Fibre classification:\nWhich of the following is NOT a natural fibre in standard materials classification?

Introduction / Context:
Natural fibres are harvested directly from plants or animals, while man-made fibres are produced by chemical processing (regenerated natural polymers or fully synthetic). Viscose rayon, although cellulosic, is regenerated and thus not a natural fibre in formal classifications used by the textile industry.

Given Data / Assumptions:

• Silk and wool are animal-derived natural fibres.
• Cotton and flax (linen) are plant-derived natural fibres.
• Viscose rayon is regenerated cellulose made by the viscose process.

Concept / Approach:
Rayon is manufactured by dissolving cellulose and extruding it into a coagulation bath to regenerate filaments. Despite its cellulose chemistry, it is not harvested as fibre; therefore, it is classed as man-made (regenerated) rather than natural. Hence it is the correct choice for “not a natural fibre.”

Step-by-Step Solution:

Verification / Alternative check:
Standards from textile associations list rayon under manufactured fibres; cotton, flax, silk, and wool are natural categories.

Why Other Options Are Wrong:

• Silk/wool: animal fibres.
• Cotton/flax: plant fibres.

Common Pitfalls:
Assuming “cellulosic” automatically means natural; the processing route determines classification.

Final Answer:
Viscose rayon