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

a. Plastic shows plasticityproperty, hence it can be molded to any shape.

b. Motor cars are coated with Teflon paint.

c. Thermocoal melts  at more than 100ºC.  

d. Alkali silicateglass dissolves in water.

Thermocol is produced from complex thermoplastic material called polystyrene. It transforms into liquid state on heating at more than 100^oc and returns to solid state on cooling.

Uses of PVC(Polyvinyl chloride): It is used for  making bottles, pipes, handbags, electric cable insulation, raincoat, high quality furniture, ropes, toys etc.

c. Write the natural or manmade raw material of the following items.

Mattress, glass vessel (beaker), bangle, chair, gunny bag, broom, knife, pen.

Main ingredients of glass are Sand and Silica

Plastics are derived from natural, organic materials such as cellulose, coal, natural gas, salt and of crude oil.

• The first synthetic plastics were derived from cellulose, a substance found in plants and trees. This cellulose was heated with chemicals and resulted in a plastic like material.
• In modern times, the different raw materials are used for making plastics, but most plastics are made from the hydrocarbons present in the natural gas, oil and coal.
• Plastics are simply chains of like molecules linked together. These chains are called polymers. Thus, many plastics begin with “poly,” such as polyethylene, polystyrene and polypropylene.
• These polymers are made of carbon and hydrogen and sometimes oxygen, nitrogen, sulphur, chlorine, fluorine, phosphorous or silicon.
• Plastic is produced in factories by suitable chemical reactions.

Natural materials:

• Natural materials are those material, which occur in nature by its own.
• Natural materials are subjected to less treatment and processing.
• Natural materials have shorter lifespan, because these materials were once alive and so gradually perish over time.
• Maintaining natural materials requires lots of care and continuous attention.
• Natural materials do not have a negative environmental impact because they can be degraded easily. They are eco-friendly.
• Examples : wood, glass, plastic, thread, soil, metals, rubber etc.

Man made materials:

• Man-made materials are a type of material that doesn't occur naturally and is made by humans.
• Man-made materials are subjected to rigorous processing to alter the material for serving the intended purpose.
• Man-made materials are typically much more durable having a very long lifespan.
• Maintaining man-made materials require less care and attention.
• They are not environmental friendly. Man-made materials can have a negative environmental impact because they are not sustainable.
• Examples : glass, plastic, artificial thread, thermocol rubber etc .  

Plastic : Plastic is non-degradable substance. Hence if thrown in any ecosystem, it remains unchanged for many years.

• It is one of the worst environmental pollutants as its disposal is a major problem.
• If thrown in water bodies, it affects the aquatic animals. Many of turtles mistake it for algae and eat the plastic. Eventually such animals die due to choking.
• In terrestrial environment, the grazing animals like cattle are affected due to plastic.
• If burnt it emits very toxic gases.
• In landfill sites, it remains unchanged for thousands of years.

Effects of glass:

During production of glass, mixture needs to be heated at very high temperature. Which will result in evolution of greenhouse gases like sulphur dioxide, nitrogen dioxide, carbon dioxide.

• The combustion of natural gas/fuel oil and the decomposition of raw materials during the melting lead to the emission of CO₂, leads to the cause of green-house effect.
• Moreover, glass being non-degradable, cause pollution.
• If broken glass pieces or any waste glass material is disposed into aquatic environment, it affects animals and plants.
• Similarly, glass pieces block the drainages.
• The waste glass thrown anywhere cause injury to terrestrial fauna.

Effects of thermocol:

• Thermocol contains carcinogenic ingredients in the form of styrene. Some research on cancer has showed that, if there is prolonged contact with thermocol, increase the risks of cancer in humans and can cause lymphoma and leukemia cancer upon prolonged exposure.

• Thermocol is non-biodegradable because it is photolysis resistant. Thermocol needs a very long time to degrade naturally in the environment.
• Even though food and drinks are served on thermocol plates and cups, these actually contaminate the food and beverages and affect the health and the reproductive systems of humans.
• When food are reheated while they are still in thermocol container the harmful effect on humans’ health are seen.
• If it is burnt for destruction, it releases toxic gases in atmosphere.

Measures will you arrange to minimize the environmental problems arising due to non-degradable plastic are as follows:

• We must reduce our plastic dependency: We use an incredible quantity of single-use plastic items, such as straws, plastic bags, packaging, plastic cups, plates and cutlery. We must put an end to it.
• Reducing the consumption, reusing the same plastic again and again, recycling the used plastic and making some new products from the used plastic are some of the measures that can be adopted.
• There are attempts to use plastic in making roads. Therefore, plastic is bought with good price at some places.
• Therefore, instead of disposing it anywhere, it should be collected and sold in best possible way.
• The better alternatives for plastic should be adopted.
• The awareness programmes about misuse of plastic should be arranged so that common man can understand the dangers of using plastic.
• To solve the plastic problem, we must ensure that action and clean-up operations are undertaken in areas where the problem is the greatest.

The manufacturing process of glass consists of four major operations: (1) Melting, (2) Shaping, (3) Annealing, (4) Finishing. The general preparation of the glass is as follows :

• Mixture of sand, soda, lime and small quantity of magnesium oxide is heated in furnace.
• At 1700 °C sand or silicon dioxide melts.
• To make the mixture melt at lesser temperature, pieces of discarded glasses are added to it.
• This addition makes the mixture to melt at lesser temperature of 850 °C.
• When all the ingredients of mixture are liquified, then again it is heated up to 1500 °C.
• This heating is immediately followed by cooling.
• The sudden cooling causes the mixture to become homogeneous, amorphous and transparent instead of crystalline.
• For variety of glass types, different proportions of ingredients are used for heating.

Optic glass is high-quality, homogeneous, color-free glass, as flint or crown glass, having specified refractive properties, used in lenses and other components of optical systems.

• Optic glass or optical glass needs to be very clear and transparent as it is used in spectacles, lenses and other devices like microscopes.
• Optic glasses are produced from the mixture of sand, soda, limestone, barium oxide and boron.

Uses of plastics are :

Thermosetting plastic materials are used for manufacturing following items :

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

Thermoplastic materials are used for manufacturing following articles :

• Polypropylene is used for making parts of loudspeakers & vehicles, ropes, mattresses, laboratory appliances etc.
• Polyethylene is used for making milk bags, packing bags, flexible garden pipes etc.
• polystyrene is used for making thermo-insulating parts of electric appliances like refrigerators, gears of machine, toys, protective coverings like covers of CD and DVD etc.

Polyvinyl chloride is used for making bottles, raincoat, pipes, handbags, shoes, electric cable insulation, furniture, ropes, toys etc.