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Material · Synthetic

Styrene-butadiene rubber

The most-produced synthetic rubber there is, and most of it is on a car — the tread compound of the world's tyres.

SBR is butadiene copolymerised with styrene, and the ratio between them is the tuning knob: more styrene gives more stiffness, more grip and more hysteresis, less gives better low-temperature flexibility and lower rolling resistance.

Against natural rubber it wears better and ages better, and it builds up more heat under repeated flexing and has lower tear strength. That trade decides the tyre industry: passenger car treads are mostly SBR, and truck and aircraft tyres, which flex a great deal and must not overheat, use far more natural rubber.

It is a thermoset once vulcanised — sulfur crosslinks the chains — with everything that implies for recycling.

Processing

Made by emulsion polymerisation, which is cheap and gives a less regular chain, or by solution polymerisation, which is more expensive and gives control over the chain architecture. Solution SBR is what modern low-rolling-resistance tyres are built from, because the placement of the styrene and the chain ends can be engineered.

Compounded with carbon black or silica, oils, sulfur and accelerators, then formed and vulcanised under heat and pressure in the mould. The filler is not an adulterant: unfilled SBR has almost no abrasion resistance, and carbon black raises it by an order of magnitude.

Uses

Tyre treads, above all — the single largest use of any synthetic rubber. Conveyor belts, hoses, drive belts, shoe soles, and moulded rubber goods generally.

As a latex rather than a solid it coats paper and backs carpets, and it binds the aggregate in some sports surfaces.

History

Developed in Germany as Buna S in the 1930s, and scaled in the United States under the Synthetic Rubber Program after the Japanese occupation of South-East Asia cut off ninety per cent of the Allied natural rubber supply in 1942. That programme took American synthetic rubber output from almost nothing to hundreds of thousands of tonnes a year within three years, and is one of the largest and fastest industrial mobilisations of a new material on record.

It is the clearest case there is of a material being created because a supply chain failed, rather than because it was better.

Environmental impact

Vulcanised rubber cannot be remelted. End-of-life tyres are shredded into crumb for sports surfaces and playground matting, ground into rubberised asphalt, burned as fuel in cement kilns, or pyrolysed for oil and carbon black — none of which returns the material to a tyre. Devulcanisation exists and remains marginal.

Tyre wear is now recognised as a major source of microplastic in the environment, plausibly the largest single one, entering water courses through road runoff. It is an emission from use rather than from disposal, and no recycling arrangement addresses it.

Medium confidence Weak evidence

How we know: checked recently · only one source, so there is nothing to cross-check it against · stated directly by the source.

How this connects

Where a connection has been confirmed by an outside reference, that reference is named beside it.

is sourced from

  • Styrene — compound · the co-monomer with butadiene, and the ratio between them is what tunes grip against rolling resistance

is produced by

  • Polymerisation — process · emulsion or solution copolymerisation of styrene with butadiene

is an alternative to

  • Natural rubber — material · the substitution the Second World War forced. SBR wears and ages better; natural rubber has higher tear strength and builds up less heat, which is why truck and aircraft tyres still use a great deal of it

succeeded

  • Natural rubber — material · in passenger tyre treads, under wartime supply pressure rather than on merit — and the substitution held afterwards because SBR wears better

is used in

is associated with

  • The wartime materials programmes — event · American production went from almost nothing to hundreds of thousands of tonnes a year in three years, with patents pooled by government direction

belongs to the group

  • Rubber — material · the most-produced synthetic, and most of it is tyre tread

Sources

  • Material World
    Our own writing
  • Wikidata
    Wikimedia Foundation · Creative Commons CC0 1.0 Universal (public domain dedication)

Questions this page answers

Where it comes from, and what it becomes

Follow Styrene-butadiene rubber back to what it starts as, and forward into what it becomes. Each step is a documented one — a real route material takes, not a chain of inference.

Upstream — what it comes from

  • Styrene-butadiene rubber → is produced by (emulsion or solution copolymerisation of styrene with butadiene) → Polymerisation → takes as input (as vinyl chloride, which is why more than half of PVC's weight is salt rather than oil) → Chlorine → is produced by (at the anode) → Chlor-alkali electrolysis → takes as input (as the brine the cell electrolyses, and as the source of the hydrogen that comes off the cathode) → Water → is sourced from (by desalination, where energy is cheap and coastline available — the only route that adds fresh water rather than moving it) → Seawater
  • Styrene-butadiene rubber → is sourced from (the co-monomer with butadiene, and the ratio between them is what tunes grip against rolling resistance) → Styrene → is sourced from (via ethylbenzene: ethylene alkylates benzene, and the product is dehydrogenated) → Ethylene → is produced by (the principal product, and the largest-tonnage organic chemical made anywhere) → Steam cracking → takes as input (the European and Asian cracker feed; North American crackers mostly run on ethane from natural gas instead, and make a different product slate as a result) → Naphtha → is sourced from (the fraction boiling between about 30 and 200 °C, separated by distillation rather than made) → Crude oil
  • Styrene-butadiene rubber → is produced by (emulsion or solution copolymerisation of styrene with butadiene) → Polymerisation → takes as input (as tetrafluoroethylene, which is where a substantial share of industrial fluorine chemistry ends up) → Fluorine → is produced by (electrolysis of potassium bifluoride, which is molten and conducts — there is no chemical oxidant strong enough to displace fluorine from a compound, so electricity is the only route and always has been) → Molten salt electrolysis → takes as input (after concentration, as one of the two routes to lithium chloride) → Lepidolite
  • Styrene-butadiene rubber → is sourced from (the co-monomer with butadiene, and the ratio between them is what tunes grip against rolling resistance) → Styrene → is produced by (by way of ethylbenzene, which is ethylene and benzene joined and then dehydrogenated) → Steam cracking → takes as input (the European and Asian cracker feed; North American crackers mostly run on ethane from natural gas instead, and make a different product slate as a result) → Naphtha → is sourced from (the fraction boiling between about 30 and 200 °C, separated by distillation rather than made) → Crude oil
  • Styrene-butadiene rubber → is produced by (emulsion or solution copolymerisation of styrene with butadiene) → Polymerisation → takes as input (as vinyl chloride, which is why more than half of PVC's weight is salt rather than oil) → Chlorine → is extracted from (by electrolysis of brine, which yields chlorine and sodium hydroxide together) → Halite
  • Styrene-butadiene rubber → is produced by (emulsion or solution copolymerisation of styrene with butadiene) → Polymerisation → takes as input (as tetrafluoroethylene, which is where a substantial share of industrial fluorine chemistry ends up) → Fluorine → is extracted from (the only significant source; hydrofluoric acid is made from it and everything fluorinated follows) → Fluorite

These are the most distinct paths back. Styrene-butadiene rubber can be traced through others besides.

Downstream — what it becomes