Fibre

I

Introduction

Fibre, fine hair-like structure of animal, vegetable, mineral, or synthetic origin. Fibres average less than 0.05 cm (0.02 in) in diameter. Used for textiles and for many other products, fibres are classified according to their origin, their chemical structure, or both.

II

Animal Fibres

Chemically, all animal fibres are complex proteins. They are resistant to most organic acids and, under proper circumstances, to certain strong mineral acids such as sulphuric acid (H₂ SO₄). But protein fibres may be damaged even by mild alkalis and may be totally dissolved by such strong alkalis as sodium hydroxide (NaOH). These fibres are also subject to damage by chlorine-based bleaches. Liquid hypochlorite bleach should never be used on wool or silk. If used undiluted, it will damage fibres or even completely dissolve them.

The principal component of silk is the protein fibroin. Silk is extruded in continuous filaments from the abdomens of various insects and spiders. It is the only natural filament—a term used to describe a fibre of indefinite length—commonly reaching a length of more than 1,000 m (3,300 ft). Several silk filament fibres are gathered to produce a filament yarn. Silk, however, is often produced and utilized in short or staple form to manufacture spun yarns. True silk as used in textiles is produced by only one insect, the silkworm.

The principal component of hair, wool, and fur, the protective skin hairs of mammals, is the protein keratin. Fibres of hair and wool are not continuous and must be spun into thread or yarn if they are to be woven or knitted into textiles, or they must be felted.

The chief hair fibre used to produce textile fabrics is sheep's wool. Individual hairs may be as long as 90 cm (36 in) but are usually no more than 40 cm (16 in). In wild sheep the wool is a short, soft underlayer protected by longer, coarser hairs; in domesticated sheep bred for their fleece, the length of the wool is greatly increased. All hair fibres have a coat of overlapping scales. The size and shape of the scales is unique to each species. In many kinds of sheep wool the scales are quite pronounced. Wool fibres that are not smooth but naturally crimped produce air-trapping yarns used for insulating materials.

Other animals used as sources of hair fibre for textiles include the llama, alpaca, vicuña, Angora goat and rabbit, Kashmir goat, and camel. The vicuña, native to the Andes, is now considered an endangered species because of overhunting. Fur fibres from animals such as mink and beaver are sometimes blended with other hairs to spin luxury yarns but the pelts are more often used. Horsehair and cow's hair are used for felts and are sometimes spun as yarn, particularly for upholstery and other applications where durability is important. Even human hair has been spun into yarn and used for textiles.

III

Vegetable Fibres

Vegetable fibres are predominantly cellulose, which, unlike the protein of animal fibres, resists alkalis. Vegetable fibres resist most organic acids but are destroyed by strong mineral acids. Improper use of most bleaches can weaken or destroy these fibres.

The chief vegetable fibres are structurally of four kinds: seed fibres, the soft hairs that surround the seeds of certain plants; bast fibres, the tough fibres that grow between the bark and stem of many dicotyledonous plants (see Dicots); vascular fibres, the tough fibres found in the leaves and stems of monocotyledons (see Monocots); and entire stems of grasses. Certain other structural types have limited utility. These include strips of leaf skins, such as raffia; fibres of the fruit case, such as coir, and palm fibres. Only two seed-hair fibres, cotton and kapok, have commercial importance. Cotton, the most adaptable and most widely used of all fibres, is the only seed fibre with textile utility. Kapok cannot be spun but is used as upholstery stuffing. Because it is hollow, kapok is buoyant. It has been used for flotation devices such as life preservers, but today it has largely been replaced by other materials.

The numerous varieties of bast fibres are used for purposes ranging from weaving fine textiles to manufacturing cordage. Linen cloth is made from flax, and coarser cloths and rope and twine are produced from hemp, jute, ramie, and sunn.

Vascular fibres are used almost entirely for cordage making. They include agave (sisal), henequen, manila hemp, yucca, and a number of others. The vascular fibres of the pineapple have been used in the production of textiles.

Entire stems of some grasses and straws are woven as fibres for hats and matting. Among such fibres is esparto.

Vegetable fibres have extensive application in making paper. Cotton and flax form the basis for fine rag papers, and grasses, hemp, jute, and manila are often used in making wrapping papers and other coarse papers. Newsprint and kraft papers are produced from wood fibre after chemical treatment. Wood fibre and bagasse, the fibre of sugar cane, are made into building board by a process analogous to papermaking.

IV

Mineral Fibres

Only one fibre of inorganic (mineral) origin is used to any great extent in conventional fabrics: glass fibre, made by drawing or blowing molten glass into threads. Fibres of asbestos, formerly used for insulation and fireproofing, have been found to be carcinogenic. Thin metal wire is sometimes used for the production of gauze and is woven with organic fibres to give special patterns. Most so-called metal thread, however, actually consists of thin strips of metal foil similar to tinsel. To impart strength, metallic foils are often sandwiched between layers of plastic film. Other metallic yarns consist of a cotton core wound with a thin metal strip or thread that has been coated with a viscous substance and dipped in metal powder. The insulation material called rock wool is a fibrous substance made from steel-mill slag, limestone, or siliceous rock.