Tyres take the majority — passenger tread compounds above all, where solution SBR is now the reference material. Beyond tyres, SBR goes into footwear soling, conveyor belt covers, industrial hose and moulded goods, and a large latex market covering carpet backing, paper coating binders and adhesives. SBR latex is also used to modify asphalt for road surfacing and to improve cement mortars.

The polymerisation, and what it lets you control. Emulsion SBR is made by free radical polymerisation in a water emulsion, usually at 5 °C, which produces a broad molecular weight distribution with some branching. It processes forgivingly and costs less. Solution SBR is made anionically with an alkyllithium initiator in hydrocarbon solvent, and because anionic polymerisation is living, the vinyl content, styrene distribution, molecular weight distribution and chain ends can all be set deliberately. That control is what allows functionalised chain ends that couple to silica filler, which is how modern tread compounds achieve low rolling resistance without losing wet grip. For anything where dynamic performance is the specification, solution grades are not an upgrade to emulsion — they are a different product.

It sets the stiffness and the glass transition, and through those, the balance of grip and rolling resistance. More styrene raises Tg, which increases hysteresis at the frequencies relevant to wet grip — good for traction — but also increases energy loss at rolling frequencies, which costs fuel economy. Standard emulsion grades sit at 23.5% because it is a workable compromise. Solution grades run from around 10% for low rolling resistance compounds to 40% and above for high grip. Higher styrene also raises hardness and abrasion resistance, and worsens low-temperature flexibility.

It is a measure of the raw polymer's resistance to shear, taken in a rotor-in-cavity instrument, and it is the standard viscosity measure for elastomers because they cannot be characterised by melt flow. The notation matters: ML(1+4) 100 °C means a large rotor, one minute preheat, reading taken after four minutes, at 100 °C. Higher Mooney means higher molecular weight, better ultimate properties and harder processing — more mixing energy, more difficulty incorporating filler and worse extrusion surface. Oil-extended grades quote a lower Mooney because the oil is already in, so comparing an oil-extended figure with a dry-polymer figure is meaningless.

Oil-extended SBR has process oil added at the plant, typically 27.3 or 37.5 parts per hundred rubber, which lets the producer make a much higher molecular weight polymer than could otherwise be processed and then bring the working viscosity back down with oil. The result is better ultimate properties at a workable Mooney. Black masterbatch grades have carbon black added as well, which improves dispersion compared with dry mixing and reduces dust exposure in the compound room. Both are supplied as bales like ordinary grades, so the oil and black loadings must be read off the certificate and accounted for in the recipe — a substitution made on grade number alone will change the compound significantly.

Every shipment includes a Certificate of Analysis covering Mooney viscosity with the test conditions stated, bound styrene, volatile matter, ash, organic acid and soap content, plus declared oil and carbon black loadings for extended and masterbatch grades; a Safety Data Sheet to GHS and REACH format; REACH polymer compliance confirmation; antioxidant type declaration for light-coloured applications; an origin certificate; and destination-market certificates where required.