Monday, April 19, 2010

Polyester History

Polyesters have been known from time immemorial. Even in antiquity man knew & used natural polyesters, known up to the present time more often as resins, such as dammar gum, shellac, yacca gum, copal, amber etc. These products find use even at the present day .

A long known form of polyesters is represented by widely used coatings, which various vegetable oils (linseed, tung etc.) form on drying in the air. However, the real blossoming of the chemistry & technology of polyesters is closely bound up with the development of methods for the production and synthesis of an enormous number of synthetic polymers, which represent a group of high molecular weight compounds. The first member of which was synthesized as long as 1833.

The first introductions for the synthesis of polyesters from hydroacids are due to Gay-Lussac & Palouze , who obtained a solid polymer on heating lactic acid. In 1861, Heintz obtained a polymer from glycolic acid by heating it to 240°C, subsequently, the preparation of polyglycollide was studied by Menshutkin , Dessaignes , Kelcule , Anschutz , Bischoff and Walden and others. Sokolov obtained three-dimensional polyester by polycondensation of glyceric acid.

Polyesters of polybasic acids & polyhydric alcohols was first synthesized by Berzelius , who reported in 1847 that on heating glycerol and tartaric acid a non-crystalline pliable mass was formed which on the heated state could be drawn into long filaments. Similar reaction was carried out by Berthelot between glycerol and sebacic and camphoric acids, and by van Bemmelen between glycerol and succinic & citric acid, Smith investigated reaction between glycerol and phthalic anhydride in 1901.

The first report on the preparation of polyesters by the polymerization of cyclic esters is due to Bischoff and Walden8 who converted cyclic ester glycollide into the polymer polycollide under influence of heat as well as in presence of traces of zinc chloride.

Menshutkin in 1881 was the first to apply kinetic methods to the investigation of the polyesterification reaction. He studied the esterification of ethylene glycol by succinic acid. In 1882, he determined the limiting degree of esterification of glycolic, lactic and dimethgycollic acids.

A particularly pronounced development in the investigation of synthetic polyesters occurred after 1925, when the work of Tilicheyev , Maksorov , Carothers , Kienel and others led to the synthesis of a series of new compounds of this type, they also demonstrated the possibility of the wide practical application of the polyesters in the industry.

Carothers and his coworkers pioneered the work on synthetic fibres. They first produced spinnable polyester of high molecular weight by condensing ,-diols with alkanedioic acid. Carothers and Hill jointly succeeded in carrying out the polycondensatoin as part of molecular distillation or simply by passing nitrogen through the condensation melt until a fibre forming polyester resulted.

In the early 1940’s the Calico Printer Association Ltd. began to study the effect of molecular symmetry on the condensation polymers. Schlack , in Germany and Whinfield and Dickson , in Great Briton used dicarboxylic acids for the production of polyester fibres almost at the same time. While Schlack used terephthalic acid and 1,4-butandiol, Whinfield and Dickson used combination of terephthalic acid and ethylene glycol.

Fibre forming aliphatic polyesters was produced in the early 1930s, but these products had low melting points and were unsuitable for commercial use17. Laboratory scale quantities of polyethylene terephthalate were prepared by 1941 in Britain. E. I. du Pont de Nemours Co. Inc . acquired US patent rights for PET in 1948, and Imperial Chemical Industries (ICI) of the UK obtained patent rights for the rest of the world. The World War II considerably retarded any further developments so that large-scale production of polyester fibres in different countries was not started until the 1950’s. In Britain the manufacture of polyethylene terephthalate fibres began on a pilot scale in 1948. The fibre being marketed as Terylene. Since then the production of Terylene was extended rapidly.

Polyester fibres became available commercially in the United States in 1953, and production expanded enormously in 1960s and 1970s. At Wilton, in Yorkshire, ICI started a large plant with annual capacity of 11 million lbs. divided equally between filament yarn and staple. In 956, a second unit of similar capacity began production and a new Terylene plant in Northern Ireland followed this .

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