Kumho Petrochemical SAN 335T is a transparent injection-moulding grade of styrene-acrylonitrile copolymer. Manufacturer-published typical values place the melt mass-flow rate at 35 g/10 min when tested under ISO 1133-1:2022 at 200 °C and 5 kg. The solid-state property set includes a tensile yield stress of 65 MPa under ISO 527-2:2012, flexural modulus of 3400 MPa under ISO 178:2019, and notched Charpy impact strength near 1.3 kJ/m² under ISO 179-1/1eA:2023. The material is distinguished from general-purpose polystyrene by higher resistance to cosmetic oils and dilute aqueous acids, and from ABS by the absence of a polybutadiene dispersed phase, which preserves haze levels below 1.5% at 3 mm thickness under ISO 14782:2021 while reducing impact energy absorption. Typical moulding applications therefore include transparent cosmetic packages, appliance lenses, and diagnostic device housings where optical clarity and dimensional stability are required but high-energy impact is not the controlling load case.

Typical density is 1.07 g/cm³ under ISO 1183-1:2019; heat deflection temperature under 1.8 MPa load is reported at 88 °C under ISO 75-2:2013, and Vicat softening temperature is 102 °C under ISO 306:2022 method B50. The mould shrinkage range is 0.2%–0.6% under ISO 294-4:2018. These values are typical supplier-published data and not a substitute for lot-specific certificate of analysis.

How does the absence of a butadiene-rich dispersed phase translate into different notched impact and optical transmission behaviour relative to ABS?

Representative comparative values for unfilled natural grades illustrate the position of SAN 335T between general-purpose polystyrene and general-purpose ABS. The comparison is based on supplier typical data and published resin-type property ranges, not on a single production lot.

The data illustrate the central difference: SAN 335T retains optical transmission approaching GPPS, but the polar acrylonitrile repeat unit raises chemical resistance and heat resistance. The absence of the butadiene-rich phase removes the impact energy absorption mechanism available in ABS, so moulders cannot substitute SAN 335T for ABS in snap-fit designs with repeated deflection without specific validation.

Barrel temperature profiles and screw geometry constraints in single-screw injection moulding

Correct melt preparation requires a general-purpose screw with an L/D ratio between 20:1 and 24:1 and a compression ratio between 2.0:1 and 2.5:1. Barrel zone settings are typically ramped from 190–210 °C at the rear feed zone to 210–230 °C in the compression zone and 220–240 °C at the metering section; nozzle temperature is maintained at 220–235 °C. Measured melt temperature at the nozzle should remain within 230–245 °C to avoid acrylonitrile thermal degradation. A shot size between 50% and 70% of barrel capacity is recommended to limit residence time below 5 min at full melt temperature. Screw surface speed for recovery is normally set at 0.5–1.0 m/s. High back pressure is not required for dispersion because the material is a single-phase amorphous melt; hydraulic back pressure of 0.5–1.0 MPa is sufficient for homogenization without excessive frictional heat.

Mould temperature is controlled in the range 40–70 °C. Higher mould temperatures reduce flow marks and increase gloss replication from polished cavity surfaces, but increase cycle time and may complicate ejection if deep draw is present. Injection velocity should be profiled to fill 80–90% of cavity volume at moderate speed, then drop sharply at the final packing transition to avoid gate blush. Packing pressure is generally 60–80% of injection pressure for 3–5 s per mm of wall thickness; hold time can be reduced where gate freeze is confirmed by part weight stabilization.

Moisture control before melt processing is a critical threshold. Equilibrium moisture uptake of SAN at 23 °C and 50% RH is approximately 0.2–0.3%. Above 0.05% residual moisture, surface splay, nozzle drool, and molecular weight reduction become increasingly probable at melt temperatures above 220 °C. Desiccant drying at 80 °C for 3 h with a supply air dew point below -30 °C reduces pellet moisture to the required level. Dried pellets should be conveyed dry and consumed within 30 min unless the hopper is insulated and purged with dry air or nitrogen. In humid production environments above 60% RH, closed-loop resin handling rather than open hopper loading is recommended.

When cosmetics packaging imposes simultaneous chemical loading and clasp retention force, environmental stress crack resistance limits the design window

Transparent components such as lipstick tubes, compact housings, and jar closures are exposed to ester-based solvents, alcohols, and surfactant systems. The polar nitrile group in SAN reduces swelling in aliphatic hydrocarbon media relative to GPPS, but formulations containing ketones, esters, or aromatic hydrocarbons can still initiate environmental stress cracking under continuous strain. Constant-strain testing under ASTM D543-21 is used to compare mass uptake and crack onset for each formulation. Field data from injection-moulded closures show that cracking usually initiates at injection flow lines, hot-runner gate vestiges, or sharp transitions in wall thickness rather than in uniformly strained sections. Therefore, cavity filling must avoid hesitation lines; gate locations are moved away from snap-fit anchoring rings.

Published data for this specific formulation configuration is limited when custom fragrance and cosmetic ester blends are introduced, so compatibility testing is required for each product. At wall thicknesses below 1.2 mm, the residual stress from ejection and cooling becomes a larger contribution than the applied assembly stress. Moulders running 8-cavity hot-runner tools with valve-gate pin diameters below 0.8 mm should increase pin diameter or reduce melt temperature in the hot drop because small gates create high shear and oriented residual stress at the gate boundary.

In appliance control-panel windows and in vitro diagnostic housings, the balancing of water-clear optics with chemical resistance to cleaning agents is often the specification driver. SAN 335T transmits light efficiently at 3 mm thickness and can be laser-welded or solvent-bonded, but bond strength must be measured under ISO 527-2:2012 on welded specimens because local solvent attack at the joint reduces tensile stress to a fraction of the bulk value. Flame rating for thin sections is typically HB under UL 94 at 1.5 mm, which is sufficient for many household appliance panels but excludes use in enclosures requiring V-2 or better. Designers must specify the exact colour and ultraviolet stabilizer package; unpigmented SAN remains transparent but yellows under prolonged UV exposure. Outdoor use is not covered by standard natural grades unless a stabilizer masterbatch is validated by accelerated weathering under ISO 4892-2:2013. Medical diagnostic applications require finished-device biocompatibility testing under ISO 10993-5; the raw resin supplier data alone does not constitute biological safety approval.

Do not exceed 30 wt% regrind in optical applications without lot-specific haze validation

Closed-loop moulding with sprues, runners, and off-spec parts recovers material cost but introduces multiple heat histories. The melt mass-flow rate of SAN 335T increases as chain scission dominates over crosslinking in this styrene-acrylonitrile system during repeated extrusion. The shift becomes measurable after two additional heat histories. Moulders can blend 20–30 wt% regrind with virgin pellets without exceeding typical lot-to-lot MFR variation if the regrind is dried identically and sorted to avoid contamination with ABS or polycarbonate dust. Blend uniformity is verified by ISO 1133-1:2022 MFR before approval.

Addition of regrind above 30 wt% is not recommended for optical parts because microgels and char particles formed during repeated melt residence appear as visible haze and specks. If a moulder chooses higher regrind fractions for non-optical internal components, the mechanical property retention must be tested under ISO 527-2:2012 and ISO 179-1/1eA:2023 on specimens taken from actual production parts, not from dry-blend pellets alone. No published data supports a universal maximum regrind fraction for all tooling configurations, so the acceptable level is established by part-specific testing.