Both natural and man-made fibres are mainly composed of the compounds belonging to high polymers or macromolecules. Macromolecular structure is necessary for the production of materials of high mechanical strength and high melting point. The natural fibres are found to consist chain molecules of linear molecular type. Further, the chain molecules are oriented into the parallel bundles in the process of growth. Based on these investigations, it is assumed that polymers must satisfy the minimum requirements, if it is to serve as a fibre. These requirements are as mentioned follows:
The polymer must be linear flexible macromolecule with a high degree of symmetry the effect of cross sectional diameter should be less than 15Å. The polymer should not contain any bulky side groups or chains.
The polymer mass must have a comparatively high molecular mass. The average length of its molecular chain should be in order of 1000 Å or more.
The molecule must have the capacity to adopt an extended an extended configuration and state of mutual alignment.
A polymer should have at least a high degree of intermolecular cohesive power. This indicates that the molecular chains should have sufficient number of sites of attraction
A high degree of orientation of the molecules in the polymer is a pre-requisite for producing good tensile strength.