Man made Materials Class 8 Science Notes Maharashtra State Board
We use various types of materials in our daily life. Those materials are made up of various materials like wood, glass, plastic, thread, soil, metals, rubber, etc. Out of those, wood, rock, minerals, water are natural. Humans performed research on various natural materials in the laboratory. With the help of it, various materials are manufactured in factories. Such materials are called manmade materials. eg. Glass, plastic, artificial threads, thermocol, etc.
Plastic
A manmade material showing the property of plasticity and made up of organic polymers is plastic. The structure of all the plastics is not the same. Some are linear while some are circular.
Depending upon the effect of heat, plastic can be classified into two types. The plastic that can be molded as per our wish is called thermoplastic. eg. Polythene and PVC are used for manufacturing toys, combs, plates, bowls, etc. Another plastic is such that once a specific shape is given with the help of mold, its shape cannot be changed on heating. It is called thermosetting plastic. eg. Electric switches, coverings over the handles of cookers, etc.
Properties of Plastic:
Plastic does not corrode. It does not decompose. It is not easily affected by humidity, heat, rain, etc. Items of any colour can be made from it. It can be molded into any shape due to the property of plasticity. It is a bad conductor of heat and electricity. Being light in weight, it is easy to carry.
Types and Uses of the Plastic
| Thermoplastic | |
| 1. Polyvinyl Chloride (PVC) | Bottles, raincoats, pipes, handbags, shoes, electric cable insulation, furniture, ropes, toys, etc. |
| 2. Polystyrene (PS) | Thermo-insulating parts of electric appliances like refrigerators, gears of machines, toys, protective coverings like covers of CDs and DVDs, etc. |
| 3. Polyethylene (PE) | Milk bags, packing bags, flexible garden pipes, etc. |
| 4. Polypropylene (PP) | Parts of loudspeakers & vehicles, ropes, mattresses, laboratory appliances, etc. |
| Thermosetting Plastic | |
| 1. Bakelite | Cabinets of radio, T.V., telephones, electric switches, toys, coverings over handles of cookers, etc. |
| 2. Melamine | Domestically useful items like cup-saucers, plates, trey, some spare parts of airplane engines, electric and sound insulating coverings, etc. |
| 3. Polyurethane | Surfing boards, small boats, furniture, seats in vehicles, etc. |
| 4. Polyester | Fiberglass, toners of laser printers, the textile industry, etc. |
Plastic and Environment
- How many plastic carry bags are brought into your home in a day? What happens to those later on?
- How are the used-up and thrown-away carry bags, water bottles, and milk bags recycled?
Some materials are naturally degraded, they are called degradable materials while some materials are not; called non-degradable. From the given on the next page chart, we can understand that plastic is nondegradable and hence it is an environmental pollutant. Which measures can we arrange to avoid this?
- Plastic is used in the healthcare sector e.g. syringes.
- Vessels used to cook food in microwave ovens are made up of plastic.
- Vehicles are coated with Teflon to protect from scratches. Teflon is a type of plastic.
- There are more than 2000 different types of plastics.
- Some types of plastic are used in assembling some parts of airplanes.
- Polyacrylic is a type of plastic used for manufacturing lenses & artificial teeth.
| Material | Degradation Period | Type of Material |
| Vegetable | 1 – 2 weeks | Degradable |
| Cotton Cloth | 1 year | Degradable |
| Wood | 10 – 15 years | Degradable |
| Plastic | Thousands of Years | Non-degradable |
We should opt for items made up of degradable material instead of plastic.
Eg. jute bags, cloth bags, paper bags, etc.
Each responsible citizen should follow the 4R principle; i.e.
- Reduce – Minimal use
- Reuse – Use again
- Recycle – Use again after processing
- Recover – Reclaiming
Then only we can save the environment from pollution.
Thermocol:
A new, easily breakable item brought to your home is usually packed in a box. To prevent that item from breaking while handling the box, it is always packed in one more wrapping. Usually, that wrapping is of thermocol. Nowadays, the plates used in mass feasts are also made up of thermocol. Thermocol is a form of a complex material called polystyrene. It transforms into a liquid state on heating at more than 100 ºC temperature and returns to a solid state on cooling. Due to this, we can give any desired shape to it. Being a good shock absorber, it is used in packing delicate items. Make a list of the use of thermocol in your daily life.
Adverse Effects of Excessive Use of Thermocol on Environment and Humans:
- Being carcinogenic ingredients in styrene, the person in contact with thermocol for a long duration may have the possibility of blood cancer like leukemia and lymphoma.
- Non-biodegradable: It takes a long duration for the natural degradation of thermocol; hence many people opt for destroying it by burning it. However, it is still a more hazardous method as it releases poisonous gases into the atmosphere.
- In mass gatherings, plates and cups used to offer food, water, and tea are made up of thermocol. It affects the health. If the food kept in thermocol is reheated, styrene may dissolve in that food. Due to this, there is the possibility of health problems.
- Effect on persons working in thermocol factory: Persons staying in contact with thermocol for the long term may develop problems with the eyes, respiratory system, skin, digestive system, etc. Pregnant women may face miscarriage. Liquid styrene may cause skin burns.
Glass:
We use glass material on a large scale in our daily lives. Glass was discovered by chance. Some Phoenician traders were cooking in the desert. The cooking vessels were supported on limestones. When the cooking vessel was kept off the limestone, they observed that a transparent material had been formed. They thought that this transparent material may have been formed due to the heating together of sand and limestone. This led to the development of the technique of glass production. Glass is a non-crystalline, hard but brittle solid material formed from a mixture of silica and silicate. Silica i.e. SiO2 which we refer to as sand. Depending upon the proportion of silica and other components in the glass; there are different types of glass as soda-lime glass, borosilicate glass, silica glass, alkali silicate glass, etc.
Production of Glass:
For glass production, a mixture of sand, soda, lime, and a small quantity of magnesium oxide is heated in a furnace. Sand i.e. silicon dioxide melts at 1700ºC. To melt the mixture at a low temperature, pieces of discarded glass are added to it. Due to this, the mixture melts at 850ºC. Once all the ingredients of the mixture are liquified, it is heated up to 1500ºC and immediately cooled. Due to sudden cooling, the mixture becomes homogenous, amorphous, and transparent instead of crystalline. This is called Soda-lime glass.
Properties of Glass:
- On heating, glass becomes soft and can be molded into any shape.
- The density of glass depends upon its ingredients.
- Glass is a slow conductor of heat. On quick heating of cool glass or quick cooling of hot glass, it cracks/breaks.
- Being a bad conductor of electricity, glass is used as an insulator in electric appliances.
- Being transparent, most of the light passes through the glass. However, if there are oxides of either chromium, vanadium, or iron in the glass, a large amount of light is absorbed in the 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. It is not affected by acid and alkali. Due to this, silica glass is used to produce laboratory glassware.
2. Borosilicate Glass:
Borosilicate glass is produced by melting a mixture of sand, soda, boric acid, and aluminum oxide. This glass does not show any effect on medicines. Hence, the bottles made up of borosilicate glass are used in the pharmaceutical industry to store the medicines.
3. Alkali Silicate Glass:
Alkali silicate glass is produced by heating the mixture of sand and soda. As this glass is soluble in water, it is called ‘water glass’.
4. Lead Glass:
Lead glass is produced by melting a mixture of sand, soda, limestone, and lead oxide. Being very clear/transparent, it is used in the manufacturing of light bulbs, tubes, etc.
5. Optical Glass:
Optical glass is produced from a mixture of sand, soda, limestone, barium oxide, and boron. This type of pure glass is useful in the production of spectacles, lenses, microscopic lenses, etc.
6. Coloured Glass:
Soda lime glass is colorless. To impart a desired color, the oxide of a specific metal is mixed during the manufacturing process. eg. Ferrous oxide is mixed to get a bluish-green glass and copper oxide to get a red glass.
7. Processed Glass:
To improve the quality and utility, some processing is performed on glass and various types like reinforced glass, plain glass, fiberglass, fen glass, translucent glass, etc. are produced.
Effect of Glass on Environment:
- In glass production, the mixture needs to be heated up to 1500ºC. During this, greenhouse gases like sulfur dioxide, nitrogen dioxide, and carbon dioxide are released through the burning of fuel.
- As the glass is non-degradable, if pieces of the waste glass material flow into a water body, it may affect that ecosystem. Similarly, drainage may be blocked due to these pieces.
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