SINOPEC EVA 155

SINOPEC EVA 155 is a nominal 15 wt% vinyl acetate ethylene copolymer with a melt flow rate of 5 g/10 min measured under ISO 1133-1:2022 at 190 °C/2.16 kg. The vinyl acetate comonomer reduces crystal lamellae thickness, lowers the melting range, and increases polarity compared with LDPE homopolymer, which sets downstream processing boundaries: the grade functions as a medium-viscosity base for crosslinked foam and filled cable compounds, while it appears as a high-viscosity modifier in cast film seal layers and as a low-flow carrier in additive masterbatches. In all subsequent scenarios, the relevant failure modes are gas permeability before gelation, screw torque in filled systems, backpressure in narrow dies, and surface tack during winding or ejection rather than ambient-temperature strength alone.

In crosslinked footwear midsole manufacturing, EVA 155 is normally compounded in a ram-type internal mixer with a first-stage fluxing temperature at 105–115 °C, then transferred to a two-roll mill at 80–95 °C for addition of dicumyl peroxide at 0.8–1.2 phr and azodicarbonamide at 3.0–5.0 phr. A representative compound includes zinc oxide at 2–4 phr, stearic acid at 0.5–1.0 phr, and calcium carbonate at 5–15 phr to control cell nucleation and demolding tack. The zinc oxide/stearic acid system activates nitrogen release from azodicarbonamide in the 160–180 °C zone, while the press cure step is run at 165–175 °C for 8–12 min so that dicumyl peroxide builds a covalent gel network during gas expansion. Because the 15 wt% vinyl acetate comonomer disrupts the polyethylene crystal lattice, EVA 155 permits lower apparent density at the same crosslinker dose than LDPE homopolymer; densities of 0.15–0.25 g/cm³ tested by ISO 845 are attainable, with Asker C hardness of 55–65 and tensile strength above 1.5 MPa by ISO 1798. The practical processing window is tighter than ±5 °C in the press cavity because the separation between peroxide cure onset and blowing-agent gas release controls cell size distribution; an overshoot of 5–7 °C produces surface pinholes and internal coalescence, while an undershoot leaves residual azodicarbonamide and anisotropic shrinkage after demolding. On multi-cavity production lines, batch-to-batch variance arises mainly from second-stage mill temperature drift above 90 °C and from uneven peroxide dispersion when dicumyl peroxide is charged together with fillers rather than pre-blended with the polymer phase. The formulation should avoid amine-based scorch inhibitors in the second stage because they can deplete peroxide activity and shift gel point beyond the press cycle tolerance. Finished footwear components must be evaluated under REACH Annex XVII restrictions on polycyclic aromatic hydrocarbons in the compounded matrix, but the base EVA 155 does not itself contain phthalate plasticizers.

What Drives the Filler Loading Ceiling in Low-Smoke Zero-Halogen Cable Sheathing Based on EVA 155?

Halogen-free cable sheathing uses EVA 155 as a base because the polar 15 wt% vinyl acetate repeat units wet precipitated magnesium hydroxide and ground alumina trihydrate surfaces more effectively than an equivalent low-density polyethylene, but this wetting advantage does not remove the practical loading ceiling imposed by tensile retention. To achieve oxygen index above 30 % under ISO 4589-2 and low acid gas emission under IEC 60754-1/2, typical formulations load magnesium hydroxide or alumina trihydrate at 60–70 wt% with zinc borate at 2–5 wt% and an organosilane such as vinyltrimethoxysilane at 0.5–1.0 wt%. On a co-rotating twin-screw extruder with L/D 40:1 and reverse kneading elements, the barrel profile is kept at 110–120 °C in the feed zone and 140–150 °C at the die head to prevent alumina trihydrate from releasing hydration water above 180–190 °C. The limiting variable is not flame performance but the elongation-at-break collapse as filler exceeds 70 wt%: tensile strength commonly falls to 10–14 MPa and elongation at break to below 150 % when measured by IEC 60811-501 or ASTM D638-14. EVA 155’s MFR of 5 g/10 min preserves melt strength during tube-on sheathing but raises torque in a fully filled compounding zone, so screw speed is normally reduced to 180–250 min⁻¹ and the main drive is sized with a service factor above 1.25. Published data for this specific grade in cable-grade formulations are limited; therefore full IEC 60332-1-2 flame spread, IEC 60754-2 acid gas, and low-smoke performance must be tested on the finished compound rather than inferred from base polymer datasheets. The compounding line must also avoid transition-metal stearates in the filler package because they can accelerate thermo-oxidative degradation of the ethylene segments during long extrusion campaigns and shift melt flow stability outside the production control limit.

Blending 10–30 wt% EVA 155 into an LLDPE-rich cast film seal layer reduces seal initiation temperature relative to unmodified LLDPE when measured as final seal strength under ASTM F88/F88M-15. The reduction is produced by the 15 wt% vinyl acetate comonomer disrupting crystal lamellae and broadening the melting endotherm, which permits a seal force above 2 N/25 mm at 95–105 °C for a typical 50 µm layer gauge. Extrusion uses a melt temperature of 220–240 °C, air gap 90–120 mm, and chill roll temperature 15–20 °C to prevent blocking and reduce surface haze. Because EVA 155 has MFR 5 g/10 min, replacement of more than 30 wt% LLDPE can raise head pressure in a wide die, so the die lip gap is generally held at 0.6–0.8 mm and line speed is reduced by 5–10 % against an all-LLDPE reference. The film should be stored below 30 °C and below 60 % relative humidity before slitting because the polar vinyl acetate groups increase surface tack and blocking tendency. For direct food contact seal layers, the finished film must comply with 21 CFR 177.1350 for ethylene-vinyl acetate copolymers and EU 10/2011 overall migration limit of 10 mg/dm²; the base EVA 155 alone does not guarantee finished-article compliance because specific tackifiers or slip additives in the seal layer can change migration behavior.

When EVA 155 Replaces Plasticized PVC in Low-Durometer Injection-Moulded Gaskets

Injection moulding of EVA 155 into low-durometer gaskets, suction cups, and handle sleeves is technically viable when the cavity design accounts for higher melt viscosity than typical plasticized PVC compounds. The recommended barrel temperature profile is 170–200 °C from feed to nozzle, with mould temperature at 10–30 °C to prevent surface tack and reduce ejection distortion. Because the MFR of 5 g/10 min requires higher injection pressure than an EVA with MFR 20–40 g/10 min, runners and gates are sized on the generous side: a cold runner gate for a 2 mm wall section is typically not less than 1.0–1.5 mm in thickness. The material’s semi-crystalline EVA matrix produces mould shrinkage in the range of 0.8–1.2 % depending on packing pressure and wall section, which must be compensated in tool design rather than by processing alone. Low-durometer parts can be ejected when the surface has cooled below 50 °C; forced ejection above that temperature may tear thin flash areas. The uncrosslinked thermoplastic matrix is not suited to continuous exposure above 70 °C under load without crosslinking because creep can occur. Published data for this specific grade in precision gasket applications is limited, so dimensional stability must be verified by ISO 294-3 and tensile set by ISO 2285 on the moulded part.

As a carrier resin in additive masterbatches, EVA 155 is used at 30–50 wt% of the total batch where the additive concentrate is 20–30 wt% and the balance is a lower-viscosity LDPE or EVA wax letdown carrier. The polar 15 wt% vinyl acetate fraction reduces polar-polar interfacial tension with silica-coated additives compared with an LDPE-only carrier, and antioxidant dispersion in the final film can be controlled by oxidation induction time measured in accordance with ISO 11357-6. The MFR of 5 g/10 min requires a twin-screw extruder with L/D 28:1–32:1 and a strand die temperature of 130–160 °C. The higher melt viscosity reduces strand breakage during pelletizing, which is an advantage for small-strand underwater pelletizers. Drying is not normally required unless the resin has been stored above 60 % relative humidity for more than 48 h, in which case surface moisture can cause pinholes in the strand. The processor should avoid formulating the masterbatch with free primary amine slip additives when the same masterbatch will later be let down into peroxide-crosslinked EVA foam, because the amine can interfere with peroxide curing and shift the gel time beyond the press cycle tolerance. When the masterbatch is used in polyolefin films, the final film must be re-evaluated under 21 CFR 177.1520 or EU 10/2011 because the carrier contributes to the overall polymer mass and affects migration test results.

Profile Extrusion and Cellular Gasket Lines Requiring Controlled Die Swell

EVA 155 can be extruded into solid and cellular profile gaskets through a single-screw extruder with a length-to-diameter ratio of 24:1–30:1 and a screw compression ratio of 2.5–3.0:1. For cellular profiles, a chemical blowing agent such as azodicarbonamide is pre-blended at 0.5–2.0 wt% and the barrel temperature is held at 130–165 °C to prevent premature gas formation before the die. The die swell of EVA 155 is lower than that of an LDPE with the same MFR because the vinyl acetate group reduces melt elasticity, but die design must still include a drawdown allowance of 5–10 % to compensate for extrudate shrinkage. Solid EVA 155 profiles from compression-moulded plaques with similar vinyl acetate content typically display tensile strength above 15 MPa and elongation at break above 600 % when tested by ISO 527-2 or ASTM D638-14, but values on extruded profiles are affected by machine-direction orientation and cooling rate. Process water or air cooling should bring the profile surface below 50 °C before haul-off to prevent deformation at the caterpillar belt. The grade should not be combined with high levels of rigid filler in a cellular profile because the filler increases melt viscosity and reduces gas retention, shifting apparent density upward; published industrial data for this specific configuration is limited and must be verified with a pilot trial on the target extrusion line.