Notes-Class 8-Science-Chapter-17-Man-Made Material-Maharashtra Board

Properties of plastic :

• Plastic is non-corrosive.
• It is non-degradable as it does not decompose.
• The factors such as humidity, heat, rain, etc. do not affect plastic.
• Any coloured item can be manufactured from plastic.
• Plastic shows property of plasticity. Thus it can be moulded into any shape that is needed. .
• Plastic is a bad conductor of heat and electricity.
• Plastic is light-weight and thus preferred for carrying.

Uses of plastic : Plastic, the man-made material is used in various forms in modern age. According to the type of plastic, its uses are different.

Thermoplastic materials are used for manufacturing following articles :

• Polyvinyl chloride or PVC is used to make bottles, raincoat, pipes, handbags, shoes, electric cable insulation, furniture, ropes, toys, etc.
• Polystyrene is used in making thermo-insulating parts of electric appliances like refrigerators, gears of machines, toys, protective coverings like covers of CD and DVD, etc.
• Polyethylene (PE) plastics are used for making milk bags, packing bags, flexible garden pipes, etc.
• Polypropylene (PP) is used in making parts of loudspeakers and vehicles, ropes, mattresses, laboratory appliances, etc.

Thermosetting plastic is used in the manufacturing of the following items :

• Bakelite for making cabinets of radio, T.V., telephones, electric switches, toys, plastic handles of cookers, etc.
• Melamine for making domestically useful items like cup, saucers, plates, tray, some spare parts of airplane engines, electric and sound insulating coverings, etc.
• Polyurethane in making surfing boards, small boats, furniture, seats in vehicles, etc.
• Polyester in fibre glass, toners of laser printers, textile industry, etc.

Degradable materials : Those materials that can be naturally degraded, are called degradable materials.

• Degradable substances are not accumulated in the nature.
• Degradable substances emit foul odour when they are being decomposed.
• Usually microorganisms play a part in the degradation process, hence such substances are also called biodegradable.
• E.g. Vegetables, fruits, wood, cotton or wool fibres, etc.

Non-degradable materials : The materials that do not degrade through natural processes are called non-degradable materials. E.g. Plastic being non-degradable, it is an environmental pollutant.

• The use of plastic should be reduced as far as possible as it causes environmental pollution. Jute bags, cloth bags, paper bags, etc. can be a better option for the plastic carry bags.
• However, certain plastic items are almost irreplaceable such as plastic in healthcare sector which is in the form of saline bottles or syringes.
• Microwave cookware is plastic. In microwave, metal cookware cannot be used. Teflon used for scratch-resistance, is a kind of plastic.
• Airplanes need some plastic parts.
• Lenses and artificial teeth are made up of polyacrylic.
• There are more than 2000 different types of plastics. But one must be careful in plastic use.

Adverse effects of excessive use of thermocol on environment and human :

• Disease causing and carcinogenic effect : Styrene in thermocol has cancer causing (carcinogenic) substances. Therefore, if anyone is in long term contact with thermocol, there are increased chances of being affected by blood cancer or lymphoma.
• Non-biodegradable nature : Natural degradation of thermocol does not take place easily. If it is destroyed by burning, poisonous gases are released through it causing toxic air pollution.
• Excessive use : People tend to use thermocol in mass gatherings. The plates and cups made up of thermocol can affect the health. Reheating food kept in thermocol can be also hazardous as styrene may dissolve in such food. Eating in thermocol cups or plates will thus not only cause environmental problems but also health effects.
• Occupational hazard to those working in thermocol factory: Long term contact with thermocol may develop the problems of eyes, respiratory system, skin, digestive system, etc. It is also harmful for pregnant women as it may induce abortion. Skin burns are caused by liquid styrene.

Production of Glass :

• For glass production, mixture of sand, soda, lime, and small quantity of magnesium oxide is heated in furnace.

• Sand, i.e. silicon dioxide melts at 1700 °C. To melt the mixture at low temperature at 850 °C, pieces of discarded glass are added to it.
• After all the ingredients of mixture are liquified, it is heated up to 1500 °C and immediately cooled.
• Sudden cooling makes the mixture homogeneous, amorphous and transparent instead of crystalline.

Properties of Glass :

• On heating, glass becomes soft and can be moulded into any shape.
• Density of glass depends upon its ingredients.
• Glass is slow conductor of heat. On quick heating of cool glass or on quick cooling of hot glass, it cracks / breaks.
• Being bad conductor of electricity, glass is used as insulator in electric appliances.
• Being transparent, most of light passes through the glass.
• Oxides of either chromium, vanadium or iron in the glass, makes large amount of light to be absorbed in glass.

Types of Glass and Uses:

1-Silica glass : This is produced by using the silica. Items made up of silica glass show minimum expansion on heating.

• Features/Uses : It is not affected by acid and alkali. Due to this, silica glass is used to produce laboratory glass-wares.

2-Borosilicate glass : Borosilicate glass is produced by melting the mixture of sand, soda, boric acid and aluminium oxide.

• Features/Uses : This glass does not show any effect on medicines. Hence, the bottles made up of borosilicate glass are used in pharmaceutical industry to store the medicines.

3-Alkali silicate glass : Alkali silicate glass is produced by heating the mixture of sand and soda.

• Features/Uses : As this glass is soluble in water, it called as 'water glass'.

4-Lead glass : Lead glass is produced by melting the mixture of sand, soda, limestone and lead oxide.

• Features/Uses : It is very clear / transparent, it is used in manufacturing of light bulbs, tubes, etc.

5-Optical glass : Optical glass is produced from the mixture of sand, soda, limestone, barium oxide and boron.

• Features/Uses : This type of pure glass is useful in production of spectacles, lenses, microscopic lenses, etc.

6- Coloured glass : Soda lime glass is colorless.So as to impart a desired colour, oxide of specific metal is mixed during manufacturing process.

• Features/Uses :  Ferrous oxide is mixed to get bluish green glass and copper oxide to get red glass.

7-Processed glass : So as to improve the quality and utility, some processing is performed on glass.

• Features/Uses : Various types like reinforced glass, plain glass, fiber glass, fen glass, translucent glass, etc. are produced.