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Wednesday, 4 November 2015

synthetic materials

                           
  synthetic materials  ,class 8 ,Sharma sir,Sharma coaching centre
synthetic materials

Þ     Synthetic materials are kinds of materials obtained from the synthesis of chemicals.

Þ     The chemicals used for synthetic materials are obtained from petroleum and natural gas(methane)

Þ     Petroleum and natural gas is compound of hydrogen and oxygen called hydrocarbon.

Þ     Monomers are simple chemical molecules of hydrocarbon.

Þ     When monomers join end to end form a long chain of monomers called polymers. The process of the formation of polymers is called polymerization.

Þ     Cellulose [beet root] is polymers of glucose while Hemoglobin is polymers of amino acid.

Þ     Fibres are thin thread like materials used to prepared cloths. 

Þ     Fibres obtained on mixing natural and synthetic fiber are called semi synthetic fibre. e.g. rayonRayon

Þ     Rayon is synthetic fibres obtained from cellulose

Þ     Rayon are of three types: Viscose Cupreammonium (cupro)  and acetate rayons.

Viscose Rayon

Þ     In industry cellulose dissolved in mixture of sodium hydroxide (NaOH) and CS2 (carbon disulphide) to get Viscous liquid [semi solid] called viscose.

Þ     Viscose is forced to spinnerets [an apparatus having small holes like shower] into anacid bath [through solution of acid like H2SO4] . Thus filaments of rayon are obtained which is spun into thread.

Cupro Rayon

Þ     Cupro Rayon are obtained on dissolving cellulose into solution of CuSO4 and NH4 . The dissolve solutions forced to spinnerets into an acid bath to get filaments of cuprammonium rayon are obtained which is spun into thread.

Acetate Rayon

Þ     Acetate Rayon is obtained on dissolving cellulose into solution of Acetate and H2SO4.Rayon in our daily life

Þ     Rayon mixed with cotton or silk to make smooth and silky cloth in textile industry.

Þ     Rayon mixed with wool to make carpet.

Þ     Rayon are also used for making reinforced tyre, bangles and surgical dressing

Þ     The name Nylon derived from the New York [NY] and London[LON] as Nylon was first produce in both places at same time.

NYLON

Þ     Nylon (polyamides) was first prepared in 1935 chemically.

Þ     Nylon are prepared using cyclic hydrocarbon Benzene(C6H6)

Þ     Nylon has silk like texture and high tensile strength[Drawn into long thin straps]

Nylon in our daily life

Þ     Nylon is mainly used for making ropes, woman’s wear, fishing net, sari socks and tie

Polyster

Þ     Polyster is obtained from polymer of ethene. It has maximum stretchable strength.

Þ     Terylene, Dacron are kinds of Polyster used for dress, cloth and curtain.

Þ     Terylene mixed with cotton and wood to produce terycot and terry wool respectively.

Þ     Polysters are also used for making sail for sail boat and conveyor belts.

 Acrylics

Þ     Acrylics fibres are obtained on dissolving acetylene[C2H2] into suitable solvent like HCN and then forced to spinneret because acetylene decompose without melting.

 Acrylics in our daily life


Þ     They are light and soft like wool. The y are crimpy (wavy) and straight like Polyster thus appear to be bulky and look like wool.

Þ     They are resistant to weather as they are not easily acted upon by moisture.

Advantages of synthetic fibres

Þ     Having long lasting luster and do not turn yellow with age

Þ     Easy to clean and dry up quickly

Þ     Durable and do not shrink on washing

Þ     They are less expensive than cotton

Þ     They do not depend on plants or animal like cotton

Advantages of synthetic fibres

Þ     The get electrically charged in dry weather and cause skin irritation

Þ     The melt and form sticky beads  on heating. There is always a risk of getting burn in kitchen 

Þ     They are hydrophilic as do not absorb sweat and moisture thus uncomfortable to wear.

Þ     They are non bio degradable and cause pollution.

Þ     They are good absorber of radiant heat and not fit in summer. 

Good to more good

To make make wide spread use of synthetic material it is mixed with natural fibre .There are called blend fibre.

PLASTIC

Þ     Plastic : Any material which can be molded into any desirable shape on heating is called plastic

Þ     Petroleum product such that Ethane, propane, benzene ,toluene etc are used for manufacturing plastic.

                                      Plastic
Thermoplastic                                  Thermosetting

Thermosetting Plastic

Þ     Thermosetting plastics are kind of plastic which once moulded cannot moulded again by heating.

Þ     Thermosetting plastics are kind of plastic whose polymers form highly cross linked chain on heating.

Þ     Bakellite , melanin, Formaldehyde are some of the examples of Thermosetting Plastic

Thermoplastic Plastic

Þ     Thermoplastic are kind of plastic which can be moulded again and again by heating and easily reused.

Þ     PVS, Polysterine , nylon , polythine are some of the examples of Thermoplastic Plastic

Þ     Polymers of thermoplastic Plastic  have long chain without cross linked to each other.

Characteristics of plastic

Þ     Plastic has much less toughness as compared to metal

Þ     having light weight 

Þ     It is not affected by acids and bases.

Þ     Plastic are non bio degradable as it is weather resistant

Þ     Plastic are bad conductor of heat and electricity

Þ     Plastic melts on heating

Some of the  common plastics are 

a. Polythene

Þ     it is obtained from polymerization of ethene. it is non bio degradable .

Þ     it is a kind of thermosetting plastic

Þ     it is insoluble in any solvent

Þ     it is light weight

Þ     it is anti corrosion and insulator

Þ     it is used for making bag ,adhesive tap, electric wire cover and can

b. Polyvinyl chloride (PVC)

Þ     it is use for making sole of shoe

Þ     it is use for making covering of electric wire

Þ     it is use for making sanitary fittings

c. Polysterine

Þ     It is a polymer of polythene . 

Þ     it is a kind of thermosetting plastic

Þ     it is highly transparent

Þ     it is use for making cups of hot drink , toy etc.

Þ     it is use for safe packaging of expensive items

Þ     it is use for making Styrofoam[themocole]

Þ     it is use as insulating material in refrigerator

d. Teflon

Þ     It is prepared by using tera- fluroethene. 

Þ     Heat and chemical are not effective on Teflon

Þ     it is use for making non stick cooking were

Þ     it is use for making corrosive proof coating in industry

e. Bakelite

Þ     it is a kind of thermosetting plastic

Þ     it is use for making electrical switches and plug

Þ     it is use for making gear wheel 

Þ      it is use for making table top

Þ     it is use for making comb, pen bodies and photograph records

f. Melanin

Þ     It is hard and highly polished polymers used for making unbreakable kitchen were.
Question:  Why plastic should not be burnt?
Answer: Burning of plastic release toxic gases  which causes air pollution that result various health hazard. This is why we should avoid burning plastic.

Question:  Why does handle of cooking utensils are made up of Bakelite?
Answer: Bakelite is a kind of thermosetting plastic that do not get deform on heating at high temperature. This is why handle of cooking utensils are made up of Bakelite.

Question:  Avoid wearing synthetic clothes while cooking. Give reason?
Answer: We should avoid wearing synthetic clothes while cooking because synthetic clothes catch fire easily and melt before burning.

Question:  Give reason; Handle of heating pans are made up of plastics?
Answer: Handle of heating pans are made up of plastics because plastic being bad conductor of heat do not allow heat to pass into body.

Question: Electric wires are covered with plastics. Give reason?
Answer: Since plastics are poor conductor of electricity, do not allow current to pass through them. This is why electric wires are covered with plastics

Question: Why do electric plug not melt even the wire inside then get overheated?
Answer: Electrical plugs are made up of Bakelite that do not get deform on heating at high temperature.

Question: Why does rayon smell like burning paper; although it is a synthetic fibre?
Answer: Rayon smell like burning paper; although it is a synthetic fibre because rayon are obtain on mixing celuse a extract of wood pulp into chemicals.

Question: Why are plastic considered as environmental hazard?
Answer: Plastic considered as environmental hazard because of the following reason:

(i) Plastics do not decay in soil by natural process and cause soil pollution

(ii) Dumping of plastic into water cause threat to aquatic life.

(iii) Plastic bags thrown in to drain choke it out and support growth of disease causing pathogen like mosquito.

Question: Distinguish between Thermosetting plastics and Thermoplastic Plastic?
Answer: 
Thermosetting Plastic
Thermosetting plastics are kind of plastic which once moulded cannot moulded again by heating.
Thermosetting plastics are kind of plastic whose polymers form highly cross linked chain on heating.
Bakellite , melanin, Formaldehyde are some of the examples of Thermosetting Plastic

Thermoplastic Plastic
Thermoplastic are kind of plastic which can be moulded again and again by heating and easily reused.
PVS, Polysterine , nylon , polythine are some of the examples of Thermoplastic Plastic
Polymers of thermoplastic Plastic have long chain without cross linked to each other.

Question: What is a synthetic fibre? 
Answer: Fibres made by human beings using chemical substance is called synthetic fibre. A synthetic fibre is a chain of small unit of chemical substance joined together. These small units combine to form a large single unit called a polymer. 

The word ‘polymer’ comes from two Greek words; poly meaning many and mer meaning part/unit. So, a polymer is made of many repeating units. 

Question: List four measures to reduce the use of plastics and pollution caused by it?
Answer:  
(i) Do not throw plastic bags in the water bodies or on the road.
(ii) Take a cotton carry-bag or a jute bag while going for shopping.
(iii) Try to minimise the use of plastic materials e.g., use a steel lunch box instead of a plastic one.
(iv) Dispose plastic properly and store separately in bin at home.


 Question: Explain why rayon is called a regenerated fibre?

Answer:  Rayon is sometimes known as a regenerated fiber because in its process the cellulose is regenerated in another form

 Question: What is the function of a spinneret in the making of rayon?

Answer: Viscose is passed through fine holes of a spinneret to give fine fibres



Question: Why thermosetting plastics can not be  moulded again by heating ?


Ans: Thermosetting plastics can not be  moulded again by heating because of the excessive cross linkage in between chain forming a three dimensional network of bond.
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Chemistry for class 8 ..

Combustion-and-flame-notes

Fibre-to-fabric-test

Coal-and-petroleum

Metals-and-non-metals-objective

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