With its electrical nonconductivity and heat-resistant properties, it became a great commercial success. It was used in electrical insulators, radio and telephone casings, and such diverse products as kitchenware, jewellery, pipe stems, children’s toys, and firearms. The “retro” appeal of old Bakelite products has made them collectable.
Pritish Kumar gives an illustration of Electrically nonconductivity and heat resistant element Bakelite
The creation of synthetic plastic was revolutionary for the chemical industry, which at that time made most of its income from cloth dyes, and explosives. The commercial success of Bakelite inspired the industry to pour money into developing other synthetic plastics.
Synthesis
Making Bakelite is a multi-stage process. It begins with heating of phenol and formaldehyde in the presence of a catalyst such as hydrochloric acid, zinc chloride, or the base ammonia. This creates a liquid condensation product, referred to as Bakelite A, which is soluble in alcohol, acetone, or additional phenol. Heated further, the product becomes partially soluble and can still be softened by heat. Sustained heating results in an “insoluble hard gum”.
However, the high temperatures required to create this tends to cause violent foaming of the mixture when done at standard atmospheric pressure, which results 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 (300 °F), Baekeland was able to suppress the foaming that would otherwise occur. The resulting substance is extremely hard and both infusible and insoluble.
Compression molding
Molded Bakelite forms in a condensation reaction of phenol and formaldehyde, with wood flour or asbestos fiber as a filler, under high pressure and heat in a time frame of a few minutes of curing. The result is a hard plastic material. Asbestos was gradually abandoned as filler because many countries banned the production of asbestos.
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. Millions of parts could be duplicated quickly and relatively cheaply.
Phenolic sheet
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. Paper, cotton fabrics, synthetic 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 many commercial grades and with various additives to meet diverse mechanical, electrical and thermal requirements. Some common types include.
1)Paper reinforced NEMA XX per MIL-I-24768 PBG. Normal electrical applications, moderate mechanical strength, continuous operating temperature of 250 °F (120 °C).
2)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 (120 °C).
3)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 (120 °C).
4)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 (70 °C).
Properties
Bakelite has a number of important properties. It can be molded very quickly, decreasing production time. 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.
Phenolic resin products may swell slightly under conditions of extreme humidity or perpetual dampness. When rubbed or burnt, Bakelite has a distinctive, acrid, sickly-sweet or fishy odor.
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