Cotton Fibre Bleaching Agent Selection
Cotton fibres are naturally yellowish due to impurities like pectin, waxes, and colouring matter. Bleaching removes these impurities to achieve a uniform white base, essential for dyeing and printing.
Bleaching Agent Properties
An effective bleaching agent for cotton should:
- Remove colour impurities effectively.
- Be stable under processing conditions.
- Not damage the cotton fibres (cellulose).
- Be cost-effective and environmentally acceptable.
Analysis of Options
Let's analyze the given options for bleaching cotton:
- Sodium hydroxide (NaOH): Primarily used for mercerization, which improves lustre and strength, but it's not a bleaching agent itself.
- Hydrogen peroxide ($\text{H}_2\text{O}_2$): A widely used oxidative bleaching agent. It effectively removes colouring matter from cotton under alkaline conditions (often stabilized with NaOH) without significantly damaging the cellulose fibres. It decomposes into water and oxygen.
- Potassium chloride (KCl): An inorganic salt, not used for bleaching textiles.
- Sodium chloride (NaCl): Common salt, not a bleaching agent for textiles.
Conclusion on Bleaching Agent
Based on its effectiveness and suitability for cotton (cellulose), Hydrogen peroxide is the preferred bleaching agent for cotton fibres.