Ionómero SURLYN AE4200

Surlyn® AE4200 ionomer is a sodium-neutralized ethylene/methacrylic acid copolymer supplied as free-flowing pellets. The neutralization reaction converts a fraction of the carboxylic acid groups into ionic clusters that behave as thermoreversible physical crosslinks. The grade is controlled by melt rheology and end-use performance rather than by a publicly disclosed comonomer ratio. Melt flow rate is 1.0 g/10 min at 190 °C under 2.16 kg load when measured according to ASTM D1238 or ISO 1133-1:2022. Density is 0.95 g/cm³ when tested by ASTM D792. Differential scanning calorimetry typically records a melting endotherm near 98 °C using ISO 11357-3. Shore D hardness is 62 under ASTM D2240. Vicat softening temperature is near 72 °C when measured by ASTM D1525 or ISO 306. These values are typical for the sodium ionomer class and should not be read as certified batch release limits. The ionic clusters in AE4200 produce melt rheology that differs from that of a linear low-density polyethylene of equivalent melt index. At low shear rates, apparent viscosity remains elevated, while at higher shear rates the ionic clusters dissociate and permit conventional thermoplastic processing. This shear-thinning response is measurable by capillary rheometry under ASTM D3835, with a power-law index typically below 0.5 at shear rates between 100 s⁻¹ and 1000 s⁻¹.

What Distinguishes AE4200 from Non-Neutralized Acid Copolymers?

Compared with non-neutralized ethylene/methacrylic acid copolymers, AE4200 exhibits higher melt strength and a broader sealing plateau as a result of ionic cluster formation. The ionic network increases zero-shear viscosity by more than one order of magnitude relative to an acid copolymer of equivalent comonomer content. Puncture resistance, measured by ASTM D5748, is higher under identical film thickness. Light transmission remains above 88% at 2 mm thickness when tested according to ASTM D1003 or ISO 13468-1. Haze is typically below 5%. Neutralization also alters adhesion to aluminium foil from interfacial to cohesive under peel testing by ASTM F88/F88M. Non-neutralized acid copolymers are softer and display lower low-temperature impact strength, while AE4200 retains toughness at temperatures down to -20 °C. The sodium cation in AE4200 contributes lower optical haze than many zinc-neutralized ionomers, but it also increases moisture sensitivity during processing. Absorbed moisture above 0.10% by Karl Fischer titration causes splay and bubble formation in molded parts. The material therefore requires closed-loop drying before extrusion or injection molding.

Differentiation from ethylene-vinyl acetate copolymers is relevant for cosmetics and personal-care packaging. EVA grades with 18% vinyl acetate are softer and can show crease whitening after flexural fatigue. In compression-molded sheets, AE4200 demonstrates greater resistance to stress whitening under repeated flexing. The ionic clusters provide a combination of rigidity and toughness that is not obtained with LDPE of similar density. At 0.95 g/cm³, AE4200 is similar in density to LDPE but has higher melt strength, higher room-temperature creep resistance, and greater resistance to environmental stress cracking under ASTM D1693 in surfactant solutions. In transparent packages for creams, lotions, and lipstick overmolding, AE4200 provides resistance to ester-based formulation contact. Oxygen transmission is higher than PET but lower than LDPE of equivalent thickness when tested at 23 °C and 50% RH by ASTM D3985. The material is used in injection-molded closures, cosmetic compacts, and thin-wall jars; wall thicknesses from 1.0 mm to 3.0 mm are common. Insert molding on glass or metal substrates requires substrate temperatures near 80 °C to prevent stress concentration and premature debonding.

When the Barrel Profile Exceeds 220 °C and Residence Time Extends Beyond Five Minutes

Thermal exposure is the principal processing boundary for AE4200. The recommended melt temperature range is 180 °C to 220 °C. At melt temperatures above 240 °C, carboxylic acid decomposition can shift viscosity and generate volatiles that appear as silver streaks and plate-out. Residence time at melt temperature should not exceed 10 min; purging with low-density polyethylene is advised when interruptions exceed this window. Injection molding machines with clamp forces from 50 tf to 250 tf are commonly used. Screw L/D ratios of 20:1 to 25:1 and compression ratios of 2.5:1 to 3.5:1 are reported in production bulletins. Mold temperature is held between 10 °C and 30 °C to obtain low haze surfaces in highly polished cavities. Pre-drying is required at 70 °C to 80 °C for 4 h to 6 h in a desiccant dryer with dew point not higher than -40 °C. Water content should be kept below 0.10% by weight. In extrusion sheet lines, a barrier screw with an L/D of 30:1 and screen packs of 40/60/100 mesh is used to generate melt pressure without excessive shear heating. Production-scale failure modes observed on injection molding lines include splay from residual moisture, gate blush from excessive injection velocity, and dimensional variability when the mold temperature is allowed to drift above 40 °C. Gate blush is controlled by reducing injection velocity or increasing gate diameter. Screw recovery times are longer than LDPE at the same screw speed because ionic clusters increase melt viscosity at low shear rates.

In extrusion coating and lamination, AE4200 is not a direct substitute for high-flow zinc ionomers or acid copolymers. The low melt index limits thin-gauge coating throughput. Line speeds above 150 m/min can produce draw resonance and neck-in unless the die gap and air gap are adjusted. Published data for this specific configuration is limited when line speed exceeds 200 m/min. For sheet extrusion, the downstream roll stack should be set with a roll gap slightly wider than the target sheet thickness to avoid surface marking. Polished chrome rolls are preferred because the ionomer melt adheres strongly to metal surfaces above 130 °C. Release agents containing silicone should be avoided because they can transfer to the sheet surface and interfere with subsequent printing or ultrasonic welding.

Optical, Mechanical and Barrier Test Methods for Transparent Cosmetic Packaging

The following table compiles representative values for AE4200. The data are typical for sodium ionomer grades and are included for process selection, not as certified release limits. The no-break Izod designation applies when a specimen does not completely fracture under the stated test geometry.

The mechanical values in the table are dependent on specimen preparation and conditioning. Tensile and flexural measurements should follow the conditioning requirements of ASTM D618 at 23 °C and 50% RH for 40 h before testing. The tensile modulus of ionomers is lower than glassy polymers and higher than plastomers, which limits the use of AE4200 in thin-wall rigid articles below 0.8 mm where creep under load can occur. The notched Izod value should be interpreted with caution because ionomers can exhibit incomplete fracture and high energy absorption.

Among Surlyn sodium and zinc grades, AE4200 is distinguished by its low melt flow and high melt strength. Zinc grades typically offer greater adhesion to metal foil in extrusion coating and higher tensile strength at yield. Sodium grades provide lower optical haze and better low-temperature toughness. AE4200 should not be substituted for high-flow zinc ionomers in extrusion coating where melt draw at line speeds above 150 m/min is required. The low melt index also requires higher head pressure in blow molding; accumulator heads with die gaps from 0.3 mm to 0.6 mm are used for bottles and containers. Blow molding parison swell is higher than HDPE at the same die gap, so tooling compensation is necessary. Published data for this specific configuration is limited when parison swell exceeds 40% at 190 °C melt temperature.

Food-Contact Use Is Controlled by 21 CFR 177.1330 and EU Regulation 10/2011

The resin falls under the ionomeric resin class described in FDA 21 CFR 177.1330 for food-contact articles. Compliance under EU Regulation 10/2011 is evaluated through overall migration testing and specific migration testing for the monomer and neutralization cation. The table below identifies the principal regulatory instruments that apply to AE4200 in food-contact and general industrial applications.

Compatibility limits include continuous contact with concentrated oxidizing acids, ketones, and aromatic hydrocarbons; swelling is measurable by mass change under ISO 175. Melt blending with amine-based stabilizers or flame retardants should be avoided because amines can neutralize the carboxylic acid group and disrupt ionic clustering. Continuous service under load-bearing conditions is limited to 40 °C to 50 °C due to thermoplastic flow. Short-term exposure to 80 °C does not cause permanent loss of optical quality but may relax molded-in stress. The resin should not be purged with PVC compounds; incompatible purge residue can crosslink or degrade at ionomer processing temperatures. Moisture barrier is moderate, and secondary packaging or desiccant inserts may be required for moisture-sensitive cosmetic formulations. The grade is not recommended for UV-stabilized outdoor applications unless a UV absorber package is evaluated according to ASTM D4329 and ASTM D4459.