Sinopec Yangzi Petrochemical Co., Ltd.

What Controls Silane Grafting Efficiency and Gel Content in Photovoltaic Encapsulant Film?

Production-scale photovoltaic encapsulant extrusion from Sinopec Yangzi Petrochemical EVA with a vinyl acetate content of 26–28 wt% and a melt flow rate of 20–30 g/10 min (ISO 1133-1:2022, 190 °C/2.16 kg) is governed by a narrow lamination window: film cast at 90–105 °C must later cure in the module laminator at 145–150 °C for 13–16 min to reach a solvent-extraction gel content above 75% (ASTM D2765). Encapsulant film for modules qualified under IEC 61215-1:2021 and IEC 61730-1:2016 is typically formulated with 100 phr EVA, 0.8–1.2 phr tert-butylperoxy-2-ethylhexyl carbonate, 0.3–0.5 phr vinyltrimethoxysilane coupling agent, 0.15–0.30 phr hindered phenolic antioxidant, and 0.15–0.30 phr UV stabilizer; the peroxide is first dispersed as a 10–15 wt% EVA masterbatch to prevent localized cure on the extruder screw. On flat-die cast film lines with screw L/D 30:1 and die gap 0.8–1.2 mm, die-lip deposit increases after 72 h when silane content exceeds 0.5 phr, a field failure mode that can transfer to the film surface and reduce glass-adhesion peel strength below 40 N/cm after damp heat aging. Laminator conditions above 155 °C can create voids at the cell edge, while conditions below 140 °C can leave unsaturated peroxide and gel content under 70%, producing creep in glass-glass bifacial modules. The terminal product types include glass-glass and glass-backsheet monofacial and bifacial modules, where the EVA layer functions as adhesion, stress-relief, and optical coupling between the cell and the front glass.

In hot-melt adhesive compounding where open time is controlled between 5 s and 15 s on kraft paper, Sinopec Yangzi Petrochemical EVA with 28 wt% vinyl acetate and melt flow rate 150–400 g/10 min (ISO 1133-1:2022) is added at 20–35 wt% of the total formulation, together with 30–45 wt% hydrocarbon or rosin ester tackifier, 15–25 wt% Fischer–Tropsch wax or microcrystalline wax, and 0.5–1.0 wt% antioxidant. For food-contact packaging adhesives, the formulation must comply with FDA 21 CFR 177.1350 for ethylene-vinyl acetate copolymers and EU 10/2011 migration limits, while general industrial adhesives are screened against REACH EC 1907/2006 and RoHS 2011/65/EU. Compounding is conducted in a co-rotating twin-screw extruder with L/D 32:1 and barrel temperature 120–150 °C, followed by underwater pelletizing at 10–12 °C water temperature; application lines using slot-die coaters run at 165–180 °C with wheel speed 30–80 m/min. A documented processing boundary is that zinc stearate release agent above 0.5 wt% can depress melt viscosity and cause tackifier phase separation; therefore, adhesive converters pre-treat EVA with 0.1–0.3 wt% low-amine stabilizer when high-humidity storage exceeds 60% RH. Terminal finished product types include case and carton sealing adhesives, bookbinding spine glue, and edgebanding adhesives for melamine-faced MDF panels.

Halogen-Free Cable Sheathing Operates Below 180 °C

Flame-retardant cable jacket compounds based on EVA supplied by Sinopec Yangzi Petrochemical are processed at maximum melt temperatures below 180 °C because the aluminium trihydroxide filler loses two water molecules between 180 °C and 200 °C, creating intumescent porosity and surface pinholes on the jacketing line. A typical sheathing formulation uses 100 phr polymer blend of EVA with 18–26 wt% vinyl acetate and LLDPE at 70:30 ratio, 120–150 phr aluminium trihydroxide, 0–30 phr magnesium hydroxide, 1.0–1.5 phr aminosilane coupling agent, 0.3–0.5 phr hindered amine stabilizer, and 0.1–0.3 phr processing lubricant. The compound must meet IEC 60332-1-2 for single-wire vertical flame propagation, IEC 60754-1 for halogen acid gas release, and IEC 61034-2 for smoke density. Compounding is done on a co-rotating twin-screw extruder with L/D 44:1, side stuffer at barrel section 6, screw speed 350–500 rpm, temperature profile 120–170 °C, and die pressure 20–35 MPa; pellets are then dried to <0.05 wt% moisture before jacket extrusion through an 90 mm barrier screw with L/D 25:1 at melt temperature 155–170 °C. If the temperature profile exceeds 180 °C, the compound loses halogen-free flame retardancy and tensile strength drops below 9 MPa (ISO 527-2), making the jacket unusable for solar DC cable applications. Terminal products include photovoltaic DC cable jackets, building riser cable sheaths, and control cable jackets for tunnels and mass transit systems.

Injection-Molded Closed-Cell Foam Cure Windows for Foam Midsoles

For injection-molded closed-cell EVA midsoles, density reduction and crosslink density are adjusted simultaneously because blowing agent decomposition overlaps with peroxide cure between 160 °C and 185 °C. Sinopec Yangzi Petrochemical EVA with 18–22 wt% vinyl acetate and melt flow rate 2–5 g/10 min (ISO 1133-1:2022) is mixed at 100 phr with 2.5–4.0 phr azodicarbonamide, 0.7–1.0 phr dicumyl peroxide, 1.0–2.0 phr zinc oxide, and 10–20 phr calcium carbonate. The compound is prepared in an internal mixer with ram pressure 0.5–0.7 MPa at 100–115 °C, sheeted on a two-roll mill at 70–90 °C, and pelletized; injection molding uses clamp force 200–300 t and nozzle temperature 85–95 °C, with mold cavity temperature 170–190 °C for 4–6 min. After demolding, the foam must undergo 24–48 h ambient stress relaxation to reach final Shore A hardness 45–55 (ISO 868) and compression set below 55% (ASTM D3574-17). Compliance for footwear compounds is governed by REACH EC 1907/2006 Annex XVII entry 51 for phthalates and entry 52 for dimethyl fumarate, with routine testing of the final foam article for restricted aromatic amines under REACH Annex XVII entry 43. Terminal finished product types include running shoe midsoles, sport sandal outsoles, and removable foam insoles.

When EVA Replaces Amorphous Polyolefin in Extrusion Coating

Extrusion coating onto paperboard for aseptic carton structure relies on EVA with 9–18 wt% vinyl acetate and melt flow rate 7–15 g/10 min (ISO 1133-1:2022), blended into LDPE at 10–30 wt% EVA to achieve peel adhesion above 2.5 N/15 mm to aluminium foil and paperboard. The food-contact legality is established by FDA 21 CFR 177.1350 and EU 10/2011, with overall migration below 10 mg/dm² for carton structures. In a tandem extrusion coating line, a 12–18 µm EVA-containing web is applied at melt temperature 280–320 °C, air gap 150–250 mm, chill roll temperature 15–25 °C, and line speed 150–300 m/min; the high melt temperature is required for oxidation at the substrate interface but is limited by neck-in and smoke when vinyl acetate content exceeds 18 wt%. Therefore, converters specify the lower-VA grades and pre-dry the polymer at 70–80 °C for 3–4 h if storage relative humidity exceeds 60%. The terminal products include aseptic beverage cartons, frozen food paperboard lamination, and woven bag coating for bulk chemical packaging.

Where closed-cell expanded EVA is calendered into gasketing with Shore A hardness 30–45 and density 0.10–0.18 g/cm³, the crosslink density is determined by dicumyl peroxide addition at 1.0–1.5 phr rather than by silane moisture cure. Sinopec Yangzi Petrochemical EVA with 18–20 wt% vinyl acetate and melt flow rate 1.5–3.0 g/10 min is compounded on a two-roll mill at 80–95 °C with 100 phr resin, 4–6 phr azodicarbonamide, 1.0–1.5 phr dicumyl peroxide, 1.5–2.0 phr zinc oxide, and 0.5–1.0 phr pentaerythritol tetrastearate lubricant. The expanded sheet is crosslinked and foamed simultaneously in a compression press at 155–165 °C under 10–15 MPa for 6–10 min, then post-expanded in a 180 °C hot-air tunnel for 15–30 min. The finished cellular material is tested according to ASTM D1056-20 for closed-cell sponge and ISO 815-1:2019 for compression set at 70 °C for 22 h. Process limitations include peroxide scorch on the mill if roll temperature exceeds 100 °C, and residual blowing agent can create dimensional instability if the post-expansion step is shortened below 10 min. Terminal finished product types include automotive door-aperture gaskets, HVAC flange seals, sports protective padding, and expansion joint filler strips.