SINOPEC EVA UE1925TS

SINOPEC EVA UE1925TS is an ethylene-vinyl acetate copolymer supplied by Sinopec under the UE1925TS sub-grade designation. The material is a high-pressure free-radical copolymer of ethylene and vinyl acetate, with CAS registry number 24937-78-8. Producer documentation for the UE1925TS grade gives a vinyl acetate content of 19 wt%, a melt mass-flow rate of 2.5 g/10 min at 190 °C under 2.16 kg load according to ISO 1133-1:2022, and a density of 0.938 g/cm³ according to ISO 1183-1:2019. Published mechanical values include tensile strength of 16.7 MPa and elongation at break of 750% when tested under ISO 527-2:2012 using type 5A specimens at 500 mm/min, with Shore A hardness near 84 according to ISO 868:2003. The grade is supplied in pellet form and is used in heat-seal webs, hot-melt adhesive compounding, foamed sheet, footwear components, and solar encapsulation films where the combination of melt flow and polar comonomer content controls substrate wetting and adhesion.

The practical effect of the 19 wt% vinyl acetate fraction is a measurable reduction in crystalline order compared with low-density polyethylene. Differential scanning calorimetry at 10 K/min heating rate according to ISO 11357-3:2018 typically shows a main melting endotherm near 84 °C and a glass transition in the region of -30 °C. These thermal transitions place heat-seal initiation for UE1925TS roughly 20–30 °C lower than that of LDPE. The TS suffix is producer-specific; the public technical bulletin does not fully disclose the additive-package difference from the UE1925 base grade, and published data for that precise formulation delta is limited.

What separates UE1925TS from ethylene-vinyl acetate grades with lower or higher comonomer content?

Comparison with adjacent EVA grades clarifies the position of UE1925TS. A lower-vinyl-acetate EVA retains greater polyethylene-like stiffness, lower cold-flow, and higher crystalline melting. A higher-vinyl-acetate EVA, such as a 28 wt% grade, exhibits stronger polar adhesion and greater low-temperature flexibility but lower heat resistance, greater surface blocking tendency, and higher melt tack. UE1925TS at 19 wt% vinyl acetate occupies an intermediate position: sufficient polarity for bonding to aluminium, glass, polar films, and cellulosic substrates, while retaining enough crystallinity for dimensional stability in extruded profiles and foamed parts.

Hot-melt adhesive compounders typically select UE1925TS where peel adhesion on polar substrates must exceed that of LDPE but where a highly amorphous 28–33 wt% vinyl acetate grade would create excessive blocking, open-time drift, or packaging-film delamination. The 2.5 g/10 min melt flow rate provides a practical viscosity window in kettle and drum-unloading equipment without requiring extreme processing temperatures. Batch-to-batch variation in vinyl acetate distribution can shift lap-shear adhesion; incoming resin should therefore be controlled against a producer certificate of analysis with limits referenced to ASTM D5594-18.

When UE1925TS is processed on high-shear twin-screw compounding lines without side-feed devolatilisation

The processing window for UE1925TS is constrained by the thermal stability of the vinyl acetate comonomer. At elevated melt temperatures, acetic acid elimination can increase acidity and corrode downstream equipment. For compounding on a co-rotating twin-screw extruder with 40:1 L/D, atmospheric venting and a vacuum vent stage are normally specified because residual moisture and low-molecular-weight degradation products must be removed before the die plate. Predrying at 70–80 °C for 2–4 h in desiccant-hopper air with a dew point of -30 °C or lower is recommended when storage relative humidity exceeds 60%. Melt temperatures should not intentionally exceed 210 °C; production-scale observations indicate that extended residence times above this threshold increase screen-pack pressure rise and generate acidic odour, which is a direct indicator of vinyl acetate degradation. The use of amine-based stabilisers is avoided because amine species can accelerate ester cleavage and generate discolouration. Published data for the exact UE1925TS additive package is limited; however, the monomer chemistry imposes these operational boundaries regardless of producer.

Foam injection moulding trials with UE1925TS commonly pair the resin with azodicarbonamide blowing agents. The decomposition window of azodicarbonamide begins near 200–210 °C, and the melt temperature must therefore be steered to balance gas evolution against viscosity retention. Dicumyl peroxide crosslinking systems are also used; the practical cure condition is governed by peroxide half-life, with a 1 min half-life near 171 °C. In a 90-tonne clamp-force injection moulding machine running rectangular edge-gated cavity inserts, the observed failure modes include premature gas loss from insufficient barrel back-pressure, gate blush at excessively high melt temperature, and post-demoulding shrinkage when the mould cooling time falls below 25 s. The 19 wt% vinyl acetate content lowers the onset of melt tackiness and expands the processing latitude relative to lower-VA foaming grades, but the mould surface must be release-treated to counter residual adhesion at demoulding temperatures above 45 °C.

Blown-film bubble stability is controlled by elongational viscosity, not only by melt index

UE1925TS is processed in blown-film lines with die gaps of 0.8–1.2 mm, blow-up ratios of 2.5:1 to 3.5:1, and melt temperatures between 160 °C and 185 °C. The bubble stability of this grade depends on strain-hardening behaviour in the bubble stalk, not solely on the 2.5 g/10 min melt index. Producers of printed packaging webs report that excessive melt temperature reduces frost-line height and increases blocking on film surfaces with high slip-agent offset. For heat-seal layers, the lower seal initiation temperature created by the 19 wt% vinyl acetate comonomer shortens seal-bar dwell time on horizontal form-fill-seal machines. However, the narrower crystalline melting range also reduces hot-tack strength compared with lower-VA sealants; seal-bar temperature windows of 105–125 °C are typical starting points, with dwell times from 0.5 s to 1.5 s depending on film thickness. These values must be re-established on the specific film line because published data for this exact UE1925TS configuration is limited.

In photovoltaic encapsulation, EVA grades with vinyl acetate near 19 wt% are evaluated for glass-to-cell and cell-to-backsheet adhesion after peroxide curing. The cured encapsulant is typically crosslinked to gel contents between 75% and 90% by solvent extraction, with damp-heat exposure at 85 °C and 85% RH for 1000 h specified under IEC 61215-1-1:2021. UE1925TS is a candidate grade for these formulations, but module qualification must be performed with the specific lamination cycle and glass type because the producer technical datasheet does not publish a complete encapsulant ageing package for this sub-grade.