Fibres for textiles are obtained from a wide variety of sources but are simply categorized as cellulosic (from plants), proteinaceous (from animals) and synthetic. There is considerable diversity in their chemistry, structure and properties but this can be addressed through a common vocabulary, of which it is useful for the conservator to be aware. Some general observations on the nature of textile fibres are followed by data for specific types, and this section concludes with some discussion of identification of textiles and fibres.
Fibre structures are made up of a mass of fibrils covered by a cuticle. For example, in wool the fibrils are contained in the central cortex and covered with a cuticle of scales (Landi, 1992). In silk they are parallel to the axis of the fibre. In cotton they are laid in spiralling layers round the lumen and similarly in flax in a different spiral form. Textile fibres are illustrated in Cook (1984). Regenerated and synthetic fibres vary depending on the processes used. Important mechanical properties of fibres include their strength, ability to stretch and recover (elasticity) and flexibility. These properties are affected by external factors such as relative humidity and temperature. For an explanation of fibre properties in relation to their structure see Gohl and Vilensky (1987) and Timar-Balazsy and Eastop (1998).
Cellulosic or ester cellulosic fibres include cotton, linen, jute and hemp. Cotton is obtained from the seed hair of Gossypium herbaceum and G. hursutuin by ginning, a mechanical process used to remove plant waste from fibres. The average length of the fibres or 'staples' is 12-55 mm. Flax, the raw material of linen is obtained from bast stem fibres of Linium usitatissimum. The unidirectional fibres which have an average length of 150-1000 mm are loosened from the stems by retting, a process of rotting in water, and further processed by scutching to remove the outer bark. Other bast (flexible, fibrous bark) fibres are processed in similar fashion. Jute is obtained from bast stem fibres of Corchorus capsularis and hemp from bast stem fibres of Cannabis sativa. All these plant fibres are formed from long chain molecules of cellulose that are flexible and very strong.
Also included in this category are man-made regenerated celluloses, including viscose from wood pulp and cellulose acetate from cotton waste. Regenerated cellulose is formed through various chemical processes in which the cellulose is dissolved, reformed and extruded through fine spinarettes to form homogeneous filaments. The properties of regenerated celluloses and synthetics vary according to the manufacturing process used.
Proteinaceous fibres include wool, silk and horsehair. Wool includes the body hair of sheep and some other animals. Wool fibres range in length from 12.5 to 250 mm. After shearing or plucking from the animal, wool is washed and carded to clean, separate and align the fibres. Silk is a continuous filament that is extruded from the head of the silk worm (e.g. Bombyx mori) to form the protective cocoon at the stage of pupation. The cocoons are degummed to remove unwanted materials and loosen the filament so that it can be unwound. Horsehair is the body hair from the tails and manes of horses. All proteins consist of polypeptides which in turn are made up of amino acids. The type and formation of these in wool are partially responsible for its ability to stretch, and those in silk for its strength.
Many synthetic and semi-synthetic polymers have been used from the early part of the twentieth century to produce textile fibres. They include casein, rayon, nylon, polyester and polypropylene. Fibres may be used alone or may be combined, or blended, in a spun thread or in a textile structure.
Spinning Bundles of aligned fibres are drawn out to a uniform thickness and spun into a yarn by a process which involves twisting the fibres to bind them together. They may be twisted clockwise (S) or anticlockwise (Z). The higher the number of twists per unit length, the stronger the thread. Two or more threads may be plied together to increase strength. Generally speaking, threads that are 'S' spun will be 'Z' plied and vice versa.
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