INEOS Styrolution ABS NOVODUR 2908 is an acrylonitrile-butadiene-styrene copolymer supplied in pellet form for injection moulding. The grade occupies a high melt-flow position within the manufacturer’s NOVODUR portfolio and is used principally for thin-wall housings, electro-mechanical enclosures, and consumer-interface components where long flow paths, fine ribs, and moderate clamp-force conditions are present. The polymer is a two-phase system consisting of a styrene-acrylonitrile matrix and dispersed polybutadiene rubber particles; melt viscosity, notched impact, and surface appearance are therefore controlled by matrix molecular weight, rubber particle size distribution, grafting efficiency, and final rubber morphology. The 2908 designation is a grade identifier and does not imply glass-fibre reinforcement, mineral loading, or flame-retardant classification.

Representative physical, mechanical, and thermal data are reported under single-point data conventions derived from standardised dry-as-moulded specimens prepared according to ISO 294-1:2017 and ISO 294-4:2018. Comparisons with other ABS grades require identical specimen preparation, conditioning, and test environment because ABS properties are sensitive to moisture uptake, melt-temperature history, and mould cooling rate. The following values are representative datasheet entries and should not be read as minimum or maximum release limits.

Mechanical, thermal, and rheological specification benchmarks

The melt volume-flow rate is a single-point rheological indicator and does not replace capillary rheometry for gate shear-rate analysis. At conditions relevant to fast injection, apparent shear rates at restrictive gates may reach 50 000 s⁻¹ or higher, where shear thinning and viscous heating become significant. Capillary measurements under ISO 11443:2021 or in-line rheometer data should therefore be used for demanding thin-wall simulation rather than extrapolation of the 22 cm³/10 min value alone.

Pre-drying is mandatory before molten processing. At ambient relative humidity above 60 % or after exposure of opened containers to uncontrolled storage, pellets should be dried in a desiccant dryer to residual moisture below 0.1 %. Typical drying conditions are 80 °C for 3 h to 4 h with a dew point below -30 °C. Drying above 90 °C or prolonged hot-hopper residence can cause pellet bridging, surface yellowing, and local thermal degradation. Moisture-related defects in moulded parts include silver streaking, surface splay, gas burn marks, and loss of Charpy notched impact strength through hydrolysis of molecular interfaces and steam expansion at the flow front.

The melt temperature should be selected between 230 °C and 260 °C. The lower end favours colour stability and reduced odour; the upper end improves filling of very thin sections but increases thermal load. At melt temperatures above 270 °C, styrene-acrylonitrile matrix degradation and polybutadiene crosslinking or chain scission become kinetically significant, producing yellow discolouration and reduced notched impact strength. Residence time at 260 °C should remain below 10 min; shorter residence times are required at higher temperatures. Injection units should use a general-purpose screw with an L/D ratio from 20:1 to 24:1, a compression ratio from 2:1 to 2.5:1, and a non-return valve with confirmed closure during decompression. Back pressure between 5 bar and 15 bar is generally sufficient for homogeneous melt delivery; excessive backpressure raises melt temperature through shear work and can generate decomposition volatiles.

Mould temperature influences surface replication, gloss, residual stress, and part dimensions. A range from 40 °C to 80 °C is typical for this grade. Lower mould temperatures shorten cycle time but increase frozen-in molecular orientation and can reduce notched impact; higher mould temperatures improve ripple-free surfaces and lower residual stress but lengthen cooling time. For gloss-critical surfaces, tool polish and grain depth should be fixed before mould trials because ABS gloss measured under ISO 2813:2014 is strongly governed by mould roughness, packing pressure, and melt-temperature uniformity.

When thin-wall flow ratios exceed 150:1

For nominal wall sections below 1.5 mm, flow length-to-thickness ratios above 150:1 cannot be managed by melt-temperature adjustment alone. Gate geometry and gate quantity determine pressure loss, shear heating, and flow-front temperature. An edge gate with 1.0 mm thickness and 2.5 mm width may produce apparent shear rates above 50 000 s⁻¹ during fast filling; high shear reduces viscosity but also increases local temperature. Hot spots above 270 °C can appear at gate lips or hot-runner tips even when the barrel setpoint is below the degradation threshold. Published data for this specific configuration is limited, so production tools require instrumented cavity-pressure and gate-temperature trials rather than reliance on datasheet melt-flow data alone.

Rib thickness should remain between 0.5 and 0.7 times the adjacent wall to avoid excessive sink marks or moulded-in stress. Rib root radii below 0.25 mm act as stress concentrators and reduce impact. Boss features with core pins increase local flow resistance and may require local thinning or flow leaders to avoid short shots at the boss base. Sequential valve-gate hot-runner systems are preferred when flow length exceeds 200 mm; a cold sprue bush should provide a minimum 3.0 mm diameter at the nozzle interface and an included taper of at least 2° to avoid premature freeze-off.

Hot-runner pressure drop should remain below 30 MPa at maximum injection velocity. If manifold or tip temperatures exceed 270 °C, polymer degradation may occur locally even when barrel melt temperature is within the recommended range. Hot-runner tip temperature should be monitored by thermocouple and controlled below 270 °C. For thin-wall tools, clamp force requirements typically fall between 3 kN/cm² and 5 kN/cm² of projected part area, but cavity-pressure data are more reliable than projected-area estimates because filling imbalance can generate high local cavity pressures and flash at the parting line.

Venting is a critical thin-wall processing boundary. For ABS, vent depths from 0.02 mm to 0.04 mm are typical at the parting line; insufficient venting causes burn marks, short shots, and gas entrapment at the last-filled regions. Injection fill time should be set between 0.3 s and 0.8 s for very thin sections, but the exact profile should be adjusted using short-shot studies and cavity-pressure transducers. If the melt cushion falls below 2.5 mm, shot-weight variation can exceed 0.5 % and create dimensional variability, sink marks, or short shots. Gate freeze time at a 1.0 mm pin gate with a 60 °C mould can be below 1 s; hold pressure should be maintained until gate freeze but not excessively beyond it, because overlengthened holding time can create overpacking, flash, and high residual stress.

Differential shrinkage between thick ribs and thin walls is controlled by packing pressure, gate freeze time, and mould temperature symmetry. Mould temperature control circuits should maintain a difference of less than 5 °C between stationary and moving halves. Larger thermal asymmetries cause differential shrinkage and part warpage. Texture depth should be included in draft-angle calculations; untextured side walls may require at least 1° draft per side, while grain depths of 0.05 mm may require 2° to 3° per side for reliable ejection without drag marks.

The differentiation between 2908 and other NOVODUR grades is primarily a melt-flow and impact-energy trade-off. Lower-flow grades in the same product family often exhibit higher low-temperature Charpy notched impact and are preferred for heavy-wall structural parts or components requiring deep-draw thermoforming. Extrusion and sheet grades may be specified at lower melt volume-flow rates to maintain melt strength; 2908 is not positioned as an extrusion or blow-moulding grade. Plating grades are formulated with controlled rubber particle size, grafting level, and surface polarity to allow adhesion of electroless nickel and copper. 2908 is not marketed as an electroplating grade and should not be selected for exterior decorative plating without plate-adhesion testing, etch-angle validation, and thermal-cycle performance data. Direct substitution from higher-impact ABS grades should be validated by cavity-pressure trials and low-temperature impact tests because flow-length improvement is often accompanied by lower Charpy or Izod performance.

Chemical resistance follows general ABS behaviour. Aromatic hydrocarbons, ketones, esters, and chlorinated solvents plasticise or stress-crack the styrene-acrylonitrile matrix. Contact with flexible PVC containing migratory monomeric plasticisers can soften the surface over time, particularly at elevated service temperature. Long-term service with alcohols, diluted aqueous acids, or alkaline cleaners requires environmental stress-cracking evaluation under ISO 22088-2:2006 and chemical resistance testing under ISO 175:2019 using the actual service fluid at the maximum expected temperature. ABS is not suitable for prolonged exposure to strong oxidising acids, chlorinated solvents, or diesel fuel blends without specific validation.

What compliance boundaries apply to global shipment and food-contact use?

Regulatory status is grade-specific and production-lot dependent. Compliance claims should be confirmed with the supplier’s product-stewardship documentation rather than assumed from generic ABS classifications. The following matrix summarises typical confirmation points but does not replace a signed statement from the material manufacturer.

Storage should be in sealed containers below 45 °C, away from direct sunlight and outdoor moisture. Partially used containers should be closed immediately and returned to dry storage. Pellet dust generated from regrind handling is combustible and should be controlled using standard powder-handling procedures. Regrind use from sprues and runners may be acceptable at controlled ratios, but each production lot of regrind must be dried to the same residual-moisture target and should not contain degraded material from previous heat cycles, paint, adhesive, or assembly residues.

For consumer-electronics enclosures with average wall thickness of 1.2 mm, the grade is processed on injection machines in the 1200 kN to 1800 kN clamp-force range. A 25 mm reciprocating screw with a shut-off nozzle prevents melt drool during mould open. Fill time is set between 0.3 s and 0.8 s, and cavity-pressure transducers in the last-filled region are used to set hold pressure and gate-freeze time. Snaps and assembly features should be evaluated using tensile stress-strain data from ISO 527-1/-2:2019 and finite-element analysis, because local strain during assembly can approach the nominal break strain of 10 %. Low-temperature snap-fit tests are required if the component may be assembled or dropped below -20 °C, since notched impact values decline with decreasing temperature and the material’s low-temperature ductility is reduced compared with higher-impact ABS grades.