Among high-flow styrene-acrylonitrile copolymers supplied for injection moulding, INEOS Styrolution Luran SAN 378P is positioned as a transparent general-purpose grade with reduced melt viscosity for thin-wall and multi-cavity tooling. Published typical data from the manufacturer’s current technical data sheet list a density of 1.08 g/cm³ under ISO 1183, a melt volume-flow rate of 24 cm³/10 min at 220 °C and 10 kg load under ISO 1133, a tensile modulus of 3600 MPa under ISO 527-2, and a Vicat softening temperature VST/B/50 of 106 °C under ISO 306. Notched Charpy impact strength at 23 °C is approximately 2.5 kJ/m² under ISO 179/1eA. These values define a rigid amorphous thermoplastic with higher chemical resistance than general-purpose polystyrene and lower impact toughness than ABS.

Because the acrylonitrile comonomer introduces polar nitrile groups, the copolymer resists aliphatic hydrocarbons, many detergent formulations, and cosmetic oils. The same polarity raises equilibrium moisture uptake relative to polystyrene. Pellets that have adsorbed atmospheric water release steam during plastication and generate splay, silver streaks, and visible flow lines in transparent parts. The material is therefore handled as a moisture-sensitive injection moulding feedstock, even though it is not hygroscopic to the level of polyamide or polycarbonate.

What Separates Luran SAN 378P from Lower-Flow SAN, ABS, and PMMA in Rigid Packaging?

The key difference in the Luran SAN portfolio is flow length at fixed melt temperature. Lower-flow grades such as Luran SAN 368R are preferred for thick-wall mouldings and extrusion because they retain higher melt strength, while Luran SAN 378P is formulated for reduced filling pressure in high-cavity injection moulds. The trade-off is a small loss in melt strength; long vertical runners, hot-runner drops, and deep draw cores may show more drool or stringing. Against general-purpose polystyrene, Luran SAN 378P provides a measurable increase in resistance to kitchen oils, aliphatic solvents, and environmental stress cracking, at the cost of a slightly higher processing temperature and higher density. Against PMMA, Luran SAN 378P has lower density, lower surface hardness, and better resistance to household cleaning chemicals, but inferior weathering resistance and lower scratch resistance. Against general-purpose ABS, Luran SAN 378P is transparent and has higher tensile modulus, while ABS in standard opaque grades has notched impact toughness roughly an order of magnitude higher.

The melt volume-flow rate of 24 cm³/10 min is better suited to closures, thin-wall cylindrical packaging, and stationery than lower-flow Luran SAN grades with single-digit MVR values. The increased flow does not come from an external plasticiser; the molecular weight distribution is adjusted during polymerisation, so tensile modulus remains close to 3600 MPa. This distinguishes Luran SAN 378P from externally plasticised styrenic compounds, in which tensile modulus and heat distortion fall more rapidly as flow is increased.

On a 1200 kN toggle-clamp injection moulding machine equipped with a three-zone screw of 22:1 L/D and compression ratio 2.4:1, Luran SAN 378P is typically plastified using a barrel profile of 210 °C, 230 °C, 240 °C, and 250 °C from feed to nozzle. The melt temperature measured at the nozzle is maintained between 235 °C and 255 °C. At the lower boundary, unmelted cores and flow hesitation occur in thin-walled cavities; above 260 °C, acrylonitrile sequences begin to degrade and the melt develops yellow-brown discoloration. Mould temperature is controlled with a pressurised water unit to 50–70 °C. Transparent parts moulded below 40 °C exhibit reduced contact clarity and higher internal haze, while mould temperatures above 80 °C extend cycle time without proportional improvement in part flatness.

Drying is not optional for this grade. A desiccant dryer with a −30 °C dew point and an airflow of approximately 1.8 m³/h per kg/h pellet throughput reduces residual moisture to below 0.05 wt% in 2–4 h at 80 °C. In open-loop hopper dryers, silver streaking originating at the gate increases as ambient relative humidity exceeds 60%; closed-loop drying is required after silo transfer under such conditions. Wet masterbatch can reintroduce moisture into a dried SAN stream and should be dried under the same regime before blending.

Shrinkage according to ISO 294-4 is anisotropic. In-flow shrinkage typically falls between 0.4% and 0.6%, while transverse shrinkage is 0.5–0.7%. The difference is sufficient to produce out-of-round conditions in hollow cylindrical parts if gate placement is not adjusted. Hold pressure in the range 60–80 MPa and hold time of at least 0.5 s/mm nominal wall thickness are used to offset sink marks and stabilise dimensional repeatability. The grade is shear-thinning; raising injection velocity from 50 mm/s to 120 mm/s reduces filling pressure more than proportionally, but excessive shear may introduce jetting and visible flow lines in transparent parts.

Hot-runner selection influences colour stability. Externally heated manifolds with open flow channels and positive nozzle shut-off are preferred; internally heated systems can create stagnant regions where degraded SAN accumulates and appears as black specks in transparent parts. Hot-runner manifold and nozzle settings are held at 240–260 °C. During interruptions, the melt cushion should be decompressed by only 3–5 mm; greater decompression draws air into the nozzle and produces silver streaks on the next shot. Thermal stability at 270 °C may be observed first as an increase in yellowness index rather than a change in melt viscosity; colour measurement should accompany any process adjustment above the standard melt-temperature range.

Chemical Resistance, Environmental Stress Cracking, and Optical Retention in Transparent Cosmetic Components

Cosmetic package components such as lipstick tubes, compact bases, and cream jar bodies are injection-moulded in Luran SAN 378P because the acrylonitrile repeat units reduce swelling in hydrocarbon-based emulsions and fragrance oils. Chemical resistance is evaluated by immersion testing under ISO 175. Mass change after short-term contact with iso-octane and oleic acid is lower than that of general-purpose polystyrene, although published data for this specific grade and exposure duration combination is limited; part-level testing is required for each formulation. The practical limitation is environmental stress cracking. Moulded-in tensile stress around snap-fit undercuts or metal inserts can initiate crazing in contact with ethanol/water mixtures above approximately 50 vol% ethanol, certain essential oils, and strongly alkaline detergent concentrates. Stress-cracked transparent parts show a network of fine reflecting fissures that cannot be polished out.

Optical retention is evaluated on 2 mm plaques under ASTM D1003. Total transmittance for the natural grade is approximately 89%, and haze is normally below 1.0%. The refractive index of SAN is near 1.57; this creates higher front-surface reflection than PMMA at 1.49, so dark transparent tints may appear slightly lighter and more reflective. In thick sections, the natural SAN edge tint is faintly yellow; this becomes visible in optoelectronic display covers and should be assessed before replacing PMMA.

For regulatory assessment, the grade is classified under the polymer exemption provisions of REACH (EC) No 1907/2006; the constituent monomers, styrene and acrylonitrile, are registered substances. For food-contact applications in the United States, the applicable reference for acrylonitrile copolymers is 21 CFR 181.32; for the European Union, compliance is established only after migration testing on the finished article under the relevant plastics measure. Residual acrylonitrile monomer content is not the same as bulk composition; migration limits apply to the finished article. The grade is not recommended for prolonged outdoor exposure because SAN yellows and loses gloss under UV without adequate stabilisation. Contact with concentrated mineral acids, strong oxidising agents, or ketone solvents should be avoided because these attack the styrene-acrylonitrile matrix. For colouring, melt blending with styrenic masterbatch carriers is preferred; polyolefin carriers can delaminate and reduce clarity.

When Luran SAN 378P Is Used in Thin-Wall Lighting and Stationery Structures

In thin-wall diffusers, writing instrument barrels, and transparent index tabs, the high-flow character of Luran SAN 378P permits filling of wall sections down to 0.8 mm using conventional gates. The melt-pressure requirement is lower than that of lower-flow SAN grades, which reduces flash formation in multi-cavity tools. However, the combination of a low notched impact value and a sharp internal corner creates a brittle failure mode. Parts subjected to snap assembly, repeated flexure, or drop impact should be redesigned with radii of at least 0.5 mm and uniform wall thickness; unpredicted breakage occurs at the gate area when frozen-in orientation is perpendicular to the impact direction. Production-scale failure investigations on stationery barrels show that gate blush and sink opposite the gate are the main reject causes, not material contamination. Process corrections include reducing the injection velocity near the gate transition, increasing hold pressure, and relocating the gate to a non-appearance edge. The grade is supplied for injection moulding, not for sheet extrusion or blow moulding; long residence times in extruders can generate crosslinked gel particles and yellow streaks.