Sinopec Shanghai Gaoqiao ABS 275 is an injection-molding acrylonitrile-butadiene-styrene terpolymer supplied by Shanghai Gaoqiao Petrochemical Corporation, a Sinopec subsidiary. The grade is supplied as natural or pre-colored cylindrical pellets with a bulk density in the 0.55–0.65 g/cm³ range and carries CAS number 9003-56-9. Commercial documentation positions the 275 series in the medium-flow segment of the Gaoqiao ABS portfolio, where the balance between melt fluidity, surface hardness, dimensional stability, and moderate impact resistance is intended for appliance housings, electronic enclosures, and selected automotive interior components. Manufacturer datasheet values for the 275 series may vary by lot, particularly after color masterbatch addition; where the current public datasheet does not report a specific property, this introduction records the corresponding injection-grade ABS range and identifies the limitation explicitly.

The material consists of a continuous styrene-acrylonitrile copolymer matrix and a dispersed polybutadiene rubber phase grafted with styrene-acrylonitrile chains. This two-phase architecture controls notch sensitivity and gloss retention. The rubber phase initiates crazing and shear yielding instead of brittle crack propagation, while the grafted SAN layer reduces interfacial tension and prevents rubber particle coalescence during melt processing. The grafted layer also influences melt elasticity, which is observed as die swell during extrusion and gate blush during injection molding.

What Molecular and Morphological Variables Control the 275 Flow–Impact Balance?

In ABS terpolymerization, the melt mass-flow rate at 220 °C and 10 kg piston load is governed by the molecular weight of the SAN matrix, the rubber particle size distribution, and the grafted SAN layer thickness. For a medium-flow grade such as the 275, the matrix molecular weight is lower than that of an extrusion-grade ABS but higher than that of a super-high-flow thin-wall grade. Published product literature for this exact Gaoqiao grade remains limited; however, ABS grades of the same nominal flow class commonly exhibit melt mass-flow rates in the 10–20 g/10 min range when measured under ISO 1133-1:2022. The molecular weight distribution is typically controlled to a polydispersity index between 2.0 and 3.5 to maintain mechanical strength while limiting injection pressure below 120 MPa in multi-cavity tools.

The polybutadiene content of the 275 series is expected to lie between 10 wt% and 18 wt%, with grafted SAN content on the rubber surface near 30–50 wt% of the dispersed phase. This rubber level places the notched Izod impact strength at 18–28 kJ/m² at 23 °C under ISO 180/A. The cross-link density within the polybutadiene particles is adjusted to prevent excessive particle deformation in high-shear compounding on 40:1 L/D twin-screw extruders. A high cross-link density increases impact strength but also reduces melt flow and surface gloss; therefore the 275 series is not optimized for ultra-high-gloss piano-black applications.

Commercial ABS polymerization often uses a bimodal polybutadiene particle size distribution to balance impact strength and gloss. Particles below 0.5 µm increase gloss and maintain flow, while particles above 1.0 µm increase impact strength and reduce gloss. For the 275 series, the particle size distribution is biased toward the smaller diameter fraction, but the exact median and span are not disclosed in public datasheets. The graft shell thickness on the rubber particles is in the 0.05–0.15 µm range for comparable grades; shell thickness below 0.05 µm can lead to rubber particle coalescence, while a shell above 0.20 µm can raise melt viscosity and reduce impact efficiency.

Thermal Degradation and Drying Limits Are Set by Nitrile Hydrolysis in the SAN Phase

Hydrolysis of nitrile groups in the SAN matrix is the dominant degradation pathway when residual moisture exceeds 0.1 wt%. Before melt processing, pellets should be dried in a desiccant dryer with a dew point not higher than -30 °C, at 80±5 °C for 3–4 h. The practical melt temperature window is 210–240 °C; exposure above 250 °C accelerates depolymerization of the SAN phase, generates yellowing species, and may increase residual acrylonitrile monomer in the molded part. Typical barrel profiles from feed throat to nozzle are 190 °C, 210 °C, 220 °C, and 230 °C across four zones.

Screw rotational speeds of 80–150 rpm and backpressure of 0.5–1.5 MPa are retained for reciprocating screws of 25–40 mm diameter. General-purpose screws with 20:1 to 25:1 L/D and compression ratios from 2.0:1 to 2.8:1 are adequate. Cushion values between 3 mm and 6 mm reduce gas entrapment and improve shot consistency in 8–16 cavity hot-runner molds. Production-scale vent ports should be held below 0.02 mm depth to prevent flash without trapping volatiles.

Moisture regain after drying is rapid at high humidity; pellets exposed to 60 % relative humidity for more than 30 min can re-absorb sufficient water to exceed 0.1 wt%. Use of hopper receivers with dry-air blankets or vacuum loading reduces moisture regain. Regrind content above 30 wt% may increase moisture pickup and lower melt stability due to repeated thermal history.

At 23 °C and 40 % relative humidity, representative mechanical data for this grade class show tensile yield stress in the 45–52 MPa range under ISO 527-2:2012, flexural modulus between 2,300 MPa and 2,700 MPa under ISO 178:2019, and Rockwell hardness between 105 and 115 R under ISO 2039-2. The notched Izod impact strength at -30 °C is usually reduced to 8–12 kJ/m². The tensile modulus is typically 2,300–2,600 MPa, and elongation at break is usually 10–20 % at 23 °C. These values are not a certificate of analysis; color concentrates, mold release, and regrind content can shift the measured values by 5–10 %.

If Grade 275 Is Substituted for a 25 g/10 min High-Flow ABS in Multi-Cavity Packaging Tools

Substitution with a 25 g/10 min high-flow ABS may require 15–25 % lower injection pressure to fill 1.0 mm walls, but it typically sacrifices weld-line strength and environmental stress cracking resistance. The 275 grade is selected when the minimum wall thickness is 1.5 mm or greater and cycle time is cooling-limited rather than flow-limited. In such molds, the medium melt flow rate can still produce short shots if the nozzle diameter is below 2.5 mm or if the gate land length exceeds 0.8 mm.

Within the Gaoqiao ABS portfolio, the 275 series is positioned as a moderate-impact, medium-flow molding resin. It differs from the high-rigidity 8434 series, which emphasizes higher stiffness and lower rubber content for office equipment and structural enclosures. It also differs from flame-retardant ABS grades in that halogenated or phosphorus-based additives are absent, and from high-heat ABS grades in that alpha-methylstyrene is not a significant comonomer. The absence of high-heat comonomer slightly lowers the heat deflection temperature but improves color stability during regrind processing.

Compared with polycarbonate/ABS blends, the 275 grade offers lower heat resistance and lower low-temperature impact strength but can be processed at 20–30 °C lower melt temperature and with lower mold temperature. Compared with ASA, the 275 grade has lower outdoor UV stability because the polybutadiene rubber phase is more susceptible to photo-oxidation than acrylic rubber. At 220 °C and shear rates from 100 s⁻¹ to 1,000 s⁻¹, apparent viscosity for medium-flow ABS typically falls from 350 Pa·s to 90 Pa·s. The power-law index is approximately 0.3–0.4; this shear-thinning behavior permits filling of reinforcing ribs and bosses without excessive pack pressure.

In electrical enclosures and appliance control-panel applications, the 275 grade is evaluated under IEC 60695-11-10. It is commonly supplied with a UL 94 HB rating at 3.0 mm thickness; this is not a fire-safety rating for unattended high-energy electronics. Compliance with RoHS Directive 2011/65/EU and REACH Regulation EC No 1907/2006 is documented by the manufacturer’s technical department. Contact with strong oxidizing acids, aromatic solvents, and ketones should be avoided because these media induce craze propagation through the SAN matrix and can reduce the retained notched Izod impact by more than 50 % after 24 h immersion at 23 °C.

Appliance housing parts molded from the 275 grade are frequently tested for dimensional stability under ISO 294-4:2018 after 48 h at 80 °C. Linear mold shrinkage is typically 0.4–0.7 % along flow and 0.4–0.6 % transverse to flow, depending on wall thickness and packing pressure. Higher packing pressures reduce shrinkage but can increase internal stress and subsequent stress cracking. Notched Izod impact values measured under ISO 180/A are sensitive to gate orientation and knit-line location; weld-line efficiency for this class is commonly 40–60 % of the un-welded value when tested perpendicular to a cold weld line.

Environmental Stress Cracking Resistance in Palm Oil and Isopropanol Environments

When molded parts are exposed to palm oil, hand cream, or isopropanol, the SAN matrix absorbs the penetrant and swells, producing surface whitening and micro-cracking at molded-in stresses. Annealing at 80 °C for 2 h after molding lowers residual stress and extends time-to-cracking in isopropanol from approximately 5 min to greater than 30 min in bending jig tests. Continuous exposure to diesel fuel and methyl ethyl ketone remains outside the recommended service envelope for the 275 grade. In high-gloss applications, solvent wiping with isopropanol should be limited to 10–15 s at 20–25 °C followed by forced-air drying at 50 °C for 15 min to reduce micro-craze formation.

On horizontal injection molding machines with clamp force from 800 kN to 2,500 kN, gate blush and jetting are reported when injection speed exceeds 120 mm/s at a melt temperature of 225 °C. Reducing screw speed to 100 rpm and backpressure to 1.0 MPa improves melt homogeneity and reduces unmelted SAN agglomerates visible as clear specks in dark colors. For cold-runner tools with 2.5 mm runners, valve-gate hot tips improve gate cosmetics but increase pressure drop by approximately 10 MPa compared with open nozzles. These are conservative starting points for this grade class; tool-specific validation is required because published data for the exact 275 configuration is limited.