LCY Chemical Globalprene® SEBS 7533 is a linear hydrogenated styrenic block copolymer prepared by selective hydrogenation of a styrene-butadiene-styrene triblock precursor. The terminal polystyrene blocks remain below their melt transition at ordinary service temperatures, while the hydrogenated midblock behaves as an ethylene/butylene random elastomer. Distributor literature associates the 7533 grade with a nominal styrene content of 33 wt%, a specific gravity of 0.90–0.92 measured under ISO 1183-1, and a melt mass-flow rate of 3–10 g/10 min at 230 °C under a 2.16 kg load per ISO 1133-1:2022. These values are representative trade-literature ranges, not specification limits, and lot-specific certificates of analysis should govern. Because the material is not chemically vulcanised, the polystyrene domains act as physical crosslinks that permit repeated melt processing.

The hydrogenated midblock reduces the residual unsaturation to a low level. In unhydrogenated SBS, the polybutadiene segment contains allylic hydrogens and double bonds that support ozone chain scission and thermo-oxidative degradation. The saturated ethylene/butylene midblock of SEBS 7533 eliminates most of these reactive sites. The polymer can be compounded with polypropylene, paraffinic or naphthenic oils, fillers, and stabilisers to produce soft-touch articles, sealing profiles, impact-modified polyolefins, medical tubing candidates, and hot-melt adhesives. The grade is selected for applications in which ultraviolet and thermal ageing resistance are required beyond the capability of SBS, while retaining a melt-processable styrenic block copolymer structure.

What Distinguishes SEBS 7533 from Unhydrogenated SBS and Higher-Styrene SEBS Grades?

Unhydrogenated SBS typically has an iodine value in the range of 200–400 g I₂/100 g because of midblock double bonds. Exposure to ozone at 50 pphm and 40 °C under ASTM D1149 commonly produces visible surface cracking within 24–72 h. SEBS 7533 has a reduced iodine value below 10 g I₂/100 g after hydrogenation, which suppresses allylic oxidation and extends ozone resistance beyond 168 h in the same test environment. The hydrogenation also improves thermal stability during melt processing at 200–230 °C because the saturated midblock does not undergo the same free-radical degradation reactions.

Compared with higher-styrene SEBS grades, the 33 wt% styrene content of 7533 lowers the polystyrene endblock volume fraction. This reduces hardness and tensile modulus but improves melt flow and oil acceptance. Higher-styrene SEBS grades in the 40–45 wt% range generally exhibit Shore A hardness above 85 under ASTM D2240, higher cohesive strength, and lower melt mass-flow rates, often below 3 g/10 min at 230 °C. In contrast, 7533 is positioned in the mid-range hardness segment, with compression-moulded specimens frequently reported at 12–18 MPa tensile strength and 500–700 % elongation at break under ISO 37:2017 or ASTM D638-14. The lower styrene content permits higher filler and oil loadings before the compound becomes hard and boardy.

During twin-screw compounding on a co-rotating intermeshing extruder with L/D 40:1 and screw diameter 25–50 mm, SEBS 7533 is fed into the main throat at barrel temperatures of 160–180 °C. Paraffinic oil is injected after the first mixing zone, commonly in barrel zones 5–7, to prevent pellet slip in the feed zone. A downstream side-feeder is used for calcium carbonate, talc, or polypropylene powder. Screw speed is typically maintained between 200 and 400 rpm, and specific mechanical energy input is often recorded at 0.15–0.30 kWh/kg. Local melt temperatures above 230 °C can cause endblock degradation and a drop in melt strength; deep-flight conveying elements after high-shear kneading blocks are used to limit residence time below 120 s.

A high-shear dispersion stage reduces gel bodies and distributes polypropylene domains in the SEBS matrix. The strand is cooled in water at 20–30 °C and pelletised. Moisture absorption above 0.1 % produces splay and voids during injection moulding. Pre-drying at 80 °C for 2–4 h in a desiccant dryer is recommended when storage humidity exceeds 60 % RH. A soft-touch compound containing 100 phr SEBS 7533, 30–50 phr white oil, 20–40 phr polypropylene, and 0–20 phr filler can produce Shore A hardness between 35 and 80. At 50 phr oil, tensile strength drops to 6–9 MPa; elongation at break generally remains above 500 % when oil content is below 40 phr. Paraffinic oil is preferred because aromatic oil plasticises the polystyrene endblocks and lowers the upper service temperature.

When SEBS 7533 Is Injection Moulded Instead of Compounded into a Polyolefin Masterbatch

When injection moulding a SEBS 7533-based compound, the nozzle melt temperature is set between 190 °C and 220 °C, with the feed zone at 160 °C and the compression zone at 200–210 °C. Barrel residence times above 5 min or melt temperatures above 240 °C cause visible streaking and a reduction in molecular weight. Injection velocity is held at 20–60 mm/s for wall sections of 1.5–3.0 mm; higher velocities can generate shear heating above 230 °C in the runner and gate. Packing pressure is typically 30–60 % of peak injection pressure, with hold time of 3–8 s. Cavity pressure in a properly packed mould generally reaches 25–40 MPa; clamp force is calculated from the projected area using this cavity pressure.

Mould temperature is controlled at 20–50 °C. Lower mould temperatures shorten ejection time but may increase internal stresses and reduce overmould adhesion. Gates smaller than 1.5 mm for wall stock of 2 mm can freeze before packing is complete and produce sink marks. Direct-gated or edge-gated configurations with land lengths below 1 mm prevent premature gate solidification. Screw recovery speed is adjusted to avoid excessive adiabatic heating; a back pressure of 0.5–1.5 MPa is applied during melt charging.

In hot-melt adhesive formulation, SEBS 7533 is mixed with hydrogenated hydrocarbon tackifiers and paraffinic oil in a sigma-blade mixer at 170–190 °C under a nitrogen blanket. Polymer loadings of 20–35 wt% provide cohesive strength while maintaining application viscosity between 2,000 and 10,000 mPa·s at 180 °C. The adhesive can be applied by slot-die coating or spiral spray at 160–180 °C. Compared with SBS-based hot melts, the hydrogenated midblock of 7533 reduces yellowing under ultraviolet exposure and improves low-odor performance during sustained heating.

Peel adhesion values to stainless steel and corona-treated polypropylene are generally reported in the range of 5–12 N/25 mm when tested under ASTM D6862 or equivalent PSTC 101, but adhesion depends strongly on tackifier softening point and substrate surface energy. Hydrogenated hydrocarbon resins with softening points of 100–110 °C are preferred; high-aromatic tackifiers plasticise the polystyrene endblocks and lower cohesive strength. Residual tack above 1.5 N/25 mm after removal indicates inadequate cooling or excessive plasticiser. The formulation should be tested for viscosity change over 72 h at 180 °C; stabilised formulations typically show viscosity drift below 10 % under nitrogen.

Medical Tubing, Overmoulding, and High-Clarity Olefin Blends

In medical tubing and overmoulding, SEBS 7533 is evaluated as a non-phthalate alternative to flexible PVC and as a replacement for unhydrogenated SBS where sterilisation resistance is required. The neat polymer may be covered by FDA 21 CFR 177.2600 for rubber articles intended for repeated food contact, but finished-compound status depends on additives and must be confirmed through lot-specific regulatory documentation. Cytotoxicity evaluation under ISO 10993-5:2009 and skin sensitisation under ISO 10993-10:2010 are performed on the final compound, not on the neat polymer. REACH compliance under EC 1907/2006 and RoHS compliance under 2011/65/EU should be verified against the current safety data sheet and restricted-substance declarations.

For overmoulding onto polypropylene, substrate temperature above 90–110 °C before injection improves interdiffusion and peel strength; published data for this specific configuration is limited. Gamma irradiation up to 25 kGy and ethylene oxide sterilisation at 55 °C have been applied to stabilised SEBS compounds. Gamma exposure may produce minor yellowing and a tensile strength shift below 10 % in suitably stabilised grades. The saturated midblock displays lower residual monomer and oligomer extractables than some SBS or SIS grades, but extractables testing under ISO 10993-12:2021 remains required for final device validation.

For initial compound screening, class-level differences are summarised in the following representative comparison. The ranges are drawn from distributor literature and general styrenic block copolymer data, not from a single lot certificate.

The data above illustrate that 7533 balances ozone resistance and melt processability. Higher-styrene SEBS grades offer higher hardness and cohesive strength but require higher melt temperatures and accept less oil. Unhydrogenated SBS offers lower cost and high elongation but fails ozone and UV ageing tests rapidly. The selection of 7533 for a particular compound should be based on a designed experiment measuring hardness, tensile properties, compression set, and peel or impact values on actual pilot-scale equipment.

For polypropylene impact modification, SEBS 7533 is added at 5–20 wt% to a polypropylene homopolymer with melt flow rate of 10–30 g/10 min under ISO 1133-1, using a twin-screw extruder at 210–230 °C. Notched Izod impact strength at 23 °C typically increases from 2–4 kJ/m² to 10–20 kJ/m² when measured under ISO 180:2020 or ASTM D256. At −20 °C, improvement is smaller unless the SEBS content exceeds 15 wt%. A 50 wt% SEBS masterbatch predispersed in polypropylene improves the final morphology and prevents agglomeration.

High Oil Loadings Can Deplete Antioxidant Protection and Alter Shrinkage

When oil loading exceeds 60 phr, the effective concentration of primary antioxidant in the compound is diluted, and the continuous oil phase can accelerate oxygen diffusion into the melt. Oxidative degradation of the ethylene/butylene midblock proceeds by hydroperoxide formation; stabiliser packages containing hindered phenols and phosphites are added at 0.1–0.5 wt% based on total polymer matter. Long-term heat ageing at 120 °C for 168 h can reduce tensile strength by 5–15 % in stabilised SEBS 7533 compounds, while unstabilised or heavily diluted compounds may lose more than 30 %. The addition of secondary antioxidants is required in high-oil soft-touch grades.

Shrinkage in soft compounds is anisotropic; flow-direction shrinkage of 1.0–2.5 % and transverse shrinkage of 0.8–2.0 % are observed in injection-moulded plaques depending on gate location and packing. High oil content increases isotropic shrinkage and prolongs dimensional stabilisation at room temperature for 24–48 h. Mould shrinkage measurements should follow ASTM D955 or ISO 294-4. The saturated midblock is not compatible with strongly polar polymers such as polyamide or polycarbonate; without a maleic anhydride-grafted compatibiliser, blends show delamination and unstable morphology. Strong oxidising acids and chlorinated solvents at elevated temperature are unsuitable for cleaning or processing equipment used with SEBS 7533.