Types of Polymers
Apart from their use as moulding materials, synthetic polymers have replaced natural polymers in many traditional technologies.
The heated glue-pot which traditionally contained glues based on animal products such as hoof, horn and fish residues has been replaced by adhesives based on synthetic polymers. There is now a wide range of adhesives and sealants suited to a variety of tasks from PVA wood, board and paper glues to two-part epoxide resins for rivet-less bonding of metal panels in aircraft.
Animal fibres, such as wool or silk, and vegetable fibres, such as cotton, continue to be used although there is a wealth of synthetic fibres now available.
The first artificial silk was developed by Chardonnet in 1884 by spinning cellulose nitrate from solution. However, this was dangerously inflammable and the first commercially successful artificial fibre was developed by Stearn by spinning regenerated cellulose from viscose. The rights to this process were acquired by S. Courtauld & Co. in 1904.
The Dreyfus brothers spun fibres from cellulose acetate solution in the 1920s and this became the Celanese Corporation.
The first fibre to be spun from a molten polymer was nylon in the 1930s and since then a number of polymers have been produced in fibre form – including acrylic fibre based on polyacrylonitrile (PAN) and polyester based on polyethylene terephthalate (PET). Carbon fibres for making advanced composites are produced by a heat treatment of polyacrylonitrile and other synthetic fibres.
Animal membranes were the only non-metallic film forming materials used before the availability of rubber and these found little application. The successful development of a drum for casting films from viscose led in the 1920s to the production of ‘Cellophane’ – still a widely used material.
In the 1930s, unsupported PVC films were manufactured but it was not until polyethylene was available in the 1940s that the production of films for bagging materials became commonplace.
The paint industry was traditionally based on naturally occurring ‘drying’ oils such as linseed but since the 1930s these have gradually been replaced by synthetic polymers. Because of toxicity problems from using paints based on solvents, many more finishes are now water-based polymer emulsions.