8th Class Science Synthetic Fibers and Plastics Plastics

       Plastics

Plastics, materials made up of large, organic (carbon-containing) molecules that can be formed into a variety of products. The molecules that compose plastics are long carbon chains give plastics many of their useful properties. In general, materials that are made up of long, chain like molecules are called polymers. Plastics can be made hard as stone, strong as steel, transparent as glass, light as wood, and elastic as rubber. Plastics are also lightweight, waterproof, chemical resistant, and produced in almost any colour. More than 50 families of plastics have been produced, and new types are currently under development.

            Uses of Plastics

Plastics are indispensable to our modern way of life. The cars we drive, the computers we use, the utensils we cook with, the recreational equipment we play with, and the houses and buildings we live and work in all include important plastic components. The average car contains almost 136 kg (almost 300 Ib) of plastics nearly 12 percent of the vehicle's overall weight. Telephones, textiles, compact discs, paints, plumbing fixtures, boats, and furniture are other domestic products made of plastics. In 1979 the volume of plastics produced in the United States surpassed the volume of domestically produced steel. Plastics are used extensively by many key industries, including the automobile, aerospace, construction, packaging, and electrical industries. The aerospace industry uses plastics to make strategic military parts for missiles, rockets, and aircraft. Plastics are also used in specialized fields, such as the health industry, to make medical instruments, dental fillings, optical lenses, and biocompatible joints.

             Types of Plastics

A wide variety of both thermoplastics and thermosetting plastics are manufactured. These plastics have a spectrum of properties that are derived from their chemical compositions. As a result, manufactured plastics can be used in applications ranging from contact lenses to jet body components. Thermoplastics: Thermoplastic materials are in high demand because they can be repeatedly softened and remolded. The most commonly manufactured thermoplastics are presented in this section in order of decreasing volume of production.

High-density polyethylene (HDPE) has a density that ranges from 0.94 to 0.97 g/cu.cm (0.62 to 0.64 oz/cu in). HDPE is stiffer, stronger, and less translucent than low-density polyethylene. HDPE is molded into grocery bags, car fuel tanks, packaging, and piping.

Polyvinyl Chloride: Polyvinyl chloride (PVC) is prepared from the organic compound vinyl chloride. PVC is the most widely used of the amorphous plastics. PVC is lightweight, durable, and waterproof. Chlorine atoms bonded to the carbon backbone of its molecules give PVC its hard and flame-resistant properties.

In its rigid form, PVC is weather-resistant and is extruded into pipe, house siding, and gutters. Rigid PVC is also blown into clear bottles and is used to form other consumer products, including compact discs and computer casings.

       A very thin, threadlike strand from which clothe is made, is known as:

(a) Fibres

(b) Yarns

(c) Plastics

(d) Fabrics

(e) None of these

Answer: (a)

      Which one of the following is a man made fibre?

(a) Cotton

(b) Jute

(c) Rayon

(d) Nylon

(e) None of these

Answer: (c)

• Fibers are hairlike structure of animal, vegetable, mineral or synthetic origin.
• Animal fibres are resistant to most organic acid.
• Synthetic fibres are produced from chemical substances.
• Rayon is a man-made fibre prepared from cellulose.
• Thermoplastics can be repeatedly softened and remolded..