LG Chem SAN SA50 is a styrene-acrylonitrile copolymer intended for transparent injection-moulded articles in which a high melt-flow class is required without sacrificing the chemical resistance and heat resistance that distinguish SAN from general-purpose polystyrene. The material does not contain a butadiene rubber phase; therefore, its optical clarity and surface hardness derive from the amorphous styrene-acrylonitrile matrix, while its notched impact strength remains below that of ABS and transparent ABS grades. Property data for this grade should be read as representative of the high-flow SAN class because the certificate of analysis supplied with the production lot is the controlling document, and published data for this specific SA50 configuration is limited. For design verification, processors commonly evaluate specific gravity to ISO 1183-1, tensile stress at break to ISO 527-2, flexural modulus to ISO 178, Vicat softening temperature to ISO 306/B50, and notched impact strength to ISO 179-1eA. Typical high-flow SAN lots in this class exhibit a specific gravity in the range 1.07–1.08 and a light transmittance of 88–91% in a 3 mm plaque when measured to ISO 13468-1; haze normally remains between 1.5% and 3.5% under ISO 14782.

What Distinguishes SA50 from Lower-Flow LG Chem SAN Grades?

The principal difference is rheological: the SA50 designation corresponds to a higher melt-volume rate than extrusion-oriented SAN grades, which enables lower injection pressure and shorter cycles in multi-cavity thin-wall tools. The benefit is not free. Higher-flow SAN resins typically have a lower molecular weight than lower-flow grades, and that shift is reflected in a slightly lower notched impact strength and a modest reduction in environmental stress cracking resistance. Table 1 lists representative values for the high-flow SAN class rather than guaranteed product minima. A lower-flow grade such as an 80HF-class material may be preferred when wall thickness exceeds 3.0 mm or when the part is clamped under constant bending stress; an SA50-class material is preferred when the limiting defect is short shots in wall sections below 1.2 mm. The selection should be confirmed by flow-length spiral tests using the production tool, because published melt-flow values do not fully predict cavity filling in hot-runner tools with restricted gates.

Pre-drying is not optional for SA50 when ambient relative humidity exceeds 60% or when regrind is added above 20%. Moisture levels above 0.05% cause splay, silver streaks, and a measurable loss of tensile strength at the weld line. A closed-loop desiccant dryer with a dew point below −20 °C is typical; the pellets are dried at 75–85 °C for 2–4 h. In an uncontrolled hopper, SAN reabsorbs surface moisture within 15–30 min. Barrel temperature profiling is generally set from 200 °C at the feed throat to 230–245 °C at the nozzle, with the melt temperature not exceeding 250 °C. If a hot-runner system is used, manifold zones are set no higher than 240 °C because stagnant SAN degrades quickly and forms carbonaceous deposits that contaminate subsequent shots.

Optical Quality and Gate Freeze-Off Control in Multi-Cavity Tools

Transparent SAN parts fail by visible haze, silver streaking, or gate blush when cavity pressure is not maintained through the gate freeze period. For an SA50-type high-flow grade, the processing window is more sensitive than that of a low-flow SAN because the lower melt viscosity reduces pressure loss but also reduces the zero-shear viscosity needed for packing. A gate diameter of 0.8–1.5 mm for a wall stock of 1.0–2.0 mm is typical. If the gate freezes before packing ends, sink marks and residual stress fields appear. Packing pressure is normally set at 50–70% of peak injection pressure, and hold time is established by part weight stabilisation curves rather than by simulation alone. Mould temperature is maintained at 40–70 °C to balance surface gloss and dimensional stability; elevating the mould above 80 °C usually increases cycle time without a proportional reduction in haze for this material class.

In cosmetic and personal-care packaging, SA50 is used for transparent jars, lipstick cases, and outer shells that must survive repeated exposure to fats, alcohol-based cleaners, and dilute acids without stress whitening. The polymer also appears in water filter housings, refrigerator interior components, transparent battery cases, and non-implantable medical device housings. In those applications, the acrylonitrile comonomer slows diffusion of aliphatic hydrocarbons and aqueous surfactants into the matrix; the component should still be tested under constant-strain exposure to the final cleaning agent using ISO 22088-3 or ASTM D543, because chemical attack in amorphous polymers is stress-coupled and cannot be predicted from simple immersion data alone. The practical continuous-use temperature in warm aqueous fluids is normally below 80 °C.

When Chemical Resistance and Transparency Are Required Without the Impact Penalty of Transparent ABS

Selection of SAN SA50 instead of transparent ABS or PMMA is driven by a different balance of properties. Transparent ABS contains a rubber phase that raises impact strength, but the refractive index matching needed for clarity imposes narrow processing windows, and chemical resistance to oils and alcohols can be lower than that of SAN. PMMA offers exceptional optical clarity and UV resistance, but it is more susceptible to attack by alcohols and ketones and may require higher melt temperatures for thin-wall filling. SAN sits between the two: the acrylonitrile content of 24–28 wt% in typical general-purpose SAN grades provides resistance to non-polar aliphatic hydrocarbons, dilute acids, and aqueous detergents, though it is not recommended for aromatic solvents, chlorinated solvents, esters, or ketones. In migration-sensitive applications, the absence of a polybutadiene rubber phase can reduce total extractables and simplify documentation under 21 CFR 177.1040, provided the supplier certifies the exact formulation.

Compliance for SA50 is not inherent in the polymer name. The converter must obtain a REACH registration confirmation, a RoHS declaration under 2011/65/EU, and any food-contact certificate for the specific lot. For electrical and electronic housings, flammability is usually evaluated according to UL 94 HB, but no Yellow Card should be assumed unless the grade is specifically listed. Residual acrylonitrile monomer is a critical specification in food-contact and medical applications; lot release should include gas chromatographic determination of residual monomer instead of a single melt-flow test. Table 2 summarises the typical documentation matrix.

Thermal Degradation Boundaries and Residence-Time Control

At processing temperatures above 260 °C, SAN degrades through depolymerization and nitrile elimination. The practical melt temperature for SA50 should remain at or below 250 °C unless hold-up is guaranteed by a dedicated hot-runner system. Degradation appears first as yellowing and a reduction in high-shear viscosity, then as black specks and surface deposits. On a production-scale injection moulding machine with a 20:1 L/D general-purpose screw, the barrel profile is normally 200–220 °C in the rear zone, 220–240 °C in the centre, and 230–245 °C at the front. If a hot runner is used, manifold temperature should not exceed 240 °C. Screw recovery should be timed so that total residence time does not exceed 5 min at melt temperatures above 240 °C; shut-down purging with general-purpose polystyrene or a commercial purging compound is required to remove carbonised residue before restart.

Regrind does not behave as a chemically identical feedstock. In high-flow SAN, repeated heat history reduces melt viscosity and can shift the measured Vicat softening temperature downward by a few degrees. Processors that add more than 20% regrind to virgin SA50 often observe an increase in gate blush and a decrease in notched impact strength because thermal chain scission is cumulative. Ground material should be dedusted and classified to remove fines below 0.5 mm, and the blend ratio should be fixed by measuring melt-volume rate and notched impact strength after three successive heat histories. When a process cannot hold impact strength after regrind addition, the processing temperature should be lowered before increasing the regrind ratio.

Flow-length-to-wall-thickness ratio is the practical expression of the SA50 flow class. In a spiral flow test, high-flow SAN can fill a 2 mm channel at a lower injection pressure than a low-flow grade, but the relationship is not linear because fountain flow behaviour and gate freeze change the effective shear rate. For hot-runner systems with valve gates, the shear rate in the gate can exceed 10,000 s⁻¹; this is sufficient to cause shear-induced molecular weight reduction in high-flow SAN if the melt temperature is already near the upper limit. The best cavity filling is obtained with a melt temperature of 240 °C and an injection speed profile that slows before the position of the last cavity, reducing gate blush and the residual pressure drop across the runner system.