equipment for packaging hot melts includes gear-pump units with volumetric outputs from 10 kg/h to 100 kg/h, heated hoses, and automatic nozzles with orifice diameters between 0.2 mm and 0.5 mm. Pressure drop is calculated from capillary rheometry data, not from melt index alone. Oil-heated hoses above 180°C can accelerate degradation and increase char formation; hose temperature should therefore be interlocked with tank temperature.

When Lower Melt Index or Lower Vinyl Acetate Grades Should Be Considered Instead

Selection between LG EVA 28025 and other EVA grades is based on the balance between adhesion, melt viscosity, melt strength, and heat resistance. The following table gives qualitative comparisons for three polymer configurations. The comparisons are based on general EVA structure-property relationships and are not finished-adhesive performance data; final selection requires formulation-specific testing.

The 28 wt% VA/25 g/10 min combination is preferred in high-speed packaging lines where the adhesive is applied through small nozzles and must wet the substrate quickly. If the line runs at moderate speed but the finished carton is stored in a hot vehicle or near a heat source, a lower MI grade may be substituted because higher molecular weight improves cohesive strength at elevated temperature. If the substrate is an untreated polyolefin film, changing VA content alone is usually insufficient; surface treatment or a different adhesive chemistry is required. A lower VA grade is selected when adhesion to polar substrates is less important and the formulation requires higher crystallinity, faster set, or improved heat resistance.

In non-packaging hot melt applications, the grade is used in furniture profile wrapping and edgebanding formulations where PVC, ABS, polyester, and paper foils are bonded to MDF or particleboard. The 28 wt% VA content improves adhesion to PVC and coated papers, while the 25 g/10 min melt index permits even distribution through narrow slot dies. Bookbinding side gluing and softcover casing-in use this grade when adhesion to coated paper and cold-flex are required. The low melt viscosity helps penetration into folded signatures, but the formulation must be adjusted to avoid bleedthrough on thin paper. For perfect binding requiring high spine pull strength, a higher-viscosity EVA or a blend is often required. Footwear assembly uses 28 wt% VA EVA hot melts for temporary bonding of insoles and for lamination. The resin retains flexibility at low temperature, but oil resistance and plasticizer resistance are limited. For oily leather or heavily plasticized PVC, a different polymer is required.

Compared with amorphous poly-alpha-olefin hot melts, LG EVA 28025 has higher polarity and generally better adhesion to cellulose but lower heat resistance and colour stability. Compared with polyamide hot melts, EVA provides lower cost and lower heat resistance. In automotive interior lamination, the base polymer may be used when low fogging and odour are not the primary requirements. Acetic acid released during thermal degradation can contribute to odour and corrosion; low-odour grades or polyolefin adhesives are sometimes preferred for closed compartments.

Regulatory compliance for LG EVA 28025 is end-use-dependent. For food packaging adhesives, assessment is typically made under FDA 21 CFR 175.105 when the adhesive is separated from food by a functional barrier, or under FDA 21 CFR 177.1350 for ethylene-vinyl acetate copolymers used in certain direct food contact articles. The appropriate section depends on food type, contact temperature, and migration limits. REACH registration status is established by the supplier for the base resin; the downstream formulator is responsible for SVHC assessment of the complete mixture. For electrical and electronic applications, the base resin may be evaluated under EU RoHS Directive 2011/65/EU for the restricted substances lead, cadmium, mercury, hexavalent chromium, PBB, and PBDE. A RoHS-compliant base resin does not automatically make the final hot melt compliant because tackifiers, waxes, stabilizers, and pigments must also be assessed. Users should obtain the supplier safety data sheet and regulatory data sheet before production.

On a high-speed corrugated case line using compressed-air spray application, the low melt viscosity of a 25 g/10 min base polymer allows a thin molten film to penetrate the top liner of clay-coated board. Compression for 0.5–1.0 s is often sufficient to produce fiber-tearing bonds when the formulation is correctly balanced. The 28 wt% VA content improves wet-out on the clay coating, but warehouse storage above 35°C may soften the bond; in such service a lower MI grade, a higher-melting wax, or a different tackifier system should be evaluated. Trial runs on the actual packaging line are required because line speed, board temperature, porosity, and compression dwell time cannot be simulated reliably in a laboratory lap-bond test alone.