LG EVA 28025 Copolímero de acetato de vinilo de etileno

Injection-molding of EVA footwear midsoles based on LG EVA 28025 is conducted with the polymer as the principal matrix because the nominal melt index of 25 g/10 min (ASTM D1238, 190°C, 2.16 kg) permits complete filling of multi-cavity molds while the 28 wt% vinyl acetate content depresses crystallinity sufficiently to improve blowing agent gas solubility and reduce melt stiffness. Pre-drying of unfilled resin is usually unnecessary when moisture is below 0.05 wt%; however, compounds containing hygroscopic fillers are dried at 60–70°C for 4–6 h when storage relative humidity exceeds 60%. A typical midsole formulation comprises EVA 28025, azodicarbonamide at 1.2–2.8 phr, zinc oxide at 0.5–1.2 phr, zinc stearate at 0.3–0.8 phr, optional peroxide for crosslinked variants, and pigment masterbatch. On a reciprocating-screw injection molding machine with clamp force above 180 metric tons, the barrel profile is set from 85°C in the feed zone to 170–175°C at the nozzle; actual melt temperature measured by an inserted thermocouple should not exceed 178°C to avoid premature gas evolution. Mold temperature is held at 165–180°C, and the shot volume is limited to 75–85% of the cavity volume so that expansion pressure does not force the parting line open. Density is checked by water immersion or according to ISO 2781, with foamed midsoles typically falling between 0.18 g/cm³ and 0.25 g/cm³ depending on blowing agent loading and mold packing. Hardness is measured with an Asker C or Shore A durometer per ASTM D2240; foam midsoles from 28 wt% VA EVA typically land in the 45–60 Asker C range, but exact values depend on density, blowing agent rate and crosslinker addition. Rebound resilience is tested per ASTM D2632 or ISO 8307, and compression set after 50% deflection for 6 h at 50°C is reported under ASTM D395 method B. On factory lines, the main failure mode is cell coalescence near the injection gate caused by shear heating; this is controlled by maintaining the gate diameter above 1.5 mm and using a delayed gas release activator that shifts azodicarbonamide decomposition to 150–170°C.

Why Does 28 wt% Vinyl Acetate Content Narrow the Peroxide Cure Window in EVA Foam Sheet?

Crosslinked EVA foam sheet made from LG EVA 28025 uses dicumyl peroxide as the free-radical initiator because the 28 wt% vinyl acetate content reduces crystalline regions and allows more uniform peroxide dispersion compared with lower-VA grades. The peroxide cure window is bounded by dicumyl peroxide half-life data: 10 h half-life at approximately 117°C and 1 h half-life near 135°C, which means mixing operations are kept below 110°C to prevent scorch while cure and expansion are carried out at 150–170°C in a hydraulic press or continuous hot-air oven. In two-roll mill compounding, the front roll is set to 95–105°C and the back roll to 90–100°C, with dicumyl peroxide added only after the EVA has banded and fillers are dispersed. The cure curve is monitored with a moving die rheometer according to ASTM D5289 or ISO 6502, using torque values to determine t_s2 and t₉₀; for EVA foam compounds with 28 wt% VA, t₉₀ at 160°C frequently falls in the 4–7 min range depending on peroxide loading. Expansion is produced by azodicarbonamide or 4,4′-oxybis(benzenesulfonyl hydrazide) at 2–4 phr, and the decomposition gas release must overlap with the peroxide cure torque rise; if gas evolution peaks before crosslink network formation, cell coalescence occurs and closed-cell content declines. Crosslinked foam sheet with thickness from 10 mm to 30 mm is typically produced by compression molding at 150–160°C for 15–25 min, followed by cooling under pressure to stabilize cell geometry. The vinyl acetate content supports lower modulus and higher elongation than low-VA EVA, and the crosslinked foam is tested for compression set under ASTM D395 method B, density under ISO 845, and tensile strength under ISO 527-2/5A. Published data for formulations based specifically on LG EVA 28025 in crosslinked foam sheet is limited; the cure and expansion parameters above are derived from standard EVA foam compounding practice and should be confirmed by rheometer and pilot-press trials on the actual formulation.

Hot Melt Adhesive Viscosity Stability and Aliphatic Tackifier Resin Compatibility Limits

Hot melt adhesives formulated with LG EVA 28025 are produced in jacketed sigma-blade mixers or vertical hot melt processors at 140–160°C under a nitrogen blanket to limit thermal oxidation. The melt index of 25 g/10 min (ASTM D1238, 190°C, 2.16 kg) places the grade in the medium-viscosity range for EVA-based hot melts, suitable for slot-die coating and multi-bead application rather than high-speed spray unless viscosity modifiers are used. A typical starting formulation includes 30–40 wt% EVA, 30–45 wt% hydrogenated rosin ester or C5/C9 aliphatic-aromatic tackifier, 15–25 wt% Fischer-Tropsch or paraffin wax, and 0.5–1.0 wt% hindered phenolic antioxidant. The 28 wt% vinyl acetate content increases polarity and improves adhesion to paper, corrugated board, and polar polymer films compared with lower-VA grades, but it also increases surface tension and can reduce compatibility with highly aliphatic waxes, producing haze or phase separation at wax loadings above 25 wt%. Viscosity stability is evaluated with a Brookfield thermosel viscometer at 180°C over 24 h; an increase above 15% typically indicates inadequate antioxidant level or excessive processing temperature. Peel adhesion is tested under ASTM D1876 T-peel or PSTC 101 on aluminum and corrugated substrates, while open time and set time are measured by controlled bond formation under defined temperature and humidity. For food packaging applications, the finished adhesive must be evaluated under FDA 21 CFR 175.105 for indirect food contact or specific end-use conditions. High VA content also increases low-temperature flexibility; adhesives based on 28 wt% VA EVA typically maintain fiber tear on corrugated board at -10°C to -20°C, but exact values depend on tackifier type and wax melting point. Thermal degradation in hot melt processing is monitored by Gardner color and viscosity drift, and processing temperatures must not exceed 180°C for prolonged hold times because the acetate group can undergo acid-catalyzed elimination at elevated temperatures, generating acetic acid odor and corroding applicator tooling.

In halogen-free flame-retardant cable sheathing compounds, LG EVA 28025 is selected as the base resin because the 28 wt% vinyl acetate content provides the polar ester functionality needed for adhesion to alumina trihydrate and magnesium dihydroxide surfaces at filler loadings between 55 wt% and 65 wt%. The melt index of 25 g/10 min (ASTM D1238) permits extrusion on a single-screw compounding line with L/D 30:1 to 36:1 at barrel temperatures from 120°C to 165°C, but the processing window is constrained by alumina trihydrate decomposition onset near 180°C, so actual melt temperatures are held below 170°C and screw speed is limited to avoid excessive shear heating. Coupling agents such as vinylsilane or aminosilane are added at 0.5–1.5 wt% relative to filler to reduce viscosity and improve tensile elongation. A typical formulation for cable sheathing includes EVA at 35–40 wt%, ATH or MDH at 55–60 wt%, zinc borate at 2–5 phr, antioxidant at 0.3–0.8 phr, and process aid at 1–3 phr. The compound is pelletized after a co-rotating intermeshing twin-screw extruder with vacuum devolatilization, and the pellets are then extrusion-sheathed onto cable cores using a crosshead die with a pressure screen pack. Mechanical and fire performance are measured according to IEC 60754-1/2 for acid gas generation, IEC 60684-3 for sheathing, ASTM D2863 or ISO 4589-2 for limited oxygen index, and ISO 527-2 for tensile properties. The inclusion of 28 wt% VA stabilizes the char layer during combustion better than low-VA grades, but it also reduces the heat deformation temperature; therefore load-bearing cable sheaths may require radiation crosslinking or silane grafting. For compounds requiring low-temperature flexibility, EVA 28025 is blended with linear low-density polyethylene or ethylene-octene elastomer at 10–20 phr to improve impact resistance, but such blending reduces limiting oxygen index and requires reformulation of the flame-retardant package.

Masterbatch carrier performance is governed by pigment wetting and letdown ratio

Color and additive masterbatches based on LG EVA 28025 are produced when the target letdown resin is EVA foam, EVA film, or polar polyolefin compounds that require carrier compatibility and high pigment dispersion. The carrier resin melt index of 25 g/10 min is high enough to wet pigment surfaces in a twin-screw extruder at 120–160°C, and the vinyl acetate content of 28 wt% reduces melt surface tension, which improves pigment wetting and reduces agglomerate formation. Masterbatches for EVA foam midsoles frequently use organic azo pigments or carbon black at 15–40 wt%, dispersed in a co-rotating twin-screw extruder with L/D 40:1 and distributive mixing elements, followed by strand pelletizing. Because the carrier and the final EVA compound share the same polymer backbone, letdown ratios of 2–5 wt% do not create localized melting point differences or interfacial haze in the finished part. For color concentrates used in packaging film, the masterbatch must comply with the relevant food contact status of the finished film; EVA 28025 can be evaluated under FDA 21 CFR 177.1350 as an ethylene-vinyl acetate copolymer, but the final migration limits must be confirmed for the intended food type and use condition. Dispersion quality is measured by pressure rise on a screen pack according to DIN EN 13900-5 or by film surface defect count; a well-dispersed masterbatch at 40 wt% carbon black should not increase backpressure by more than 5 MPa over the base resin after 20 min of extrusion. Process oil is generally omitted to avoid bleeding in the finished foam part, and the carrier relies on the high VA content and melt index for internal lubrication.

When EVA 28025 Is Used to Modify Bitumen Waterproofing Membranes

Bitumen modification with EVA 28025 is carried out in high-shear mixer tanks at 160–180°C for 30–60 min, with the EVA added at 3–6 wt% relative to bitumen to raise the softening point and reduce low-temperature brittleness. The polymer melt index of 25 g/10 min allows rapid dispersion in oxidized bitumen, but the high vinyl acetate content of 28 wt% increases polarity and can accelerate phase separation compared with lower-VA grades if shear is removed. Storage stability is tested by keeping the modified bitumen at 160°C for 72 h in a vertical tube and measuring the difference in softening point between the top and bottom sections; a difference above 5°C indicates polymer-rich phase segregation. The modified bitumen is calendered into a reinforced membrane with polyester or glass-fiber mat, and low-temperature flexibility is assessed by bending a specimen at -10°C to -20°C around a mandrel without cracking per ASTM D5147 or EN 1109. EVA 28025 contributes resistance to rutting at elevated service temperatures, and the compound is evaluated by dynamic shear rheometer under ASTM D7175 for performance grade or softening point under ASTM D36. Because the vinyl acetate group is sensitive to prolonged thermal exposure, the mixing tank must be purged with nitrogen and residence time at 180°C should not exceed 90 min; otherwise viscosity increases and gel particles can appear in the membrane. Published data for this specific LG grade in bitumen waterproofing is limited, and trial quantities should be evaluated against the bitumen source because asphaltene content and aromatic oil fraction control compatibility.