SINOPEC EVA 155

SINOPEC EVA 155 is an ethylene–vinyl acetate copolymer grade identified by a nominal vinyl acetate content of 15 wt% and a melt mass-flow rate of 5 g/10 min at 190 °C/2.16 kg when tested according to ISO 1133-1:2022 or ASTM D1238. The grade is supplied as translucent pellets with a density near 0.937 g/cm³ measured according to ISO 1183-1:2019 or ASTM D1505. The designation 155 is read as nominal 15 wt% vinyl acetate and nominal 5 g/10 min melt flow; because this is a sales-grade notation rather than a lot-specific certificate, batch values should be confirmed against the certificate of analysis. Representative grade-sheet values for tensile strength at break are not less than 15 MPa, and elongation at break is not less than 650%, when measured on 2 mm compression-moulded plaques according to ISO 527-2 or ASTM D638-14. The melt peak is commonly reported near 90 °C under ISO 11357-3, and the Vicat softening temperature is near 64 °C under ISO 306/A50. These values place SINOPEC EVA 155 between low-VA EVA extrusion grades and high-VA elastomeric EVA grades used for adhesives and sealants.

The combination of 15 wt% vinyl acetate comonomer and 5 g/10 min melt flow imparts moderate polarity, reduced crystallinity, and lower flexural modulus relative to LDPE. The resin is typically formulated with an antioxidant package that supports melt processing up to 210 °C; however, vinyl acetate repeat units undergo thermal deacetylation if the melt is held at elevated temperature for excessive residence time. Pellets should be stored below 40 °C away from direct sunlight and strong oxidizing agents. When bags are opened under relative humidity above 60%, pre-drying at 60–70 °C for 2–4 h with a desiccant dryer at a dew point of -40 °C is a standard moisture-control measure. The material should not be melt blended with strong Lewis acid residues or untreated acidic filler systems, because acid catalysis can accelerate deacetylation and generate acetic acid at lower melt temperatures.

What Limits the Processing Window for SINOPEC EVA 155 at Elevated Shear Rates?

Thermal degradation is the dominant process limit. In continuous extrusion, the practical melt-temperature ceiling is 210 °C; thermogravimetric analysis under ISO 11358-1 typically shows measurable mass loss near 230 °C. On a 40 mm single-screw blown-film line with L/D 30:1 and a barrier screw, a barrel profile of 150 °C, 160 °C, 170 °C, 180 °C, and 190 °C usually produces a melt temperature of 195–205 °C. Screw speeds above 120 min⁻¹ can generate shear heating greater than 10 °C per zone and push the melt above the ceiling; below 170 °C, homogenization of masterbatch and pressure stability can become marginal. For foam extrusion containing azodicarbonamide, the decomposition onset near 205 °C narrows the melt-temperature window to approximately ±5 °C. This is a critical threshold because gas evolution rate and cell-size distribution are sensitive to small temperature differences.

Venting is recommended for twin-screw compounding. A vacuum level of -0.08 MPa at the devolatilisation port can remove residual moisture and trace acetic acid. Stagnant melt should not remain in the barrel for more than 5 min at 190 °C; wall-adherent resin can discolour and contaminate subsequent material. Capillary rheometry according to ISO 11443 is advised when the grade is used in high-shear operations such as thin-wall injection moulding, because the MFR value alone does not define shear-thinning behaviour. In masterbatch carrier applications, the polar vinyl acetate groups reduce the need for external wetting agents; however, the lower zero-shear viscosity relative to EVA 14-2 requires screw profiles with greater dispersive mixing length rather than increased barrel temperature.

Film, Foam, and Injection Moulding Operations with Equipment-Specific Settings

Blown film operations using SINOPEC EVA 155 typically employ a die gap of 0.8–1.2 mm and a blow-up ratio of 2.0–2.5:1. The 5 g/10 min MFR reduces screw torque relative to 2 g/10 min EVA 14-2 on the same extruder, but melt strength is lower, and bubble instability may appear at blow-up ratios above 3.0:1 unless 10–20 wt% LDPE or EVA 14-2 is added. Haze of 50 µm film measured by ASTM D1003 is generally below 8%; water vapour transmission rate measured by ASTM F1249 at 38 °C/90% RH is higher than LDPE because of the polar comonomer. Sealing performance is evaluated with a heat-seal strength of 10 N/15 mm as a common acceptance target; SINOPEC EVA 155 requires a sealing jaw temperature 5–10 °C higher than EVA 18-3 but exhibits better hot-tack stiffness and lower blocking after 24 h at 40 °C.

Foam extrusion with azodicarbonamide at 1.5–3.0 phr requires melt temperatures of 180–200 °C. The lower melt strength of EVA 155 relative to EVA 14-2 makes closed-cell foam below 0.15 g/cm³ difficult without crosslinking. Dicumyl peroxide at 0.5–1.0 phr or blending with 20–30 wt% EVA 14-2 increases strain hardening and reduces cell coalescence. Compression set after 24 h at 50 °C according to ISO 815-1 is typically below 60% only for crosslinked formulations; non-crosslinked formulations may exceed that value and should be tested under the intended load.

Injection moulding uses melt temperatures of 180–200 °C and mould temperatures of 20–40 °C. Shrinkage measured on 2 mm plaques according to ISO 294-4 is typically 1.0–1.5%. Mould design should use draft angles above 1° because the low Shore D hardness can cause ejector-pin deformation. The lower melt viscosity permits filling of thin sections at lower injection pressure than EVA 14-2, but hold-pressure time should be extended to reduce sink marks in thick sections. Clamp force calculations should use the lower viscosity rather than generic LDPE data.

When SINOPEC EVA 155 Substitutes for EVA 14-2 or EVA 18-3 in Existing Tooling

When SINOPEC EVA 155 replaces EVA 14-2 in an existing foam line without screw-speed adjustment, the higher MFR reduces viscous dissipation and can lower melt temperature by 3–5 °C at identical barrel set points. That temperature shift may delay azodicarbonamide decomposition and alter cell-size distribution; increasing die temperature by 5 °C or reducing screw speed by 10–15% is usually required to maintain closed-cell morphology. Conversely, replacing EVA 18-3 with EVA 155 raises crystallinity and stiffness, which can improve surface hardness but reduces low-temperature flexibility and shifts heat-seal initiation upward by 5–10 °C. Dynamic mechanical analysis according to ISO 6721-1 shows that the β-relaxation tan δ peak for EVA 155 is narrower than for EVA 18-3; published data for this specific configuration is limited, so comparative testing on the final formulation is required before tooling modification.

Representative comparison with adjacent Sinopec grades is provided below. The values are drawn from sales-grade documentation and are not a substitute for lot-specific certificates; users should verify all values before qualification.

The primary processing distinction between SINOPEC EVA 155 and EVA 14-2 is the melt-flow difference: EVA 155 produces lower head pressure and enables longer flow length in injection moulding, while EVA 14-2 provides better bubble stability at high blow-up ratios and higher melt strength for uncrosslinked foam. EVA 18-3 offers higher VA content, lower Vicat softening temperature, and greater elastic recovery, but also higher surface tack and lower stiffness. SINOPEC EVA 155 is therefore specified when moderate polarity, a mid-range melt flow of 5 g/10 min, and a melt-temperature ceiling of 210 °C are acceptable process boundaries; applications outside these limits should use EVA 14-2 for melt strength or EVA 18-3 for sealing and flexibility.