Textile Raw Materials and Fibre Science
Fibre classification and identification
Begin with the classification tree: natural fibres split into vegetable (cotton, jute, flax), animal (wool, silk) and mineral (asbestos); man-made fibres split into regenerated (viscose, acetate) and synthetic (polyester, nylon, acrylic, polypropylene). Know the polymer repeat units, because questions often ask which linkage defines a fibre - cotton is cellulose with beta-1,4 glucosidic bonds, wool is a protein with peptide bonds and disulphide cross-links, polyester is a condensation polymer of terephthalic acid and ethylene glycol.
Property relationships
Link structure to behaviour: degree of polymerisation and crystallinity govern strength and moisture regain. Cotton has high crystallinity and about 8.5% standard moisture regain; viscose is less crystalline, weaker when wet and with about 11-13% regain; polyester is hydrophobic at about 0.4%. Wool's scales give felting shrinkage and its crimp gives bulk; silk's triangular filaments give lustre.
Traps in examinations
- Confusing regain (moisture as a percentage of oven-dry mass) with moisture content (percentage of total wet mass).
- Assuming all regenerated fibres are natural; they are man-made from natural polymers.
- Mixing burning-test observations: cotton smells of burning paper, wool of burning hair, synthetics melt and bead.
Worked rule of thumb
To convert between the two moisture expressions, use regain R = 100M/(100 − M) and content M = 100R/(100 + R). A sample at 10% moisture content has regain 100×10/90 = 11.1%. Always state which basis the question uses before calculating.