16.2.Production and Properties of Natural Fibers 333 16.2.Production and Properties of Natural Fibers Animal Fibers Animal fibers (wool,silk,etc.)are composed mostly of proteins, as already mentioned in Section 16.1.(Proteins are highly com- plex substances which consist of long chains of alpha amino acids involving carbon,hydrogen,nitrogen,sulfur,and oxygen.)All taken,animal fibers do not contain cellulose.They are therefore more vulnerable to chemical damage and unfavorable environ- mental conditions than cellulose. After extraction of the fibers as described above,they need to be spun into yarn.For this the individual fibers are arranged in parallel to overlap each other,yielding a ribbon.These rib- bons are then softened with mineral oil,lubricated,and even- tually drawn down to the desired sizes and twisted for secur- ing the position of the fibers.The yarn is eventually woven into fabrics. Wool consists mainly of the animal protein keratin,which is common in the outermost layers of the skin,nails,hooves,feath- ers,and hair.Keratin is completely insoluble in cold or hot wa- ter and is not attacked by proteolytic enzymes (i.e.,enzymes that break proteins).Keratin in wool is composed of a mixture of pep- tides.When wool is heated in water to about 90C,it shrinks ir- reversibly.This is attributed to the breakage of hydrogen bonds and other noncovalent bonds. Wool fibers are coarser than those of cotton,linen,silk,or rayon,and range in diameter between 15 and 60 um,depending on their lengths.Fine wool fibers are 4-7.5 cm long,whereas coarse fibers measure up to 35 cm.Unlike vegetable fibers,wool has a lower breaking point when wet.The fibers are elastic to a certain extent,that is,they return to their original length after stretching or compression and thus resist wrinkling in garments. The low density of wool results in light-weight fabrics.Wool can retain up to 18%of its weight in moisture.Still,water absorp- tion and release are slow,which allows the wearer not to feel damp or chilled.Wool deteriorates little when properly stored and is essentially mildew-resistant.However,clothes moths and carpet beetles feed on wool fibers,and extensive exposure to sun- light may cause decomposition.Further,wool deteriorates in strong alkali solutions and chars at 300C. Felting shrinkage,that is,compaction,occurs when wet,hot wool is subjected to mechanical action.Thus,washing in hot water with extensive mechanical action is harmful.On the other hand,felting produces a nonwoven fabric,as already mentioned in Section 16.1.This is possible due to the fact thatAnimal fibers (wool, silk, etc.) are composed mostly of proteins, as already mentioned in Section 16.1. (Proteins are highly com￾plex substances which consist of long chains of alpha amino acids involving carbon, hydrogen, nitrogen, sulfur, and oxygen.) All taken, animal fibers do not contain cellulose. They are therefore more vulnerable to chemical damage and unfavorable environ￾mental conditions than cellulose. After extraction of the fibers as described above, they need to be spun into yarn. For this the individual fibers are arranged in parallel to overlap each other, yielding a ribbon. These rib￾bons are then softened with mineral oil, lubricated, and even￾tually drawn down to the desired sizes and twisted for secur￾ing the position of the fibers. The yarn is eventually woven into fabrics. Wool consists mainly of the animal protein keratin, which is common in the outermost layers of the skin, nails, hooves, feath￾ers, and hair. Keratin is completely insoluble in cold or hot wa￾ter and is not attacked by proteolytic enzymes (i.e., enzymes that break proteins). Keratin in wool is composed of a mixture of pep￾tides. When wool is heated in water to about 90°C, it shrinks ir￾reversibly. This is attributed to the breakage of hydrogen bonds and other noncovalent bonds. Wool fibers are coarser than those of cotton, linen, silk, or rayon, and range in diameter between 15 and 60 m, depending on their lengths. Fine wool fibers are 4–7.5 cm long, whereas coarse fibers measure up to 35 cm. Unlike vegetable fibers, wool has a lower breaking point when wet. The fibers are elastic to a certain extent, that is, they return to their original length after stretching or compression and thus resist wrinkling in garments. The low density of wool results in light-weight fabrics. Wool can retain up to 18% of its weight in moisture. Still, water absorp￾tion and release are slow, which allows the wearer not to feel damp or chilled. Wool deteriorates little when properly stored and is essentially mildew-resistant. However, clothes moths and carpet beetles feed on wool fibers, and extensive exposure to sun￾light may cause decomposition. Further, wool deteriorates in strong alkali solutions and chars at 300°C. Felting shrinkage, that is, compaction, occurs when wet, hot wool is subjected to mechanical action. Thus, washing in hot water with extensive mechanical action is harmful. On the other hand, felting produces a nonwoven fabric, as already mentioned in Section 16.1. This is possible due to the fact that Animal Fibers 16.2 • Production and Properties of Natural Fibers 333 16.2 • Production and Properties of Natural Fibers