Synthetic Fibres and Plastics

This chapter introduces synthetic fibres and plastics, materials made by humans from petrochemicals. Both are polymers, long chains formed by joining many small units called monomers; cotton, for example, is a natural polymer of glucose units called cellulose. You will study rayon, or artificial silk, obtained from wood pulp; nylon, the first fully synthetic fibre, made in 1931 and so strong that it is used for parachutes and ropes; polyester, such as Terylene and PET, which does not wrinkle easily; and acrylic, used as artificial wool. You will learn their properties: they are strong, light, durable, cheap and dry quickly, but melt on heating, which makes them unsafe in the kitchen. Plastics are also polymers. Thermoplastics such as polythene and PVC soften on heating and can be reshaped, while thermosetting plastics such as bakelite and melamine cannot. You will learn why plastics are useful, why they are non-biodegradable and harm the environment and animals, and how the 5 R principle and the habit of reduce, reuse and recycle help.

Detailed Worksheet: Synthetic Fibres and Plastics Section A - Definitions (10 marks) 1. What are synthetic fibres? Why are they called synthetic? (2 marks) 2. What is a polymer? Name one natural polymer and its monomer. (2 marks) 3. What is rayon? Why is it called artificial silk? (2 marks) 4. Distinguish between thermoplastics and thermosetting plastics with one example each. (2 marks) 5. What are biodegradable and non-biodegradable materials? Give one example of each. (2 marks) Section B - Calculations and Applications (15 marks) 6. A nylon thread of a certain thickness can hold a load of 12 kg, while a cotton thread of the same thickness breaks at 3 kg. How many times stronger is the nylon thread? What use of nylon depends on this property? (3 marks) 7. The approximate time taken by some materials to degrade is: vegetable peels 1 to 2 weeks, paper 10 to 30 days, cotton cloth 2 to 5 months, wood 10 to 15 years, tin and aluminium cans 100 to 500 years, plastic bags several hundred years. Arrange them from the fastest to the slowest degrading, and classify each as biodegradable or non-biodegradable. (3 marks) 8. A family uses 6 plastic carry bags a day. How many bags does it use in a year of 365 days? If it switches to cloth bags and cuts this by 80%, how many plastic bags does it still use in a year? (3 marks) 9. A school collects 250 kg of plastic waste in a month. If 40% is recyclable thermoplastic and the rest is mixed waste, find the mass of each. Why can thermosetting plastics not be recycled by melting? (3 marks) 10. Choose the most suitable material, giving a reason, for each: (i) the handle of a frying pan (ii) a parachute (iii) a raincoat (iv) electric switches (v) a kitchen apron (vi) a sweater. (3 marks) Section C - Diagrams (10 marks) 11. Draw diagrams to show (i) a linear polymer chain and (ii) a cross-linked polymer arrangement. State which type of plastic each represents and why. (4 marks) 12. Draw a labelled diagram of the activity to compare the strength of threads of cotton, wool, silk and nylon using a stand, clamp, pan and weights. (3 marks) 13. Draw a flowchart showing the 5 R principle (Reduce, Reuse, Recycle, Recover, Refuse) with one example of each. (3 marks) Section D - Analysis and Higher-order Thinking (15 marks) 14. Explain why we should not wear synthetic clothes while working in the kitchen or a laboratory. Why are synthetic clothes uncomfortable in hot and humid weather? (5 marks) 15. Plastics are said to be both a boon and a curse. Give three reasons why plastic is widely used and three ways in which it harms the environment and animals. (5 marks) 16. Why are the uniforms of firemen coated with melamine? Why are cooking pan handles made of bakelite? Explain the properties of thermosetting plastics that make them suitable for these uses. (5 marks) Instructions: Time allowed 2 hours. Attempt all sections. Give one example for every property you describe and label all diagrams.