2020年7月25日雅思阅读真题+题目+答案：The History of Plastics

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2020年7月25日雅思写作范文：Some people believe that the government should not spend money on international aid when they have their own disadvantaged people like homeless and unemployed. To what extent do you agree or disagree?

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2020年7月25日雅思阅读真题+题目+答案：The History of Plastics

When rubber was first commercially produced in Europe during the nineteenth century, it rapidly became a very important commodity, particularly in the fields of transportation and electricity. However, during the twentieth century a number of new synthetic materials, called plastics, superseded natural rubber in all but a few applications.

Rubber is a polymer - a compound containing large molecules that are formed by the bonding of many smaller,simpler units,repeated over and over again.The same bonding principle - polymerisation - underlies the creation of a huge range of plastics by the chemical industry.

The first plastic was developed as a result of a competition in the USA. In the 1860s,$ 10,000 was offered to anybody who could replace ivory - supplies of which were declining - with something equally good as a material for making billiard balls.The prize was won by John Wesley Hyatt with a material called celluloid.Celluloid was made by dissolving cellulose, a carbohydrate derived from plants? in a solution of camphor dissolved in ethanol. This new material rapidly found uses in the manufacture of products such as knife handles, detachable collars and cuffs, spectacle frames and photographic film. Without celluloid the film industry could never have got off the ground at the end of the 19th century.

Celluloid can be repeatedly softened and reshaped by heat and is known as a thermoplastic. In 1907 Leo Baeketand,a Belgian chemist working in the USA, invested a different kind of plastic by causing phenol and formaldehyde to react together. Baekeland called the material Bakelite,and it was the first of the thermosets - plastics that can be cast and moulded while hot, but cannot be softened by heat and reshaped once they have set.Bakelite was a good insulator,and was resistant to water, acids and moderate heat.With these properties it was soon being used in the manufacture of switches,household items,such as knife handles,and electrical components for cars.

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