What are the bonds present in textile fibers?
The formation of any textile material requires a certain amount of bond that would hold the molecules in a polymer (intra-polymer bonds) and further link the polymers together in order to form a fiber (inter-polymer bonding).
These are the bonds that hold the atoms together to make up the fiber polymer. Textile fiber polymers are also regarded as a molecule that owns a property that exists independently.
• Single covalent bond: This bond is described as chemically very stable and unreactive and forms the backbone of many fibers. These bonds are unbreakable when they exist between carbon and carbon atoms, carbon and hydrogen, carbon and oxygen, carbon and chlorine, and carbon and fluorine atoms. Thus, since these bonds greatly consist of carbon segments and so form the backbone of many fibers.
• The amide or peptide linkage: These linkages are referred to as peptide links when they exist in protein or animal fibers like silk, wool, mohair, and amide group when present in nylon. The amide or peptide group can be broken only upon hydrolysis and this leads to damage of fiber as well. Such hydrolysis damages and breaks the single covalent bond present between carbon and nitrogen.
• Benzene Ring: It is an aromatic radical that impart chemical stability to the polymer structure and is present in polyester. The benzene molecule is a hexagon, and so forms a ring structure composed of carbon and hydrogen atoms.
• Ether linkage: These bonds exist between the carbon and oxygen atoms. These linkages when present in cellulose are called glucoside linkage i.e. links all glucose units. Ether linkage is generally unreactive and quite stable because of the presence of carbon-oxygen bonds. These linkages make the fiber polymer durable. Ether linkages are present in polymers such as cellulose, elastomeric, ester-cellulose, and polyester.
• Ester groups or organic salts: When the carboxyl group reacts with a hydroxy group, the ester is formed. The ester group is not resistant to alkalis.
• Hydroxyl group: This group is represented as the -OH group. These groups are responsible for moisture absorbency because the -OH group is easily attracted by water molecules and results in the formation of hydrogen bonds.
• Nitrile group: This group does not react with acids but can undergo alkaline hydrolysis. These are present as a side- group polymers in acrylic and modacrylic fibers.
The bonds that are present between the polymer in fiber is called an inter-polymer bond. There are four such types of bonds:
• Cross-links: These bonds are also called covalent bonds. Covalent bonds are regarded as the strongest among all the inter-polymer bonds in nature.
However, these links can result in making a textile material stiff and non-resilient. They contribute towards the tenacity of wool fibers. The fibers in which these links are present are elastomeric, protein fibers except silk.
• Salt linkage: These are also considered to possess strong bond energy and attract water molecules. These bonds also impart tensile strength to the fibers. These are known greatly for their ability to absorb water readily and good dye pickup because they attract anion of acid dyes. These bonds are present in fibers like nylon and protein fibers.
• Hydrogen bonds: Bonds that are formed between hydrogen and oxygen atoms or hydrogen and nitrogen atoms are referred to as hydrogen bonds. Also, the hydrogen-oxygen bond is stronger than the hydrogen-nitrogen bond. However, these bonds are overall weak in nature.
The characteristics that these bonds impart to fiber mainly are tenacity and elastic-plastic nature. They also account towards the heat setting property of nylon and protein fibers.
Cellulose, protein, nylon, polyvinyl alcohol, polyester are some of the fibers whose polymers are bonded with hydrogen bonds.
• Van der Waals forces: These interpolymer forces of attraction are weakest in nature. All fibers and predominantly acrylic and polyester own these bonds in their polymer system.