Supplied as transparent pellets, INEOS Styrolution Luran SAN 51 is a general-purpose styrene–acrylonitrile random copolymer. Density is 1.08 g/cm³ when measured to ISO 1183-1. Melt-volume rate is 25 cm³/10 min under ISO 1133-1 at 220 °C with a 10 kg piston load. The material is unmodified with rubber; notched Charpy impact is 2 kJ/m² at 23 °C under ISO 179-1/1eA. These properties place the grade among rigid transparent thermoplastics rather than impact-modified clear resins. The product is specified for thin-wall injection-moulded parts where optical clarity, surface hardness, dimensional stability in humid interiors and resistance to dilute detergent contact define acceptance.

The acrylonitrile comonomer increases tensile modulus and chemical resistance relative to crystal polystyrene. Mould shrinkage is reported as 0.4–0.6 % under ISO 294-4. Water absorption after 24 h at 23 °C is approximately 0.2 % under ISO 62. These values support the use of SAN 51 in clear household goods, cosmetic packaging, stationery and appliance panels. No long-term weathering statement is supplied on the general-purpose datasheet.

What separates Luran SAN 51 from crystal polystyrene, PMMA and transparent ABS in rigid component design?

General-purpose polystyrene typically shows tensile modulus near 3.0–3.3 GPa and Vicat softening below 100 °C, and it stress-cracks in contact with hydrocarbon-based processing aids and release agents. Luran SAN 51 increases short-term tensile modulus to 3700 MPa under ISO 527-2/1A/50 and Vicat VST/B/50 to 106 °C under ISO 306. Compared with cast PMMA, Luran SAN 51 transmits approximately 90 % of visible light at 2 mm wall thickness to ISO 13468-1, whereas PMMA commonly exceeds 92 %. PMMA retains superior outdoor UV resistance and scratch resistance; SAN 51 offers lower melt viscosity and fills long thin-wall paths at lower barrel temperature. Transparent ABS grades raise notched impact above 10 kJ/m², but their modulus is typically below 2500 MPa, so SAN 51 is selected when stiffness and chemical resistance exceed impact requirements. Within the Luran SAN family, the 51 grade is differentiated by its comparatively high MVR; lower-flow grades are used for thick sheet and profile extrusion where higher molecular weight is needed for melt strength.

In injection moulding, the 25 cm³/10 min MVR does not by itself define filling pressure because SAN 51 is shear-thinning. Simulation of filling should use grade-specific rheological data obtained by capillary rheometry rather than default GPPS curves. The material routinely fills 1.2 mm wall sections over flow lengths up to 150 mm at injection pressures of 100–140 MPa. In multi-cavity tools, pressure-limited machines can exhibit short shots in the final cavity when runner pressure drop consumes the available injection pressure. Balanced runner layouts and consistent venting are required; SAN 51 does not have a broad processing window for both transparency and dimensional repeatability at high flow. Flow fronts meeting at weld lines retain lower local strength even when the bulk material is processed within specification.

Thermal–mechanical property envelope at 23 °C and short-term load

Typical values from the manufacturer’s single-point datasheet are summarised below. They are not batch-to-batch specification limits unless the procurement agreement states otherwise.

These values do not define long-term creep, fatigue or chemical-loading limits. Under sustained flexural load, the apparent modulus decreases with time and temperature; no creep master curve is included in the standard datasheet, so load-bearing parts require additional testing to ISO 899-2. The tensile yield strain of 3.2 % is an upper bound for reversible deformation; local stress concentrations at gates, bosses and sharp corners reduce the allowable strain below 2 % unless fillet radii of at least 0.5 mm are used. Notched Charpy impact of 2 kJ/m² indicates brittle failure in sharply notched sections under sudden load.

Pre-drying is mandatory before melt processing. Residual moisture above 0.05 % by mass, measured by Karl Fischer titration or ISO 15512, produces splay, gate haze and bubble defects at weld lines. Desiccant drying at 80 °C for 2–4 h is typical; the shorter residence time is valid only when drying-air dew point is held at or below −30 °C. In bulk rail deliveries to humid coastal plants, pellet moisture after outdoor silo storage has exceeded 0.15 % by mass and caused intermittent clear-part bubbling even when hopper controllers indicated the target dew point. Inlet drying air should not exceed 85 °C; higher temperatures soften pellet surfaces, generate fines and create feed-bridging at the machine throat.

If the hot-runner gate temperature exceeds 270 °C, degradation indicators and detection

Thermal degradation accelerates when hot-runner gate drops remain above 270 °C. The first indicator is yellowness-index drift in clear parts measured to ASTM E313. At residence times above 5–10 min at upper barrel settings, black specks, surface splay and local molecular-weight reduction at the gate follow. Degraded boundary layers reduce weld-line strength and increase melt-pressure variability. Gate drops and nozzle tips are therefore limited to 270 °C or below. Low-viscosity colorant carriers can lower the thermal stability margin further because the carrier phase may degrade and contaminate boundary layers. After hot-runner interruptions, purging should use rigid SAN or GPPS purging compound; olefinic purges are incompatible and leave visible contamination. The practical clear-part melt-temperature window is 240–250 °C when hot-runner shear heating is present, even though barrel settings can span 230–260 °C.

Barrel zones are set between 230 °C and 260 °C, with the rear zone at the lower end. Mould temperature is controlled between 40 °C and 80 °C; lower values reduce cycle time and preserve transparency, and higher values improve weld-line strength and reduce internal stress in thick sections. A three-zone screw with L/D ratio of 20:1 to 25:1 and a non-return valve is adequate. Holding pressure is typically set at 60–70 % of peak injection pressure. Higher packing pressures raise residual stress and increase sensitivity to environmental stress cracking when parts later contact alcohol-based cleaners. In a 24-cavity valve-gated cosmetic closure tool, fill times below 0.8 s have been recorded at 245 °C melt temperature; short shots occur when screw-forward time is ended before gate freeze. Cosmetic defects are concentrated at gate vestige and micro-sink opposite gates. These are controlled by balancing decompression, holding time and mould temperature.

Shot-size utilisation should remain above 30 % of barrel capacity. At lower utilisation, residence time extends beyond the stable range and yellowing appears in clear parts before black specks are visible. Injection velocity is set to avoid jetting; excessively high velocity creates wavy surface defects and gate blush. Mould venting depth for SAN 51 is typically 0.02–0.03 mm. Insufficient venting causes burn marks and weak weld lines at the end of fill.

Weld-line strength is a function of melt-front temperature at the meeting plane. When two flow fronts meet downstream of a core or boss, local temperature below 200 °C produces visible weld lines and reduces local tensile strength relative to the bulk value. Mould temperature at the upper end of 40–80 °C, sequential valve gating, or repositioning of the gate can shift weld lines away from the section with maximum stress. For snap-fit arms, the nominal outer-fibre strain should not be designed to 3.2 %; a practical limit of 1.5–2.0 % is used when weld lines or gate stress concentrations are unavoidable. Failure in field testing has been traced to weld-line location rather than bulk material property when snap arms crack at assembly. This production experience supports gate-location validation before tool steel is cut.

Short-contact resistance to dilute acids, aqueous alkalis and aliphatic hydrocarbons is characterised by immersion testing to ISO 175. Aromatic hydrocarbons, chlorinated solvents, ketones and esters attack the matrix; under residual moulded-in stress, microcracks appear within minutes to hours after wipe exposure to toluene or methyl ethyl ketone. Ethanol–water formulations are stress-cracking-active above approximately 50 % by volume, so bent-strip testing under ISO 22088-3 is required for hand-rub dispenser components. The acrylonitrile comonomer improves resistance to aliphatic oils relative to GPPS but does not provide solvent resistance equivalent to semicrystalline polyolefins.

For European Union food-contact parts, finished-article compliance is established under Commission Regulation (EU) No 10/2011 using migration tests with prescribed food simulants. Raw-resin statements do not replace article-level verification because processing history, wall thickness, surface-to-volume ratio and contact time shift migration. The grade is stated not to contain deliberate additions of cadmium, lead, mercury or hexavalent chromium, which supports RoHS (EU) 2015/863 screening; it does not replace XRF or wet-chemical verification on the moulded article. No USP Class VI statement is supplied on the general-purpose datasheet; change-controlled biocompatibility data must be requested for medical or drug-contact applications.

Luminous transmittance at 2 mm wall thickness is approximately 90 % to ISO 13468-1. Haze and flow-line visibility depend on mould polishing, cavity surface temperature and gate design. In multi-cavity production, inconsistent cavity temperature can generate visible flow lines and colour difference in tinted parts. Published optical data for specific pigmented or laser-marked configurations are limited; processors should generate haze, colour and near-gate clarity data on the actual cavity geometry before release.

Transparent appliance control panels, cosmetic caps, office-stationery components and durable consumer goods are produced from Luran SAN 51. The melt-volume rate permits thin walls of 1.2 mm without flash when parting-line flatness is maintained at 0.01 mm across the tool. In a clear appliance panel with a 0.8 s fill time, gate blush at the tunnel gate and micro-sink at bosses are controlled by melt temperature of 240–250 °C and holding pressure of 60–70 % of peak injection pressure. Ultrasonic welding of SAN 51 to itself is performed at 20 kHz with an energy director; shear strength above 10 MPa is obtained on dry joint surfaces free of mould-release residue. Hot stamping, pad printing and laser marking must keep local surface temperature below the Vicat region of 106 °C to avoid gloss change and distortion. Solvent bonding with cyclohexanone or dichloromethane is restricted to non-load-bearing aesthetic assemblies because residual moulded-in stress reduces bond strength; joints are validated by tensile-shear testing to ISO 527-2 on representative moulded coupons.