Textile Fibres: Classification, Properties and Identification
What the exam tests
This domain checks whether you can place any sample in the correct class, then predict behaviour from structure. Questions usually give a property - absorbency, tenacity, elastic recovery, flammability - and ask which fibre or which structural feature explains it.
Classification you must be able to draw
- Natural: vegetable - cotton, linen (flax), jute, coir, ramie; animal - wool, silk, mohair, cashmere; mineral - asbestos.
- Man-made: regenerated - viscose, modal, lyocell, acetate; synthetic - polyester, nylon 6 and 6.6, acrylic, polypropylene, elastane; inorganic - glass, metallic.
- Staple (short, must be spun) versus filament (continuous). Silk is the only natural filament; synthetics are extruded as filament and may be cut into staple.
Structure explains properties
Cotton is a flattened, convoluted ribbon of cellulose with hydroxyl groups, so it is absorbent and strong when wet. Wool has overlapping scales and crimp, giving bulk, warmth and felting. Silk is a smooth triangular filament of fibroin. Polyester is hydrophobic and thermoplastic, so it melts, dries fast and takes heat-set pleats.
Identification
Burning: cotton and viscose smell of burning paper and leave grey ash; wool and silk smell of burnt hair and leave a crushable black bead; polyester melts and leaves a hard bead. Microscopy: convolutions (cotton), scales (wool), triangular cross-section (silk), longitudinal striations (viscose). Solubility: acetate dissolves in acetone, nylon in formic acid, polyester in hot m-cresol.
Worked example
A lustrous, cream fabric burns with a burnt-hair smell and the bead crumbles; it dissolves in sodium hypochlorite. Protein fibres dissolve in hypochlorite, so it is silk or wool. Under the microscope the fibres are smooth, straight and continuous, with no scales - therefore silk. Had the fibres been short, crimped and scaly, the answer would be wool.
Traps that cost marks
Viscose is often mistaken for cotton in the burn test; use lustre, striations and low wet strength to separate them. Silk is not a staple fibre. Asbestos is natural but not a textile in the usual sense. Do not say polyester is absorbent because it wicks moisture.