SINOPEC Maoming SBS F875 is a linear styrene-butadiene-styrene block copolymer produced by solvent-based anionic polymerisation. The grade is used in bitumen modification, solvent-borne and hot-melt adhesives, footwear compounds, and elastomeric waterproofing membranes. The base polymer is not extender-oil-filled; it is supplied as a porous pellet or crumb that absorbs process oils during mixing. The nominal styrene content is 30 ± 1 wt%, and the butadiene midblock accounts for approximately 70 ± 1 wt%. Certificate-of-analysis limits commonly report volatile matter at ≤1.0 wt% under ISO 248-1:2011 and ash at ≤0.2 wt% under ISO 247-1:2018. Tensile properties on solvent-cast, compression-moulded sheet measured per ASTM D638-14 Type IV specimens at 500 mm/min are typically ≥18 MPa ultimate tensile stress and ≥700 % elongation at break. Hardness under ISO 868:2003 is 70–75 Shore A, read at 15 s. Melt flow rate under ASTM D1238-20 at 200 °C/5 kg is reported as 0.5–2.5 g/10 min. These are nominal range values, not simultaneous release limits; each production lot can vary because coupling-agent efficiency, vinyl content, and residue level shift rheological and mechanical data.

Why Does Linear Architecture Influence Melt Fracture Limits in F875?

The linear triblock architecture places styrene endblocks at the chain ends; under melt shear the endblock aggregates act as physical crosslinks. F875 therefore shows pronounced shear-thinning but lower melt elasticity than equivalent radial grades. On a co-rotating twin-screw extruder with L/D 44:1 and vacuum venting at -0.08 MPa, barrel set points from 150 °C to 170 °C are used. Screw speed 300 rpm and die pressure 7–12 MPa maintain melt temperature in the 185–195 °C range. If melt temperature exceeds 200 °C for more than 4 min, strand surface roughness and die-lip gel accumulation increase. The boundary is not related to a single chemical degradation event; it is the combined result of residual coupling-agent residues, oxygen ingress at the feed throat, and shear-induced chain scission. Reducing screw speed to 250 rpm and raising the feed-zone set point to 160 °C lower melt temperature to 180–185 °C and restore strand clarity. Capillary rheometry under ASTM D3835 at 200 °C and 100 s−1 is used to compare lot-to-lot zero-shear viscosity; lot shifts of 5–10 % are normal and require closed-loop melt pump correction.

Bitumen modification uses F875 at 3.5–5.5 wt% of neat asphalt in polymer-modified bitumen for road paving and waterproofing membranes. The polymer is pre-swelled in the aromatic maltene phase of a hot binder at 170–180 °C before high-shear dispersion. A rotor–stator mixer with tip speed 18–22 m/s is run for 45–90 min, followed by low-shear digestion at 150–160 °C for 2–4 h. Dispersion quality is verified by fluorescence microscopy and by softening-point homogeneity under ASTM D36. Storage stability is assessed by EN 13399:2017; F875 can produce separation values below 5 °C when the base bitumen contains sufficient aromatic oil and the mixer creates a preblend without free polymer particles. The linear structure enables faster solvent swelling than radial grades at equivalent tip speed 20 m/s, but it may generate lower zero-shear viscosity than a radial SBS. This trade-off is relevant when high-temperature rutting resistance is measured by dynamic shear rheometer under ASTM D7175 after rolling thin-film oven ageing per ASTM D2872.

Comparative Values for F875, F675, and a Radial SBS Grade

F875 differs from F675 primarily in melt flow and tensile-tear balance. F675 is the lower-viscosity linear grade in the same styrene block range; it is preferred in solvent adhesives where fast dissolution and low Brookfield viscosity are required. F875 is selected when higher cohesive strength and higher softening point after bitumen modification are required. The radial grade provides higher high-shear melt strength and lower creep under static load, as expected from branched topology. Published data for F875 in specific reactive hot-melt configurations is limited; formulators should compare capillary viscosity under ASTM D3835 rather than relying on a single melt flow value.

In solvent-borne adhesive manufacture, F875 is dissolved into a toluene/ethyl acetate mixture at 70:30 to a solids content of 25–35 wt%. Dissolution at 50–60 °C with a turbine stirrer at 300–500 rpm reaches a clear solution in 4–6 h; higher shear only increases solvent loss and reduces viscosity stability. Brookfield viscosity under ISO 2555:2018 is adjusted with tackifier. For a pressure-sensitive adhesive compound, a C9 hydrogenated tackifier at 40–60 phr and naphthenic oil at 5–15 phr are added after polymer dissolution. Paraffinic oil above 10 phr migrates to the bond line and causes tack loss; 180° peel under ASTM D3330/D3330M and loop tack under ASTM D6195 are used to validate performance. F875 is not recommended for oil-resistant adhesive applications because the butadiene midblock swells in aliphatic and aromatic solvents; for such exposure, a styrene-isoprene-styrene or acrylic solution is required.

In footwear sole compounds, F875 is combined with general-purpose polystyrene, naphthenic oil, silica, coupling agent, and blowing agent. Injection moulding takes place at melt temperature 160–180 °C, mould temperature 30–40 °C, and injection pressure 60–80 MPa. The compound is shear-sensitive; gate freeze time is influenced by styrene endblock content. F875 delivers higher Shore A hardness than F675 at comparable oil loading; the difference is typically 2–5 Shore A under ISO 868:2003. Tear strength is measured under ASTM D624; abrasion resistance under DIN 53516 is monitored for shoe sole compounds. Because F875 does not contain vulcanising agents, it is processed as a thermoplastic rubber; no sulphur cure is required.

Pellet pre-treatment before extrusion is straightforward but often overlooked. F875 pellets are dried at 60–70 °C for 2–4 h only when surface moisture is suspected. Drying above 80 °C can deform the porous structure and create caking in the hopper; this is a batch-to-batch variability point in plants without insulated hoppers. The pellets absorb process oil during compounding at rates that depend on oil viscosity; a naphthenic oil of 40–100 mm²/s at 40 °C wets the pellet surface but does not fully penetrate until shear is applied. Single-stage addition of 50 phr oil to a cold mixer can induce wall slip and extend compounding time; split addition at 60:40 during two mixing stages gives more uniform oil distribution.

When Oxygen Migration During Twin-Screw Compounding Narrows the Processing Window

In compounding and masterbatch production, oxygen migration into the feed throat and melt pool is more critical for F875 than for lower molecular weight F675. Melt temperature above 200 °C accelerates autoxidation of the butadiene midblock and increases gel formation. The processing window narrows to ±5 °C around a target melt temperature of 185 °C in vented twin-screw extrusion. Stabilisation with hindered phenol at 0.2–0.5 phr and phosphite at 0.1–0.3 phr is standard; amine-based antidegradants are avoided in light-coloured or rosin-ester-tackified formulations because staining and ester interaction can occur. The hopper and feed throat should be blanketed with nitrogen, with oxygen level below 100 ppm. Vacuum venting at -0.09 MPa removes volatile residues and absorbed moisture from pellets stored above 60 % RH. Yellowness index under ASTM E313 and gel count on a 25 µm mesh pack are used as lot-release checks in production; increased gel count indicates residence time or oxygen excursion.

For elastomeric bitumen waterproofing membranes, F875 is blended with oxidised bitumen, calcium carbonate filler, and sometimes atactic polypropylene at 170–190 °C. The compound is calendered or extruded onto a polyester carrier. Low-temperature flexibility is evaluated by bending at -20 °C under EN 1109:2013; the linear midblock of F875 contributes to flexibility without the higher processing viscosity of a radial SBS. In production-scale paddle mixers of 2–5 t batch size, adding F875 as a single charge can create undispersed gel domains; pre-swelling with 10–15 % of the process oil for 30 min before filler addition reduces optical gel counts.

F875 should be stored away from direct sunlight and ozone sources. Storage below 35 °C preserves antioxidant content and prevents pellet blocking. Extended exposure to atmospheric ozone produces surface crazing in unstabilised SBS; ozone resistance testing under ASTM D1149 is relevant for outdoor ageing. The product is insoluble in water but soluble or swellable in toluene, cyclohexane, methyl ethyl ketone, ethyl acetate, and chlorinated solvents. It should not be combined with strong oxidising acids or high-aromatic process oils above the level required for compatibility, because excessive aromatic oil swells the styrene domains and reduces tensile strength. No halogens or intentionally added heavy metals are used in the base polymer; users must verify end-product compliance with REACH, RoHS 2011/65/EU, and FDA 21 CFR where applicable.