SINOPEC Sanren EVA 12/0.5

SINOPEC Sanren EVA 12/0.5 is an ethylene-vinyl acetate copolymer whose designation encodes a nominal vinyl acetate content of 12 wt% and a nominal melt flow rate of 0.5 g/10 min when measured at 190°C under a 2.16 kg load in accordance with ISO 1133-1:2022. The product falls in the low-melt-index, medium-low vinyl acetate region of EVA copolymer space. In this region the vinyl acetate comonomer disrupts polyethylene crystallinity enough to lower the crystalline melting point and increase toughness relative to low-density polyethylene, while the low MFR preserves a high melt viscosity that supports bubble stability and melt strength in extrusion processes. The producer has not published a full English-language technical datasheet for this exact configuration at the time of writing; therefore, numerical values in this document are class reference data and must not replace a lot-specific certificate of analysis. The grade is generally positioned for heavy-duty film substructures, surface protection films, flexible profile extrusion, and foam masterbatch carriers where high melt strength is valued more than high flow. It is not designed for thin-wall injection molding or high-speed thin-gauge cast film.

When 12 wt% Vinyl Acetate Content Is Specified for Heavy-Duty Film Backsheets

In heavy-duty film structures, the combination of 12 wt% vinyl acetate and 0.5 g/10 min MFR changes the processing constraint from extruder output to bubble stability and melt pressure. On blown film lines, low-MI EVA grades of this type are processed with barrier screws having 25:1 to 30:1 L/D, often with grooved-feed throat sections. Die gaps are typically held between 1.8 mm and 2.4 mm, and blow-up ratios are set in the 2.0:1 to 3.0:1 range. The frost-line height is adjusted to permit sufficient strain recovery before crystallization; setting it too low freezes orientation and creates directionally weak film, while setting it too high increases bubble sag and gauge variation. Melt temperatures below 190°C are generally avoided because the high melt viscosity can produce melt fracture and excessive head pressure. Melt temperatures above 230°C are avoided because the vinyl acetate groups undergo deacetylation, releasing acetic acid that can corrode unplated tooling and create pinholing. A nitrogen thermogravimetric scan should be performed on the specific lot before establishing the extrusion profile.

The low MFR also alters the solidification profile. Because the vinyl acetate units interrupt ethylene sequences, the crystalline melting peak of this product class is lower than low-density polyethylene and the quiescent crystallization rate is slower. On blown film lines this shifts the frost-line requirement; a frost-line height that is too low freezes in molecular orientation before stress relaxation, creating film that tears preferentially in the machine direction. A frost-line height that is too high produces excessive bubble sag and gauge variation. Production lines therefore use air-ring adjustment rather than screw speed alone to control gauge. Optical inspection of the bubble and continuous thickness measurement with beta or capacitance gauges provide feedback. For critical packaging structures, gel count and optical defects should be monitored with a camera-based inspection system, and the melt filter should be maintained above 100 mesh to remove char particles that originate from thermal degradation. These requirements become more important as melt temperature is raised to compensate for the low MFR.

Thermal and mechanical property data for this product class are described below. Density in the 0.932–0.936 g/cm³ range is common for 12 wt% vinyl acetate copolymers when measured by ISO 1183-1:2019. Vinyl acetate content is verified by Fourier transform infrared spectroscopy according to ASTM D5594. Vicat softening temperature under method A50 typically falls between 60°C and 75°C per ISO 306:2022, and the crystalline melting peak appears between 85°C and 95°C by ISO 11357-3:2018. Tensile strength at break is generally reported from 15 MPa to 25 MPa, with elongation at break exceeding 600% under ISO 527-1:2019. Shore D hardness is usually 42–48 when tested under ISO 868:2003. The values indicate a material that is tougher and more flexible than low-density polyethylene but less flexible and more crystalline than 18 wt% or 28 wt% vinyl acetate EVA grades. Additive packages and cooling rate alter these properties; lot-specific data should be obtained.

Foam processing uses the low MFR as a cell-wall stabilization tool. The high melt viscosity resists cell coalescence, but it also raises gas encapsulation pressure and can reduce expansion ratio if the gas injection system is undersized. Chemical blowing agent dosage for polyolefin foam, typically 0.5–2.0 wt%, must be re-optimized for the low MFR because diffusion and pressure decay differ from higher-flow grades. Published data for this exact configuration in foamed articles is limited. Therefore, foam density and compression set should be measured under ISO 845:2006 and ISO 1856:2018. Differences from higher-MFR EVA grades appear mainly in extrusion back-pressure and cell structure; foamed sections from low-MI EVA often show finer cell dimensions when the gas injection or chemical blowing agent dispersion is sufficient. This is an operational trade-off, not an intrinsic product defect.

What Are the Practical Melt-Processing Limits of a 0.5 g/10 min EVA Grade?

A single melt flow rate is not a complete rheological specification. Capillary rheometry according to ISO 11443:2021 should be performed at 190°C and 210°C over 100–1000 s⁻¹ before calculating die pressure drops or specifying screw geometry. The flow curve for this class shows pseudoplastic shear thinning, but the degree of thinning cannot be inferred from MFR alone. During start-up on extruders with 25:1 to 30:1 L/D, screw speed should be ramped slowly because melt pressure can rise faster than with 2–8 g/10 min EVA grades. Where pellet surfaces are humid from outdoor storage or condensation at relative humidity above 60%, pre-drying at 60–70°C for 2–4 h is applied to reduce surface defects. EVA itself is not strongly hygroscopic, but surface moisture produces steam defects and melt fracture in film and sheet. The processing window is bounded at the low end by torque overload and melt fracture, and at the high end by thermal deacetylation. Local overheating from poorly distributed barrel temperature can generate acetic acid before the bulk melt reaches 230°C; this is an operational boundary, not a set-point target.

For compounding on twin-screw extruders, segmented screws with 32:1–44:1 L/D and vacuum devolatilization are preferred when filler loadings exceed 20 wt%. The vacuum port should be placed after the main mixing zone and before the die to vent moisture, acetic acid, and low-molecular-weight fractions. Fluoropolymer processing aids may be added in the 200–500 ppm range to suppress melt fracture, but compatibility with the vinyl acetate phase must be confirmed by a plate-out test. Basic amine-based additives should be screened carefully because acetic acid from any thermal degradation can protonate basic species and form deposits. Published data for this exact grade in filled, flame-retardant, or crosslinked formulations is limited; therefore, no flammability class, crosslink density, or retention of mechanical properties can be assumed without production-scale validation.

Rheological Boundaries and Interchangeability With 18/3 and 28/25 Grades

The product is not directly interchangeable with EVA grades in which the second number is higher. The table below shows general class behavior for three designations. Higher vinyl acetate content reduces crystalline melting temperature, density, Shore hardness, and stiffness while increasing polarity, adhesion, and flexibility. Higher MFR reduces molecular weight, melt viscosity, and melt strength while improving flow into thin sections. The 12/0.5 designation therefore sits at the high-melt-strength, medium-stiffness corner of this comparison. It will not fill intricate injection molds as easily as EVA 28/25, and it will not match the polar adhesion or low-temperature flexibility of a 28 wt% VA grade. Conversely, it retains more room-temperature stiffness and may be selected where high-VA materials are too soft or where poor melt strength causes bubble instability. When replacing EVA 18/3 with EVA 12/0.5, processors should expect higher extruder current, elevated die pressure, and a need to raise die temperatures by 5–10°C to maintain surface finish. Replacement in injection molding is not recommended without a full rheology and mold-filling analysis; the low MFR may produce short shots and weld-line weakness in thin-wall cavities.

In coextruded sealant layers, the 12 wt% vinyl acetate content places the seal initiation temperature between unmodified low-density polyethylene and 18 wt% VA grades. Hot-tack strength should be measured according to ASTM F1921-12 on the finished film rather than inferred from comonomer content. The low MFR contributes to high melt strength, which can improve layer uniformity in large-bubble coextrusion but can also increase interfacial instability if the adjacent layer has much lower viscosity. To minimize encapsulation and gauge bands, the melt viscosity ratio between the EVA and the adjacent LDPE or tie resin should be held within a range established by the die manufacturer; published data for this exact product in coextruded structures is limited. Where the structure requires reproducible seal strength under rapid packaging cycles, production trials should include seal temperature, dwell time, and chilled-peel testing across the intended operating window.

For applications in food-contact materials, compliance must be demonstrated under 21 CFR 177.1350 for ethylene-vinyl acetate copolymers or under Commission Regulation (EU) No 10/2011, as applicable. A general-purpose resin designation does not establish food-contact compliance. Migration testing, extraction testing, and organoleptic evaluation must be performed on the finished article, because the adhesive, tie layer, and print substrate may affect overall migration. For electrical and electronic applications, the finished part must be assessed against Directive 2011/65/EU for lead, cadmium, mercury, hexavalent chromium, polybrominated biphenyls, and polybrominated diphenyl ethers, and against the applicable IEC material specification. The supplier should be requested to provide REACH registration data under Regulation (EC) No 1907/2006, a safety data sheet, and a statement of composition for the specific lot. Because EVA copolymers can generate acetic acid during thermal decomposition, processing and incineration systems should be equipped with acid-resistant ducts and appropriate scrubbing. The resin should be stored away from direct sunlight and strong oxidizing agents, and inventory should be rotated to limit long-term additive migration to pellet surfaces.