Introduction to the Topic

Welcome to NCERT Class VIII Science Chapter 3: Synthetic Fibres and Plastics. In our daily lives, we use a wide variety of materials for clothing, containers, furniture, and household items. Some of these materials are obtained from plants and animals, while others are man-made. These man-made materials are known as synthetic fibres and plastics. Understanding these materials helps us make sustainable choices, recognize their chemical nature, and appreciate how modern manufacturing shapes our world.

Key Concepts Explained

To truly understand synthetic fibres and plastics, we need to break down the underlying chemistry and everyday applications into simple concepts:

1. What are Synthetic Fibres?

Just as a necklace is made by joining small beads together in a repetitive pattern, a synthetic fibre is a chain of small units joined together. Each small unit is a chemical substance. Many small units combine to form a large single unit called a polymer. The word 'polymer' comes from two Greek words: poly meaning many and mer meaning part/unit. Therefore, a polymer is made of many repeating units. Polymers occur in nature too; cotton, for instance, is a polymer called cellulose. When humans create polymers artificially in laboratories using petrochemicals, we call them synthetic fibres.

2. Types of Synthetic Fibres

There are several types of synthetic fibres that you study in this chapter:

  • Rayon (Artificial Silk): Although obtained from a natural source (wood pulp), rayon is chemically treated and is therefore a man-made or regenerated fibre. It is cheaper than silk, can be woven like silk fibres, and can be dyed in a wide variety of colours. Often mixed with cotton to make bed sheets or with wool to make carpets.
  • Nylon: Fully synthetic fibre created in 1935 without using any natural plant or animal raw material. It is strong, elastic, lightweight, lustrous, and easy to wash. Used for making socks, ropes, tents, toothbrushes, car seat belts, and sleeping bags. In fact, a nylon thread is stronger than a steel wire!
  • Polyester: Made from repeating units of a chemical called an ester. Fabrics made from this fibre do not get wrinkled easily, remain crisp, and are easy to wash. Terylene is a popular polyester. PET (Polyethylene terephthalate) is a very familiar form of polyester used for making bottles, utensils, and films.
  • Acrylic: Synthetic wool made from petrochemicals. It is durable, affordable, lightweight, and available in various bright colours, making it a popular substitute for natural wool which is quite expensive.

3. Characteristics of Synthetic Fibres

Why have synthetic fibres become so popular? They possess remarkable characteristics:

  • They dry up quickly.
  • They are durable and less expensive.
  • They are readily available and easy to maintain compared to natural fabrics.
  • However, they also have drawbacks: they melt on heating, which makes them dangerous to wear while working in the kitchen near fire, as they can stick to the body of the person wearing them.

4. Plastics: Properties and Environmental Impact

Like synthetic fibres, plastic is also a polymer. All plastics do not have the same type of arrangement of units; some are linear, while others are cross-linked. Plastics can be easily molded into any shape and recycled, reused, coloured, melted, rolled into sheets, or made into wires.

Plastics are classified into two main types:

  • Thermoplastics: Plastics that get deformed easily on heating and can be bent easily. Examples include polythene and PVC (Polyvinyl Chloride). Used for manufacturing toys, combs, and various types of containers.
  • Thermosetting Plastics: Plastics which when moulded once, cannot be softened by heating. Examples include Bakelite and Melamine. Bakelite is a poor conductor of heat and electricity, making it ideal for making electrical switches, handles of various utensils. Melamine resists fire and can tolerate heat better than other plastics, used for floor tiles, kitchenware, and fabrics that resist fire.

Plastics and the Environment: While plastics are \textremely convenient, their disposal is a massive environmental hazard. Materials that get degraded through natural processes (like bacteria action) are called biodegradable (e.g., vegetable peels, paper). Materials that are not easily decomposed by natural processes are called non-biodegradable (e.g., plastics, which take hundreds of years to degenerate). Burning plastics releases poisonous fumes into the atmosphere causing air pollution, while dumping them on land chokes soil and harms stray animals.

Summary & Key Takeaways

  • Synthetic fibres and plastics are polymers made up of smaller repeating units derived mostly from petroleum (petrochemicals).
  • Common synthetic fibres include Rayon, Nylon, Polyester, and Acrylic, each offering unique strengths like elasticity, wrinkle-resistance, and durability.
  • Plastics are divided into thermoplastics (which melt on heating) and thermosetting plastics (which retain their shape permanently once set).
  • Due to their non-biodegradable nature, plastics pose severe environmental challenges. We must follow the 4R principle: Reduce, Reuse, Recycle, and Recover.