LyondellBasell Hiloy SAN 247 is an amorphous styrene-acrylonitrile copolymer supplied as a pelletised injection-moulding grade. The designation “SAN” identifies the polymer backbone as poly(styrene-co-acrylonitrile), while the Hiloy prefix places it within the LyondellBasell engineering thermoplastics portfolio. Grade-specific datasheet values for this exact material are limited in public literature and should be obtained from the current LyondellBasell technical data sheet. The performance boundaries described below are therefore based on the established behaviour of unfilled styrene-acrylonitrile copolymers and on standardised test methods.

What Separates SAN 247 from ABS and Polystyrene in Chemical and Thermal Loading?

The key structural distinction is the absence of a dispersed polybutadiene rubber phase. ABS contains grafted rubber particles that raise notched impact strength but introduce oxidative and thermal-degradation pathways. Unfilled SAN grades comparable to Hiloy SAN 247 typically exhibit notched Charpy impact values of 2–4 kJ/m² at 23 °C under ISO 179-1:2010, while medium-impact ABS grades commonly exceed 10 kJ/m². The trade-off is higher resistance to aliphatic hydrocarbons and detergent solutions, with lower yellowing linked to rubber-phase oxidation. General-purpose polystyrene has lower tensile yield stress, generally below 55 MPa under ISO 527-2:2012, whereas unfilled SAN grades have yield stress in the range 60–75 MPa. Vicat softening temperature under ISO 306:2022 method B50 is typically 95–110 °C for SAN, approximately 10–20 °C higher than standard polystyrene grades. These differences position Hiloy SAN 247 where transparency or translucency, chemical resistance, and moderate heat resistance are required but low-temperature ductility can be sacrificed.

Chemical resistance evaluation under ISO 175:2010 is performed by measuring mass change, dimensional change, and tensile property retention after immersion in service fluids. SAN copolymers generally resist aqueous detergents, food oils, cosmetic emollients, aliphatic hydrocarbons, and many dilute acid and alkali solutions. Aromatic hydrocarbons, chlorinated solvents, ketones, and esters act as stress-crack agents; stressed mouldings exposed to these fluids can lose more than 30% of tensile strength after short contact. Applications involving aggressive ester-based cosmetic formulations therefore require validation, and published data for this exact Hiloy SAN 247 configuration in such media is limited. For food-contact and medical housings, compliance must be verified against the final article because migration behaviour depends on wall thickness, processing history, and surface-to-volume ratio.

Within the Hiloy SAN family, the 247 grade is distinguished from glass-reinforced and high-flow SAN compounds by mechanical and rheological positioning. Glass-reinforced SAN can exceed flexural modulus 7000 MPa under ISO 178:2019, whereas unfilled SAN is generally in the range 3700–3900 MPa. The reinforced grades lose translucency and have higher density, typically above 1.20 g/cm³, limiting their use in transparent enclosures. High-flow SAN grades may achieve melt volume-flow rates above 25 cm³/10 min under ISO 1133-1:2022, allowing thin-wall fill below 1.0 mm but reducing weld-line strength and chemical stress-crack resistance. A medium-flow designation such as Hiloy SAN 247 is therefore selected when section thickness exceeds 1.5 mm and sink resistance, surface quality, and solvent resistance outweigh the need for extreme flow. Published grade-specific MVR for Hiloy SAN 247 is not stated here; the current LyondellBasell datasheet should be consulted.

Thermal Degradation and Residence-Time Limits in Melt Processing

Unfilled SAN is thermally sensitive during melt processing. Degradation is identified by yellowing, reduced melt viscosity, and volatile oligomer evolution. On production equipment, barrel residence time at melt temperatures above 240 °C should remain below 5 min unless the material is frequently purged. A screw with L/D ratio 20:1 to 25:1 and compression ratio 2.0:1 to 2.5:1 is usually suitable; high-compression screws above 3.0:1 raise local shear heating and produce silver streaks in transparent parts. Pre-drying at 80 °C for 2–4 h in a desiccant dryer with dew point ≤ −20 °C is required to reduce residual moisture below 0.10%. If ambient relative humidity exceeds 60%, drying should be extended toward 4 h unless the material is supplied in moisture-proof packaging. Moisture above 0.15% at processing temperature can hydrolyse acrylonitrile repeat units and reduce molecular weight, causing splay, lower melt strength, and reduced notched impact in the moulded part.

Injection moulding conditions for unfilled SAN grades are commonly set with nozzle temperature 220–250 °C and mould temperature 40–80 °C. Higher mould temperature improves flow and reduces surface stress but extends cycle time; lower mould temperature shortens cycle time but increases orientation and internal stress. Holding pressure is typically 50–80 MPa, injection speed is adjusted to fill 90–95% of cavity volume before transfer, and back pressure is maintained at 0.5–1.5 MPa. Clamp force is calculated from projected area and expected cavity pressure; thin-wall applications may reach 35–60 MPa cavity pressure. Grade-specific melt viscosity from the LyondellBasell datasheet for Hiloy SAN 247 must be used for accurate hydraulic pressure drop and clamp force calculations; published data for this exact grade is limited.

On production-scale hydraulic injection lines, batch-to-batch melt viscosity variation in SAN can appear as fill variation if acrylonitrile content changes by 2 wt% or more. Switch-over melt pressure monitoring should flag fluctuations above 3 MPa for thin-wall tools. The granulate should not be purged with PVC or acetal in the same barrel; their degradation residues can generate black specks in transparent SAN. Regrind addition is possible up to 20% in non-critical parts if the regrind is dried and dust-free. For transparent parts, regrind above 10% increases haze and lowers mechanical consistency. Nozzle decompression of 2–5 mm controls drool; excessive decompression draws air and produces bubbles in the next shot. Screw recovery time should remain shorter than cooling time by at least 15% to avoid melt residence-time drift.

Optical Clarity After Repeated Detergent Exposure

In unpigmented form, unfilled SAN can show luminous transmittance of 88–92% at 3 mm thickness and haze below 2% under ISO 13468-2:2021 and ISO 14782:2021. Detergent contact can produce microcrazing that reduces gloss and, in severe cases, transmission. For dishwasher fascia and detergent reservoir applications, cyclic exposure in 0.5–1.0% detergent solution at 60–75 °C for 100–500 cycles should be part of qualification, with haze, gloss, and visible crazing evaluated before and after. Published data for Hiloy SAN 247 under this exact cyclic test is limited, so production-tool validation is required.

Post-moulding shrinkage continues for 24–48 h after demoulding. Conditioning at 23 °C and 50% relative humidity under ISO 291:2008 is required before dimensional inspection. Typical unfilled SAN shrinkage after conditioning is 0.4–0.7% under ISO 294-4:2018, with flow-direction shrinkage generally lower than cross-flow shrinkage when high holding pressure is applied. Sections above 3 mm show greater shrink anisotropy. Dimensional measurements should use coordinate measuring equipment rather than manual callipers for warp-sensitive parts. Gate location and holding-pressure profile are the main process variables controlling shrinkage anisotropy; changing injection speed alone rarely corrects non-uniform shrink.

Shear viscosity of unfilled SAN decreases with increasing shear rate. During injection, melt shear rates at the gate may exceed 10,000 s⁻¹. At such shear rates, pseudoplastic behaviour reduces viscosity relative to low-shear values, but shear heating can also generate local temperatures above the set melt temperature. Rheological measurement under ISO 11443:2021 using a capillary rheometer is therefore recommended for gate sizing and pressure-drop simulation. For cavity filling, a gate land length of 0.5–1.0 mm and gate diameter of 30–50% of wall thickness are typical starting points for unfilled SAN. Pressure drop across a small subgate can exceed 10 MPa, so edge gates are preferred for larger transparent parts.

When Styrene-Acrylonitrile Replaces Polycarbonate in Thin-Walled Consumer Housings

Polycarbonate replacement is possible only when notched impact loads remain moderate and service temperature is below the SAN heat distortion limit. Polycarbonate has notched Charpy impact values above 20 kJ/m² and can operate above 120 °C; unfilled SAN typically fails in brittle mode and distorts under load above 80–90 °C at 1.8 MPa under ISO 75-2:2013. The benefit of SAN is lower melt viscosity in thin walls, transparency, and detergent resistance. For wall sections below 1.2 mm, flow-length validation should use spiral-flow moulding or injection simulation with grade-specific viscosity data. Published spiral-flow data for Hiloy SAN 247 is limited; simulation without measured viscosity can underestimate pressure drop by 10–20%. In hot-water contact above 85 °C, SAN can stress crack or distort; service temperature should be set from HDT under load, not from Vicat alone.

Part design for unfilled SAN should keep nominal wall thickness between 1.0 mm and 4.0 mm. Abrupt wall changes create internal stress; transitions should use 1:3 ramps or radii above 0.5 mm. Rib thickness should be 50–60% of the adjacent wall. Snap-fit arms in SAN require root radii of at least 1.0 mm and gate position away from the tensile face. For transparent parts, weld lines are more visible in unpigmented grades; a single edge gate or fan gate is preferred over multiple subgates. Mould cooling should be designed for uniform heat removal; sections differing by more than 10 °C in demould surface temperature produce differential shrinkage and warp.

Typical application contexts for Hiloy SAN 247 include injection-moulded appliance control fascias, cosmetic packaging closures, personal care accessory components, electrical-equipment windows, and pump filter housings. The material is selected where translucent or transparent parts require chemical resistance to detergents or oils and where long-term load is moderate. In bearing or gear applications with continuous contact stress above 30 MPa, reinforced engineering polymers should be selected instead. In outdoor glazing applications without UV stabilisation, SAN yellows and embrittles under solar UV; this grade should not be specified for continuous exterior exposure.

Incoming resin quality control should include melt flow rate or melt volume-flow rate, moisture content, and visual pellet colour. For transparent grades, yellowness index on moulded plaques under ISO 17223:2014 can be used as a batch acceptance criterion. A shift in yellowness index of more than 2 units may indicate thermal degradation or raw material variation. Shore D hardness under ISO 868:2003 is typically 78–82 for unfilled SAN and can be used for incoming material verification. More detailed verification requires infrared spectroscopy of the acrylonitrile absorption or nitrogen analysis by combustion. Published Hiloy SAN 247 batch acceptance limits should be obtained from LyondellBasell.

Process failures observed on hydraulic injection machines include feed-throat bridging when pellets are stored above 30 °C or dried with insufficient airflow. The feed throat should be held at 25–40 °C to avoid condensation. Splay is usually moisture-related rather than colour-related and appears when moisture exceeds 0.12%. Barrel set-point error of ±10 °C in the transition zone can produce unmelted granules and inconsistent fill. Peak cavity pressure below 30 MPa often indicates gate freeze before adequate packing; it is corrected by increasing hold pressure or gate diameter, not by increasing melt temperature. These machine-level checks are essential because Hiloy SAN 247 is processed in the same thermodynamic window as other unfilled SAN grades, and published data for the exact product remain limited.