SABIC ABS MG38F is a medium-flow acrylonitrile-butadiene-styrene terpolymer supplied in pelletised form for injection moulding. The grade is positioned as an unplated, general-purpose ABS with a balance between melt processability and notched impact resistance. The resin producer’s published typical properties place melt volume-flow rate at 21 cm³/10 min under ISO 1133-1:2022 at 220 °C/10 kg, density at 1.04 g/cm³ under ISO 1183-1, and tensile stress at yield at 44 MPa under ISO 527-2/50. These are typical values from a natural, unfilled formulation and do not constitute specification limits; colour concentrates, regrind content, and moulding conditions shift mechanical response, particularly notched impact and heat deflection. The product is not a high-heat ABS, nor a high-impact extrusion grade; it is intended for short-cycle injection moulding of housings, appliance parts, and consumer goods where surface gloss and dimensional consistency are required.

What separates MG38F from high-impact, high-gloss, and extrusion ABS families?

The separation is based on melt rheology, rubber-phase content, and process window. High-impact ABS grades typically contain a larger butadiene rubber phase and report notched Izod impact values above 30 kJ/m² under ISO 180/1A at 23 °C; MG38F is published at 24 kJ/m². The lower rubber content reduces melt viscosity and permits longer flow lengths at reduced injection pressure, but the trade-off is lower ductility in snap-fit and drop-impact events. High-flow ABS grades with melt volume-flow rates above 30 cm³/10 min under ISO 1133-1:2022 at 220 °C/10 kg may exhibit notched Izod values below 18 kJ/m², placing MG38F in a middle position. Extrusion-grade ABS is formulated for high melt strength and low sag, with MVR commonly below 10 cm³/10 min; MG38F is not designed for profile extrusion or sheet because its melt strength is insufficient to resist sag during cooling. High-gloss surface potential is achieved only when tool temperature and cavity surface finish are controlled; gloss values above 90 GU at 60° under ISO 2813 are attainable on polished tools, while matt or textured surfaces reduce the reading to 10–30 GU.

Before injection moulding, the granulate must be dried in a desiccant dryer at 80 °C for 2–4 h when ambient relative humidity exceeds 60 %. Residual moisture above 0.05 % produces splay, silver streaks, and weld-line strength loss. A batch-to-batch MVR variation of ±2 cm³/10 min under ISO 1133-1:2022 is commonly observed on production lots; when MVR shifts toward the upper limit, barrel temperature should be reduced by 5–10 °C to maintain melt viscosity. The recommended barrel profile is 220 °C at the rear zone, 235 °C in the centre, 245 °C at the front, and 245 °C at the nozzle. Melt temperature measured by an immersion pyrometer should be 240–260 °C. If melt temperature exceeds 250 °C, total residence time must not exceed 10 min; the butadiene phase undergoes thermo-oxidative degradation that reduces notched Izod impact before tensile strength falls. A screw with L/D of 20:1 to 24:1 and compression ratio of 2.2:1 to 2.6:1 is appropriate. Back pressure is maintained at 0.5–1.0 MPa; injection pressure in production tools typically falls between 70 MPa and 100 MPa. Wall stock below 0.8 mm is not recommended for long flow paths because flow-length-to-wall-thickness ratio above 150:1 increases short-shot risk at a 245 °C melt set-point.

Property Profile and Test Methods

Table 1 lists supplier-reported typical values for unfilled MG38F. Tests are performed on injection-moulded plaques conditioned at 23 °C and 50 % relative humidity for 48 h according to ISO 291. Colour and reprocessing alter the values; therefore the table should be used for material selection rather than final-part validation.

Dimensional control is influenced by mould shrinkage and frozen-in molecular orientation. Mould shrinkage for MG38F is reported at 0.5 %–0.7 % under ISO 294-4 on a 60 mm × 60 mm × 2 mm plaque. Flow-direction shrinkage is typically lower than transverse-direction shrinkage because of orientation at the gate. Hold pressure should be 60–80 % of the injection peak and held for 3–8 s per millimetre of nominal wall thickness to limit sink marks. Gate diameter should not be below 1.0 mm for a 2 mm wall; smaller gates raise shear rate above 100,000 s⁻¹, causing gate blush and local degradation. Draft angles of 0.5° on polished surfaces and 1° on textured surfaces prevent ejection drag and distortion. Clamp force can be estimated from projected cavity area and expected cavity pressure; MG38F typically develops 35–45 MPa cavity pressure at gate freeze. A 1,200 kN machine is adequate for a total projected area up to 250 cm² at 45 MPa cavity pressure. Post-mould dimensional audits should follow ISO 294-5 or an internal control plan. After 20 % regrind incorporation, notched Charpy impact must be revalidated under ISO 179/1eA; field data show measurable impact drift after three regrind cycles even when visual colour shift is absent.

When barrel temperatures exceed 250°C, residence-time control becomes the dominant degradation defence

MG38F contains an unsaturated polybutadiene phase that is sensitive to oxygen at elevated temperature. At 250 °C and above, oxidation begins at the rubber-particle surface and propagates into the styrene-acrylonitrile matrix, increasing yellowness index and reducing notched Izod impact. Yellowness index change can exceed 2.0 units under ASTM E313 after 10 min of static residence in a hot barrel. Production equipment must be purged after any interruption longer than 5 min at processing temperature. Hot-runner manifolds should be designed without dead spots; all internal surfaces should be polished to Ra 0.2 µm or better, and heater-band setpoints should not exceed 260 °C. The melt cushion should be maintained between 2–5 mm to avoid stagnant material in front of the screw tip. If the machine is stopped, barrel temperature should be reduced to 180 °C or the barrel purged with a low-MFR acrylic-based purging compound. Venting is critical because overheated material generates dissolved volatiles that produce burn marks at end-of-fill; vent depth for ABS should be 0.02–0.04 mm with land length 0.5–1.0 mm. Published capillary rheometry data for this specific formulation is limited; therefore process validation on the production tool is required before setting shear-rate limits.

For high-gloss surface replication, tool-temperature selection outweighs melt-flow adjustments

The surface fidelity of MG38F is controlled by solidification rate at the polymer–steel interface. A mould temperature of 60–70 °C delays skin formation and allows the melt to replicate polished cavity surfaces, producing gloss readings above 90 GU at 60° under ISO 2813. At mould temperatures below 40 °C, the surface freezes quickly, leaving visible flow-direction microgrooves and reducing gloss to 50–70 GU. The trade-off is cooling time: increasing mould temperature from 40 °C to 70 °C may extend cooling time by 10–20 % for a 2 mm wall. Tool steel should be polished to N1–N2 finish; textured surfaces require a minimum texture depth of 25 µm to remain legible. External mould release agents are not recommended because they lower surface energy and contaminate subsequent painting or solvent bonding. If silicone release is unavoidable, the moulded part should be subjected to plasma or corona pre-treatment with a surface-energy target of 40–42 mN/m before adhesion. For solvent-bonded parts, moulded surfaces must remain free of silicone-based release; migration kinetics into the polymer matrix can cause delamination after adhesive cure.

Why notched impact rather than tensile strength limits the design envelope

For unfilled ABS, tensile strength is relatively forgiving across normal processing conditions, while notched impact is sensitive to rubber-phase degradation, moisture, and regrind. The notched Izod impact of MG38F under ISO 180/1A at 23 °C is published at 24 kJ/m², but degraded material can fall below 12 kJ/m² after excessive residence time at melt temperature. Snap-fit assemblies should not be designed with sharp inside corners; a minimum radius of 0.5 mm reduces stress concentration. Living hinges are not recommended in ABS because repeated flexing leads to stress-whitening and hinge failure; rigid snap fits with deflection angle below 2° are preferred. If a part is subject to drop loading at low temperature, notched Charpy impact under ISO 179/1eA should be measured at −30 °C to establish the ductile-to-brittle transition. Published data for this specific configuration is limited, so part-specific validation is required. Tensile stress at yield of 44 MPa under ISO 527-2/50 should not be used as the sole design basis; creep, fatigue, and chemical exposure require separate part-specific testing.

Appearance defects in MG38F mouldings are typically associated with moisture, shear, and venting. Silver streaks are observed when residual moisture exceeds 0.05 % or when screw speed exceeds 100 m/min at the feed zone; corrective action is to reduce screw rotation to 50–80 m/min and increase back pressure to 0.5 MPa. Splay at the gate often indicates shear heating in small gates; the gate shear rate should be calculated from part weight, injection time, and gate cross-section, and kept below 100,000 s⁻¹. Burn marks at end-of-fill indicate insufficient venting. Sink marks are corrected by increasing hold pressure from 50 MPa to 80 MPa or by reducing nominal wall-thickness variation below 20 %. Warpage in flat parts is controlled by differential mould temperature: the core should be 10–20 °C cooler than the cavity to direct shrinkage toward the non-appearance surface. If a hot runner is used, the valve gate should close before screw recovery ends; a delay of 0.2–0.5 s minimises drool and stringing. These adjustments are based on injection-moulding-machine behaviour with a 20:1 L/D screw and a 25 mm-diameter check-ring non-return valve; actual settings require tool-specific optimisation.

The chemical resistance profile of MG38F is governed by the styrene-acrylonitrile matrix and the unsaturated butadiene phase. Ketones, esters, chlorinated hydrocarbons, and aromatic solvents attack the matrix and can induce environmental stress cracking when moulded-in stress exceeds the critical strain. For components exposed to isopropyl alcohol, hand creams, or food oils, design strain should be limited to 0.5 % and parts should be annealed for 2 h at 70 °C to relax orientation. Continuous exposure to hot water above 60 °C can produce surface crazing; published data for MG38F in hot-water immersion is limited, and testing under ISO 22088-3 is required for part-specific validation. Ultraviolet light causes yellowing and surface embrittlement because the polybutadiene rubber phase absorbs UV and forms carbonyl species. Outdoor use of unpigmented MG38F is not recommended; a UV-stabilised grade or an opaque coating must be specified. For indoor applications, lightfastness under ISO 105-B02 should be evaluated if the part is continuously illuminated. The material is not inherently flame-retardant; a UL 94 classification of HB at 1.5 mm is typical for natural unfilled grades, but final classification is colour- and thickness-dependent and must be verified on the production tool.

Regulatory compliance remains the converter’s obligation on the finished article

Regulatory compliance depends on lot-to-lot verification and the final article’s additives. The natural resin is not expected to contain substances of very high concern above the 0.1 % w/w threshold under REACH Article 33; however, the converter carries responsibility for finished-article communication. RoHS screening under IEC 62321 verifies that lead, mercury, cadmium, hexavalent chromium, and the phthalates remain below the maximum concentration values in Directive 2011/65/EU Annex II. The material is not classified as a hazardous substance under CLP; safety data sheet section 2 should be consulted for melt fumes and thermal degradation products. For food-contact or medical use, no implicit approval can be assumed; specific migration testing under Regulation (EU) 10/2011 or FDA 21 CFR 177.1020 must be completed on the final moulded article. The following checklist summarises typical regulatory positions for natural, unfilled MG38F.