Sinopec INEOS Styrolution ABS GP-35 is a general-purpose acrylonitrile-butadiene-styrene injection moulding resin supplied in pellet form within the Sinopec INEOS Styrolution joint-venture portfolio. The grade is classified as a medium-flow, balanced-impact ABS for technical components that require predictable filling behaviour, acceptable heat resistance, and moderate toughness. The polymer is composed of a styrene-acrylonitrile continuous phase with dispersed polybutadiene rubber particles, without halogenated flame retardant. It is used in appliance housings, small electrical enclosures, office equipment components, and automotive interior trim when the mechanical demand does not require high-impact or high-heat specialised grades.

The GP-35 designation identifies a flow-impact compromise within the general-purpose ABS range. It differs from high-impact ABS resins by a lower rubber content and a higher melt volume-flow rate, which reduces injection pressure and improves moulding productivity but lowers notched impact strength, particularly at sub-zero temperatures. The grade is intended for injection moulding; it is not optimised for sheet extrusion or profile extrusion because melt strength and drawdown behaviour are not the primary design targets.

What separates GP-35 from low-flow high-impact ABS grades?

The principal difference is observed under ISO 1133-1:2022 at 220 °C with a 10 kg load. GP-35 exhibits a melt volume-flow rate of approximately 21 cm³/10 min, whereas many high-impact ABS grades with larger rubber particle structures fall in the range of 8–12 cm³/10 min under identical conditions. The rheological gap directly affects mould-filling pressure and clamp force in identical cavities. The higher flow of GP-35 permits longer flow paths, thinner wall sections, and increased cavitation on the same injection moulding machine, but the melt can also penetrate small vent gaps more easily if the vent depth is not controlled.

The impact trade-off is quantified under ISO 179-1/1eA. At 23 °C, GP-35 is typically reported at 18 kJ/m², while high-impact ABS grades commonly exceed 25 kJ/m². At −30 °C, the notched Charpy value drops to approximately 6 kJ/m², indicating cold-temperature brittleness and reduced suitability for low-temperature impact duties. The lower rubber content also raises surface hardness and improves dimensional stability, but it makes the material more susceptible to notch sensitivity and weld-line embrittlement.

For moulders, the practical consequence is that GP-35 should be selected when cycle time, cavity balance, and surface appearance are more critical than ductile failure resistance. If the part must withstand repeated impact at freezer temperatures or heavy drop loads, a higher-impact grade with a lower melt flow is required.

Mechanical, thermal, and rheological data under ISO and ASTM protocols

Representative published property values for the unfilled injection moulding grade are summarised below. Values measured on dry-as-moulded specimens under ISO 527-2 and ISO 179-1/1eA may differ from ASTM D638-14 or ASTM D256 results because specimen geometry, strain rate, and notch radius are not identical.

The tensile modulus of 2300 MPa places the product in the medium-stiffness ABS class. The low nominal elongation at break of 2.5 % indicates that the material is relatively brittle under tensile deformation; part geometries should avoid sharp notches, abrupt wall-thickness changes, and high local strain. The heat deflection temperature under 1.80 MPa load is 94 °C, which is adequate for indoor appliance and enclosure applications but is below that of heat-resistant ABS grades that may reach 105–115 °C under the same protocol.

Mould shrinkage of 0.4–0.7 % is direction-dependent and influenced by gate type, packing pressure, and pigment loading. The shrinkage anisotropy of unfilled ABS must be considered when fitting metal inserts, snap-fit features, or chassis-mounted bosses.

Published data for this specific joint-venture label under UL 746B relative thermal index testing is limited. Processors should not assume a formal electrical or mechanical long-term temperature index without obtaining the current product stewardship documentation from the manufacturer.

Once pellet moisture content exceeds 0.1 wt%, dried-pellet hopper residence should not exceed 30 minutes

GP-35 pellets absorb atmospheric moisture during storage. At 23 °C and 50 % relative humidity, equilibrium moisture content of unfilled ABS can reach 0.2–0.35 wt%. Injection of undried pellets produces splay marks, silver streaks, jetting, and structural defects caused by vaporisation of water at the nozzle and in the cavity. A dew-point controlled desiccant dryer is required. Pre-drying at 80 °C for 2–4 h reduces residual moisture below 0.1 wt%. Drying beyond 4 h should be avoided because prolonged heat exposure in the hopper can cause yellowing and odour development.

The dryer should deliver air at a dew point below −30 °C. If an open hopper is used in an environment above 60 % relative humidity, the dried pellet bed can re-absorb surface moisture within 20–30 min. The feed throat should be purged with dry air or the hopper should be closed and insulated. Pellets that have remained in a non-dried hopper beyond this period should be returned to the dryer before processing.

Melt temperature should not exceed 260 °C. At nozzle temperatures above 280 °C, the butadiene phase begins oxidative and shear-induced degradation within 5 min of residence time, generating yellowing, free butadiene odour, and reduced impact strength. Injection units with hot runners should avoid dead spots where molten resin can stagnate and degrade.

Melt pressure loss, gate freeze-off, and clamp tonnage estimation

Injection moulding of GP-35 is normally conducted with melt temperatures of 230–250 °C and mould surface temperatures of 40–80 °C. Reciprocating-screw machines with general-purpose screws of L/D 20:1–25:1 and compression ratio 2:1–2.5:1 are acceptable. Screw peripheral speeds should be kept in the 0.1–0.3 m/s range; excessive screw speed can generate frictional heat and reduce melt viscosity control.

Back pressure is maintained at 0.5–1.5 MPa to homogenise the melt without extending residence time. The exact value depends on colour dispersion requirements. Higher back pressure increases melt temperature and may degrade the butadiene phase if the cycle is interrupted.

Mould-filling pressure is geometry-dependent. For a typical 2.5 mm wall-thickness plaque, cavity pressure at end of fill often falls between 30 MPa and 50 MPa for unfilled ABS. Clamp tonnage can be estimated from the projected part area multiplied by the expected cavity pressure. A part with projected area of 200 cm² therefore requires approximately 600–1000 kN of clamp force. Actual clamp pressure must be increased when the mould is overpacked or when the screw cushion is too large. In multi-cavity tools, flow imbalance of 10–15 % can occur unless runner balancing is verified with short-shot studies.

Gates should be sized to prevent premature freeze-off before the packing phase is complete. For an unfilled ABS of this flow class, a round tunnel gate diameter of 0.8–1.5 mm is typical for wall thicknesses of 2–3 mm. Edge gates should use a land length of 0.5–1.0 mm. Hold pressure should be maintained for 1–3 s/mm of nominal wall thickness to control sink marks and shrinkage variation.

Hot runner systems should be operated at 240–260 °C. Elevated hot runner temperatures above 280 °C are not permitted. Internal valve gates should be adjusted so that the gate mark does not remain recessed or raised; ABS of this grade is sensitive to gate vestige cracking if the gate diameter is below 0.8 mm and high injection speed is used.

Regrind can be incorporated at a maximum of 20 wt% without eliminating the required impact properties, provided the regrind is clean, dry, and not degraded by previous thermal cycles. Higher regrind fractions shift the melt volume-flow rate upward and reduce notched impact strength below the as-published value. A mixture containing regrind should be re-qualified against the relevant section of ISO 179-1/1eA because batch-to-batch variability in recycled rubber particle size affects crack propagation and weld-line strength.

Chemical resistance of GP-35 follows the solubility behaviour of styrene-acrylonitrile copolymers. Aromatic hydrocarbons, ketones, esters, chlorinated solvents, and strong acids can cause stress cracking and softening. Alcohols, aliphatic hydrocarbons, dilute acids, and dilute alkalis are generally tolerated at room temperature, but chemical exposure should be tested under realistic load conditions using ISO 22088 or equivalent stress-cracking protocols.

Paint adhesion and electroplating are possible but require surface preparation. When painting, an ABS-specific primer is recommended. Because GP-35 is not a plating-optimised ABS grade, electroplated adhesion may be inferior to grades with larger, swellable rubber particle structures. Published peel strength data for this specific configuration is limited. If the component must meet a minimum chrome-plating peel strength, a plating-grade ABS should be specified instead of GP-35.

GP-35 differs from heat-resistant ABS grades by a lower Vicat softening temperature of 98 °C and a lower continuous-use ceiling. It is not an outdoor weatherable material because it contains no UV stabiliser package; prolonged sunlight exposure causes yellowing and surface embrittlement. For exterior unpainted applications, an ASA or ASA/PC grade should be considered. For applications requiring UL 94 V-0 flame retardancy, GP-35 is not suitable because it is a non-flame-retarded general-purpose grade.

For appliance housings, small electronic enclosures, and interior trim parts with moderate mechanical loading, GP-35 provides a reproducible processing window when the melt is dried, the hot runner is controlled, and the mould is packed correctly. The material should be specified only after a physical trial confirms that the part meets the required impact, heat, and chemical exposure standards defined in the end-use specification.