But as polymer chains get bigger, their solutions, or melts, become more viscous and difficult to process. Proteins and Carbohydrates Life as we know it could not exist without polymers. Proteins, with large numbers of amino acids joined by amide linkages, perform a wide variety of vital roles in plants and animals. Carbohydrates, with chains made up of repeating units derived from simple sugars, are among the most plentiful compounds in plants and animals. Both of these natural polymers are important for fibers.
Proteins are the basis for wool, silk and other animal-derived filaments.
Cellulose as a carbohydrate occurs as cotton, linen and other vegetable fibers. The properties of these fibers are limited by the form provided in their natural state. Some, like linen and silk, are difficult to isolate from their sources, which makes them scarce and expensive. There are, of course, many other sources of proteins and cellulose, such as wood pulp, but natural polymers tend to be very difficult to work with and form into fibers or other useful structures. The inter-chain forces tend to be strong because of the large number of polar groups in the molecular chains.