Material · Synthetic

Polycarbonate

Transparent and almost unbreakable — the safety glazing, the riot shield, the headlamp lens and the spectacle lens.

Polycarbonate is the plastic that does not break. It is transparent, roughly as clear as glass, and absorbs impact energy on a scale nothing else transparent comes close to — which is why it is the material of riot shields, machine guards, safety glazing and the canopy of an aircraft.

What it is not is scratch resistant. Untreated polycarbonate scuffs from ordinary handling, so almost every optical use is hard-coated, and a headlamp lens that has gone yellow and cloudy is a coating that has failed rather than a plastic that has.

Economic significance

Its markets are the ones where the failure mode of glass is unacceptable: glazing where people might fall against it, lenses in front of eyes, guards on machinery, and the enormous business of vehicle headlamps, which changed from glass to polycarbonate within about a decade because a moulded lens can be any shape a designer wants.

Bisphenol A is the standing problem. Most polycarbonate is made from it, traces can migrate from a container into what it holds, and its behaviour as a weak endocrine disruptor is well enough established to have driven bans on polycarbonate baby bottles and a general retreat from it in food contact. The replacements are chemically similar enough that the argument has followed them.

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.

contains

Carbon — element · the backbone and the aromatic rings that supply the stiffness
Hydrogen — element · the balance
Oxygen — element · in the carbonate links the polymer is named for

is produced by

Polymerisation — process · from bisphenol A and a carbonate source — and the bisphenol A is the material's standing regulatory problem

is an alternative to

Soda-lime glass — material · as glazing where breakage is unacceptable: polycarbonate absorbs perhaps two hundred times the impact energy and scratches far more easily
PMMA — material · the two transparent plastics, and the choice is sharp: polycarbonate absorbs vastly more impact and scratches easily, PMMA is clearer, harder, cheaper and cracks. Which is the safety material depends on the threat
ABS — material · in housings: polycarbonate is stronger and more heat resistant, ABS is cheaper and moulds more easily, and blends of the two are common precisely because the trade is close

is an input to

Injection moulding — process · headlamp lenses and optical discs, where the process has to reproduce a surface accurately enough to work optically

is used as

Protective equipment — application · eye and face protection, machine guards and riot shields, on impact energy nothing else transparent approaches

is commonly confused with

PMMA — material · sold under trade names, both clear, and routinely substituted for each other by people who need the one that does not shatter. Perspex cracks; polycarbonate does not

belongs to the group

Plastic — material · the transparent one that shatters rather than scratches

Sources

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

Questions this page answers

Where it comes from, and what it becomes

Follow Polycarbonate 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

Polycarbonate → is produced by (from bisphenol A and a carbonate source — and the bisphenol A is the material's standing regulatory problem) → 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
Polycarbonate → is produced by (from bisphenol A and a carbonate source — and the bisphenol A is the material's standing regulatory problem) → 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
Polycarbonate → is produced by (from bisphenol A and a carbonate source — and the bisphenol A is the material's standing regulatory problem) → 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
Polycarbonate → is produced by (from bisphenol A and a carbonate source — and the bisphenol A is the material's standing regulatory problem) → 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
Polycarbonate → is produced by (from bisphenol A and a carbonate source — and the bisphenol A is the material's standing regulatory problem) → 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 (the largest single use of salt, and the process the whole chlorine and caustic soda industry rests on) → Salt → is produced by (in the solar route — the same process, read from the other end) → Brine evaporation
Polycarbonate → is produced by (from bisphenol A and a carbonate source — and the bisphenol A is the material's standing regulatory problem) → 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 brine; the salt is the feedstock for both products at once) → Halite

These are the most distinct paths back. Polycarbonate can be traced through others besides.

Downstream — what it becomes

Polycarbonate → is an input to (headlamp lenses and optical discs, where the process has to reproduce a surface accurately enough to work optically) → Injection moulding
Polycarbonate → is used as (eye and face protection, machine guards and riot shields, on impact energy nothing else transparent approaches) → Protective equipment