LG Chem ABS ER-873 is an extrusion-grade acrylonitrile-butadiene-styrene terpolymer specified for thick-gauge sheet extrusion and subsequent thermoforming, chiefly in refrigerator inner liners, freezer door panels, and cold-chain packaging panels. The material comprises a continuous styrene-acrylonitrile matrix and grafted polybutadiene rubber domains; this biphasic architecture supplies low-temperature ductility while the high-molecular-weight SAN fraction and broad molecular-weight distribution contribute melt strength. Public grade datasheets report a density of 1.04 g/cm³ under ISO 1183-1:2019 and a melt mass-flow rate of 4.5 g/10 min at 220 °C and 10 kg under ISO 1133-1:2022. The grade is therefore situated between general-purpose injection ABS and very low-flow extrusion grades: it is selected where sag resistance and deep-draw stability dominate over high-speed mould filling.

The tabulated values are typical release-data figures and are not batch certificates. Batch-to-batch variation in melt mass-flow rate for extrusion ABS, generally within ±0.5 g/10 min, is enough to shift die pressure and sheet thickness at constant screw speed. Converters should therefore set barrel zones and line speed from lot-specific certificates rather than from historical internal averages. Where imperial comparison is required, the tensile yield value corresponds to approximately 6,500 psi under ASTM D638-14.

How Does the Rubber-Phase Morphology Affect Low-Temperature Ductility and Thermoforming Melt Strength?

Low-temperature impact retention is the controlling specification in refrigeration applications. The notched Izod impact at −30 °C remains near 12 kJ/m² under ISO 180:2023, while many high-flow injection ABS grades fall below 8 kJ/m² at equivalent test thickness. The difference originates in the polybutadiene particle-size distribution, crosslink density, and the extent of styrene-acrylonitrile grafting onto the rubber surface. A coarse grafted rubber fraction absorbs energy at low temperatures and stabilizes craze formation, whereas an excessively fine rubber dispersion may retain stiffness but reduces cold impact. In extrusion processing, the same rubber phase raises storage modulus at low shear rates and contributes to sag resistance during oven preheat. Capillary rheometry under ISO 11443:2021 shows a stronger shear-thinning slope for ER-873 than for typical high-flow injection ABS; the practical result is lower draw-down under gravity and a wider forming window at sheet surface temperatures between 130 °C and 170 °C.

The thermoforming window for ABS sheet is therefore not simply a heater setpoint. In thick gauges above 3 mm, surface heating must be slowed to allow the core to reach forming temperature without overheating the sheet surface. The rubber phase in ER-873 resists sag better than a high-flow injection ABS at equivalent gauge, but the formability limit is not indefinite: male-tool corners below 5 mm radius and draw ratios above 3:1 may still crack in the frozen zone if sheet temperature is not uniformly maintained. On rotary thermoforming machines with quartz heating banks, the measured surface-temperature spread across the sheet should be held within ±5 °C to avoid uneven wall thickness and stress whitening in the polybutadiene-rich phase.

At the same time, the higher rubber content and higher melt viscosity impose equipment constraints. On a single-screw extruder, the available torque and drive-current capacity should be verified before replacing a lower-viscosity grade. A 90 mm barrier screw with an L/D of 32:1 typically contains adequate melting capacity for ER-873, but shorter conventional screws may generate unmelted rubber agglomerates. The screw should maintain a compression ratio of 2.5:1 to 3.5:1 and a moderated screw-cooling jacket temperature, because excessive screw heating can cause polybutadiene gel formation at the metal interface.

Production-Scale Drying and Sheet Extrusion Boundaries for ER-873

A pre-drying step is not optional for ER-873 because residual moisture in ABS produces splay, gloss loss, and pinholes at the roll stack. Desiccant drying at 80 °C for 2–4 h to a residual moisture content at or below 0.1 % is the standard start-up boundary; shorter hopper residence times can remain acceptable when entering granulate is already below 0.1 % moisture. On high-humidity shop floors with relative humidity above 60 %, dried material should not be left in open convey lines because moisture regain accelerates surface defect formation during sheet takeoff.

Deviations above 250 °C melt temperature initiate polybutadiene degradation, visible as yellow-to-brown surface streaks and gel particles; the lower melt-temperature boundary of 210 °C is set by incomplete plastication and excessive die pressure. Roll stack temperatures below 80 °C freeze the sheet surface before sufficient relaxation and can increase warpage during later oven heating. Roll temperatures above 100 °C may cause sheet-to-roll adhesion and reduced line speed because cooling time increases. When ER-873 regrind is blended, the proportion is generally limited to 20–30 wt% because repeated heat history narrows molecular-weight distribution and lowers sag resistance. Purging from ER-873 to another ABS should use a lower-viscosity general-purpose ABS purge compound at 220 °C; PVC or polycarbonate purging compounds are not automatic substitutes because decomposition and compatibility differ. Residue of ER-873 in dead spots can degrade over time and release black specks, so screw pull and cleaning should be scheduled when frequent colour changes are required.

When ER-873 Replaces High-Flow Injection ABS in Sheet, the Differentiating Variable Is Melt Pressure, Not Tensile Strength

The short-term tensile yield strength of 45 MPa and flexural modulus of 2,200 MPa are not the primary differentiation from general-purpose ABS; many injection grades occupy a similar stiffness range after moulding. The decisive difference appears in the melt state. With a melt flow index near 4.5 g/10 min, ER-873 develops a higher pressure drop per unit die width than a 20–30 g/10 min injection ABS. This shift reduces sheet sag, but it can rise above the pressure limits of small extruders or expose drive-current alarms on older lines. Melt pumps and screen changers should be specified for the higher viscosity curve, and the die lip gap typically requires a wider initial setting to compensate for orientation-driven thickness reduction during draw-down.

In coextruded structures, ER-873 may serve as the high-gloss cap layer or the liner layer. In such cases, the viscosity ratio between ER-873 and the adjacent HIPS or ABS substrate must be checked by shear-viscosity curves under ISO 11443:2021 to prevent layer rearrangement and edge encapsulation defects. The grade is also differentiated from flame-retardant ABS and metal-plating ABS; those products contain additive packages or modified rubber phases that alter surface polarity, thermal stability, and melt-fracture limits. ER-873 is not automatically interchangeable with those platforms, even when the rockwell hardness or flexural modulus appears comparable on a condensed datasheet.

Regulatory Verification and Chemical Exposure Limits Are Grade-Specific, Not Universal

For electrical and electronic equipment applications, the part is assessed under Directive 2011/65/EU Restriction of Hazardous Substances requirements; a resin supplier’s declaration is not a substitute for article-level conformity. For food-contact uses, the processor must verify grade-specific authorization to U.S. FDA 21 CFR 180.22 or Commission Regulation (EU) No 10/2011, including migration limits and permitted residual acrylonitrile levels. The grade may be registered under REACH (EC) No 1907/2006, but registration alone does not establish downstream food-contact status.

Chemical resistance must be treated as a processing boundary, not an absolute property. ABS is consistently attacked by ketones, esters, aromatic hydrocarbons, and certain chlorinated solvents. In refrigerator applications, incidental exposure to cleaning agents, blown-foam blowing-agent condensates, or compressor oils should be evaluated by stress-rupture testing on formed parts. Published data for ER-873 compatibility with all polyurethane foam polyol systems is limited; converter-specific exposure trials are required when a new blowing agent or liner adhesive is introduced. Long-term air aging above 70–80 °C gradually reduces impact strength through thermo-oxidative degradation of the polybutadiene phase, even though the short-term heat deflection temperature remains near 90 °C under ISO 75-2:2013.

When a converter replaces a high-flow injection ABS with ER-873 on an existing sheet line, the first qualified trial should compare melt temperature at the die lips, roll-stack grip, and formed-part low-temperature impact after actual regrind inclusion; these three variables typically decide whether the grade change is feasible before a full production run is committed.