Natural Fibers

Fibers (or fibres) form a class of hair-like materials that occur as continuous filaments or in discrete elongated pieces, similar to pieces of thread. They are of two types: natural fibers and man-made or synthetic fibers.

Natural fibers may be obtained from plant, animal, and mineral sources. Those from plant sources include cotton, flax, hemp, sisal, jute, kenaf, and coconut. Fibers from animal sources include silk, wool, and mohair. Those from mineral sources include asbestos and metal fibers.

Many natural fibers can be spun into filaments, thread, or rope. Some can be matted into sheets to make products such as paper or felt. Others can be used as components of composite materials. In recent years, natural fibers are being increasingly used in the textile, building, plastics, and automotive industries.

Sources of natural fibers

Natural fibers can be classified according to their sources.

Vegetable fibers

Cellulose is the main component of vegetable fibers, several of which serve in the manufacture of paper and cloth. Examples include cotton, jute, flax, ramie, sisal, and hemp.

Vegetable fibers can be further categorized into the following types:

• Seed fiber: These are fibers collected from seeds or seed cases. Examples include cotton and kapok.
• Leaf fiber: These are fibers collected from leaves. Examples include sisal and agave.
• Bast fiber or skin fiber: These fibers are collected from the skin or bast surrounding the stem of the plant source. They have higher tensile strength than other fibers. Therefore, these fibers are used for durable yarn, fabric, packaging, and paper. Some examples are flax, jute, kenaf, industrial hemp, ramie, rattan, soybean fiber, and even vine fibers and banana fibers.
• Fruit fiber: These fibers are collected from the fruit of the plant, such as coconut (coir) fiber.
• Stalk fiber: These fibers are actually the stalks of the plant. Examples are straws of wheat, rice, barley, and other crops including bamboo and grass. Tree wood is also such a fiber.

The most used natural fibers are cotton, flax and hemp, although sisal, jute, kenaf, and coconut are also widely used.

Hemp fibers are mainly used for ropes and aerofoils because of their high suppleness and resistance within an aggressive environment. Hemp fibers are currently used by the heating and sanitary industries to make seals.

Animal fibers

Animal fibers are generally made up of proteins. Examples include silk, wool, angora, mohair, and alpaca.

• Animal hair (wool or hairs): Fiber or wool taken from animals or hairy mammals. For example, sheep's wool, goat hair (cashmere, mohair), alpaca hair, horse hair, and so on.
• Silk fiber: Fiber collected from dried saliva of bugs or insects during the preparation of cocoons. Examples include silk from silk worms.
• Avian fiber: Fibers from birds, for example, feathers and feather fiber.

Mineral fibers

Fibers obtained from mineral sources may be used in their naturally occurring form or after slight modifications. They can be placed in the following categories:

• Asbestos: This is a mineral that occurs naturally in fibrous form. Variations are serpentine (chrysotile) and amphiboles (amosite, crocidolite, tremolite, actinolite, and anthophyllite).
• Ceramic fibers: Glass fibers (glass wool and quartz), aluminum oxide, silicon carbide, and boron carbide.
• Metal fibers: Aluminum fibers

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