HANWHA EVA 1631 (em inglês)

Hanwha EVA 1631 occupies a defined position within the manufacturer’s range of ethylene-vinyl acetate copolymers. The grade designation indicates a nominal vinyl acetate incorporation of 16 wt% and a nominal melt flow rate of 3.1 g/10 min under ISO 1133-1:2022 at 190 °C with a 2.16 kg load. It is supplied as a pelletized thermoplastic resin for injection moulding, profile extrusion, sheet extrusion, foam expansion, masterbatch carrier systems, and polymer modification where increased polarity relative to low-density polyethylene is required. The acetate comonomer disrupts the polyethylene crystalline network, lowering flexural stiffness, reducing heat-seal initiation temperature, increasing filler wetting, and improving adhesion to polar substrates. Published data for the specific configuration should be confirmed against the manufacturer’s technical data sheet.

Molecular Architecture and Melt-State Properties

The random incorporation of 16 wt% vinyl acetate produces a polymer with a density near 0.940 g/cm³ when measured under ISO 1183-1:2019. Melt flow rate is determined under ISO 1133-1:2022 using a 190 °C barrel, a 2.16 kg load, and a piston wait time sufficient to achieve thermal equilibrium. The nominal melt flow rate of 3.1 g/10 min places the material in the medium-flow category, suitable for moderate-pressure injection moulding and for extrusion operations where draw resonance and melt strength must be balanced. Thermal analysis under ASTM D3418-21 typically records a main melt endotherm near 84 °C and a crystallization exotherm near 72 °C. Room-temperature hardness under ASTM D2240-15 is commonly reported near 94 on the Shore A scale. Tensile testing of compression-moulded specimens under ASTM D638-14 reveals stress at break in the range of 15–20 MPa and elongation at break between 700 and 850%. The modulus is lower than that of EVA 1531 and significantly lower than that of low-density polyethylene grades with equivalent melt flow rate.

Production-scale handling of Hanwha EVA 1631 typically begins with desiccant drying at 60–70 °C for 4–6 h when ambient relative humidity exceeds 60%. The target residual moisture is below 0.05 wt% to prevent surface splay and hydrolysis reactions in the melt. Single-screw extrusion is performed on machines with an L/D ratio of 24:1 to 30:1, a feed-zone compression ratio near 3.0:1, and a breaker plate/screen pack of 60/80/100 mesh to generate homogeneous back pressure. Barrel profiles typically rise from 160 °C in the feed zone to 200 °C at the die; the melt thermocouple should not exceed 220 °C. Injection moulding uses clamp forces from 3.5 to 5.0 kN/cm² of projected area, barrel temperatures from 140 °C to 190 °C, and mould temperatures of 20–40 °C. Screw speeds for a 45 mm diameter single-screw extruder are normally held between 60 and 90 rpm; higher speeds can generate excessive shear heating.

Compared with metallocene-catalysed ethylene-octene copolymers of similar density, EVA 1631 exhibits higher polar adhesion and greater gamma-radiation response but lower heat resistance and lower inherent oxidative stability. The acetate group raises dielectric constant and improves printability. These differences become relevant in flexible packaging and footwear where radio-frequency welding or hot-melt bonding is required. Tensile strength, elongation, and melt fracture behavior should be compared under the same test methods because the branched architecture of EVA and the linear architecture of metallocene polyolefins respond differently to shear.

Why Are Zone Temperatures and Screw Compression Ratios Critical for Acetate Retention?

Degradation of the acetate comonomer proceeds through thermal deacylation, which liberates acetic acid at elevated temperatures. Above 220 °C, the deacetylation rate accelerates measurably, resulting in viscosity loss, yellowing, surface defects, and corrosion of exposed tool and downstream equipment surfaces. Because the screw compression ratio controls the portion of energy input that becomes dissipative heating, a high-compression screw in the 3.5:1 to 4.0:1 range can raise melt temperature in the metering section beyond the barrel setpoint. A compression ratio near 3.0:1 is therefore specified for this grade. Twin-screw compounding equipment should use co-rotating screws with an L/D of 44:1 and shear rates below 1,000 s⁻¹ in the mixing section to limit temperature overshoot. Purging before shutdown should be carried out with a low-vinyl-acetate EVA or LDPE. Amine-containing purging compounds and amine-functional processing additives are avoided because residual amines can interfere with peroxide cure in subsequent crosslinking operations and can contribute to discoloration at process temperatures above 180 °C.

Accelerated aging of moulded EVA 1631 is evaluated under ISO 188:2011 at 100 °C for 168 h; changes in tensile strength and elongation are reported. The stabilizer package is typically tailored for processing at 200 °C and continuous service below 60 °C. Continuous exposure above 80 °C in oxidative environments can reduce elongation retention and increase carbonyl absorption in infrared spectra; published data for this specific grade under those conditions is limited.

Crosslinked midsoles and industrial foam sheet are produced by compounding EVA 1631 with azodicarbonamide at loadings between 2 and 6 phr, dicumyl peroxide at 0.5–1.2 phr, and a zinc oxide/stearic acid activator package. Mixing is carried out in an internal mixer at 90–120 °C, followed by sheeting into preforms. Foam expansion in a hydraulic press at 170–180 °C and 150–180 bar produces density reductions from 0.94 g/cm³ to 0.15–0.25 g/cm³. The expansion ratio is controlled by plate temperature, pressure, and peroxide-derived crosslink density. The 16 wt% acetate content and 3.1 g/10 min melt flow rate allow uniform cell nucleation without severe coalescence, although published data for this specific foaming configuration is limited and must be confirmed by pilot trials. Compression set is evaluated under ASTM D395-18, cell size under ASTM D3576-20, and rebound resilience under ASTM D2632-15.

Masterbatch carrier formulations use EVA 1631 at loading levels up to 70 wt% when high pigment or additive acceptance is demanded. The polar acetate group improves dispersion of carbon black, titanium dioxide, and heat stabilizers relative to nonpolar LDPE carriers. The melt flow rate of 3.1 g/10 min permits compounding in internal mixers at 120–140 °C without exceeding the 220 °C degradation boundary. Hot-melt adhesive formulations may use EVA 1631 as a viscosity modifier; final viscosity is measured under ASTM D3236-15 at 180 °C, and ring-and-ball softening point is evaluated under ASTM E28-18. Published data for this specific configuration is limited and must be confirmed by formulation-specific viscometry.

When EVA 1631 Replaces EVA 1531 or EVA 1828 in Crosslinked Midsole Formulation

Grade selection between EVA 1531, EVA 1631, and EVA 1828 rests on the comonomer content and the resulting melt elasticity, hardness, and adhesion after crosslinking. EVA 1531, with a lower nominal vinyl acetate level, produces a harder moulding and higher flexural modulus but requires higher processing temperatures to achieve comparable flow. EVA 1828, with a higher nominal vinyl acetate level, provides lower hardness, softer hand feel, and better low-temperature flexibility at the expense of higher tack and lower service modulus. EVA 1631 occupies the intermediate position for midsoles and sheets requiring moderate softness, controlled shrinkage, and acceptable rebound resilience. The following comparative matrix is based on representative manufacturer data, not interpolated values.

For applications covered by the European Union plastics regulation, migration testing is performed under Commission Regulation (EU) No 10/2011 with simulants selected according to the food type and contact time. EVA copolymers are evaluated against a specific migration limit for vinyl acetate monomer; the grade composition must be verified against the positive list for ethylene-vinyl acetate copolymer. In the United States, 21 CFR 177.1350 provides conditions of safe use for ethylene-vinyl acetate copolymers in food-contact applications, subject to extraction limitations and end-use temperature limits. Automotive interior applications may require compliance with VDA 278 or chamber methods under ISO 12219-4, depending on OEM specification. The manufacturer should be consulted for a compliance statement for the specific supply lot because additive packages and batch-to-batch vinyl acetate distribution can affect migration results.

Compliance Requires Migration Testing Under Specific Simulant Conditions

The following checklist lists the test methods and typical evaluation conditions used to qualify EVA 1631 in food-contact and industrial applications. Results are batch-dependent and are not intrinsic material constants.