As a high-flow styrene-acrylonitrile copolymer, INEOS Styrolution Luran SAN 388S is supplied as pellets for injection molding and is positioned within the Luran SAN family for thin-wall, transparent, dimensionally stable parts. The grade is produced by continuous mass polymerization and is not a rubber-modified impact material, blend, or alloy. In the manufacturer’s nomenclature, the 388S designation identifies a high-melt-volume-rate formulation, with a typical melt volume rate of 35 cm³/10 min at 220 °C under 10 kg load according to ISO 1133-1. This flow behavior is intended for multi-cavity tools where filling pressure, cycle time, or gate freeze-off limit the use of lower-flow SAN grades. The material is an amorphous, rigid copolymer with high transparency, moderate heat resistance, and low residual haze. Applications for which the grade is specified include cosmetic packaging, transparent household articles, appliance windows, display covers, and non-invasive diagnostic housings. The use of Luran SAN 388S in each of these applications depends on chemical contact, molded-in strain, and thermal load during end use. The table below lists representative physical properties published for this grade; the values are not specification limits and should be verified against the current certificate of analysis for tool trials.

Representative property values for INEOS Styrolution Luran SAN 388S

Property	Test standard	Typical value
Density	ISO 1183-1	1080 kg/m³
Melt volume rate, 220 °C/10 kg	ISO 1133-1	35 cm³/10 min
Tensile modulus	ISO 527-2	3600 MPa
Tensile stress at break	ISO 527-2	72 MPa
Nominal strain at break	ISO 527-2	2.5%
Flexural modulus	ISO 178	3700 MPa
Flexural strength	ISO 178	115 MPa
Charpy notched impact strength, 23 °C	ISO 179-1/1eA	2.0 kJ/m²
Vicat softening temperature VST/B/50	ISO 306	95 °C
Heat deflection temperature HDT/A, 1.8 MPa	ISO 75-2	82 °C
Total luminous transmittance, 3 mm	ISO 13468-1	90%
Haze, 3 mm	ISO 14782	<1%

Because the quoted data are generated on standard specimens under ISO 10350-1 preparation and conditioning protocols, direct conversion to thick-section or high-stress parts requires mold-filling simulation or part-level mechanical testing. In particular, the notched Charpy value measured at 23 °C should not be extrapolated to sharply notched or snap-fit geometries without testing on the actual molded part.

What Distinguishes Luran SAN 388S from Lower-Flow Luran SAN Grades and Clear GPPS?

The primary difference between Luran SAN 388S and lower-flow grades in the Luran SAN family is molecular weight expressed indirectly through melt volume rate. Lower-flow grades such as Luran SAN 358N and Luran SAN 368R have higher melt viscosity and generally higher notched impact strength, while Luran SAN 388S has the higher MVR required for long flow lengths and thin wall sections. The trade-off is reduced Charpy notched impact strength, approximately 2.0 kJ/m² at 23 °C by ISO 179-1/1eA. Designers should not select Luran SAN 388S solely for high transparency; the grade is optimized for moldability in complex, long-flow-length parts rather than for maximum impact resistance. Compared with crystal-clear general-purpose polystyrene, the SAN chemistry introduces acrylonitrile into the styrene backbone, which raises cohesive energy density and improves resistance to aliphatic oils, cosmetic oils, and mild cleaning formulations. However, this chemical resistance is not universal. Under environmental stress, the material can craze in the presence of alcohols, esters, and aromatic solvents, especially at high-strain locations such as hot-runner gates, weld lines, and snap-fit undercuts. The practical consequence is that Luran SAN 388S is selected for transparent cosmetic caps and housings where GPPS may blush or crack after contact, but it is not specified for perfume reservoirs or continuous high-ethanol exposure. From a thermal standpoint, Luran SAN 388S has a higher heat deflection temperature under load than many clear GPPS grades; the HDT/A at 1.8 MPa is approximately 82 °C by ISO 75-2. This allows short hot-water and dishwasher exposure only if stress levels are low and cycle times are limited. Compared with weatherable ASA grades in the Luran S family, Luran SAN 388S has lower impact strength and no ultraviolet stabilizer package, so outdoor exposure produces yellowing and surface microcracking. When notching and drop loading are design variables, a lower-flow SAN or an impact-modified ASA or ABS should be evaluated. On multi-cavity hot-runner platforms running 32- or 64-cavity cosmetic closures, the high-flow characteristics of Luran SAN 388S permit gate diameters between 0.4 mm and 0.8 mm for wall thicknesses of 1.0 mm to 2.0 mm, provided the runner balance and valve-gate sequencing are correct. Production-scale experience indicates that gate blush becomes more frequent when hot-runner tip temperatures exceed 260 °C or when injection velocity is too low to maintain a continuous melt front across thin sections. Drying before molding is mandatory. At ambient relative humidity above 60%, absorbed moisture can hydrolyze the polymer and generate silver streaks, splay, and loss of optical clarity. A desiccant dryer operating at 80 °C for 2 h to 4 h with a supply-air dew point below -20 °C reduces residual moisture to below 0.05%. Processors should not rely on vented barrels alone for moisture removal in optical parts. Melt temperature measured at the nozzle should be maintained between 230 °C and 250 °C. A barrel profile from 180 °C in the rear zone to 220–240 °C in the metering zone is generally used on 25 mm reciprocating-screw machines with 20:1 to 22:1 L/D ratios. Extended residence time above 300 s at 250 °C or melt temperatures above 260 °C can cause yellowing and molecular weight reduction. Mold surface temperatures should be held between 50 °C and 70 °C; mold temperatures below 40 °C increase frozen-in stress and reduce surface gloss, while mold temperatures above 75 °C extend cycle time without proportionate optical improvement. Injection velocity should be set to fill 90–95% of the cavity during the velocity-controlled phase, with pack pressure applied at 40–60% of peak injection pressure. Back pressures from 0.5 MPa to 1.5 MPa and screw surface speeds of 5–10 m/min are typical starting points for melt homogenization, but shot size and colorant loading may require adjustment.

Melt Rheology, Thermal Properties and Dimensional Stability of Luran SAN 388S

Because Luran SAN 388S is amorphous, solidification is not governed by crystallite formation. The result is isotropic mold shrinkage of approximately 0.3–0.7% per ISO 294-4, with the lower values obtained at higher pack pressures and lower melt temperatures, and the higher values in thick sections or when cooling time is shortened. The coefficient of linear thermal expansion is approximately 7.0×10⁻⁵ K⁻¹ between 23 °C and 80 °C by ISO 11359-2. This is lower than many clear polyolefins and contributes to dimensional stability in assembled components such as level indicators and cosmetic closures. Melt rheology is shear-thinning, and the MVR value of 35 cm³/10 min at 220 °C and 10 kg does not replace a viscosity curve. Mold-filling simulations require viscosity data across shear rates from 10² s⁻¹ to 10⁴ s⁻¹. Gate shear rates above 10⁵ s⁻¹ can induce molecular orientation, birefringence, and gate blush, particularly in transparent parts. Thermal properties include a Vicat softening temperature VST/B/50 of approximately 95 °C by ISO 306 and an HDT/A of approximately 82 °C by ISO 75-2; these values should not be read as continuous-use temperatures under mechanical load. For unstressed parts in air, long-term service is commonly limited to 70–80 °C, but published data for oxidative stability under specific applied load is limited. Optical performance is a key specification. Total luminous transmittance on 3 mm polished plaques is approximately 90% by ISO 13468-1, and haze is below 1% by ISO 14782. These values depend on mold surface finish, melt temperature, and the absence of moisture and incompatible color concentrates. Styrene-acrylic carrier concentrates tend to preserve clarity, whereas concentrates based on polyolefin carriers can reduce transmission and create visible streaking. For transparent household articles requiring repeated contact with oils, creams, and mild cleaning products, Luran SAN 388S provides a useful balance of clarity and stress-crack resistance, but chemical compatibility testing must reproduce the intended contact temperature and molded-in strain. The grade resists aliphatic hydrocarbons, mineral oils, vegetable oils, and dilute acids and bases at room temperature. It is not recommended for continuous contact with ketones, chlorinated solvents, aromatic hydrocarbons, concentrated mineral acids, or high-polarity solvents. Alcohol-containing products can initiate environmental stress cracking at gates, weld lines, and snap-fit undercuts where local strain is highest. Critical strain thresholds should be determined by compatibility testing under EN ISO 22088-2 or an equivalent method because published data for this specific configuration is limited. Food-contact and medical-device regulatory status should be confirmed with INEOS Styrolution for the specific grade, color, and target jurisdiction. The supplier provides compliance statements and manufacturing documentation under its quality system; final article conformity requires migration testing under the applicable food-contact or medical standard. The grade should not be specified for exterior unpainted parts due to UV yellowing and gloss loss. If impact strength above that of standard SAN is required, a rubber-modified clear grade or an impact-modified ASA should be evaluated.