Post 583 –by Gautam Shah
Clay was the first plastic material that could be formed to desired shape. Clay gains ‘plasticity’ -a moulding or shaping capacity, due to its grain shape, size and distribution and addition of water. A natural metal nodule or a purified one from the ore, on heating becomes, ‘plastic’. This property was not available with materials like wood and stone. Materials like Bamboo or Cain, have the capacity to bend, but cannot be reshaped or moulded. Plasticity is the property of material to be deformed repeatedly without rupture by the action of a force, and remain deformed after the force is removed.
Historically few natural materials that exhibited the plastic behaviour were known, but without clear perception of the categorical behaviour. These natural materials were organic polymers or bio-derived materials such as egg and blood proteins. In 1600BC. Mesoamericans used natural rubber for balls, bands, and figurines. Treated Cattle’s horns were used for their translucency in lanterns and windows. Materials with similar properties were developed by treating casein -a milk-protein with lye. Casein was also used as gum material. Bitumen was used as a water proofing material for boats and also as a joint material for masonry. Plant-based starch materials on being cooked showed flow-behaviour. Lac, an insect exudate was used as gum or joining material in India. The lac was used for cast mouldings since 1868. Rubber, a plant exudate was used since 1535, as water proofing material and for shoe making.
Polymers were not distinctly identified till around 1900s, however during 1860s Thomas Graham noted that some dissolved organic compounds -typically cellulose, cannot be purified into a crystalline form. This was different organization of matter. Graham called them ‘colloids’, after the Greek word for glue =kolla. This was the beginning of the Age of Plastics or Polymer Age. (Plastic =plastikos Gk = mouldable) (Poly+mer=many molecules).
Parkesine (London) developed the first plastic from plant origin cellulose by reacting it with nitric acid, to form a cellulose nitrate. Celluloid was plasticized with camphor, dissolved in alcohol and hardened into a transparent elastic material. On heating it could be moulded and coloured with pigments. It was a substitute material, for than (1860) widely used ivory balls for billiards. The product was patented under the trademark Celluloid. It was also used later in the manufacture of objects ranging from dental plates to men’s collars. Celluloid, despite its flameability and capacity deteriorate when exposed to light, was commercially successful.
The first totally synthetic plastic was the phenol-formaldehyde resin, Bakelite. In the early 1900s, Bakelite, the first fully synthetic thermoset, was reported by Baekeland. Baekeland’s was looking for a replacement for shellac that had difficult supply. And that is the reason, their first product a soluble phenol-formaldehyde like shellac was called ‘Novolak’. Baekeland also worked on a process to strengthen wood by saturating it with a synthetic resin of phenol and formaldehyde.
Baekeland reacted Phenol with Formaldehyde (an exothermic reaction) but stop the reaction midway, while the product was in liquid state (called A stage). ‘ The A resin (Resol) could be made directly into a usable plastic, or it could be brought to a solid B stage (Resitol) in which, though almost infusible and insoluble, it could still be ground into powder and then softened by heat to a final shape in a mould. Both stages A and B could be brought to a completely cured thermoset C stage, by heating under pressure. This last stage was Bakelite C, or true Bakelite.’
In 1927 the Bakelite patent expired and the market were flooded with competitive thermo setting resin products of Urea and Melamine formaldehyde, and other new thermoplastic resins such as cellulose acetate, polyvinyl chloride, poly-methyl methacrylate, and polystyrene.
Bakelite, was recognized as the ‘National Historic Chemical Landmark’. Bakelite was mouldable material with electrical non-conductivity and heat-resistance properties. He saw a wide variety of uses of the resin with many different filling materials such as cotton, powdered bronze, slate dust, wood and asbestos fibres. It was used widely in electrical appliances replacing bulky ceramic components. It was used for kitchen handles, radio and telephone casings, kitchenware, jewellery, pipe stems, toys etc. His one of the first patents describes ‘Method of making insoluble products of phenol and formaldehyde’. Bakelite Company began to produce many material forms, but laminating varnish, was most successful products. Laminating varnishes are used for coating copper circuits, paper, fabrics and for manufacturing laminate sheets. Blocks or rods of transparent cast resins, known as ‘artificial amber’, that could be machined or carved to shapes were used for pipe stems, cigarette holders and jewellery.
Baekeland’s heat and pressure patents expired in 1927 soon placing the company under severe pressure from competitors like Catalin. Catalin is also a phenol formaldehyde resin, but produced by a different, two-stage process. It was produced without any fillers like sawdust or carbon black. It can be worked with nominal carpentry tools like files, grinders and cutters, and polished to dull gloss. Another advantage of it was its transparency and capacity to take bright colours.