Polymer Chemistry

Class 7 | Science — Chemistry | Unit 3

Class 7 Unit 3 Science

Polymer Chemistry

Learning Objectives: Recognize various types of fibres. Conduct activities to learn the characteristics of synthetic fibres. List the advantages and disadvantages of synthetic fibres. Differentiate between thermoplastics and thermo-setting plastics. Identify various types of plastics based on the resin codes. Realize the impacts of plastics on humans, animals and the environment. Recall the different methods and hierarchy of disposing waste based on the 5 R principle. Explore the complexities of bio plastics. Gather information about plastic eating bacteria. Learn about glass and its types and uses.

3.1 Introduction

Polymer chemistry has a positive impact on your everyday life. Many of the materials you use are linked to polymer chemistry. When you get ready for school, you wear clothes, shoes, brush your teeth and take a school bag. Did you ever ask yourself what these items are made of? They are created from fibers. Fibers are made up of long chains of natural or synthetic polymers. As a society, we are consuming more and more. The more things we buy the more things we throw away. 30 years ago, most of the waste in Tamil Nadu was biodegradable or easily recyclable. Today it is more complex. Many of the materials we use are non-biodegradable and difficult to recycle. For example, in the past people used many natural materials such as cotton, silk and jute fibers. Today we use a lot of synthetic materials such as plastics. In this lesson you will learn about polymers, different types of fibers, plastics and the waste we produce and how we should manage it.

3.2 What Are Polymers?

The word 'Polymer' is of Greek origin. 'Poly' means many and 'mer' means basic smaller unit. 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. The diagram below shows how repeating monomers join to form a polymer. Polyvinyl Chloride (PVC) is a common plastic used for water pipes. The monomer and polymers of PVC is shown below.

Activity 1

Compare the following things. Ice cubes and a polythene bag. In both the materials, there are large number of molecules combined together. Are both polymers?

3.2.1 Polymer

Polymers can be classified into natural and synthetic polymers. Can you imagine that your body produces and you are made up of natural polymers? The most familiar polymers that we use in our daily life are man-made and synthetic.

3.2.2 Natural Polymers

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. 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. 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. 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.

3.2.3 Synthetic Polymers

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 by products. We have already seen that polymer such as 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. 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 fibers, plastics, proteins. Let us study about few of them in the following sections.

3.3 Fibers

We wear clothes, use bags, rope, blankets, etcetera. in our daily life. They are made of fibers. Once upon a time, people used natural fibers such as cotton and wool. Nowadays, we use a lot of synthetic fibers. All natural and synthetic fibers are polymers. Observe the difference between the natural and synthetic fibres: Natural Coconut Rope versus Nylon Fishing rope

3.3.1 Natural and Synthetic Fibres

Fibres are long strands of polymers interwoven to form linear, string-like structures. Fibers that are obtained from plant or animal sources are called natural fibres. Examples include cotton, coconut fibre, hair, wool and silk. Fibers that are made using raw materials from petroleum are synthetic fibres. Examples include polyester, acrylic and nylon. Historically, humans used natural plant fibres and animal fur for shelter, clothing and protection from the weather. Today, 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.

Three main sources of natural fibers are:

• (i) Animal Example: Silk moth
• (ii) Plants Example: Cotton
• (iii) Minerals Example: glass fibre.

The discovery of making synthetic fibers out of petrochemicals has replaced the use of many natural fibers. Synthetic fibers 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.

3.3.2 Types and Uses

Silk: Natural Fiber

Natural silk fibers are obtained from boiling the cocoons of silkworms from specific species of moths. There are four types of natural silk: Mulberry silk, Taser silk, Mega silk and Eri silk. Most of the mulberry silk worldwide is produced in India. Silk is one of the strongest natural fibers and has many uses such as clothing, carpets and parachutes.

Rayon: A Semi-synthetic fibre

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. Rayon is a man-made fiber, 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. First sodium hydroxide is added followed by carbon di sulphide. 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 fiber is called rayon. Some types of rayon are made from the short cotton fibers left on cottonseeds after ginning. Rayon is cheaper than silk, can be woven like natural silk fiber 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.

Nylon: Synthetic Fiber

Nylon is the first fully processed synthetic fiber. 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 fibers. Nylon fiber 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, etcetera. Nylon thread is actually stronger than a steel wire.

Do You Know?

Nylon is very strong and can be used for rock climbing!

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

Activity 2. How Strong is Nylon?

Take an iron stand with a clamp. Take samples of cotton, wool, nylon and silk threads of about 50 cm in length. First tie cotton thread to the stand so that it hangs freely from it. At the free end, attach a CD as plate so that weights can be placed on it. Add weights starting from 10 grams one by one, until the thread breaks. Note down the total weight required to break the cotton thread. Repeat the same activity with the wool, silk and nylon threads.

NOTE: All the varieties of threads should be of same thickness.

Fill the data in the following table:

Serial Number	Type of thread or fibre	Total weight required to break the thread (in gram)
1	Cotton
2	Wool
3	Silk
4	Nylon

Arrange the threads in the order of increasing strength:

What do you infer from the above activity?

Which type of fibre is the strongest?

Which type of fibre is the weakest?

Polyester and Acrylic: Synthetic Fibers

Polyester is another synthetic fiber. It can be drawn into very fine fibers that can be woven like any other yarn. Polyester is sold in the name of polycot, polywool, terry cot, etcetera. 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. Many of the clothes we wear are made out of polyester fibers. Fabrics made from this fiber do not get wrinkled easily and are easy to wash making polyester fabrics suitable for dress materials.

We wear sweaters and use shawls and blankets in the winter. Many of these are not made from natural wool although they appear to resemble wool. These are prepared from another type of synthetic fiber called acrylic. 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 fibers are more durable and affordable which has contributed to their widespread use.

Activity 3. Identify The Fibre

Let us do an activity. Look at the images below and identify and write down the name of the different types of fibre observed.

Activity 4. Synthetic or Natural Fibres

The teacher can give the learner a piece of each and every type of fibre. The learner can feel the fibre and write down the name of the fibre and state whether it is natural or synthetic fibre.

Serial number	Name of the fibre	Type of the fibre (Natural OR Synthetic)
1
2
3
4
5

We have done four activities so far. Which activity helped you better to identify the type of fibre?

(Both the use of familiar images as well as touch can help us to identify the different types of fibres. Right!)

We have learned about fabrics such as polyester, nylon and acrylic and their common uses. These synthetic fibres are polymers which we will learn about later in this chapter.

Characteristics of Synthetic Fibres

Activity 5. Burning A Piece of natural fibre and a synthetic Fibre

Note: This activity should be performed only by the teacher.

Take a piece of cotton cloth and a piece of polyester cloth. Both the pieces of cloth can be of same size (2cm x 2cm is enough). Hold the pieces of cloth using tongs to protect yourself from the flame and heat. Burn both the pieces of cloth one by one and see what happens when they burn.

What do you observe while the cotton cloth burns?

What do you observe while the polyester cloth burns?

You must have noticed that natural (cotton) fibres burn very differently compared to synthetic (polyester) fibres. The cotton cloth will burn when it is held in flame. On the other hand, the synthetic polyester cloth will melt on burning. This is one of the disadvantages of wearing clothes made out of synthetic fibres. If a synthetic cloth comes into contact with fire the fabric melts and sticks to the body causing severe burns. Therefore, one should not wear synthetic clothes while cooking or working in a laboratory.

Activity 6. Wetting A Cotton Cloth and An Umbrella Cloth

We use an umbrella on rainy days. What kind of umbrella do we use?

Can you use an umbrella made of cotton? Let us do an activity to see why we do not use a cotton umbrella to protect ourselves from the rain.

Take a piece of cotton cloth of approximately 10 cm X 10 cm size and a piece of nylon or polyester cloth 10 cm X 10 cm in size from an old unusable or untorn umbrella. Ask four students to hold the four corners of the piece of cotton cloth and pour a glass of water over it. Then ask four students to hold the piece of umbrella cloth and pour a glass of water over it. Compare the effect of water on the piece of cotton cloth and umbrella cloth and record your observation in the notebook.

Which of these fabrics allows water to pass through? Cotton cloth or Umbrella cloth (nylon or polyester)?

Now ask the students to put both the pieces of cloth in the hot sun to dry. Which of these fabrics dries the fastest? The cotton cloth or the umbrella cloth?

Do You Know?

Synthetic fibres are made from the byproducts of processing petroleum oil and gas. You will learn about fractional distillation of petroleum in your higher classes.

3.3.3 Advantages of Synthetic Fibers

Do you ever think about why some of your clothing does not need ironing and looks bright and colorful for many years? This is because they are made from synthetic fibers 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 fibers such as cotton. A lot of materials such as fishing nets are made from synthetic fibers. One of the main advantages of using synthetic fibers such as nylon, is that they are stronger than many natural fibers such as silk or wool. For example, a trampoline is made of woven synthetic fibers. These fibers are strong and elastic which gives it the properties to bounce.

3.3.4 Drawbacks of Synthetic Fibers

We have already learned that it is safer to use cotton clothing instead of synthetic clothing when a person is cooking or working in a laboratory. This is because one disadvantage of synthetic fibers 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 fibers absorb very little moisture and do not allow air circulation making them hot and uncomfortable to wear. If you could recall that we already found out that synthetic fibers are made out of petrochemicals and last in the environment for a very long time. The disadvantage is that they break down into very small pieces called microplastics which cause pollution to soil and water bodies such as rivers, lakes and oceans.

3.4 Plastics

Ask yourself what is the first plastic thing you touched today! Maybe it was your alarm clock or the filling in your pillow or the synthetic clothes that you were wearing. Almost everything around us today is plastic. You have seen water and oil in polythene pouches. Right! In the past, people used to bring milk, oil and other liquids from a shop in vessels made of materials such as metal and glass. Think about what the containers, buckets, mugs, chairs and tables used in the past were made of? What do we use today to make many of these products? Plastic as a material has taken over and replaced metal and wood which were previously used. Plastics have also replaced many glass items. If we continue to write the list of everyday items that are made of plastic, it will be endless! Why is plastic so popular? What are the different uses of plastic? What are the various types of plastics? Let us now learn about plastics:

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. Plastics have many positive qualities such as lightweight, strong and they can be molded into complex shapes. They are also flexible and water proof and some plastics are even UV resistant. Plastics are also cheap and convenient for us to use. Now that you have discovered why plastics are so popular, let us find out more about the different uses of plastics.

3.4.1 Do plastics give benefits in human life?

There are different types of plastics that are excellent materials when they are used for the right application. For example, let us take a syringe that is made from a type of plastic called polypropylene. These syringes do not have to be sterilized and reused; hence they provide a high standard of hygiene and eliminate the risk of spreading diseases. Just as plastic is a material that can be used for a good application, it can also be used for the wrong application. Think about the different items you use that are plastic. For example, a simple article such as a thin plastic carry bag. You use this bag for a very short time and then throw it in a dustbin. Many of these carry bags do not get recycled and they litter and pollute our environment for a long time. If you want to learn more about plastic which is used for the wrong application then you can refer to the Government of Tamil Nadu's ban on one-time use and throwaway plastics (Environment and Forests Department, Tamil Nadu Government Order Number: 84, dated 25th June 2018, with effect from 1st January 2019).

Do You Know?

It is estimated that every year we use a trillion plastic carry bags (2 million a minute) around the world and out of which only 1 to 3% are recycled.

Do You Know?

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

Activity 7. Right and wrong application of plastics

Look at the list of eight plastic items. Decide which four plastic items are used for the right application and which four are used for the wrong application by filling in the chart below:

Plastic items: straws, helmets, cutlery, thin carry bags, syringes, electrical wires, teacups and blood bags.

Right Application	Wrong Application

3.4.2 Types of plastics

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. Depending on the type of arrangement, we have two main types of polymers thermoplastics and thermoset. Let us see what these are!

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. 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.

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

3.4.3 Resin code of plastics

Now that you have learnt about the differences between Thermoplastic and Thermosetting polymers, let us find out more about the different types of plastics that you use in your daily life. Plastics are very useful in our daily life, but some types contain dangerous chemicals. Did you know that there are many different types of plastics? You can tell these plastics apart by searching for a resin code. 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. How can you identify the resin code? Where can you find the resin code on a plastic item? Look at the chasing arrow triangle-shaped symbol on the bottom of a bottle, on the brand label sticker or on the lid of a container. What number is marked in the center of the triangle? What letters (acronym) are below this? This is what we call a resin code. If the number is 1 within the chasing arrow triangle and or has the acronym PET or PETE, then it is a type of plastic which is called PET. Now that you have found out that the bottle has a specific resin code, let us see what gives the bottle and other plastic products certain qualities. Different chemicals (additives) are added to plastic to give them various qualities and characteristics, for example flexibility, strength, softness or transparency. There are some chemicals that are used in plastics that are dangerous for our health, animals and the environment. For example, Polyvinyl Chloride PVC resin code #3 has heavy metals such as cadmium and lead which are toxic chemicals which are harmful to your health. Polystyrene PS resin code #6 has styrene which is a toxic chemical known to cause cancer.

Activity 8. Identify the different types of plastics

Collect different kinds of plastic products and look carefully for the resin code and or acronym on them. With the help of the resin code chart, mark the resin code number, acronym, if you think it is a safer, unsafe, or questionable (when you cannot find the resin code on the article) type of plastic.

What resin codes do you find? Is the resin code safer, unsafe, or questionable?

Product	Resin code number	Acronym	Category of safety	Use of product

Impacts of plastics

Plastics are cheap, light weight, strong and durable and have contributed to a range of advances and benefits to our modern life. But the increase in the use of plastics, particularly the one-time use and throwaway plastics has serious impacts on the environment, animals, and our health. We have seen garbage dumps with different plastics. One big problem with plastics is that they do not decompose or biodegrade. This leads to large amounts of waste that will not disappear and end up accumulating and polluting the environment. A lot of one-time use plastic such as polythene bags and food packaging that are thrown away are responsible for littering the environment and clogging drains. Standing water breeds mosquitoes that can spread diseases such as malaria, dengue and chikungunya and also lead to flooding. Why do you think some animals eat plastic? Many animals confuse plastic for food and eat it by accident. When left over food is thrown away it is often packed in plastic. Animals smell the leftover food and eat the plastic by accident. For example, animals in urban areas, particularly cows, often eat polythene plastic bags by accident as they contain food waste. Can you imagine the consequences?

Can you imagine the consequences?

A lot of the plastic waste we use such as plastics bags, bottles and straws end up in the oceans. Plastics in the ocean are exposed to sunlight, water and the physical movement of the waves, which breaks it down in tiny pieces called microplastics. Some microplastics are also found in household products. Examples are microbeads that can be found in toothpaste, face wash and body scrubs. Microbeads are washed down in drains and end up in the soil, rivers, lakes and the ocean. Microbeads are washed down in drains and end up in the soil, rivers, lakes which cause pollution. Many birds eat plastic items and small pieces of plastic, which are covered in algae. Once in the stomach of animals, plastics cannot be digested, and this decreases the amount of space for food and can lead to starvation. In 2015, plastics were found in 90% of seabirds. We have already read that Government of Tamil Nadu has banned one-time use and throwaway 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.

3.4.5 PLA Plastics

Can you see how much plastic litter pollutes our environment? How nice would it be if a material that had similar qualities to plastic could be biodegradable, be absorbed by the soil and give nutrients to the soil!

Do You Know?

We have seen that synthetic clothes are made from plastic. Every time we wash synthetic clothes, small fibres called microfibers escape and end up in the soil, streams, rivers and oceans. 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 microplastics, 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. Microplastics can be found in the food we eat, the water we drink, and the air we breathe.

Yes, scientists have thought about alternatives to synthetic plastics and have found Poly Lactic Acid (PLA), a substitute for some types of plastics. Poly Lactic Acid or polylactide 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.

3.4.6 Various methods of disposing plastics

Plastics are everywhere! Our increasing consumption and production of plastic waste needs a solution. Let us find out more about how and where plastic waste is disposed of and the better methods of disposing plastics. Organic waste such as the peels of vegetables, fruits and food remains can get broken down by bacteria in the soil to create a rich source of nutrients in the form of compost. A material that gets decomposed through natural processes and action by bacteria is called biodegradable. Plastics do not decompose by natural processes and action of bacteria and are therefore not biodegradable. It is important for us to separate our biodegradable and non-biodegradable waste and dispose of them separately. A lot of the plastic produced globally is designed to be used only once and thrown away, creating a large amount of plastic waste. Plastic waste ends up being recycled, incinerated, landfilled, dumped, or ends up littering our environment. 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. Let us learn more about what happens with the plastic waste.

One way to look at plastic disposal is the 5R Principal: 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 favourable in this order: Refuse (Avoid), Reduce, Reuse, Recycle, recover (Compost), and Incinerate and Landfill.

Refuse (Avoid)

The best thing to do is to avoid using plastic products. One time use throwaway plastics can often be avoided. For example, we can carry cotton or jute bags when we go shopping and say no when a shopkeeper offers us a plastic bag.

Reduce

Reducing the amount of plastic we use is important. Before buying a plastic product, we can check to see if there are any substitutes or alternatives that can be used. If we use fewer plastics, we will create less plastic waste. However, even if we try to reduce the amount of plastics we use and throw away, it is impossible to stop using plastics completely.

Reuse

If possible, products made of plastics can be used again and again. For example, if we have a plastic bag in good condition, instead of throwing it away we can use it again the next time we go for shopping. If we have a plastic product and if you do not feel like using it again, we can give it to others instead of throwing it out.

Recycle

It is better to recycle plastic waste. Separating plastic waste and making sure it gets recycled is good as it turns waste materials into something new. Then it will not be thrown away in landfills, open dumps or ending up as litter in the environment. Many thermoplastics can be recycled. They can be softened by heating and can be made into another article by recycling, but thermosetting plastics cannot be recycled. Recycling 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 'downcycling'. Recycling of plastic waste cannot be the only solution to plastic pollution.

Recover (Compost and Incinerate)

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. Open burning 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 is widely used to produce energy. This is often seen as a positive way to deal with plastic waste. However, burning plastics releases super toxic gases, and the remaining ash contains toxic chemicals and heavy metals. Burning of plastics is not a good solution, as we end up wasting non-renewable resources and produce super toxic chemicals that are difficult to store or dispose safely.

Landfill

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 to 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.

3.4.7 Biodegradable plastics

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. 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 break down faster than conventional plastics when they are exposed to sunlight, oxygen, or water. What do you think will happen to degradable plastics? Degradable plastics break down into tiny pieces called microplastics and these stay in our environment for a very long time. It is very important to understand that degradable plastics do not break down completely in the environment. Scientists have found that microplastics in the ocean are really bad and it is likely that these tiny pieces in the soil are also harmful. Compostable plastics are derived from renewable resources such as corn, sugar cane, avocado seeds, or shrimp shells. Compostable plastics can be broken down completely by microbes and turned back into food for plants carbon dioxide, methane, water, and other natural compounds.

Do You Know?

A recipe for PLA a compostable plastic!

What you need:

1. 1 tablespoon of corn starch
2. 1 teaspoon of vegetable glycerine (available at the pharmacy)
3. 1 teaspoon of vinegar (5% acidity)
4. 4 Tablespoons of water
5. Cooking spoon
6. Cooking pot
7. Stove
8. Aluminium foil

Method: Mix the water with the starch in a cooking pot. Add the vinegar and the glycerine. Mix all the ingredients on medium heat. Make sure you continuously stir. The mixture should turn from liquid white into a clear gel. When it begins to bubble, then it is ready and should be taken off the stove. Spread the gel onto the aluminium foil. Let it cool down for one hour. You can then shape the material to form a cup or bowl. Let the article you made cool for another 24 hours before you try and use it.

3.4.8 Plastic Eating Bacteria

In 2016, scientists from Japan tested different bacteria from a bottle recycling plant and found that Ideonella sakaiensis 201-F6 could digest the plastic used to make single use drinks bottles that are made of polyethylene terephthalate (PET). The bacteria work 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. The working of the enzyme is diagrammatically shown below. Although the discovery of the bacteria breaking down plastics is seen as a potential solution to the plastic pollution it is still very complex! A big issue is the scale of the plastic pollution problem. We consume and produce such large quantities of plastics, and this is only increasing. The scale of the bacteria breaking down plastics is much slower and will therefore not solve the crisis we are facing. Another limitation is that it is restricted to PET resin code #1 plastics, which currently is one of the most recyclable plastics worldwide. It will not be a feasible solution to the issue of the large quantities of non-recyclable low grade plastics which are polluting the environment. That is why it cannot be the solution to plastic pollution on its own!

3.5 Glass Types and Uses

Glass can be found wherever we look a glass window or glass mirror or glass light bulb. 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. 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. 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 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. But if we cool the liquid fast enough, the atoms of the silica will be halted in their tracks, they won't have time to line up, and they will be stuck in any old arrangement, with no order to the arrangement of the atoms. We call materials like this as amorphous. At this stage, glass is linear in arrangement inorganic in nature and has a structure very similar to glass and they are considered as polymers. 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. 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 mostly use in our daily life. Usually, 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. Oven proof borosilicate glass (widely sold under the trade mark 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. Toughened glass used in car wind shields is made by cooling molten glass very quickly to make it much harder. When silver iodide is added to molten glass the glass obtained becomes dark glasses when exposed to sunlight or any other light. These glasses are used in the production of lenses for eyes and spectacles.

Points to Remember

• Fibers are long strands of molecules interwoven to form linear, string-like structures that can be woven, knitted, matted, or bonded.
• Fibers can be natural or synthetic.
• Our increasing consumption and production of waste has negative impacts on humans, animals, and the environment.
• Nylon is a synthetic fiber made from petrochemicals oil and gas.
• Polycot is a mixture of polyester and cotton, Polywool is a mixture of polyester and wool.
• Synthetic fibers melt on burning while cotton fibers catch fire on burning.
• Polymers are very long chains made of repeating smaller molecules called monomers that are joined together with different types of bonds.
• Plastics that get deformed easily on heating and can be bent are known as thermoplastics.
• Plastics that do not get deformed easily on heating and cannot be bent are known as thermosetting plastics.
• There are many different types of plastics. Some of which are safe or unsafe for us. We can find out what type of plastic an item is by identifying the resin code or acronym found on it.
• Poly Lactic Acid or polylactide is a biodegradable and bioactive thermoplastic.
• The management of plastics can be considered by the 5 R Principle: Refuse, Reduce, Reuse, Recycle and Recover as well as to Landfill.
• Ideonella Sakaiensis 201-F6 is a bacterium discovered by scientists that digests plastic resin code #1 PET used to make single use drinks bottles.

EVALUATION

Exercise 1. Choose the correct answers

1. The first man-made fiber is ____

a) Nylon b) Polyester c) Rayon d) Cotton

2. Which of the following is the strongest? ____

a) Rayon b) Nylon c) Acrylic d) Polyester

3. When you place a natural fiber in a flame it ____

a) melts b) burns c) gets nothing d) explodes

4. A synthetic fiber which has similar properties to wool is ____

a) Nylon b) Polyester c) Acrylic d) PVC

5. A good application of plastic is the use of ____

a) Blood bags b) Plastic cutlery c) Plastic straws d) Plastic carry bag

6. ____ is a non-biodegradable material

a) Paper b) A plastic bottle c) Cotton cloth d) Wool

7. PET is the acronym for ____

a) Polyester b) Polyester and terylene c) Polyethylene terephthalate d) Polyethene Terylene Exercise 2. Fill in the Blanks

1. is an example of polyester fabric.

2. are used to identify different types of plastics.

3. A is a long chain made up of many repeated small units called monomers.

4. A natural fiber is called

5. A natural fiber obtained by boiling cocoons is called

Exercise 3. True or False 1. A lot of plastic pollutes our environment. 2. Refuse (avoid) is the best way to manage plastic. 3. It is good to wear clothes made of synthetic fibers while cooking. 4. Degradable plastics break down into tiny pieces called microplastics. 5. Cotton is a natural polymer. Exercise 4. Match the following

Nylon
PVC
Bakelite
Teflon
Rayon

Options: Thermoplastic, Thermosetting plastic, fiber, Wood pulp, Non-stick cookware

Exercise 5. Arrange in Correct Sequence Mix water, starch, vinegar and glycerin in a cooking pot. Let the article cool for 24 hours before we use it. Shape material to form a cup or bowl. Continuously mix on medium heat until the liquid turns clear. When the liquid begins to bubble it is ready to be taken off the stove. Spread the gel onto aluminum foil and cool. Exercise 6. Analogy

1. Cotton: natural: Polyester:

2. PLA spoon: compostable: Plastic spoon:

3. Nylon: melts on heating: Silk:

Exercise 7. Assertion and Reason

1. Assertion: Vegetable peels buried in the soil disappear within two weeks.

Reason: Vegetable peels are compostable.

2. Assertion: It takes a very long time for nylon clothes to break down into microfibers, but cotton clothes need only six months to decompose.

Reason: Nylon made out of petrochemicals is non-biodegradable and cotton cloth is biodegradable.

3. Assertion: It is good to avoid plastics.

Reason: Plastics end up polluting the environment.

Exercise 8. Crossword

Across

1. Fibre that is used as synthetic wool.

2. A plastic used for making water bottles.

3. A long chain made of small repeating monomers.

4. Another name for this semi-synthetic fibre is artificial silk.

Down

5. A type of fibre that is naturally obtained from a cocoon.

6. A synthetic fibre classified as polyester.

7. A polymer used for making rope.

Exercise 9. Very Short Answer

1. What is the chemical name of the polymers that make up cotton?

2. What gives plastic different qualities and characteristics?

3. It is not advisable to burn plastic and synthetic fabrics. Why?

4. A bucket made of plastic does not rust like a bucket made of iron. Why?

5. Why is it better to avoid the use of plastic products?

6. Give two examples of thermosetting plastics.

7. What is the 5 R principle?

Exercise 10. Short Answer

1. What does the term biodegradable mean?

2. What kind of fabric is suitable to dress-up and play in the summer?

3. How do plastics impact animals and the environment?

Exercise 11. Long Answer

1. List the advantages and disadvantages of synthetic fibers.

2. Suggest safe methods of disposing plastics.

Exercise 12. Higher Order Thinking Skills

1. The Tamil Nadu Government has banned the use of one-time use throwaway plastics. Why do you think this is important?

2. A plastic bag dumped in the soil stays without breaking down for 500 years. If a new generation starts in every 30 years, how many generations would it take to see the plastic bag finally broken down?

Exercise 13.

1) Fill in the blanks

2) Look at the following picture and explain what is happening.

3) Read the following information and convert them into a graph to compare the countries and the amount of plastic they use.

China contributes the highest share that is around 28% of the total plastic used globally. Indonesia uses 10%, both the Philippines and Vietnam use 6% each; Thailand uses 3.2%, Egypt 3%, Nigeria 2.7% and South Africa 2%.

📝 Summary

1. Polymers are very long chains made of repeating smaller molecules called 'monomers' that are joined together by covalent bonds through a process called polymerization.
2. Natural polymers are found in living systems including proteins and carbohydrates in our bodies, cellulose in wood and paper, with examples like DNA, enzymes, silk, and chitin.
3. Synthetic polymers are man-made polymers produced using raw materials from petroleum oil and gas, with plastics being the most common synthetic polymers we use daily.
4. Fibers are made up of long chains of natural or synthetic polymers and are used to create clothes, shoes, and other everyday items we use.
5. Modern waste management has become more complex because many materials we use today are non-biodegradable synthetic materials like plastics, unlike 30 years ago when most waste was biodegradable or easily recyclable.