Study Unit 3.1 Physical and Chemical properties Flashcards
Physical structure
Length
Diameter/size
Cross-sectional shape
Surface contour
Crimp
Physical structure
Length
Diameter/size
Cross-sectional shape The cross-sectional shape of the fibre is important in the texture, lustre, hand and bulk of a fabric. The spinneret and the spinning method control the shape of manufactured fibres. The fibres may be solid or hollow, having one or more voids along the length of the fibre. The shape of natural fibres is determined by cellular growth, the shape of hair follicles, the formation of proteins, and the shape of the orifice through which silk fibre is extruded. Plant fibres such as cotton and flax have a central cavity known as the lumen. Figure 3.1 shows some typical fibre cross-sectional shapes. Surface contour The surface contour of a fibre influences the hand, lustre, texture and soiling of the fabric. Fibres may be smooth (silk), serrated, have striations, nodes (flax), scales (wool) or cracks, or may be rough (cotton). For manufactured fibres, many types of surface contour can be produced. Figure 3.1 shows some typical surface contours. Round Angular Lobal Serrated Oval Flat wool lumen fibrillated/ cracked surface mushroom Bicomponent pie wedge for microfibres sea/islands for microfibres smooth surface serrated surface surface scales dog-bone side by side bowtie for stretch recovery silk Flax hollow Figure 3.1: Typical fibre cross-sectional shapes and surface contours Crimp Crimp refers to the waves, twists, curls, coils or bends along the length of the fibre. Inherent crimp occurs in wool. Manufactured bicomponent fibres can also have inherent crimp. Crimp increases abrasion resistance, increases cohesiveness (required for fibre spinning), resiliency, stretch, bulk and warmth.
Lenght
The length of the fibre plays an important role in the aesthetic properties of the fabric. It is also a key requirement for fibre spinning. Filaments may be many metres or even kilometres in length. Staple fibres generally range from 2–50 cm in length.
Diameter/size
The diameter of fibres is often referred to as fineness. Fibre fineness has a great influence on the aesthetic properties of a fabric. Coarse (thick) fibres are stiffer and this affects the drape, hand and texture of the fabric. Fabrics made with fine fibres generally have a luxurious hand.
The measurement of fineness poses some difficulties:
- The cross-section of the fibre may not be circular (eg silk, cotton, trilobal fibres).
- The cross-section of the fibre may not be uniform along its length (natural fibres).
- The cross-section may vary from fibre to fibre (natural fibres).
Fineness
Fineness is a relative measure of fibre size expressed in denier or tex (linear density) for manufactured fibres. For cotton, fineness may be expressed as the mean fibre weight in micrograms per inch. For wool, fineness is the mean fibre width or mean fibre diameter expressed in micrometres (microns).
denier
– equal to the mass in grams of 9000 metres of the fibre or yarn.
tex
– equal to the mass in grams of 1000 metres of the fibre or yarn.
decitex (dtex)
– equal to the mass in grams of 10000 metres of the fibre or yarn.
1–3 denier corresponds to:
fine cotton, cashmere or wool
5–8 denier corresponds to:
average cotton or wool
Apparel fibres range from:
1–7 denier but different fibres of the same denier are not always suitable for the same end-use
Apparel fibres range from:
Lenght
The length of the fibre plays an important role in the aesthetic properties of the fabric. It is also a key requirement for fibre spinning. Filaments may be many metres or even kilometres in length. Staple fibres generally range from 2–50 cm in length.
Diameter/size
The diameter of fibres is often referred to as fineness. Fibre fineness has a great influence on the aesthetic properties of a fabric. Coarse (thick) fibres are stiffer and this affects the drape, hand and texture of the fabric. Fabrics made with fine fibres generally have a luxurious hand.
