LG Chem ABS HI-121H is an amorphous acrylonitrile-butadiene-styrene terpolymer supplied as a high-impact injection moulding resin. The material’s published nominal density is 1.04 g/cm³ under ISO 1183-1, with a melt mass-flow rate of 20 g/10 min at 220 °C and 10 kg under ISO 1133-1. Typical datasheet mechanical values include tensile stress at yield of 44 MPa under ISO 527-2, flexural modulus of 2.25 GPa under ISO 178, and notched Izod impact strength of 28 kJ/m² at 23 °C under ISO 180/1A. The butadiene-rich rubber phase is the primary contributor to impact absorption; it also lowers short-term modulus relative to general-purpose ABS grades. Applications documented for this chemistry include vacuum cleaner housings, electrical breaker enclosures, automotive interior trim, toys, and appliance control panels. In these applications the grade is usually selected after comparing notched impact retention, heat deflection temperature, and mould filling pressure rather than ultimate tensile strength alone. Typical values are not lot-specific; each incoming lot should be verified against the supplier’s certificate of analysis before production release.

What Processing Limits Appear During Injection Moulding of HI-121H?

Pre-drying is the first critical boundary. At ambient relative humidity above 60%, pellets can take up sufficient surface moisture to generate splay and silver streaking if processed without drying. Desiccant-bed drying at 80 °C for 2 h to 4 h is the standard recommendation; a residual moisture target below 0.05 wt% is required to protect surface gloss and impact reproducibility. A barrel temperature profile from rear 180 °C to front 230 °C, with nozzle temperature limited to 220 °C to 230 °C, is representative. Melt temperature measured by an immersion pyrometer should remain between 210 °C and 240 °C. Above 250 °C, the polybutadiene phase begins thermo-oxidative degradation, visible as yellow shift and reduced notched Izod and Charpy values. Below 210 °C, cavity pressure rises, filling becomes pressure-limited in ribs and bosses, and weld-line length increases.

Tool temperature is typically set between 40 °C and 80 °C. Higher mould temperatures within this range improve surface replication and reduce internal stress but extend cooling time; lower temperatures shorten cycle time at the expense of impact-critical skin orientation. Injection pressure commonly falls between 70 MPa and 120 MPa. Holding pressure should be selected by part-weight stabilization, usually 50% to 80% of peak injection pressure. Back pressure of 0.5 MPa to 1.5 MPa is sufficient for homogeneous melt quality without excessive shear heating. On production-scale equipment, a 1,200 kN toggle-clamp injection moulding machine with a 30 mm general-purpose screw and 20:1 L/D ratio can process this grade when shot volume is limited to 30% to 70% of barrel capacity. Total cycle interruptions beyond 8 min promote surface yellowing and notched impact loss; when interruptions exceed this threshold, the melt cushion should be purged before restart. Gate freeze in direct-edge or tunnel gates occurs rapidly with this amorphous terpolymer. Holding time should be verified by gate-seal studies because underfeed causes sink marks over bosses, while overpacking raises frozen-in stress and reduces environmental stress cracking resistance.

Electrical enclosure covers and circuit-breaker housings formed from HI-121H are evaluated for creep current tracking under IEC 60112, for glow-wire ignition under IEC 60695-2-11, and for tensile impact after damp-heat conditioning under ISO 291. The material is not inherently flame-retardant and should not be specified where a UL 94 V-0 rating is required without an external flame-retardant modification. Moulded enclosure prototypes typically exhibit shrinkage in the flow direction of 0.4% to 0.7% when measured by ISO 294-4; tooling compensation for inside dimensions should use the upper end of this range at long flow lengths and low packing pressure. Thick-to-thin transitions in boss areas are prone to sink and blush when packing pressure is withdrawn before gate freeze. Rib-to-wall ratio should not exceed 60%; bosses should be cored and connected to outer walls with stiffening gussets. Inserts can be ultrasonically or heat-staked, but thread-forming screws in undersized bosses can exceed the yield strain of the polymer at the hole periphery and cause radial cracks. For snap-fit geometries, allowable strain should be validated by flexural creep tests under ISO 899-2 rather than short-term tensile strain at break. Comparative trials on flat plates of 2 mm wall thickness show that a melt temperature reduction from 240 °C to 220 °C lowers flash tendency but increases weld-line visibility in double-gated panels. Published data for this specific plate configuration is limited; the observed trend follows standard amorphous ABS shear sensitivity behaviour.

Mechanical and Thermal Property Benchmarks

Because the butadiene rubber phase influences notched Izod more than flexural modulus, lot-to-lot impact variation is a more sensitive incoming quality metric than tensile yield. Receiving inspection protocols often include melt mass-flow rate, notched Izod, and Vicat softening temperature because these are the three values most likely to shift when rubber-particle size distribution changes. If melt mass-flow rate drops below 15 g/10 min, thin-wall fill within normal pressure limits may be compromised; if it exceeds 25 g/10 min, the material may be degraded or contaminated with a lower-viscosity grade.

When HI-121H Replaces Standard High-Impact ABS in Thin-Wall Moulds

In comparison with lower-flow high-impact ABS grades, HI-121H permits shorter filling times but requires larger gate sizes to minimize shear-induced blush. The trade-off appears in flexural modulus: the rubber modification that raises impact also reduces modulus. In load-bearing enclosures, rib thickness and wall section must be increased when substituting HI-121H for a glass-filled ABS or a higher-stiffness general-purpose grade. The grade’s heat deflection temperature under 1.8 MPa load of 85 °C under ISO 75-2/A is not a maximum service temperature; continuous load-bearing use should be revalidated by creep modulus measurements under ISO 899-2. At 60 °C and 20 MPa initial stress, typical amorphous ABS grades exhibit significant creep; published data for this specific grade at that stress is limited.

Compared with high-impact polystyrene, HI-121H has higher practical toughness and better upper service temperature but higher material cost. Compared with PC/ABS blends, HI-121H has lower heat distortion and tensile modulus but offers lower melt temperature and easier processing. The product is not suitable for exterior weather-facing use without UV stabilization; prolonged UV exposure causes yellowing and gloss reduction. Acrylic-modified ABS or ASA grades are usually specified when weathering is critical. For applications requiring repeated exposure to aromatic hydrocarbons, chlorinated solvents, or strong organic esters, environmental stress cracking must be assessed under ISO 22088-2 because these solvent classes attack the styrene-acrylonitrile matrix of ABS.

Compliance Matrix Covers RoHS, REACH, and Food-Contact Documentation

For automotive interior trim, part approval usually hinges on odour, fogging, and emission tests such as VDA 278 and VDA 270. Specific emission values for HI-121H are supplier-dependent and must be validated on production tooling because mould release agents, lubricants, and regrind content influence the result. At moulded wall thicknesses above 3 mm, cooling time becomes the cycle-time driver; conformal cooling in large housing inserts is often more effective than increasing melt temperature. Any regrind addition above 20 wt% should be qualified because repeated heat history accelerates thermo-oxidative consumption of the butadiene phase and narrows the processing window.

Surface-finish defects in HI-121H mouldings are commonly misattributed to moisture when the actual cause is insufficient venting or low screw decompression. Vent grooves should be maintained at 0.02 mm to 0.04 mm depth at the parting line, and decompression distance should not exceed 2 mm to 4 mm to avoid air entrapment and nozzle drool. Screw rotation speed is typically set between 40 rpm and 80 rpm depending on screw diameter; excessive screw speed causes melt discoloration and lowers notched impact retention. The grade should not be blended with flame-retardant additives or color concentrates without compatibility testing because acidic or metallic additive residues can accelerate hydrolytic and oxidative breakdown during processing.