Polymer Chemistry Online Test 7th Science Lesson 14 Questions in English

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Fibers are made up of long chains of natural or synthetic polymers.

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The word ‘Polymer’ is of Greek origin. ‘Poly’ means many and ‘mer’ means basic smaller unit.

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Polymers are very long chains made of repeating smaller molecules called ‘monomers’ that are joined together by covalent bonds and the process is called polymerization.

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Polyvinyl Chloride (PVC) is a common plastic used for water pipes. The monomer and polymers of PVC is shown below.

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Polymers can be classified into natural and synthetic polymers. The most familiar polymers that we use in our daily life are man-made and synthetic.

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Natural polymers are found in living systems that include proteins and carbohydrates in our bodies
and cellulose in wood and paper. They play a very important role in living things to provide structural materials and molecules needed for life processes.

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Protein polymers are made from amino acid monomers (20 different kinds of amino acids). Different combinations of the amino acid monomers create many different protein polymers.
Examples of protein polymers include DNA, enzymes, silk, skin, hair, fingernails, feathers and fur.

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Examples of carbohydrate polymers include cellulose, chitin and lignin found in plants. Cellulose is made of sugar molecules and is the main component of cotton used in clothing.

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Chitin is found in the cell walls of fungi such as mushrooms and exoskeletons of insects such as
crabs and spiders. Lignin consists of a network of polymers and is important in giving structure to
plants.

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Synthetic polymers are man-made polymers produced by using raw materials from petroleum oil
and gas. Plastics are synthetic polymers. When oils and gases are processed to make petrol, ethylene and propylene monomers are removed as byproducts.

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The Poly Vinyl Chloride (PVC) is made up of many monomers joined together. Ethylene and propylene are the building block monomers that make up many different types of plastics.

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Based on the nature of the monomers the way they are arranged in the polymer and the characteristics of final polymer. There are grouped into different categories such as fibres, plastics, proteins.

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We wear clothes, use bags, rope, blankets, etc. in our daily life. They are made of fibres. Once upon
a time, people used natural fibres such as cotton and wool. Nowadays, we use a lot of synthetic fibres. All natural and synthetic fibres are polymers.

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Fibres are long strands of polymers interwoven to form linear, string-like structures. Fibres that
are obtained from plant or animal sources are called natural fibres. Examples include cotton, coconut fibre, hair, wool and silk.

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Fibres that are made using raw materials from petroleum are synthetic fibres. Examples include
polyester, acrylic and nylon.

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A large variety of natural fibres are still grown and processed such as cotton, silk, and wool. Natural
fibres can be spun into filament, thread or rope. Then they can be woven, knitted, matted or bonded
and are used to make clothing, containers, insulation material and many other products we use in
our daily life.

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The discovery of making synthetic fibres out of petrochemicals has replaced the use of many natural fibres. Synthetic fibres such as nylon, polyester and acrylic are used to make many different plastic items you use in your daily life such as clothing, blankets, tooth brushes and stuffing in cushions.

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Natural silk fibres are obtained from boiling the cocoons of silk worms from specific species of moths. There are four types of natural silk: Mulberry silk, Tasar silk, Muga silk and Eri silk.

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Most of the mulberry silk worldwide is produced in India. Silk is one of the strongest natural fibres and has many uses such as clothing, carpets and parachutes.

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In the 19th century scientists were successful in producing the first artificial silk known as rayon. The first rayon factory in India was established in Kerala in 1946.

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Rayon is a man-made fibre but it is not considered fully synthetic as it is made out of natural cellulose collected from wood pulp. The cellulose that is collected from wood or bamboo pulp is treated with several chemicals.

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First sodium hydroxide is added to the natural wood pulp followed by carbon disulphide. The cellulose dissolves in the chemicals added to it and produces syrup called Viscose. Viscose is forced through a spinneret (a device made of metal plates with very tiny holes) into a solution of
dilute Sulphuric acid. This produces silk-like threads that are cleaned with soap and dried. This new fibre is called rayon.

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Rayon is cheaper than silk can be woven like natural silk fibre and can be dyed in a wide variety of
colors. It can be mixed with cotton to make bed sheets or with wool in the production of carpets and home furnishing products. Rayon is also found in sanitary products, diapers, bandages and gauze for dressing wounds.

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Nylon is the first fully processed synthetic fibre. It was popular during the Second World War for
the use of parachutes and rope materials for climbing. Nowadays, nylon has replaced natural silk
in many textiles, and has become one of the most commonly used synthetic fibres.

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Nylon fibre is strong, elastic and light. It is lustrous and easy to wash, which has made it popular
for the clothing industry. We use many products made from nylon such as socks, ropes, tents, toothbrushes, car seatbelts, sleeping bags, curtains etc.

Explanation

Nylon is a plastic polymer made of chemical units called polyamides. Polyamides are made with monomers –hexa methylene di-amine and adipic acid. Solid chips of these polyamides are melted and forced through a heated spinneret which has very, very tiny holes.

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Polyester is another synthetic fibre. It can be drawn into very fine fibres that can be woven like any other yarn. Polyester is sold in the name of polycot, polywool and terrycot etc.

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Polycot is a mixture of polyester and cotton; Polywool is a mixture of polyester and wool. PET (Polyethylene Terephthalate) is a very familiar form of polyester. It is used for making water and soda bottles, utensils, films and wires amongst many other useful products.

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Many of the clothes we wear are made out of polyester fibres. Fabrics made from this fibre do not get wrinkled easily and are easy to wash making polyester fabrics suitable for dress materials.

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The wool obtained from natural sources is quite expensive whereas clothes made from acrylic are
relatively cheap because they are a byproduct of the production of plastics. They are available in a
variety of colors. Synthetic fibres are more durable and affordable which has contributed to their widespread use.

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Synthetic fibres such as polyester and the advantages are that they do not wrinkle easily and they keep their color and brightness for a much longer time than natural fibres such as cotton.

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A lot of materials such as fishing nets are made from synthetic fibres. One of the main advantages of using synthetic fibres such as nylon is that they are stronger than many natural fibres such as silk or wool. For example a trampoline is made of woven synthetic fibres. These fibres are strong and elastic which gives it the properties to bounce.

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Drawbacks of Synthetic Fibres: This is because one disadvantage of synthetic fibres such as polyester is that they are not heat resistant and catch fire easily. In summer it is better to wear clothing that is made out of cotton materials rather than synthetic. This is because most synthetic fibres absorb very little moisture and do not allow air circulation making them hot and
uncomfortable to wear. The disadvantage is that they break down into very small pieces called
micro-plastics which cause pollution to soil and water bodies such as rivers, lakes and oceans.

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Plastics have helped us to make advancements in technology, building, healthcare, transport and food safety. Plastics have completely occupied our life because of their characteristic qualities.

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Plastics have many positive qualities such as lightweight, strong and they can be molded into complex shapes. They are also flexible and waterproof and some plastics are even UV resistant. Plastics are also cheap and convenient for us to use.

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Plastic has been around for less than 200 years. Edmund Alexander Parkes was the creator of the first plastic called ‘Parkesine’.

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The plastics we use in our daily life are also made up of polymers. All plastics do not have the same type of arrangement of units. In some articles, the arrangement of a monomer is linear, and in some other items, the arrangement of articles is cross-linked.

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Depending on the type of arrangement, we have two main types of polymers – thermoplastics and thermoset.

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Thermoplastics: Polyethylene (also called polythene) is an example of a plastic. It is used for making polythene carry bags which are commonly used. When you burn a polythene carry bag, it melts and turns into liquid along with the production of an offensive odor a bright flame and soot

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Another example is a PET (Polyethylene Terephthalate) bottle, when we fill it with boiling water, it gets deformed. Plastics which can be easily softened and bent when heated are known as thermoplastics. These plastics can be modified and turned into another plastic item through the process of recycling.

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Thermoset: On the other hand, there are some plastics, which once they are molded cannot be softened through heating them. These are called thermosetting plastics.

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Bakelite and melamine are some examples of thermosetting plastics. Bakelite is a poor conductor of heat and electricity. It is used for making electrical switches and handles of various utensils.

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Melamine resists fire and can tolerate heat. It is used for making floor tiles and fabrics that resist
fire.

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The resin codes are a universal way of categorizing different types of plastic, which helps us separate plastics so that it is easier to recycle them.

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Polyvinyl Chloride- PVC resin code#3 has heavy metals such as cadmium and lead which are toxic chemical which are harmful to your health.

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PLASTIC RESIN CODE CHART

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Some micro plastics are also found in household products. Examples are micro beads that can be found in toothpaste, face wash and body scrubs. Micro beads are washed down in drains and end up in the soil , rivers, lakes and the ocean Micro beads are washed down in drains and end up in the soil, rivers, lakes which cause pollution.

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The Government of Tamil Nadu has banned one-time use and throws away plastics such as plastic carry bags, plates, straws and water pouches. This is an indication that important efforts are taking place to reduce negative consequences of plastics on the environment.

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Dangerous pollution called Persistent Organic Pollutants (POPs) floating in the ocean sticks to these small pieces of plastic making them toxic. Marine animals such as shrimp and fish often eat micro plastics, confusing them for their natural source of food. The toxins build up in these animals and move up the food chain and can end up in our bodies. Micro plastics can be found in the food we eat, the water we drink, and the air we breathe.

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Poly Lactic Acid (PLA) a substitute for some types of plastics. Poly Lactic Acid or poly lactide is
compostable and bioactive thermoplastic. This polymer is obtained from plant starch such as corn, sugarcane and pulp from sugar beets. PLA is a biodegradable material. It is useful for making food packaging, garbage bags and disposable table ware.

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Plastic waste ends up being recycled, incinerated, landfilled, dumped or ends up littering our environment.

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It is estimated that from all the plastic waste ever produced, 79% is in landfills, dumps or in the environment 12% has been incinerated and only a small 9% is recycled.

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One way to look at plastic disposal is the 5R Principle – Refuse, Reduce, Reuse, Recycle and Recover. We have already learned about the waste pyramid and how the different methods of waste disposal can be seen in terms of the best option to the least favorable in this order: Refuse (Avoid), Reduce, Reuse, Recycle, Recover (Compost and Incinerate) and Landfill.

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Recycling of plastics is challenging and it is important to know that plastics cannot be recycled forever. There are so many different types of plastics, which are often mixed together making it difficult to separate them back into the original material. Every time plastic is melted and recycled it loses quality this is called ‘Down-cycling’. Recycling of plastic waste cannot be the only solution to plastic pollution.

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Solid waste can be converted into resources such as electricity and compost through thermal and biological means. Burning plastics in a large furnace or in the open is bad for the environment.

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Open burning of plastics releases toxic pollutants into the air and soil, which are harmful to our
health animals and the environment. Burning plastics at high temperatures in incinerators and trapping the gases and collecting the toxic ash are widely used to produce energy. This is often seen as a positive way to deal with plastic waste.

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Plastic waste often ends up in landfills that are huge holes where waste is buried to keep it separate
from the environment. This is the most common way for plastics to be disposed of around the world. Plastics make up 7-13% of waste that is sent to landfills on a global scale. Plastics in landfills
can still lead to pollution of the air, soil and groundwater. Over time landfills can degrade, and the
toxic chemicals in certain plastics can leak out into the environment.

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The concept of biodegradable plastics or bio-plastics was first introduced in the 1980s. Based on the nature of degradation, there are two main types of plastics: degradable plastic and compostable plastic.

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Degradable plastics are made from petroleum oil or gas which is the same as conventional plastics.
The difference is that they have a chemical or additive added to them to make them breakdown faster than conventional plastics when they are exposed to sunlight, oxygen or water.

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Degradable plastics breakdown into tiny pieces called micro-plastics and these stay in our environment for a very long time. It is very important to understand that degradable plastics do not breakdown completely in the environment. Scientists have found that micro-plastics in the ocean are really bad and it is likely that these tiny pieces in the soil are also harmful.

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Compostable plastics are derived from renewable resources such as corn, sugar cane, avocado seeds or shrimp shells.

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Compostable plastics can be broken down completely by microbes and turned back into food for plants carbon dioxide, methane, water and other natural compounds.

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In 2016, scientists from Japan tested different bacteria from a bottle recycling plant and found that
Ideonellasakaiens is 201-F6 could digest the plastic used to make single-use drinks bottles that are
made of polyethylene terephthalate (PET).

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The Ideonellasakaiens bacteria works by secreting an enzyme known as ‘PETase’, that breaks down plastic into smaller molecules. These smaller molecules are then absorbed by the bacteria as a food source.

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Glass is one of the world’s oldest and most versatile human created materials. Glass is the only
material that can be recycled over and over again without losing its quality.

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Glass is bit of a riddle. It is hard enough to protect as but it shatters with incredible ease. It is made
from opaque sand, yet, it is completely transparent. Most surprisingly, it behaves like a solid
material, but it is also a sort of weird liquid in disguise.

Explanation

Glass is prepared by heating (SiO2) silicon-di-oxide until it melts, say to about 1700◦C and Sodium Carbonate is added to it. Then it is cooled down really fast. When SiO2 silicon-di-oxide melts, the silicon and oxygen atoms break out of their crystal structure. If we cooled it slowly, the atoms would slowly line up back into their crystalline arrangement.

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Materials like glass are called as amorphous. At the cooling stage glass is linear in arrangement inorganic in nature and has a structure very similar to glass and they are considered as polymers.

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In a commercial glass plant, sand is mixed with waste glass (obtained from recycling collections), soda ash (sodium carbonate) and limestone (calcium carbonate) and heated in a furnace.

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The soda ash reduces the sand’s melting point and produces a kind of glass that would dissolve in water. The limestone is added to stop that happening. The end product is called soda-lime-silica glass. It is the ordinary glass we see all around us.

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Other chemicals are added to change the appearance or properties of the finished glass. For example, iron and chromium based chemicals are added to the molten sand to make green-tinted
glass.

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Oven-proof borosilicate glass (widely sold under the trademark PYREX) is made by adding boron oxide to the molten mixture. Adding lead oxide makes from a sandwich or laminate of multiple layers of glass and plastic bonded together.

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Toughened glass used in car wind shields is made by cooling molten glass very quickly to make it much harder.