Difference between revisions of "Perspex"
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Latest revision as of 23:33, 13 March 2021
Brand of ICI.
Rowland Hill, working in the laboratories of British Dyestuffs Corporation at Blackley was studying artificial resins and polymers, including poly(methyl 2-methylpropenoate), otherwise known as polymethyl methacrylate or PMMA. A patent was applied for in 1931 and this covered not only the polymer and its use as a thermoplastic material but also the preparation of the monomer. It was surprising that other acrylic polymers which were much softer.
At the same time, Dr. John Crawford was working in the laboratories of Explosives Group of ICI at Stevenston, investigating the suitability of various resins and polymers as interlayers for safety glass. The cellulose-based materials then being used had the disadvantage of turning yellow in sunlight which PMMA did not. John Crawford recognised, as had Rowland Hill, the unique combination of physical and optical properties shown by PMMA.
Both researchers recognised also that, although the patent had specified a way to prepare the monomer, methyl 2-methylpropenoate, the process described in the patent was not capable of producing it in large quantities at an economic price. Before the polymer could be properly developed and made commercially available a way would have to be found to make the monomer on a commercial scale.
John Crawford's great contribution to the story of Perspex was the discovery of a commercially viable manufacturing process for methyl 2-methylpropenoate. The process used cheap and readily available starting materials, namely propanone, hydrogen cyanide, methanol and sulphuric acid. A patent covering this process was granted on 12th August 1932. The process is known as the Stevenston Process and, with some modifications, it is still used today, throughout the world.
1933 The first sheet of clear PMMA was made at ICI's Ardeer Works. The technique devised then still forms the basis for the method used today for large scale production of cast acrylic sheet. .
The task of making methyl 2-methylpropenoate monomer was then given to ICI's General Chemicals Division at Billingham. Research into the manufacture of sheet materials from this monomer was also transferred to Billingham and by 1934, the year in which the trade name "Perspex" was registered, a semi-technical plant to produce sample quantities of the new sheet had been established there.
1940 ICI acquired Orchard Mill, Darwen for use as a shadow factory to manufacture Perspex sheet and mouldings such as aircraft cockpit canopies and windows.
Sources of Information
- John Stevenson