Synthetic Fibres And Plastics (Class 8 Science NCERT)

What are Synthetic Fibres and Plastics?

At their core, both synthetic fibres and plastics are types of polymers. Imagine tiny beads (monomers) joining together in a long, repeating chain to form a huge necklace (a polymer). Natural polymers like cotton, silk, and wood exist, but synthetic polymers are man-made. Synthetic fibres are essentially thread-like materials made from these artificial polymers, designed for textiles and other applications where flexibility and strength are needed. Plastics, on the other hand, are also polymers but can be moulded into various shapes and forms, making them incredibly versatile for packaging, construction, and countless other products. They are often cheaper, more durable, and more readily available than their natural counterparts, which is why they have become so prevalent in modern society. Understanding these basic building blocks is key to appreciating the vast array of materials we encounter every day, from the clothes we wear to the containers we use for food.

Types and Properties of Synthetic Fibres

Synthetic fibres are broadly classified based on the chemical compounds used to make them. Each type has unique properties that make it suitable for specific uses:

1. Rayon (Artificial Silk): Though man-made, rayon is produced from natural raw material – wood pulp (cellulose), which is chemically treated. It has a silky feel, absorbs moisture, and can be dyed in various colours, making it a good substitute for silk in clothing and home furnishings like bed sheets and carpets.

1. Nylon: This was the first fully synthetic fibre, made from coal, water, and air. Nylon fibres are incredibly strong, elastic, and light. They are also lustrous and easy to wash. You'll find nylon in parachutes, ropes, tents, toothbrushes, car seat belts, and even socks.

1. Polyester: Known for its wrinkle resistance and crispness, polyester is excellent for dress materials and fabrics that don't need ironing. Terylene is a popular polyester. PET (Polyethylene Terephthalate) is a very common form of polyester used for making bottles, utensils, films, wires, and many other useful products due to its lightness and strength.

1. Acrylic: This fibre is often used as a substitute for wool because it's warm, light, and relatively inexpensive. It resists shrinking and wrinkles and is commonly found in sweaters, shawls, blankets, and tracksuits. A big advantage is its resistance to moths and chemicals, unlike natural wool.

Plastics: Types and Environmental Concerns

Plastics are also polymers but differ from fibres in their structure and how they react to heat. We can broadly classify plastics into two main types:

• Thermoplastics: These plastics can be softened repeatedly by heating and hardened by cooling. This property allows them to be remoulded and recycled. Examples include polythene (used for plastic bags, squeeze bottles) and PVC (Polyvinyl Chloride, used for water pipes, electrical insulation, toys).

• Thermosetting Plastics: Once moulded and heated, these plastics become hard and cannot be softened or remoulded by heating again. They are used for making electrical switches, handles of cooking utensils (like Bakelite), and floor tiles or dinnerware (like Melamine), where heat resistance and rigidity are crucial.

While incredibly useful, plastics pose significant environmental challenges. Most plastics are non-biodegradable, meaning they do not decompose naturally by bacteria or other natural processes. This leads to massive accumulation in landfills, oceans, and natural habitats, causing pollution and harming wildlife. The burning of plastics releases toxic fumes, contributing to air pollution. It is crucial to understand and practice the 4R principle to mitigate these effects: Reduce, Reuse, Recycle, and Recover.

Understanding the 4R Principle for Plastic Management

1. Step 1: Reduce — The first and most effective step is to reduce the consumption of plastics. This means choosing products with less plastic packaging, using reusable shopping bags, and avoiding single-use plastic items like straws and disposable cutlery.
2. Step 2: Reuse — Instead of throwing away plastic items after one use, find ways to reuse them. For example, plastic bottles can be refilled, plastic containers can be used for storage, and old plastic bags can be used as bin liners. This extends their life and reduces demand for new plastic production.
3. Step 3: Recycle — Recycling involves collecting discarded plastic items, processing them, and then manufacturing new products from the recycled material. Many thermoplastic plastics can be recycled. Proper segregation of waste (separating plastic from other waste) is essential for effective recycling. Look for recycling symbols on plastic products.
4. Step 4: Recover — When plastic cannot be recycled, energy recovery through incineration (burning plastic to generate electricity) can be an option, but this must be done in controlled environments to prevent air pollution. While not ideal, it's sometimes considered for plastics that have no other viable disposal or reuse options, helping to recover some value.

Exam Tip: Differentiating Biodegradable and Non-Biodegradable

A common point of confusion for students is the difference between biodegradable and non-biodegradable materials, especially in the context of environmental impact. Remember:

• Biodegradable materials are those that can be decomposed by natural processes, such as bacterial action, over a period of time. Examples include paper, cotton cloth, wood, and vegetable peels. These materials eventually return to the environment without causing lasting harm.
• Non-biodegradable materials are those that do not decompose easily or take hundreds of years to decompose through natural processes. Most synthetic fibres and all plastics fall into this category. Their persistence in the environment leads to pollution and ecological imbalance. When asked to classify materials, always consider how long they would remain in nature if left undisturbed.

Practice Questions with Solutions

• Q: Give two reasons why synthetic fibres are preferred over natural fibres for certain applications like making parachutes and ropes. A: Step 1: Consider the properties required for parachutes and ropes. They need high strength and resistance to environmental factors. Step 2: Recall properties of synthetic fibres like Nylon. Nylon is known for its high tensile strength and durability, as well as being lightweight and water-resistant. Final answer: Synthetic fibres like nylon are preferred because they are stronger and more durable than natural fibres. They are also often lighter and more resistant to water and pests.
• Q: Differentiate between thermoplastics and thermosetting plastics with one example for each. A: Step 1: Define thermoplastics based on their reaction to heat. Step 2: Provide an example of a thermoplastic and its common use. Step 3: Define thermosetting plastics based on their reaction to heat. Step 4: Provide an example of a thermosetting plastic and its common use. Final answer: Thermoplastics can be softened repeatedly by heating and hardened by cooling, allowing them to be remoulded and recycled (e.g., polythene for plastic bags). Thermosetting plastics, once moulded and heated, become hard and cannot be softened or remoulded again (e.g., Bakelite for electrical switches).
• Q: Explain the 4R principle in the context of plastic waste management. A: Step 1: Introduce the purpose of the 4R principle. Step 2: Briefly explain each 'R' (Reduce, Reuse, Recycle, Recover) and its significance. Final answer: The 4R principle for plastic waste management includes: 1. Reduce: Minimizing the use of plastics. 2. Reuse: Finding alternative uses for plastic items instead of discarding them. 3. Recycle: Processing used plastics to create new products. 4. Recover: Extracting energy from plastic waste that cannot be recycled, often through incineration in controlled environments.
• Q: Why is it advised not to wear synthetic clothes while working in the kitchen? A: Step 1: Recall the property of synthetic fibres when exposed to heat. Step 2: Consider the safety implications of this property in a kitchen environment. Final answer: It is advised not to wear synthetic clothes while working in the kitchen because synthetic fibres melt and stick to the body if they catch fire. This can cause severe burns and is much more dangerous than natural fibres like cotton, which only burn.

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