Polyethylene under High Pressure: From an Experimental Product to Manufacturing

In March 1933, Imperial Chemical Industries conducted high-pressure chemistry research at Winnington in Cheshire. Reginald Oswald Gibson and Eric William Fawcett investigated whether pressure could promote otherwise difficult reactions. Polyethylene was not the designated target. The Royal Society of Chemistry later commemorated 27 March as the discovery date.

Their ethylene and benzaldehyde experiment began on 24 March. Opening the apparatus after the weekend, they found a small amount of waxy solid. It lacked the properties expected of a benzaldehyde reaction product but had the composition of an ethylene polymer. The intended experiment had failed, yet its residue became a new subject of research. The start on the 24th and identification on the 27th mark separate steps in the process.

References: [2] [3] [4]

The initial yield was small, and repeated experiments could cause violent decomposition. Apparatus limitations and safety constrained further work. Late in 1935, Michael Willcox Perrin and colleagues revisited ethylene with improved equipment and obtained more white polymer. Establishing the role of trace oxygen in the feedstock was an important step toward consistent preparation.

Oxygen’s role was sensitive to concentration. Early patents discussed its amount alongside pressure, temperature and heat removal. Small quantities could promote rapid polymerization, while excessive oxygen or inadequate removal of reaction heat could trigger dangerous decomposition. Turning an accidental product into a manufacturing method required measurable, adjustable and reproducible variables.

References: [1] [2] [4]

Ethylene is a small-molecule gas; polymerization joins many ethylene units into longer molecules. ICI’s U.S. patent describes semisolid and solid polymers, emphasizing toughness in the solids compared with the oily low-molecular-weight products already obtainable. It records waxy feel, thermoplastic behavior and some crystallinity, with heating producing a softened, viscous material.

The method of removing the product also affected appearance. Cooling under pressure and releasing pressure while hot could give different forms of material from similar reactions. White powder, waxy residue and tough masses were therefore not necessarily unrelated substances. Understanding the material required comparison of composition, molecular size, thermal behavior and processing.

References: [1]

Polymerization releases heat. A temperature rise acceptable in a small vessel might be difficult to control at larger scale. Early patents discussed vessel conductivity, localized heating, stirring and cooling to prevent local temperatures crossing the decomposition threshold. Research moved from identifying a product into reactor design.

The patent also proposed continuous operation: passing feedstock through a reaction zone, separating polymer and recycling unreacted ethylene with fresh feed. The process involved compression, reaction, heat exchange, separation and recovery. The initial British application was made in 1936; the examined U.S. patent was filed in February 1937 and granted in April 1939, dates distinct from discovery in 1933.

References: [1] [2]

ICI needed uses sufficient to support a plant. Polyethylene’s flexibility, chemical resistance and electrical properties made cable insulation an important direction. Finding customers and evaluating sample processing and performance mattered to manufacturing prospects alongside establishing chemical composition.

The company history in Chemistry & Industry records ICI opening a polyethylene plant in 1939 with initial annual capacity of about 100 tonnes, followed by expansion. Radar insulation consumed substantial production during the Second World War. Widespread packaging and everyday plastic goods developed later. The 1933 node marks identification of a valuable polymer during high-pressure research, at the beginning of that industrial history.

References: [2] [4]