INEOS Styrolution Styrolux SBC is a transparent styrene-butadiene block copolymer produced by sequential anionic polymerization. The product line is engineered with a high styrene-to-butadiene ratio relative to conventional SBS elastomers, which produces a continuous styrenic matrix and a discrete butadiene rubber phase. Commercial grade designations include Styrolux 3G 33, 656C, 684D, and 693D. These grades are differentiated by melt mass-flow rate, rubber-phase content, and slip or antiblock additive packages. Density is typically 1.01 g/cm³ to 1.02 g/cm³ under ISO 1183-1. Melt volume-flow rate at 200 °C/5 kg spans approximately 3 cm³/10 min to 20 cm³/10 min when measured under ISO 1133-1:2022. The material is supplied as cylindrical or lenticular pellets with bulk density sufficient for railcar and silo handling. Because the butadiene phase is constrained by the high styrene content, the material exhibits lower rubber odor and better color than low-styrene SBS grades. Typical uses include transparent rigid sheet, food packaging trays, medical device components, labels, and packaging film.

What separates Styrolux from lower-styrene SBCs in clear rigid packaging?

Lower-styrene SBS grades are rubber-continuous or co-continuous, giving tensile elongation values above 600% but flexural modulus often below 300 MPa. Styrolux reverses this ratio, placing flexural modulus in the 700–1,200 MPa range under ISO 178. That modulus allows converted sheet to resist stacking deformation without orientation. The reduced rubber phase also lowers haze: a 2 mm molded plaque typically measures 1% to 5% haze under ASTM D1003, whereas conventional low-styrene SBS frequently exceeds 10%. Oxygen and water vapor transmission remain film-thickness dependent and are not comparable to PET; however, Styrolux provides better water vapor barrier than uncoated cellulosic film and better clarity than high-impact polystyrene. In direct comparison with SEBS, the absence of an ethylene-butylene midblock in Styrolux preserves stiffness and surface hardness but sacrifices low-temperature flexibility below -20 °C. Published data for food-simulant migration in fatty media is available for selected food-contact grades through supplier compliance statements.

Monolayer cast film from Styrolux is processed on a 90 mm single-screw extruder with L/D 30:1 and a barrier screw. Barrel temperatures from feed to metering are maintained at 180 °C to 220 °C. Die gap is set from 0.5 mm to 0.8 mm, and the chill roll temperature is held at 15 °C to 25 °C to prevent blocking while retaining gloss. Blown film lines use a die diameter of 100 mm to 250 mm and a frost-line height of 1.5 to 3 times the die diameter. Bubble ratios up to 3:1 are attainable because melt strength is higher than LLDPE. Screw speeds above 100 rpm can push melt temperature above 230 °C, producing pinholes and gel fisheyes in film thinner than 250 µm. In-line embossing with engraved steel rolls is performed at 70 °C to 90 °C roll surface temperature; the high styrene phase retains embossing depth better than low-density polyethylene.

Medical device components such as suction canisters and spike ports are injection molded on conventional machines with clamp capacities from 1,000 kN to 2,500 kN. Melt temperature is controlled at 190 °C to 220 °C, and mold temperature is set from 15 °C to 40 °C. Thin-wall sections below 0.8 mm require injection speeds above 150 mm/s to avoid flow hesitation. Gate blush is reduced with hot-tip cold-runner systems rather than hot-runner valve gates because the butadiene phase is shear-sensitive. Parts molded under these conditions have survived ethylene oxide sterilisation at 55 °C and 80% relative humidity for 2 h without measurable haze increase under ASTM D1003. Gamma sterilisation above 25 kGy produces yellowing; published dose-response data for specific medical grades is limited and must be validated according to ISO 10993-5.

Drying, regrind and melt-temperature constraints observed on production lines

Styrolux pellets are not hygroscopic, but surface condensation in unheated silos at relative humidity above 60% can cause splay in extruded sheet. Supplier technical bulletins recommend drying at 60 °C for 2 h to 4 h with a drying-air dew point of -30 °C before processing when high-humidity storage occurs. Regrind from edge trim and punch scrap is mechanically compatible with virgin resin, but levels above 20 wt% can reduce melt viscosity and sidewall crush resistance because of repeated shear history. For food-contact sheet, closed-loop regrind is limited to 10 wt% unless migration testing under EU Regulation 10/2011 demonstrates overall migration below 10 mg/dm². Melt temperatures above 230 °C generate gel formation as visible fisheyes in 250 µm film. The practical cast-film processing window narrows to 200 °C to 230 °C, and residence time in the die adapter is kept below 5 min to limit butadiene-phase oxidation. Production lines that process regrind above 20 wt% often add 0.05 wt% acid-neutralized lubricant to prevent plate-out on polishing rolls.

Extruded sheet for food trays is produced on a 120 mm single-screw extruder with L/D 32:1 and a gear melt pump. The melt pump is specified to damp pressure pulsations because Styrolux exhibits pronounced shear thinning; capillary rheometry at 200 °C gives a power-law index of approximately 0.6 to 0.7. Die temperature is held at 220 °C, and polishing rolls are run at 60 °C to 80 °C to control shrinkage. Sheet thickness tolerance is maintained within ±2% at line speeds up to 25 m/min. The sheet is thermoformed at core temperatures between 105 °C and 125 °C with plug-assist speeds below 250 mm/s to prevent stress whitening. At draw ratios above 2.5:1, corner thinning exceeds 15%, reducing local crush resistance; this process boundary is not captured in datasheet mechanical properties.

Rheological and thermal property envelope across standard grades

The following table summarizes grade-dependent property ranges reported in supplier literature for general-purpose film, sheet, and injection molding Styrolux grades. The ranges are a class envelope and are not a single lot specification; individual grade datasheets must be used for lot acceptance.

When high-gloss rigid packaging is required, Styrolux is blended with general-purpose polystyrene at 10 wt% to 30 wt%. GPPS addition raises Vicat softening temperature from approximately 65 °C to 75 °C under ISO 306 and increases flexural modulus, but it reduces notched impact strength. Addition of high-impact polystyrene at 30 wt% lowers transparency and can raise haze above 15% under ASTM D1003. For medical tubing, a 70 wt% Styrolux / 30 wt% SEBS blend has been used to shift the lower service temperature to -20 °C while maintaining kink resistance. Calcium stearate at levels above 0.2 wt% increases plate-out on polishing rolls; acid-neutralized lubricant packages are preferred. Batch-to-batch variability in melt volume-flow rate is specified by suppliers within ±1.5 cm³/10 min for standard grades; medical device grades are available with narrower tolerance windows.

Venting is critical in medical molding because volatile low-molecular-weight butadiene oligomers can deposit on core pins. Molds are vacuum-vented at 0.02 mm land length, and core temperatures are held below 60 °C to reduce plate-out. A production failure mode observed on multi-cavity syringe barrel molds is gate blush when hot-runner valve pins are used; converting to hot-tip drops eliminates the blush but can increase stringing if the tip temperature exceeds 230 °C. Batch-to-batch color variation is controlled within ΔE < 0.5 under CIE Lab for medical grade lots, evaluated with a spectrophotometer using D65 illuminant and 10° observer according to ISO 11664-4.

If medical device housings require clarity and repeated EtO sterilisation, Styrolux competes with polystyrene and transparent ABS

General-purpose polystyrene is lower in cost but exhibits notched Charpy impact values below 2 kJ/m² at 23 °C under ISO 179-1/1eA, whereas Styrolux maintains a notched Charpy impact range of 3–8 kJ/m². Transparent ABS provides higher notched impact and heat deflection temperature but can yellow after repeated EtO sterilisation and has a higher density. Styrolux withstands EtO sterilisation at 55 °C and 80% relative humidity for 2 h without significant haze increase, but repeated cycles above 10 may reduce optical clarity. Gamma sterilisation at 25 kGy to 50 kGy induces a yellow shift; published data for specific medical grades under gamma irradiation is limited. Ultrasonic welding is performed at 20 kHz with energy director amplitudes of 20 µm to 30 µm; welded joint strength exceeds 70% of parent tensile strength when tested according to ISO 527-2. The material does not contain phthalate plasticisers and does not require chlorine-containing stabilisers.

Under food-contact statutes, migration data rather than resin composition defines clearance

Specific Styrolux grades are supplied with food-contact statements that reference EU Regulation 10/2011 and FDA 21 CFR 177.1810 for styrene block polymers. The EU framework requires an overall migration limit of 10 mg/dm² for plastics in food-contact applications. Specific migration limits for styrene and butadiene are listed in Annex II of the regulation. FDA 21 CFR 177.1810 permits styrene block polymers for food-contact use under specified end-use conditions, but the regulation is not a lot-level certification; converters must conduct end-use testing on finished articles. Residual butadiene is controlled during polymerisation and devolatilisation. Supplier certificates of analysis typically report residual butadiene below 1 mg/kg for packaging grades, but published data for every grade is not uniformly available. Compliance with RoHS Directive 2011/65/EU is limited to restricted heavy metals and does not imply food-contact safety. REACH registration under EC 1907/2006 is maintained by the manufacturer for substances placed on the EU market.

Lot acceptance for medical applications includes measurement of melt volume-flow rate, yellowness index, and notched Charpy impact. Yellowness index is controlled below 1.0 under ASTM D1925 for uncolored medical grades. Melt-flow-rate mismatch between lots above 1.5 cm³/10 min changes fill pressure in multi-cavity molds and may alter part weight. Storage beyond 24 months at ambient conditions may increase yellowness; published shelf-life data for specific ultraclear grades is limited.

Grade interchangeability must not be assumed. Low-melt-flow Styrolux grades are preferred for blown film, while high-flow grades are used for medical syringes and thin-wall closures. The product is not recommended for continuous contact with aromatic hydrocarbons, ketones, or chlorinated solvents, which soften or stress-crack the styrenic phase. Outdoor exposure without ultraviolet stabilisation produces yellowing and surface microcracking; UV-stabilised packages are available only on request. Post-consumer recyclate streams containing more than 10 wt% PET or PVC cause delamination and haze in cast film because the incompatible phases separate under shear. When runners and sprues are re-ground for non-medical applications, regrind fines below 1 mm should be limited to 5 wt% to avoid feeding inconsistency. These operational boundaries define the practical use window for the styrenic block copolymer in industrial conversion.