Natural fiber

Natural fibers or natural fibres (see spelling differences) are fibers that are produced by plants, animals, and geological processes. They can be used as a component of composite materials, where the orientation of fibers impacts the properties. Natural fibers can also be matted into sheets to make paper or felt. The earliest evidence of humans using fibers is the discovery of wool and dyed flax fibers found in a prehistoric cave in the Republic of Georgia that date back to 36,000 BP. Natural fibers can be used for high-tech applications, such as composite parts for automobiles. Compared to composites reinforced with glass fibers, composites with natural fibers have advantages such as lower density, better thermal insulation, and reduced skin irritation. Further, unlike glass fibers, natural fibers can be broken down by bacteria once they are no longer in use. Natural fibers are good sweat absorbents and can be found in a variety of textures. Cotton fibers made from the cotton plant, for example, produce fabrics that are light in weight, soft in texture, and which can be made in various sizes and colors. Clothes made of natural fibers such as cotton are often preferred over clothing made of synthetic fibers by people living in hot and humid climates. Natural fibers are made from plant, animal, and mineral sources. Natural fibers can be classified according to their origin. Animal fibers generally comprise proteins such as collagen, keratin and fibroin; examples include silk, sinew, wool, catgut, angora, mohair and alpaca. Chitin is the second most abundant natural polymer in the world, with collagen being the first. It is a “linear polysaccharide of β-(1-4)-2-acetamido-2-deoxy-D-glucose”. Chitin is highly crystalline and is usually composed of chains organized in a β sheet. Due to its high crystallinity and chemical structure, it is insoluble in many solvents. It also has a low toxicity in the body and is inert in the intestines. Chitin also has antibacterial properties. Chitin forms crystals that make fibrils that become surrounded by proteins. These fibrils can bundle to make larger fibers that contribute to the hierarchical structure of many biological materials. These fibrils can form randomly oriented networks that provide the mechanical strength of the organic layer in different biological materials. Chitin provides protection and structural support to many living organisms. It makes up the cell walls of fungi and yeast, the shells of mollusks, the exoskeletons of insects and arthropods. In shells and exoskeletons, the chitin fibers contribute to their hierarchical structure.