Phenolic resin

Phenolic resin is phenol reacted with formaldehyde into a densely crosslinked, highly aromatic network. It is rigid, dimensionally stable, a good electrical insulator, and it does not melt — heated far enough it chars, forming a carbon layer that insulates what is underneath.

That charring behaviour is why it survives in an era of better plastics. Where fire performance is the requirement — smoke, flame spread, toxicity — phenolic outperforms almost every other polymer, and it holds the aircraft interior panel and the rail vehicle market for that reason alone.

It is dark, brittle, and cannot be made in light colours because the resin itself is amber to brown. Every Bakelite object is black, brown or mottled for that reason, and the mottling was a way of disguising it.

Made in two forms. Resol resins carry enough formaldehyde to cure with heat alone and are used as liquid adhesives and impregnants. Novolac resins need a separate hardener and are the basis of moulding compounds, which are supplied as a filled powder, compression moulded and cured in the tool.

Compression moulding rather than injection moulding, because the material cures in the mould and cannot be melted again. That is slower per part than a thermoplastic and is one reason phenolic lost the consumer market it once owned.

The largest use by tonnage is invisible: the adhesive bonding plywood, oriented strand board and engineered timber. Phenolic resin is what holds the world's sheet timber products together, and its water resistance is what makes exterior-grade plywood exterior grade.

Also: aircraft and rail interior panels, where fire performance decides; foundry sand binders; brake pads and clutch friction materials; abrasive wheel bonding; circuit board substrate in cheaper grades; laboratory worktops; and the handles of saucepans and irons, which is one of very few consumer uses it never lost, because a thermoset handle does not soften.

Leo Baekeland patented Bakelite in 1907 — the first plastic made entirely from synthetic components rather than modified natural ones, and therefore the beginning of the modern plastics industry.

It arrived at the moment electrification needed a mouldable insulator, and for thirty years it was the material of switches, sockets, plugs, radio cabinets, telephones and distributor caps. Thermoplastics displaced it from consumer goods after the Second World War on colour, toughness and moulding speed, and it retreated to the applications where not melting is the entire point.

A thermoset: not meltable, not mechanically recyclable, and usually landfilled or burned for energy. Ground phenolic is used as a filler in new moulding compound, which is a partial route.

Free formaldehyde is the live issue, particularly in wood panel products, where residual resin can off-gas into indoor air. Formaldehyde is classified by IARC as carcinogenic to humans, and emission limits for panel products — the European E1 class, the Californian CARB standards — exist specifically to control it. Modern resins emit far less than those of the 1970s and 1980s, and the panels in older buildings do not improve.