Classification and identification of textile fibres
Fibres are natural or man-made. Natural fibres are cellulosic, protein or mineral; man-made are regenerated or synthetic. A burning test sorts an unknown fibre into its group.
Classification of textile fibres
| Group | Sub-group | Examples |
|---|---|---|
| Natural: cellulosic (plant) | Seed hairs | Cotton, kapok |
| Natural: cellulosic (plant) | Bast (stem) fibres | Flax (linen), jute, hemp, ramie |
| Natural: cellulosic (plant) | Leaf and fruit fibres | Sisal and pineapple (leaf); coir from coconut husk (fruit) |
| Natural: protein (animal) | Wool and hair | Sheep's wool; specialty hair such as pashmina (cashmere), mohair, camel hair, angora rabbit |
| Natural: protein (animal) | Secretion | Silk: mulberry, tasar (tussar), eri and muga |
| Natural: mineral | Rock fibre | Asbestos (no longer used, because its dust causes lung disease) |
| Man-made: regenerated | Cellulose | Viscose rayon, cuprammonium rayon, modal, lyocell; acetate and triacetate (modified cellulose) |
| Man-made: regenerated | Protein | Casein (milk) and soya or corn protein fibres (azlon) |
| Man-made: synthetic | Built from petrochemicals | Nylon (polyamide), polyester, acrylic, polypropylene (olefin), spandex (elastane) |
| Man-made: inorganic | Mineral or metal | Glass fibre, metallic yarn (zari, lurex), carbon fibre |
Staple and filament
Activity: how to identify an unknown fibre
In the practical, test the warp and weft separately, because they may be different fibres.
- 1Look and feel: note lustre, length, crimp and hand. Untwist a yarn: short fibres mean staple; long, smooth strands mean filament.
- 2★Burning test: hold a few fibres with forceps and bring them slowly to a small flame. Note how they behave near the flame, in it and after removal, the smell and the residue.work over a steel tray, away from cloth and the gas stove
- 3Microscope test: mount a few fibres in a drop of water or glycerine and study the length view; a cross-section needs fibres cut very thin.
- 4Solubility test: place fibres in a test tube with the reagent and watch whether they dissolve.lab only, with gloves and goggles
- 5Confirm: name the fibre only when two or more tests agree. A blend gives mixed results.
★ one-way, controls the pace
Burning test
| Fibre | Near and in the flame | Smell | Residue |
|---|---|---|---|
| Cotton, linen, viscose rayon (cellulose) | Catch fire quickly, burn with a yellow flame and keep glowing after removal; do not melt | Burning paper | Soft grey feathery ash (very little from rayon) |
| Wool and silk (protein) | Curl away, burn slowly, sputter, usually go out on their own | Burning hair or feathers | Black, crushable bead |
| Nylon | Shrinks from the flame, melts and drips, burns slowly, may go out | Celery-like | Hard grey or tan bead; cannot be crushed |
| Polyester | Shrinks, melts and burns with black, sooty smoke | Sweetish chemical smell | Hard black bead; cannot be crushed |
| Acrylic | Melts and burns with sputtering; keeps burning | Acrid (sharp, bitter) | Hard, irregular black bead |
| Acetate | Melts and burns, dripping | Vinegar | Hard black bead |
Microscope and solubility tests
| Fibre | Under the microscope (length view; cross-section) | Solubility clue |
|---|---|---|
| Cotton | Flat, twisted ribbon (convolutions); kidney-shaped with a lumen | Dissolves in 70% sulphuric acid; survives boiling 5% caustic soda |
| Linen | Straight rod with cross-marks (nodes) like bamboo; many-sided | As cotton |
| Wool | Overlapping scales like roof tiles; round to oval | Dissolves in boiling 5% caustic soda and in chlorine bleach; resists dilute acids |
| Silk | Smooth, glass-like rod; triangular with rounded corners | Dissolves in boiling 5% caustic soda, in chlorine bleach and in cold concentrated hydrochloric acid |
| Viscose rayon | Lengthwise lines (striations); circle with a wavy (serrated) edge | Dissolves in 70% sulphuric acid |
| Nylon | Smooth rod, often with dark specks of delustrant; round or three-lobed | Dissolves in 20% hydrochloric acid and in formic acid |
| Polyester | Smooth rod like nylon; round | Resists most reagents; dissolves in hot meta-cresol |
| Acrylic | Smooth or faintly lined; round or dog-bone shaped | Dissolves in warm dimethylformamide (DMF) |
Before buying a kitchen apron or hospital uniform, check the fibre on the label or burn one loose thread over a steel plate: cotton turns to ash, but polyester and nylon melt and can stick to skin near a flame.
2 marks: “What is a filament fibre? Give an example.” A long, continuous fibre measured in metres or kilometres. Silk is the only natural filament; nylon and polyester are made as filaments.
5 marks: “Describe the burning test for identifying textile fibres.” Method (forceps, small flame; behaviour near, in and after the flame), then a table for cellulose, protein, nylon and polyester: flame, smell, residue.
10 marks: “Classify textile fibres with suitable examples.” Define fibre; draw the chart (natural: cellulosic, protein, mineral; man-made: regenerated, synthetic, inorganic); two examples per group with Indian ones; staple vs filament.
Burning test in three words: cellulose = paper, protein = hair, synthetic = melts to a hard bead.