?? JEC History - 10 MILESTONES IN THE HISTORY OF COMPOSITES (episode 3)

?? THE ERA OF ENABLING INVENTIONS: MAKING MATERIAL REVOLUTIONS INDUSTRIAL (1930-1940) AND CREATING PROCESSES “OUT OF THE BLUE” (1930-1950)

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The 1930s saw the invention of most of the plastics we still use today, as well as the most popular composite reinforcement – glass fiber. In 1933, Carleton Ellis (USA) invented unsaturated polyester as the first “low pressure“ thermoset resin. Another important step, improving the applicability of these resins, came in 1942, when American Cyanamid developed polyester copolymers using peroxide curing agents.

Epoxy resins followed. Pierre Castan (Switzerland) filed his first patent on epoxy in 1938 and then licensed it to Swiss company Ciba. Important developments were realised by German scientist Schlack (1933) and S.O. Greenlee (1939, USA), leading to the most used bisphenol A epoxy.

Several thermoplastics were invented in the same period (polyamide, polystyrene, polypropylene), but their use as a matrix in composites came much later than that for thermosets.

The first “upscalable” production process to draw glass fibers from the melt was developed. Games Slayter (USA), working at Corning-Illinois, filed a 1933 patent to produce glass wool, and in 1938 a patent for producing continuous (crimped) glass fibers. Industrial production started, and as the company Owens was also able to produce glass fibers (1932), they joined forces with Corning to create the company Owens-Corning Fibers (1935). They licensed the technology to Balzaretti Modigliani (Italy), who transferred it to Saint-Gobain (France) in 1939.

Processing advances

The first concepts to make composites did not use the new low-pressure thermoset resins but tried to realise what Kemp (see Episode 2) had described in his 1916 patents: to pre-impregnate a fibrous reinforcement with a phenolic resin and “cure” it under high pressure. British scientist Norman de Bruyne had already developed an experimental aircraft using stressed, curved plywood. In January 1937, he presented a paper to the Royal Aeronautical Society in London stating that “phenolic resin with suitable reinforcement could have the necessary mechanical properties for aircraft construction, and also the potential to produce lighter-weight components.”

A paper by Tony Kinloch explained that de Bruyne had chosen flattened flax rovings (obtained from an undergraduate student, Mr Gordon, whose family was in the linen business) to create a unidirectional reinforcement. Although Kemp had already reported that curved panels could be produced, the first panels produced by de Bruyne and Gordon in 1938 were flat. Their “stop-and-go” semi-continuous process produced phenolic composite panels up to 10 m long. This was the start of the Gordon Aerolite (flax-phenolic, and later Kraft paper-phenolic) composite production.

Gordon and de Bruyne’s concept was based on composite structural elements that directly replace metallic ones and was first tried on the ‘Blenheim bomber’ and then a Spitfire fuselage. It failed because the multiple connections typical for a metal-like structure made the parts too heavy. The hygroscopic nature of the natural fiber reinforcements and the high pressures needed during production also presented problems. J.E. Gordon and colleagues from the Royal Aircraft Establishment (RAE) then switched to the low-pressure polyester resins now available, enabling them to make large “one piece“ parts, even with complex shapes, such as the Spitfire’s seat.

This step towards using low pressure resins led to the development of a range of novel processing methods dedicated to composites with continuous fiber reinforcements, using bio-based as well as glass fibers. The wet lay-up (contact molding) process was used from the beginning, as well as the technique of pre-mixing matrix and fibers into a “molding compound” which is then compressed at high temperature into the desired shape of the product. The use of such molding compounds rapidly expanded in the 1950s. Later, processing methods like filament winding and pultrusion were invented. Filament winding was initially developed for rocket motors and pipes (J.F. Stephens patent, 1944-1949), and later Lubin and Greenberg started production at Basons Industries (1945). Pultrusion followed (Meyer & Howell patent, 1951) and was then perfected by Brandt-Goldsworthy.

Continue your journey into history with our celebration of 50 Years of Composites : https://www.jeccomposites.com/about-composites/

Check back next month for the next episode : The first two decades (1940-1960) of hesitating enthusiasm (engineers) and (un)limited imagination (designers).

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