Characteristics of Fabrics
Senior 2 · Home Science
Characteristics of Fabrics
Lesson 3 of 4
20 min
Most school uniforms, sports kits, school bags and umbrellas sold in Rwanda contain man-made fibres. They are cheap to produce in large amounts, strong, and easy to care for. They also have weaknesses, such as feeling hot and melting under a hot iron, that you need to know before you buy, wear or iron them.
This lesson describes the three man-made fibres in your syllabus and shows you how to read a fibre-content label.
The raw material is turned into a thick liquid and pushed through a spinneret, a nozzle with many tiny holes, rather like a shower head. Each jet hardens into a long filament. The filaments can be used long, for smooth shiny fabrics, or cut short and spun like cotton, for softer fabrics.
Rayon was the first successful man-made fibre: the viscose process was developed in England in 1894. Wood pulp, which is cellulose, is dissolved in chemicals and forced through a spinneret into a bath that turns it back into solid cellulose. Because it starts from a natural material, rayon is called a regenerated fibre.
Polyester is a synthetic fibre made from chemicals obtained from petroleum. It was patented in Britain in 1941 and is now the most widely produced fibre in the world.
Nylon, developed in the United States in 1935, was the first fully synthetic fibre. It was first made famous as a replacement for silk in stockings.
Polyester and nylon are thermoplastic: they soften and then melt when heated. This has good and bad effects:
A polyester-cotton blend combines cotton's comfort and absorbency with polyester's strength, crease resistance and quick drying. This is why so many school shirts are 65% polyester and 35% cotton.
A bedsheet label reads: 65% polyester, 35% cotton. Mass 400 g. Wash at 40 °C. Iron: two dots.
(a) How much of each fibre is in the sheet? Polyester: 65% of 400 g = 0.65 × 400 = 260 g. Cotton: 35% of 400 g = 0.35 × 400 = 140 g. Check: 260 + 140 = 400 g.
(b) What do the dots mean? On an iron symbol, one dot means a cool iron (up to about 110 °C), two dots a medium iron (up to about 150 °C) and three dots a hot iron (up to about 200 °C).
(c) Why two dots and not three, when cotton takes a hot iron? A blend must be ironed at the setting for its most heat-sensitive fibre. Polyester is thermoplastic, so three dots could melt it.
Tip
Memory hook: synthetics are plastic, so treat them like a plastic bottle. They do not soak up water, they do not rot, and they melt with heat. Iron a blend at the setting for the fibre that melts first.
Why is rayon called regenerated and not synthetic?
Solution. It is made from a natural material, wood pulp (cellulose), which is dissolved and re-formed. Synthetic fibres such as polyester are built entirely from chemicals.
A school shirt label says 70% polyester, 30% cotton, and the shirt weighs 250 g. Find the mass of cotton.
Solution. 30% of 250 g = 0.30 × 250 = 75 g of cotton (and 175 g of polyester).
Byiringiro wears a 100% polyester shirt to play football on a hot afternoon and feels hot and sticky. Explain.
Solution. Polyester has low absorbency, so it does not take up sweat. The sweat stays on the skin and the shirt feels hot and clammy. A cotton or cotton-rich shirt would absorb the sweat.
Give one advantage and one danger of synthetic fibres being thermoplastic.
Solution. Advantage: pleats can be heat-set to stay in permanently. Danger: near a flame the fabric melts and sticks to the skin, causing serious burns (also, a hot iron can melt a hole).
Remember
Sources and credits
This lesson adapts CC BY-SA material and is shared under CC BY-SA 4.0.
