|Thermal conductivity||0.2 W/(m·K)|
Refractive index (nD)
Except where noted otherwise, data is given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
Bakelite (// BAY-kə-lyt, sometimes spelled Baekelite), or polyoxybenzylmethylenglycolanhydride, is an early plastic. It is a thermosetting phenol formaldehyde resin, formed from an elimination reaction of phenol with formaldehyde. It was developed by Belgian-born chemist Leo Baekeland in New York in 1907.
One of the first plastics made from synthetic components, Bakelite was used for its electrical nonconductivity and heat-resistant properties in electrical insulators, radio and telephone casings, and such diverse products as kitchenware, jewelry, pipe stems, firearms, and children's toys. The "retro" appeal of old Bakelite products has made them collectible.
Baekeland was already wealthy, due to his invention of Velox photographic paper, when he began to investigate the reactions of phenol and formaldehyde in his home laboratory. Chemists had begun to recognize that many natural resins and fibres were polymers. Baekeland's initial intent was to find a replacement for shellac, a material that was in limited supply because it was made naturally from the excretion of lac bugs. Baekeland produced a soluble phenol-formaldehyde shellac called "Novolak", but it was not a market success.
Baekeland then began trying to strengthen wood by impregnating it with a synthetic resin, rather than coating it. By controlling the pressure and temperature applied to phenol and formaldehyde, Baekeland produced a hard moldable material which he named "Bakelite". The first synthetic thermosetting plastic ever made, it was often referred to as "the material of 1000 uses," a phrase originated by Baekeland himself. Baekeland speculated on the possible uses of a wide variety of filling materials, including cotton, powdered bronze, and slate dust, but was most successful with wood and asbestos fibers.
Baekeland filed a substantial number of patents in the area. His "Method of making insoluble products of phenol and formaldehyde" was filed on July 13, 1907 and granted on December 7, 1909. Baekeland also filed for patent protection in other countries, including Belgium, Canada, Denmark, Hungary, Japan, Mexico, Russia, and Spain. He announced his invention at a meeting of the American Chemical Society on February 5, 1909.
Baekeland started semi-commercial production of his new material in his home laboratory, marketing it as a material for electrical insulators. By 1910, he was producing enough material to justify expansion. He formed the General Bakelite Company as a U.S. company to manufacture and market his new industrial material. He also made overseas connections to produce materials in other countries.
The Bakelite Corporation was formed in 1922 (after patent litigation favorable to Baekeland) from a merger of three companies: Baekeland's General Bakelite Company; the Condensite Company, founded by J.W. Aylesworth; and the Redmanol Chemical Products Company, founded by L.V. Redman. A factory was built near Bound Brook, New Jersey, in 1929.
Bakelite Limited, a merger of three British phenol formaldehyde resin suppliers (Damard Lacquer Company Limited of Birmingham, Mouldensite Limited of Darley Dale and Redmanol Chemical Products Company of London) was formed in 1926. A new factory opened in Tyseley, Birmingham, England around 1928. It was demolished in 1998.
In 1939 the companies were acquired by Union Carbide and Carbon Corporation. Union Carbide's phenolic resin business including the Bakelite and Bakelit registered trademarks are owned by Momentive Specialty Chemicals.
In addition to the original Bakelite material, these companies eventually made a wide range of other products, many of which were marketed under the brand name "Bakelite plastics". These included other types of cast phenolic resins similar to Catalin, and urea-formaldehyde resins, which could be made in brighter colors than polyoxybenzylmethylenglycolanhydride.
Once Baekeland's heat and pressure patents expired in 1927, Bakelite Corporation faced serious competition from other companies. Because Bakelite incorporated fillers to give it strength, it tended to be made in concealing dark colors. In 1927, beads, bangles and earrings were produced by the Catalin Company, through a different process which enabled them to introduce 15 new colors. Translucent jewelry, poker chips and other items made of phenolic resins were introduced in the 1930s or 1940s by the Catalin Company under the Prystal name. The creation of marbled phenolic resins may also be attributable to the Catalin Company.
Making Bakelite was a multi-stage process. It began with the heating of phenol and formaldehyde in the presence of a catalyst such as hydrochloric acid, zinc chloride, or the base ammonia. This created a "liquid condensation product", referred to as "Bakelite A", which was soluble in alcohol, acetone, or added phenol. Heated further, the product became partially soluble and could still be softened by heat. Even more heating resulted in an "insoluble hard gum". However, the high temperatures required to create this tended to cause violent foaming of the mixture, which resulted in the cooled material being porous and breakable. Baekeland's innovative step was to put his "last condensation product" into an egg-shaped "Bakelizer". By heating it under pressure, at about 150 °C., Baekeland was able to suppress the foaming that would otherwise occur. The resulting substance was extremely hard and both infusable and insoluble.:38–39
Powdered "Bakelite A" could be combined with chopped asbestos fibers or wood floor and molded in hydraulic presses to create solid objects. Bakelite A acted as a binder, surrounding the filler, and solidifying with a smooth finish.:42–43 Bakelite's molding process had a number of advantages. Bakelite resin could be provided either as powder, or as preformed partially cured slugs, increasing the speed of the casting. Thermosetting resins such as Bakelite required heat and pressure during the molding cycle, but could be removed from the molding process without being cooled, again making the molding process faster. Also, because of the smooth polished surface that resulted, Bakelite objects required less finishing. One of the first Bakelite molded products, produced by the Boonton Rubber Company, was a tiny bushing, the size of a mustard seed, created for Weston Electric in 1908. Millions of parts could be duplicated quickly and relatively cheaply.:42–43
Another market for Bakelite resin was the creation of phenolic sheet materials. Phenolic sheet is a hard, dense material made by applying heat and pressure to layers of paper or glass cloth impregnated with synthetic resin.:53 Cellulose paper, cotton fabrics, synthetic yarn fabrics, glass fabrics and unwoven fabrics are all possible materials used in lamination. When heat and pressure are applied, polymerization transforms the layers into thermosetting industrial laminated plastic.
Bakelite phenolic sheet is produced in dozens of commercial grades and with various additives to meet diverse mechanical, electrical and thermal requirements. Some common types include:
- Paper reinforced NEMA XX per MIL-I-24768 PBG
- Normal electrical applications, moderate mechanical strength, continuous operating temperature of 250 °F (121 °C).
- Canvas reinforced NEMA C per MIL-I-24768 TYPE FBM NEMA CE per MIL-I-24768 TYPE FBG
- Good mechanical and impact strength with continuous operating temperature of 250 °F (121 °C).
- Linen reinforced NEMA L per MIL-I-24768 TYPE FBI NEMA LE per MIL-I-24768 TYPE FEI
- Good mechanical and electrical strength. Recommended for intricate high strength parts. Continuous operating temperature 250 °F (121 °C).
- Nylon reinforced NEMA N-1 per MIL-I-24768 TYPE NPG
- Superior electrical properties under humid conditions, fungus resistant, continuous operating temperature of 160 °F (71 °C).
Bakelite has a number of important properties. It can be molded very quickly therefore identical units can be mass produced. Moldings are smooth, retain their shape and are resistant to heat, scratches, and destructive solvents. It is also resistant to electricity, and prized for its low conductivity. It is not flexible.:44–45
Applications and usage
|This section does not cite any references or sources. (February 2014)|
These characteristics made Bakelite particularly suitable as a molding compound, an adhesive or binding agent, a varnish, and as a protective coating. This positioned it as an extremely desirable material for the emerging electrical and automobile industries.:44–45 Bakelite was soon used for non-conducting parts of telephones, radios and other electrical devices, such as bases and sockets for light bulbs and electron tubes, supports for any type of electrical components, automobile distributor caps and other insulators.
Phenolics are more rarely used in general consumer products today, due to the cost and complexity of production and their brittle nature. Nevertheless they are still used in some applications where their specific properties are required, such as small precision-shaped components, molded disc brake cylinders, saucepan handles, electrical plugs and switches and parts for electrical irons. Today, Bakelite is manufactured and produced in sheet, rod and tube form for hundreds of industrial applications in the electronics, power generation and aerospace industries, and under a variety of commercial brand names.
In its industrial applications, Bakelite was particularly suitable for the emerging electrical and automobile industries because of its extraordinarily high resistance – not only to electricity, but to heat and chemical action. It was soon used for nonconducting parts of radios and other electrical devices, such as bases and sockets for light bulbs and vacuum tubes, supports for electrical components, automobile distributor caps and other insulators.
In the early 20th century, it was found in myriad applications including saxophone mouthpieces, whistles, cameras, solid-body electric guitars, telephone housings and handsets, early machine guns, pistol grips, and appliance casings. In the pure form it was made into such articles as pipe stems, buttons, etc.
The thermosetting phenolic resin was at one point considered for the manufacture of coins, due to a shortage of traditional material; in 1943, Bakelite and other non-metal materials were tested for usage for the one cent coin in the US before the Mint settled on zinc-coated steel.
After the Second World War, factories were retrofitted to produce Bakelite using a more efficient extrusion process, which increased production and enabled the uses of Bakelite to extend into other genres: jewelry boxes, desk sets, clocks, radios, game pieces like chessmen, poker chips, billiard balls and Mah Jong sets. Kitchenware such as canisters and tableware were also made of Bakelite through the 1950s.
The primary commercial uses for Bakelite today remain in the area of inexpensive board and tabletop games produced in China, India and Hong Kong. Items such as billiard balls, dominoes and pieces for games like chess, checkers, and backgammon are constructed of Bakelite for its look, durability, fine polish, weight, and sound. Common dice are sometimes made of Bakelite for weight and sound, but the majority are made of a thermoplastic polymer such as acrylonitrile butadiene styrene (ABS).
Bakelite is used to make the presentation boxes of Breitling watches and sometimes as a substitute for metal firearm magazines. Bakelite is also used in the mounting of metal samples in metallography.
Bakelite is still used today for wire insulation, brake pads and related automotive components, and industrial electrical-related applications. Phenolic resins have been commonly used in ablative heat shields. Soviet heatshields for ICBM warheads and spacecraft reentry consisted of asbestos textolite, impregnated with Bakelite.
The United States Patent and Trademark Office granted Baekeland a patent for a "Method of making insoluble products of phenol and formaldehyde" on December 7, 1909. Producing hard, compact, insoluble and infusable condensation products of phenols and formaldehyde marked the beginning of the modern plastics industry.
- Catalin – another phenolic resin, similar to Bakelite, but with different mineral fillers that allowed the production of light colors
- Celluloid – another early plastic
- Condensite – a similar material of the age having much the same properties, characteristics, and uses
- Crystalate – another early plastic
- Galalith – another early plastic, derived from milk
- Micarta – early composite insulating plate that used Bakelite as a binding agent, trademarked 1912 by Westinghouse Elec. & Mfg Co.
- Novotext – brand name for cotton textile-phenolic resin
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