The styrene-acrylonitrile copolymer INEOS Styrolution Luran SAN 368R Crystal Clear 77851 is a high-flow, transparent injection moulding grade. The numeric grade identifier 368R denotes a low-viscosity SAN formulation, while the 77851 designation identifies the crystal-clear colour package. The material is amorphous, contains no butadiene phase, and derives clarity from a homogeneous copolymer matrix rather than from clarification additives. This grade is specified for transparent consumer goods that require thin-wall fill performance, dimensional rigidity, and resistance to household cleansing agents. Typical production applications include clear cosmetic packaging, appliance indicator lenses, transparent kitchenware components, and clear industrial housings where clarity must be maintained after contact with aliphatic oils. Published datasheet values place the density at 1.08 g/cm³ when measured to ISO 1183-1:2019, and the melt volume-flow rate at 26 cm³/10 min under 220 °C/10 kg loading in ISO 1133-1:2022. The high-flow architecture can reduce injection pressure and short-shot frequency in wall sections below 1.0 mm, but the same molecular-weight reduction requires stricter thermal discipline than a medium-flow SAN.

What processing-stability limits are established for thin-wall transparent moulding?

Moisture uptake above 0.1% by weight is the primary processing-stability boundary for transparent mouldings. Before plastication, the granules are dried in a dehumidified-air dryer at 80 °C for 2–4 h, with a dew point no higher than -20 °C. Residual moisture is measured according to ISO 15512:2019; when drying is omitted or reduced, dissolved water promotes chain scission of the acrylonitrile segments and generates splay, haze, and silver streaking radiating from the gate on polished transparent surfaces. In production-scale trials on hydraulic injection moulding machines with screw diameter between 30 mm and 45 mm, this defect is the primary cause of reject material in clear mouldings. The practical melt-temperature window is 230–260 °C. Operation below 230 °C in thin-wall sections raises melt viscosity sufficiently to produce short shots and visible flow hesitation lines. Operation above 260 °C accelerates thermal yellowing and can shift the transparent 77851 colour package toward a measurable increase in yellowness index. Mould temperature is maintained at 40–70 °C, with lower settings used for fast cycle times and higher settings used for high-gloss replication. On polished transparent mouldings, cavity-surface temperature variation greater than ±5 °C creates visible differences in gloss and haze because cooling-rate changes alter surface replication. Conformal cooling or high-conductivity tool steel reduces this variation.

Back pressure in the range of 0.3–1.0 MPa hydraulic pressure or 3–10 bar plastic pressure may be used to homogenize the melt without excessive shear heating. Screw rotation should maintain a peripheral speed of 0.2–0.4 m/s; higher speeds can increase melt temperature and produce visible degradation streaks. For screw geometry, a three-zone screw with L/D ratio between 20:1 and 24:1 and compression ratio between 2:1 and 2.5:1 is suitable for SAN. Hot-runner systems should use externally heated manifolds with no dead spots; residence time at 250 °C should not exceed 8 min before colour shift becomes measurable. For transparent tooling, parting-line vents should be kept at 0.02–0.04 mm depth to avoid flash with the high-flow grade. Clean regrind may be added at up to 20% by weight without altering haze below the datasheet limit, but higher regrind content increases the risk of black specks and reduces notched impact.

Optical Performance and Haze Criteria

Published optical data for the 77851 crystal-clear colour package are obtained on injection moulded plaques with a polished surface finish of SPI/SPE A1 or A2. Under ISO 13468-2, total luminous transmittance at 3.0 mm thickness is reported at 90%. Haze measured according to ISO 14782 remains below 1.0% for a 2.0 mm test plaque. These values are not maintained if the mould surface is textured, scratched, or contaminated by outgassing deposits. Transparent mouldings require uniform wall thickness and correctly positioned gate locations to prevent jetting; direct edge gates should enter along a rib or flow leader to avoid a visible snake-like flow mark. The refractive index of SAN is typically near 1.565, which places the grade closer to polycarbonate than to PMMA in optical density. This higher index produces stronger surface reflection than PMMA and may require anti-reflective coating or texture in display lenses.

Optical performance is thickness-dependent. At 1.0 mm, total transmittance can appear higher because fewer internal absorptive events occur; at 5.0 mm, transmittance decreases and edge yellowness becomes more visible. The 3.0 mm plaque value of 90% is therefore a practical comparison point, not a universal constant for all moulded geometries. Haze measurements on textured or matte surfaces are not comparable to polished specimens. Incoming quality-control protocols should use plaques with the same cavity finish as the production mould, conditioned at 23 °C/50% RH for 24 h before measurement according to ISO 291:2008. Colour coordinates may be measured with a spectrophotometer under CIE D65/10°; published data for this specific configuration is limited and must be established per colourant lot.

The values are typical and do not constitute a specification; lot-specific certificate of analysis should be consulted for release testing.

When Luran SAN 368R Crystal Clear 77851 substitutes PMMA in clear packaging

Substitution of PMMA with INEOS Styrolution Luran SAN 368R Crystal Clear 77851 is appropriate when the application requires faster thin-wall filling and better resistance to aliphatic hydrocarbons, but it is not a direct optical drop-in. PMMA evaluated under ISO 13468-2 can reach total transmittance of 92% at 3 mm, while the SAN grade is reported at 90%. More important is the melt-flow basis: PMMA is frequently tested at 230 °C/3.8 kg under ISO 1133-1:2022, whereas the SAN grade is tested at 220 °C/10 kg, so direct MVR comparison is invalid. On the injection moulding line, the practical difference appears as lower required clamp force for the same projected area. For transparent packaging with wall thickness below 1.2 mm, the high-flow SAN can often fill at 20–30% lower peak injection pressure than a medium-flow PMMA, although this value depends on gate diameter, flow length, and mould temperature. Published data for this specific configuration is limited because pressure drop is mould-specific.

The SAN grade also absorbs less water at saturation than PMMA; 0.2% versus approximately 0.3% according to ISO 62:2008. This reduces the pre-drying burden and dimensional movement in humid service. However, SAN has lower UV weathering resistance than PMMA and will yellow after prolonged outdoor exposure; the 77851 crystal-clear package is not UV-stabilized and should not be considered for external glazing unless shielded or coated.

Mechanical property benchmarks support load-bearing transparency.

Under tensile loading to ISO 527-2:2012, the reported tensile modulus of 3700 MPa exceeds typical PMMA grades and provides snap-fit stiffness without glass fibre. Tensile stress at break is reported at 68 MPa and elongation at break at 3.0%, indicating brittle failure with limited deformation. The flexural modulus measured to ISO 178:2019 is 3600 MPa, and flexural strength at 120 MPa supports short-term clip and latch deflection. The Charpy notched impact resistance of 2.0 kJ/m² at 23 °C is lower than ABS and polycarbonate; the product is therefore not appropriate for transparent articles requiring ductile puncture or high-energy drop performance. Because the failure mode is notch-sensitive, design validation should include finite-element stress analysis around gate-side stress concentrators and avoid sharp internal corners below 0.5 mm radius.

The Vicat softening temperature B/50 is 108 °C, and the HDT/A under 1.80 MPa is 84 °C. Continuous load-bearing service above 75 °C may allow creep, especially near ribs and bosses. Annealing at 70 °C for 2 h can reduce moulded-in stress but may change critical dimensions by up to 0.1%. The amorphous matrix gives more isotropic shrinkage than semicrystalline transparent polymers, but gate location and packing pressure still control warpage in flat parts.

Food-contact suitability is assessed under FDA 21 CFR 177.1040 for styrene-acrylonitrile copolymers and EU Regulation (EC) No 10/2011 with overall migration limit of 10 mg/dm²; final article compliance depends on colourants, processing aids, and mould contamination. REACH registration for polymer monomer residues styrene and acrylonitrile is established, but downstream users must verify exposure scenarios for their workplace. RoHS screening is normally limited to electrical/electronic applications; SAN 368R Crystal Clear 77851 is not a formulated flame-retarded grade and should not be used where UL 94 V-0 or 5VA classification is required. The resin has moderate resistance to dilute acids, alkalis, and aliphatic oils, but aromatic hydrocarbons, ketones, and chlorinated solvents cause softening, grazing, or dissolution. Prolonged immersion testing should follow ISO 175:2010 with the specific fluid and service temperature. Published data for this specific configuration is limited for aggressive solvent exposure.

Rheological separation from medium-flow SAN grades

The principal difference between Luran SAN 368R and a medium-flow SAN grade such as Luran SAN 358N is the melt volume-flow rate under 220 °C/10 kg in ISO 1133-1:2022. The 368R grade is reported at 26 cm³/10 min, while medium-flow SAN grades in the same family are typically below 14 cm³/10 min. A direct flow-comparison factor therefore exceeds 1.8. The higher MVR is achieved by controlled molecular-weight reduction, which lowers shear viscosity in the injection moulding shear-rate range of 10³–10⁴ s⁻¹. This produces measurable advantages in spiral-flow length and cavity-pressure transmission. It does not alter density or optical clarity, but it reduces Charpy notched impact compared with higher molecular-weight SAN grades. In transparent housings with wall-thickness variation, the high-flow grade provides more uniform packing and lower residual stress if gating remains balanced. Published rheological data obtained by capillary rheometry under ISO 11443:2021 for this grade are limited; commercial flow-simulation databases should be populated with MVR, thermal conductivity, and pvT rather than assuming equivalence to PMMA or polycarbonate. Users attempting styrene-acrylonitrile replacement of PMMA in outdoor glazing should first generate ISO 175:2010 immersion data for the specific fuel, oil, or cleaning agent.