O’zbekiston respublikasi oliy va o’rta maxsus ta’lim vazirligi mirzo ulug’bek nomidagi o’zbekiston milliy universiteti

XII. Answer the following questions after reading the text given below

1. 
   What is the place of plastics in chemical industry nowadays?
   
2. 
   What is the polymers structure?
   
3. 
   What are the two naturally occurring polymers?
   

PLASTICS
The use of plastics in particularly every field of activity is now so that it is difficult to realize how quick the plastics industry has grown. In no other branch of the chemical industry has there been such a large and consistent growth in production as in the plastics industry. In its widest sense the word "plastics" includes synthetic rubber and fibres, resins, adhesives, films, coatings and similar materials. These materials are to most people familiar in their final form such as a moulded plastic textile fibre, or a package material and are not normally thought of as chemicals.

But they are all in fact¹ derived from natural or synthetic chemicals and belong to a class of chemicals known as polymers. These materials have a common basic structure in that they are composed of very large molecules and enormous in size compared to the more familiar or common chemical substances. The most remarkable properties of these substances and the ones which differentiate them from other types of chemicals are their mechanical properties such as strength, toughness, elasticity, hardness and deformability.

Although high polymers compose the essential and most widely distributed kind of organic matter, the form of cellulose and proteins — two classes of substance which are components of all living plants and animal cells — the first truly synthetic plastics — as distinct from nitrocellulose (celluloid and xylonite) developed earlier — were not discovered until the early part of this century. The plastics industry grew steadily in the 1920-30 and new plastic materials began to be used.

But something of much greater significance was happening during this period — attention was being directed towards the chemical nature and structure of these materials. These fundamental researches revealed the nature of these new substances and it was established that they were composed of large molecules and that each of the molecules was made up from a large number of simple building blocks. The acceptance of the so-called "micro-molecular hypotheses" in the early 1930 s forms the basic of the science of high polymers and has been largely responsible for the rapid advances in polymer research and the tremendous development of the plastics industry.

Although no one polymer can satisfy all the requirements for an end product — whether it be the nose fan of an aircraft, a bottle, the fabric of a tent or an article of lingerie — there appears to be no serious limitation to the fashioning from simple chemical raw materials of polymer products to meet any reasonable property and specification.
No t e s

1. in fact — haqida

2. in its widest sense — keng manosiga ko’ra