Making Bakelite — The First Fully Synthetic Plastic That Launched the Age of Polymers

This synthesis uses two acutely toxic chemicals and MUST be performed in a functioning fume hood. Wear a full-face respirator with organic vapour cartridges, chemical splash goggles, a lab coat, and double-layer nitrile gloves (change the outer pair every 15 minutes when handling phenol). Phenol penetrates skin rapidly and painlessly — it destroys tissue beneath the surface before pain is felt. If phenol contacts skin, flush immediately with water for 15 minutes, then apply polyethylene glycol (PEG 400) if available. Formaldehyde is a suspected carcinogen — never inhale the vapour.

Weigh 10 g of phenol (C₆H₅OH) — a white crystalline solid with a sharp, medicinal odour (the smell of old-fashioned disinfectant). Phenol melts at 41 °C, so it may be partly liquid in warm weather. Place in a 250 ml borosilicate beaker. Phenol was first isolated from coal tar by Friedlieb Runge in 1834 and was used as 'carbolic acid' antiseptic by Joseph Lister in the 1860s. It is the simplest aromatic alcohol — the hydroxyl group activates the benzene ring, making the ortho and para positions reactive toward electrophilic substitution by formaldehyde.

Measure 15 ml of formalin — a 37% aqueous solution of formaldehyde (HCHO, methanal). Add to the phenol in the beaker. Formaldehyde is the simplest aldehyde — a single carbon with a double-bonded oxygen and a hydrogen. It is intensely reactive because the carbonyl is unhindered. In the Bakelite reaction, each formaldehyde molecule bridges two phenol rings by forming a methylene (-CH₂-) link. The molar ratio is approximately 1:1.5 (phenol:formaldehyde), providing a slight excess of formaldehyde to ensure complete cross-linking.

Add 1 ml of concentrated hydrochloric acid (HCl) as an acid catalyst. Stir the mixture with a glass rod. Place the beaker in a water bath heated to 70–80 °C. The acid catalyses the reaction by protonating the formaldehyde, making it a stronger electrophile. The hydroxymethylation reaction begins: formaldehyde attacks the activated ortho and para positions of the phenol ring, forming hydroxymethyl (-CH₂OH) intermediates. Under acidic conditions, these intermediates condense with other phenol molecules, releasing water and forming methylene bridges.

Maintain the water bath at 70–80 °C and stir occasionally for 60 minutes. The mixture gradually thickens and turns from clear to amber to dark brown as the phenol-formaldehyde oligomers grow longer. Eventually, two layers separate: an upper aqueous layer and a lower viscous, amber resin layer — this is the novolac (from Latin 'nova lacca', new lacquer). Novolac is a thermoplastic prepolymer — the chains are linear or branched but not yet cross-linked. At this stage, the resin can still be dissolved in alcohol or acetone and melted by gentle heating.

Carefully pour off the upper aqueous layer (containing water, excess formaldehyde, and HCl). Add 50 ml of warm water to the resin and stir to wash out residual acid and formaldehyde. Pour off the wash water. Repeat twice more. The washed novolac is a sticky, amber, translucent mass with a characteristic phenolic smell. In Baekeland's original process, this resin was produced in bulk and sold to moulding companies who added the curing agent and shaped the final product.

Weigh 1.5 g of hexamethylenetetramine (hexamine, (CH₂)₆N₄) and mix thoroughly into the warm novolac resin. Hexamine decomposes when heated, releasing formaldehyde directly into the resin — this provides the additional formaldehyde needed to form the final cross-links without the water that liquid formalin would introduce. The released formaldehyde bridges the remaining unreacted positions on the phenol rings, converting the linear novolac into a fully cross-linked, three-dimensional network. This is the step that transforms a mouldable thermoplastic into an irreversible thermoset.

Press the resin-hexamine mixture into a small metal or silicone mould — a muffin tin, a small baking mould, or a purpose-made compression mould. Press firmly to eliminate air pockets. The mixture is still workable at this stage — warm it gently if it has become too stiff to mould. This is the last moment the material can be shaped — once curing begins, the shape is permanent. Baekeland's genius was recognising that this mouldability before curing, combined with the hardness after curing, made phenol-formaldehyde ideal for mass production of complex shapes.

Place the mould in an electric oven preheated to 150–170 °C. Cure for 2–3 hours. During curing, the hexamine decomposes and the final cross-linking reactions proceed: every phenol ring becomes linked to two or three neighbours through methylene bridges, building an infinite three-dimensional network. The material darkens to deep brown or black, hardens progressively, and shrinks slightly. A faint formaldehyde odour is released — ensure adequate ventilation. The curing temperature and time determine the final hardness: higher temperature and longer time produce a harder, more completely cross-linked product.

Allow the oven to cool, then remove the moulded piece. The finished Bakelite is a hard, dark brown or black material with a smooth, glossy surface where it contacted the mould. It is dense and heavy in the hand. Tap it — it produces a sharp, resonant click (the characteristic 'Bakelite sound'). It cannot be scratched with a fingernail. It does not soften when heated — hold it near a hot surface and it remains rigid. It does not dissolve in any common solvent. This is a thermoset: the cross-links are permanent, and the material's shape is fixed forever.

Test electrical insulation: touch a multimeter across the sample — resistance is effectively infinite. This property made Bakelite the standard material for electrical components for half a century. Test heat resistance: place the sample on a hot plate at 200 °C — it remains rigid with no softening, distortion, or melting. Test chemical resistance: place a chip in concentrated hydrochloric acid — no visible reaction. Compare with celluloid (which is thermoplastic and dissolves in acetone) to demonstrate the fundamental difference between thermoplastic and thermoset polymers.

Label the sample: BAKELITE (PHENOL-FORMALDEHYDE THERMOSET). Unlike celluloid, Bakelite is chemically stable and can be stored indefinitely — museum Bakelite from the 1910s remains in perfect condition. Leo Baekeland's 1907 patent (US Patent 942,699) for 'Bakelite' was the first fully synthetic plastic — a material created entirely from simple chemicals with no natural polymer precursor. It proved that chemists could engineer materials with properties impossible in nature: hard as stone, light as wood, an insulator like glass, mouldable like clay, and permanent as metal. Every modern thermoset — epoxies, polyurethanes, silicones — descends from Baekeland's phenol-formaldehyde chemistry.