CBSE Class 8 Science Advanced Chemistry Synthetic Clothing Material and Polymer Notes Set 01

Synthetic Clothing Material and Polymer

Key Terms

Polymer, polymerisation, rayon, nylon, polyester, acrylic, spandex, Koroseal, blended fibres, plastic, melamine, Bakelite, Teflon, PET, HDPE, PVC, LDPE, PP, PS, biodegradable wastes, non-biodegradable wastes.

Introduction

People have always tried to make new materials out of the ones nature gives us. Natural materials are limited in quantity and have certain drawbacks, and advances in science and technology made it possible to build man-made (synthetic) materials that overcome them. Synthetic fibres and plastics are the best-known examples.

1.1 Polymer and Polymerisation

1. Polymer: a compound of very high molecular mass, formed when a very large number of small molecules join together.
2. Monomer: each small molecule that forms the repeating unit of a polymer.
3. Polymerisation: the process in which monomers are changed into a polymer. In symbols: n (monomer) gives (monomer)_n, the polymer, where n is a whole number.
4. In Greek-Latin word roots, poly means many and mer means unit, so a polymer is a molecule made of many units.
5. Polymers are of two kinds: synthetic polymers (for example PP and PVC) and natural polymers (for example cellulose and protein).
6. The two groups of synthetic polymers studied here are fibres and plastics. Both are polymers because both are built from many repeating units.

1.2 Fibres, Their Types and Properties

(a) Fibres

Clothes such as shirts and socks are made of fabrics, and fabrics are made of fibres. A fibre is a thin thread or filament from which cloth is made. Fibres are spun into yarn (a spun thread used for sewing, weaving or knitting), and yarn is woven or knitted into fabric.

(b) Types of Fibres

1. Natural fibres: obtained from plants and animals, for example cotton, wool and silk. They are usually short; silk is the exception and a single filament can be as long as 1 km.
2. Synthetic fibres: made by people, for example nylon, polyester, acrylic and spandex. They are continuous filament fibres. All of them are prepared from petroleum-based raw materials called petrochemicals.
3. Semi-synthetic fibres: natural fibres that have been chemically modified, for example rayon (viscose).

Making of a synthetic fabric (schematic). The polymer solution is pumped through a filter and forced through a spinneret into a spin bath. The fibres then pass through the stretching, washing, finishing and drying stages and are finally wound on a package or cut.

(c) Synthetic Clothing Material

Nylon, rayon, polyester, acrylic and spandex are the commonly used synthetic fabrics for clothing.

(i) Rayon

1. Rayon was the first man-made (semi-synthetic) fibre. It is regenerated cellulose, the substance of plant cell walls, and it can imitate the feel and look of silk, wool, cotton and linen.
2. In Europe it is made by the viscose process, and the rayon so obtained is also called viscose.
3. The raw material is wood, which is first made into wood pulp and then changed into a thick solution called viscose.

Preparation of rayon (steps):

The viscose solution is pushed through the fine holes of a spinneret (which works like a shower head) into a bath of sulphuric acid. The thin streams harden into cellulose filaments, which are collected and spun into rayon yarn.

Properties of rayon:
1. It absorbs moisture and therefore absorbs sweat, so it is preferred to other synthetic fabrics in summer.
2. It is shiny and lustrous and looks like silk, which is why it is called artificial silk.

Uses of rayon:
1. Shirts, ties and linings.
2. Home furnishings such as bed sheets, curtains, table cloths and sofa covers, and also bandages.

(ii) Nylon

Nylon is the first fully synthetic fibre. It was prepared in 1931 using coal, water and air.

Properties: it is a high-strength fibre, elastic (so it does not lose strength even after repeated use), light, lustrous and easy to wash.

Uses:
1. Sarees, socks and stockings; it is blended with wool to add strength.
2. Tents, umbrellas, parachutes and tarpaulins.
3. Bristles of tooth brushes.
4. Because of high strength and elasticity: fishing nets, climbing ropes, seat belts, sleeping bags and strings of badminton and tennis racquets.

Note: the name nylon is popularly said to come from New York (NY) and London (LON). The most common nylon is nylon-66, whose monomers are adipic acid and hexamethylene diamine. Nylon-6 is a polyamide made from the monomer caprolactam.

(iii) Polyester

Polyester is made of repeating units of a chemical called an ester, which has a fruity smell. Most polyester fabrics are easy to wash and wear and need very little care.

Properties: it absorbs very little water and so dries quickly; it is strong, light and elastic; it resists wrinkles and springs back into shape when creased.

Uses:
1. Sarees, dress materials and curtains.
2. Terrywool (Terylene blended with wool) for suits, and Terrycot (Terylene blended with cotton) for skirts, shirts and other dress materials.
3. Light and strong, so it is used for the light sails of boats.
4. Very elastic, so it is used for conveyor belts.
5. Polyester film (mylar) is used for magnetic recording tapes of audio cassettes, video cassettes and floppy discs.

Note: Terylene is also called Dacron or Mylar.

(iv) Acrylic

Acrylic fabric behaves very much like wool.

Properties: it is warm, soft, light and flexible; its yarn is easily knitted; it is cheaper than natural wool and comes in many colours; it resists moths, chemicals and sunlight.

Uses: sweaters, socks and shawls; carpets and blankets; car tops, boat covers and filtration material.

Note: acrylic fibre is also known as Orlon or Acrilan.

(v) Spandex

Properties: excellent elasticity, which makes it suitable for snug-fitting clothes such as swimming costumes. It is mixed with other fibres such as cotton to make stretch fabrics for T-shirts and caps. It is a copolymer of polyester and polyurethane.

Uses: swimming costumes, caps, T-shirts, leggings and wrestlers' wear.

Note: spandex is also known as Lycra or elastane.

(vi) Koroseal

Koroseal is both water-proof and air-proof; it is a trade name for a high polymer of vinyl chloride. It is used as a coating on silk, rayon or cotton fabrics to make them water-proof, which can then be used on rainy days, as bathroom curtains and as wall covering.

(vii) Blended Fibres

A blended fibre is formed by mixing two different fibres. Usually a synthetic fibre is mixed with a natural one, but two natural fibres can also be mixed.

Polythene and polypropylene are both macromolecules and polymers, because their molecules contain a large number of repeating structural units.

Natural fibres are comfortable because they take up moisture and let the skin breathe, but they are not very strong, they shrink on washing and moths attack them. Synthetic fibres are very strong, do not shrink and resist moths, but they are less comfortable to wear. Blending two types of fibre combines the advantages of both and removes their drawbacks.

(d) Advantages and Disadvantages of Synthetic Fabrics

Advantages:
1. Most synthetic fibres can bear heavy loads without breaking. This ability is called tensile strength.
2. Most are elastic: they regain their original shape after being stretched or compressed.
3. Most do not wrinkle easily and keep their shape after washing, so they are convenient (wash and wear). Fibres drawn through the spinneret can be made very fine, so the fabric is generally soft.
4. They are cheaper and easily available.

Disadvantages:
1. Most absorb very little moisture, so they feel sticky when we sweat. In natural fibres sweat evaporates easily, so the skin feels as if it can breathe.
2. Most melt easily, so they should not be worn when working in the kitchen or the laboratory, and they must be ironed very carefully.

Note: ropes of nylon and polyester are used in cranes and elevators because of their high elasticity and tensile strength.

(e) Structure of Various Fibres (Activity)

Place fibres of cotton, silk, wool, rayon, nylon and polyester on a glass slide and look at them under a magnifying glass or a microscope. The observations are:

Conclusion: silk, nylon and polyester feel smooth because their fibres are long, even, straight and fine. Cotton and wool feel rough because their fibres are uneven, folded and porous.

(f) Effect of Flame on Different Fibres (Activity)

Requirements: 10 cm long pieces of cotton, rayon, wool, silk, nylon, polyester and acrylic fibres; a spirit lamp or candle; fire-tongs; a china-clay or glass plate.

Method: light the lamp or candle and keep the plate beside it. Hold a fibre with the tongs over the flame until it catches fire, then move it over the plate and watch it until a small piece is left. Drop that piece on the plate. Repeat with each fibre.

(g) Relative Tensile Strength of Different Fibres (Activity)

Fix a clamp on an iron stand and tie a cotton thread about 60 cm long to it so that it hangs freely. At the free end hang a pan, and add weights one by one until the thread breaks. The total weight needed to break the thread shows the strength of that fibre. Repeat with wool, silk and nylon threads of the same length and nearly the same thickness, then arrange the threads in increasing order of strength. A hook or nail on the wall, a polythene bag in place of the pan and marbles or pebbles in place of weights can also be used.

Increasing order of strength: wool < cotton < silk < nylon. Precaution: all the threads must have the same length and almost the same thickness.

1.3 Plastic

A plastic is a polymeric material that can be easily moulded or set into any desired shape and size. Plastics do not all have the same arrangement of monomer units.

(a) Types of Plastics on the Basis of Structure

1. Linear plastics: the monomer units are joined into long straight chains, and these chains lie packed over one another. Examples: HDPE, PVC, polythene.
2. Branched chain plastics: besides the main chain, branches of different lengths grow out of it. Example: LDPE.
3. Cross-linked (three-dimensional network) plastics: the linear chains that form first are joined to one another, giving a three-dimensional network. These plastics are hard and rigid. Examples: Bakelite, melamine-formaldehyde.

(b) Types of Plastics on the Basis of Reaction to Heat

1. Thermoplastics: they soften on heating, become fluid, and harden again on cooling. This reversible change can be repeated, so they can be melted and moulded into new shapes again and again. Examples: polythene (polyethylene), polyvinyl chloride (PVC), polystyrene.
2. Thermosetting plastics: harder and stronger than thermoplastics, and they keep their shape and size even at high temperature. Once set by heating, they cannot be softened or melted again; they change permanently and set to a solid that cannot be remelted. Examples: Bakelite, melamine.

Synthetic Materials in Daily Life

Plastics and synthetic fibres have come into wide use only in about the last 50 years. They are called synthetic because they are man-made. They are cheap to make, light, strong and durable, can be moulded into many shapes, and are excellent insulators of heat and electricity.

Melamine: a thermosetting polymer that is hard and takes a high polish. It is used for unbreakable dinner-ware and decorative objects.

Bakelite: also a thermosetting polymer; once set, it does not melt or soften. It is obtained by reacting phenol with formaldehyde in the presence of a catalyst.
Properties: hard, stiff and an insulator.
Uses: electrical switches and plugs; gear wheels and table-top laminates; combs, fountain pen bodies and phonograph records.
Note: Bakelite, the first completely synthetic substance, is a thermosetting plastic created by Leo Baekeland in 1907.

(c) General Properties of Plastics

1. Thermal conductivity: plastics such as Bakelite are poor conductors of heat. So they are used for handles of cooking containers, as the foam core of refrigerators (to keep outside heat from entering), in thermal inner-wear for severe winters, and for containers and films used in microwave ovens.
2. Electrical conductivity: plastics are poor conductors of electricity, so they cover electrical appliances, cords, outlets and wiring.
3. Solubility in water: plastics do not dissolve in water, so bottles, buckets, tumblers and cups of plastic are used for storing and drinking water.
4. Effect of flame: most plastics are inflammable; a polybag melts if it touches a hot pan.
5. Non-reactivity: plastics do not react with air and water and, unlike metals, do not corrode, so they can store many materials, including chemicals.
6. Plastics are light, strong, durable and can be moulded into any shape and size.

(d) General Characteristics of Plastics

1. Chemical resistance: strong acids and alkalis hardly affect plastics, whereas natural fibres such as cotton, wool, jute, silk and wood cellulose are affected by them.
2. Weather resistance: plastics are not affected by weather, unlike natural fibres, because they are non-biodegradable.
3. Light weight: plastics weigh far less than natural fibre materials such as wool and jute.
4. Toughness (tensile strength): plastics can bear a lot of force without breaking. A plastic thread holds much more weight than a cotton thread of the same thickness.
5. Insulation: plastics are far better insulators of heat and electricity, which is why electric wires are covered with plastic and not with cotton or silk.
6. Appearance: plastics can be made as transparent as glass and used to make a great variety of household articles.

(e) Uses of Plastics

Plastics can be recycled, reused, coloured, melted, rolled into thin sheets or drawn into wires, so they have many uses.

Teflon: the brand name of polytetrafluoroethylene (PTFE), whose monomer is tetrafluoroethylene, \( \ce{CF2=CF2} \). Teflon coatings are used on non-stick cooking pans and other cookware. Food does not stick to it and it has a high melting point, so it is good for easy cooking and cleaning. It was discovered by the US company DuPont in 1938.

Note: plastics catch fire easily, but some synthetic plastics, such as melamine, are fire-proof and are used to coat the uniforms of fire-fighters.

1.4 Types of Wastes

Waste materials are of two types: biodegradable and non-biodegradable.

(a) Biodegradable wastes: wastes that natural processes, such as the action of micro-organisms, break down into simpler and less harmful substances. Different materials take different times to decay:

(b) Non-biodegradable wastes: wastes that natural processes do not easily break down. Metal cans of tin or aluminium take about 100 to 500 years to decay, and plastic bags take several years.

Problems of Plastic Disposal

Plastics are very useful, but their disposal harms the environment and health because they are non-biodegradable (micro-organisms cannot decompose them), and most ways of getting rid of them cause pollution.
1. Plastic buried in soil is not decomposed. It stops rain water from seeping into the ground, so water stays on the surface as muddy puddles, and plants do not get enough water.
2. Plastic waste on roadsides, floating in lakes and streams and piled in dumps gives a home to disease-causing germs.
3. Plastic dumped in water pollutes it, and toxic substances in it can cause death or failure of reproduction in fish and other aquatic animals.
4. Burning plastic gives toxic gases and smoke, which pollute the air.
5. Polybags thrown carelessly cause the death of many animals, especially cows, which swallow bags and food wrappers along with food waste; these choke the breathing passage or form a lining in the stomach.

Solutions to the Problems of Plastic Disposal

1. Reduce the use of plastics: avoid plastics as far as possible, take cotton or jute bags when shopping, and collect biodegradable and non-biodegradable wastes separately and dispose of them separately.
2. Recycle plastics: collect, sort and process the waste so that the material can be reused to make other products. For example, polyester soft drink bottles can be melted and the molten material spun into fibres. The municipality provides two bins: a green bin for biodegradable waste such as food, and a blue bin for recyclable waste such as plastic and glass, which micro-organisms cannot break down.

4 R principle: a responsible citizen should Reduce, Reuse, Recycle and Recover, and develop environment-friendly habits.

Scientists are trying to produce biodegradable plastics (decomposed by micro-organisms) and photodegradable plastics (decomposed in sunlight). Starch-based biopolymers and polyhydroxyalkanoates (PHAs), such as poly-3-hydroxybutyrate (PHB), are examples of biodegradable plastics.

Recycling numbers. A number is allotted to each type of plastic so that the product can be identified and sorted. The smaller the number, the easier the plastic is to recycle.

Activity: Thermosetting Plastic is a Poor Conductor of Heat

Requirements: a steel sauce pan with a bakelite handle, a steel sauce pan with a steel handle, water and a gas stove.
Procedure: fill the pan with the steel handle half with water and heat it on the stove for five minutes. Switch off the gas and try to touch the handle carefully. Repeat with the pan that has the bakelite handle.
Observation: the steel handle is too hot to hold, so the pan is hard to remove. The bakelite handle does not get hot, so the second pan can be picked up easily.
Conclusion: Bakelite is a thermosetting plastic and a poor conductor of heat.

Add to Your Knowledge

1. Fibre manufacture is classified by the type of spinning the polymer liquid goes through: melt spinning, dry spinning or wet spinning.
2. High density polyethylene (HDPE) is a thermoplastic made from petroleum. Because of its high strength-to-density ratio it is used for plastic bottles, corrosion-resistant piping and similar products.
3. Bakelite is an early plastic: a thermosetting phenol-formaldehyde resin formed by the condensation reaction of phenol and formaldehyde.
4. Spandex (Lycra, elastane) is a synthetic fibre of exceptional elasticity, stronger and more durable than natural rubber. It is a polyether-polyurea copolymer (polyurethane) invented in 1958 by the chemist Joseph Shivers.
5. Plastics are also used in medicine, for example for implants. The term plastic surgery comes from the general meaning of plasticity (reshaping), not from plastic material.
6. Melamine is an organic base, a trimer of cyanamide with a 1,3,5-triazine skeleton.
7. Fastskin is a stretch fabric of polyester and Lycra; swimsuits made from it help swimmers move faster through water.
8. Mylar, a polyester plastic, insulates space shuttles by reflecting the intense heat produced when they re-enter the Earth's atmosphere.
9. Nylon-6 is also known as polyamide, and its monomer is caprolactam.

Summary

1. A synthetic fibre is made of many small units joined into a single large unit called a polymer.
2. Rayon, nylon, polyester, acrylic and spandex are examples of synthetic fibres.
3. Plastics are also polymers, and their units may be arranged in a linear or a cross-linked way.
4. Most plastics can be moulded into any shape after heating, so they are used to make articles of many shapes and sizes.
5. Important plastics are PET, HDPE, LDPE, PVC, PP and PS.
6. Plastics are poor conductors of heat and electricity, insoluble in water, inflammable (most) and do not corrode or rust.
7. Plastic disposal is an environmental hazard because plastics are non-biodegradable.
8. Reducing the use of plastics and recycling plastic objects are the two ways to counter the harm of plastic waste.

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