Effect of Sunlight on Fibres MCQs Quiz | Class 9

This is an online MCQs quiz for Class 9 Home Science (Code 064), Unit V: Fibre and Fabric. The quiz focuses on the topic: Effect of Sunlight on Fibres, covering key concepts such as sun damage, colour fading, and the weakening of different textiles. Attempt all questions and click ‘Submit Quiz’ to see your score. You can then download a PDF of your answers.

Understanding the Effect of Sunlight on Fibres

Sunlight, while essential for life, can be very damaging to textile fibres. This damage is primarily caused by the Ultraviolet (UV) radiation present in sunlight. Prolonged exposure can lead to irreversible changes in a fabric’s appearance and structural integrity, including fading of colours, loss of strength, and yellowing. Understanding these effects is crucial for proper fabric care and selection.

Key Concepts of Sun Damage

1. Fading (Photodegradation of Dyes)

Fading is the loss of colour in a fabric when exposed to sunlight. The high-energy UV rays break down the chemical bonds within dye molecules. This process, called photodegradation, alters the structure of the dye, reducing its ability to absorb specific wavelengths of light. As a result, the colour we perceive becomes less intense or changes completely. Some colours, particularly reds and blues, are more susceptible to fading than others.

2. Weakening and Brittleness

Sunlight not only affects the dye but also the fibres themselves. UV radiation breaks down the long polymer chains that give fibres their strength and flexibility. For natural fibres like cotton, this means the degradation of cellulose chains. In protein fibres like silk and wool, the protein structure is damaged. This molecular breakdown leads to a significant loss of tensile strength, making the fabric weak, brittle, and easy to tear.

3. Yellowing

Yellowing is a common issue for white or light-coloured fabrics, especially natural ones like wool, silk, and cotton. The UV energy triggers an oxidation process within the fibre’s molecular structure. This chemical reaction creates yellowish compounds, leading to a visible discoloration of the fabric that is often irreversible.

Sunlight Resistance of Common Fibres

Different fibres have varying levels of resistance to sun damage. This is an important factor when choosing fabrics for applications like curtains, upholstery, or outdoor wear.

Fibre Sunlight Resistance Notes
Cotton Fair Tends to weaken and yellow over time.
Wool Good Better UV resistance than cotton but can still yellow.
Silk Poor Very sensitive to sunlight; weakens and yellows rapidly.
Polyester Excellent Highly resistant to UV degradation and fading.
Nylon Good Strong, but can yellow and lose some strength with prolonged exposure.
Acrylic Excellent Often used for outdoor fabrics due to its superior resistance to sunlight.

Quick Revision Points

  • Ultraviolet (UV) radiation is the primary component of sunlight that damages textiles.
  • Sun damage manifests as colour fading, fibre weakening (loss of strength), and yellowing.
  • Natural fibres, especially silk, are generally more susceptible to sun damage than synthetic fibres.
  • Synthetic fibres like polyester and acrylic are engineered for excellent UV resistance.
  • The process of colour fading due to light is called photodegradation.
  • Fibre weakening is caused by the breaking of long polymer chains by UV energy.
  • Protecting fabrics involves avoiding direct sunlight, using window coverings, and proper storage.

Practice Questions

  1. Why is silk a poor choice for curtains in a very sunny room?
  2. What is the chemical difference between the fading of a dye and the yellowing of a white cotton fabric?
  3. If you were to manufacture an outdoor furniture cover, which fibre would be the most suitable choice and why?
  4. Explain the term “polymer chain scission” in the context of a cotton t-shirt left in the sun for a month.
  5. Some fabrics are sold with a “UV protection factor” (UPF). What does this imply about the fabric’s composition?