In the portfolio of LG Chem styrene-acrylonitrile copolymer resins, SAN S82TR is positioned as a high-flow, transparent injection-moulding grade for thin-wall packaging, cosmetic closures, and appliance lenses. The resin is produced by continuous mass polymerisation; the bound acrylonitrile content for a transparent SAN grade is typically reported between 24% and 32% by weight, with styrene as the balance. That comonomer ratio elevates the glass transition temperature above general-purpose polystyrene and increases resistance to aliphatic hydrocarbons, fats, and aqueous detergent solutions, while retaining the low melt-viscosity envelope required for multi-cavity filling. Manufacturer-published datasheet values for S82TR commonly cite a melt volume-flow rate near 25 g/10 min when measured under ISO 1133-1:2022 at 220°C with a 10 kg load; however, lot-specific certificates of analysis should be used for process setup because minor molecular-weight variation alters gate-zone viscosity. The optical profile is normally supplied as a total luminous transmittance near 91% and haze below 1.5% on a 3.2 mm plaque under ASTM D1003. Density is approximately 1.07 g/cm³ under ISO 1183-1. Unlike impact-modified ABS, S82TR contains no discrete polybutadiene rubber phase; notched Izod impact strength is therefore below 3 kJ/m² under ISO 180/1A, while gloss retention and optical clarity remain above ABS. The absence of a rubber phase also reduces mould-fouling deposits on hot-runner valve stems during extended runs, a line-productivity factor reported in transparent packaging production.

What processing limits control S82TR melt preparation?

Predrying is mandatory for defect-free moulding when ambient relative humidity exceeds 60%. A desiccant dryer with a dew point at or below -40°C and a set-point of 75°C to 85°C for 2 h to 4 h reduces residual moisture to less than 0.02 wt%, which is the commonly accepted ceiling for transparent SAN to avoid splay, silver streaks, and surface microvoids. On reciprocating-screw injection moulding machines with a general-purpose screw of 18:1 to 22:1 L/D and compression ratio 2.2:1 to 2.6:1, barrel temperature profiles are generally held between 200°C and 250°C, with nozzle temperature at 240°C to 250°C. Melt residence time above 260°C should not exceed 5 min, because thermo-oxidative yellowing of the SAN phase becomes measurable as an increase in yellowness index under ASTM E313. Melt temperature should be selected from the lower third of the range for thin-wall parts and raised only when short shots appear; mould temperatures of 40°C to 70°C are typical, with the upper band used for high-gloss surfaces and lower levels used to reduce cycle time. Injection pressures between 80 MPa and 140 MPa are common, and packing pressure should initially be set at 50% to 65% of the peak injection pressure, then adjusted for gate-seal time. Hot-runner manifold zones should not exceed 260°C, and field experience on eight-cavity closure moulds indicates that manifold temperature uniformity within ±3°C is required to avoid cavity-to-cavity colour and haze variation.

Because S82TR is an amorphous copolymer, its shear-thinning behavior under injection-moulding conditions is less pronounced than that of semi-crystalline polyolefins; apparent melt viscosity at 220°C and 1,000 s⁻¹ is typically below 500 Pa·s when measured by capillary rheometry under ISO 11443, but exact lot-specific curves should be generated before CAE simulation. At shear rates above 10⁵ s⁻¹, viscous heating can raise melt temperature by 5°C to 15°C depending on gate diameter and injection speed; this shear-induced temperature rise narrows the processing window in hot-runner systems and must be offset by lowering barrel set-points. Gate-seal time for S82TR at 2.0 mm wall thickness typically falls between 1.5 s and 3.0 s with a gate diameter of 0.8 mm to 1.2 mm; releasing hold pressure before gate seal produces sink marks and warpage, while maintaining pressure after seal only extends cycle time. Packing-pressure decay profiles are preferred over a single hold step for transparent parts because abrupt pressure transitions induce birefringence in high-stress regions.

Secondary processing constraints appear most clearly in transparent multi-cavity tooling, where gate geometry and vent depth influence haze formation as strongly as melt temperature. For S82TR moulded at wall thicknesses of 0.7 mm to 1.5 mm, valve-gated hot-runner systems are preferred because cold-runner scrap reprocessing increases optical defect rates. Gate diameters in the range 0.8 mm to 1.5 mm are typically sufficient for thin-wall fill, and round or oval gates reduce jetting compared with rectangular edge gates. Venting should be machined to 0.02 mm to 0.05 mm depth at the end-of-fill locations; insufficient venting produces burn marks from adiabatic compression of trapped gas, while excessive vent depth creates flash in high-flow SAN grades. Polished mould surfaces of SPI A-1 to A-2 finish are required to reproduce the resin’s optical clarity; texturing reduces measured gloss but can mask flow lines in thin-wall packaging. A mould temperature at the upper end of the processing range, typically 60°C to 70°C, improves replication of polished surfaces and reduces internal stress in the gate region. Birefringence in injection-moulded transparent SAN parts is assessed qualitatively under crossed polarisers; high packing pressure and low melt temperature increase flow-induced orientation. The lower melt viscosity of S82TR permits lower packing pressure, which reduces birefringence compared with higher-viscosity transparent SAN grades, although excessive lowering of melt temperature can produce flow lines from differential fill speed. When flow-length data for a specific S82TR lot are unavailable, published data for this specific configuration is limited, and a Moldflow verification using measured melt viscosity is recommended before cutting steel for deep thin-wall parts.

Solvent resistance, thermal ageing, and regulatory boundary conditions

Short-term immersion in aliphatic hydrocarbons, dilute acids, and alkali solutions up to 10% concentration at ambient temperature normally yields negligible weight change when tested under ISO 175. By contrast, aromatic hydrocarbons, ketones, esters, and chlorinated solvents cause crazing, stress cracking, or dissolution; S82TR is unsuitable for prolonged direct contact with acetone, methyl ethyl ketone, methylene chloride, or high-aromatic gasoline blends. Environmental stress cracking resistance under constant strain should be evaluated by ISO 22088 because injection-moulded SAN parts can exhibit solvent-induced cracks at gate locations where frozen-in orientation is highest. Thermal ageing in air at temperatures between 70°C and 85°C is generally acceptable for non-load-bearing parts; short-term excursions above 95°C risk dimensional relaxation, and the published heat deflection temperature for S82TR is approximately 88°C at 1.8 MPa under ISO 75-2/A, with Vicat softening temperature near 106°C under ISO 306. Under continuous UV exposure, SAN, like most styrenic copolymers, undergoes surface yellowing; therefore outdoor use requires UV-stabilised formulations or a protective coating.

For food-contact moulded articles, the resin is typically positioned for compliance with United States 21 CFR 181.32 for acrylonitrile copolymers and, in the European Union, the final article falls under Regulation (EU) No 10/2011. Verifying authority of lot-specific declarations from LG Chem is required before migration testing, especially for fatty-food simulants. Extraction protocols assigned in Annex III of Regulation (EU) No 10/2011 and the specific migration limit for acrylonitrile should be confirmed for the final article geometry and wall thickness. The table below summarises the verification basis used in downstream compliance documents.

When S82TR is selected as a PMMA alternative in cosmetic packaging

Where PMMA is replaced to reduce part density and improve resistance to cosmetic solvent-borne emollients, the design must account for lower surface hardness and lower outdoor UV stability. The tensile strength of S82TR is generally reported between 65 MPa and 72 MPa under ISO 527-2, and flexural modulus falls between 3,500 MPa and 3,900 MPa under ISO 178. These values are close to PMMA, but scratch resistance and weathering performance are not equivalent; PMMA remains superior for transparent parts subjected to repeated wiping or direct sunlight. In closure thread-engagement designs, SAN shows more stable torque retention after contact with esters and aliphatic oils than PMMA, which is a documented substitution driver in cosmetic packaging. Differences from high-impact ABS are more severe: ABS notched Izod values typically exceed 15 kJ/m², while S82TR remains below 3 kJ/m², so impact-modified ABS should be retained for enclosures likely to experience drop loads. Compared with GPPS, S82TR increases tensile strength by roughly 10 MPa to 20 MPa and improves chemical resistance, at a slight density penalty of approximately 0.03 g/cm³. The comparative property envelope is shown below.

Mould shrinkage for S82TR is typically 0.4% to 0.6% measured after 24 h under ISO 294-4; anisotropic shrinkage is lower than that of semi-crystalline resins, but gate location still influences dimensional stability in rectangular covers. Weld-line tensile strength retention in SAN mouldings commonly falls to 60% to 80% of the bulk value under ISO 527-2, so knit lines should be moved away from load-bearing snap-fit features. In extrusion compounding and masterbatch dilution, the grade must be let down with styrenic-compatible carriers; incompatible olefinic carriers reduce transparency and produce delamination. Barrel zones in twin-screw compounding should be kept below 260°C; residence time near the upper limit should remain below 3 min because SAN can generate carbonised residue during shutdown and colour shift. Reprocessing of S82TR runners and regrind is generally limited to 20% with virgin material for transparent parts because each heat history increases yellowness and reduces notched impact strength; higher regrind levels require optical and mechanical property revalidation under ISO 527-2 and ASTM D1003. In applications requiring higher chemical resistance than SAN, amorphous copolyesters or styrene-methyl methacrylate copolymers may be considered, but their melt-flow and cost profiles differ; published data for their use as direct substitutes in S82TR tooling is limited.