TEXTILE FIBER FIBER STRUCTURE The structure of a

TEXTILE FIBER

FIBER STRUCTURE The structure of a fiber is described in terms of degree of polymerization, molecular orientation, molecular bonds, amorphous regions, crystallinity and cross links.

CHARACTERISTICS OF FIBER FORMING POLYMERS Both natural and man made fibers are mainly composed of the compounds belonging to high polymers or macromolecules. Macromolecular structure is necessary for production of materials of high mechanical strength and high melting point. The natural fibers are found to consist chain molecules of linear macromolecular type. Further, the chain molecules are oriented into parallel bundles in the process of growth. Based on these investigations, it is assumed that a polymer must satisfy minimum requirements, if it is to serve as a fiber. These requirements are mentioned below: Flexibility Molecular mass Configuration Crystallinity Orientation

FLEXIBILITY The polymer must be a flexible macromolecule with a high degree of symmetry. The effective cross sectional diameter should be less than 15 Angstrom. The polymer should not contain any bulky side groups or chains.

MOLECULAR MASS The polymer must have a comparatively high molecular mass. The average length of its molecular chain should be in order of 1000 Angstrom or more.

CONFIGURATION The molecule must have the capacity to adopt an extended configuration and state of mutual alignment.

CRYSTALLINITY 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.

ORIENTATION A high degree of orientation of the molecules in the polymer is a pre-requisite for producing good tensile strength.

FIBER FORMATION The conversion of fibers from polymers involves the following principles: 1. Reduction of the polymeric materials to a liquid state by melting or dissolving in a solvent or in some solubilizing agent. 2. Extrusion of the liquid under pressure through fine holes or orifices in a spinnerette. 3. Rapid and continuous solidification of the extruded liquid. The main methods used for fiber formation is spinning.

Ref: Textbook of Fiber Science by SP Mishra

RELATION BETWEEN FIBER STRUCTURE AND FIBER PROPERTIES Density: Crystalline polymer chain packed closely so density is high. Strength: For crystalline polymer, inter molecular force are high, so strength is high. Also long chain molecules exhibits higher strength. Refractive index: More crystalline polymers exhibit high refractive index. Hardness & stiffness: Crystalline polymer are less pliable & stiffer handling. Its surface is hard.

CONTD… Permeability: Permeability decreases if the crystallinity increase. Melting point: Crystalline polymers melting point is higher than amorphous polymer due to higher inter molecular attraction. Dyeing ability: More crystalline polymers are more compact due to their inter-molecular forces, so they are not easy to dye i. e dye absorption percentage is less than amorphous polymer.

EFFECT OF FIBER STRUCTURAL FACTORS ON FIBER PROPERTIES 1) Chemical bonding: a) Single bond-Less strength, More flexibility b) Double bond - More strength, Less flexibility 2) Character of polymer chin: a) Long chain, such as [-CH 2 -CH 2 -]n-More strength, less flexibility b) Sort chain, such as [-CH 2 -]n-Les strength, more flexibility c) Long side chain-More strength, less flexibility d) Sort side chain-Less strength, more flexibility

CONTD… 3) Molecular packing: a) Regular packing: More strength, less flexibility b) Irregular packing: Less strength, more flexibility 4) Crystallinity: High crystallinity, higher strength and less flexibility 5) Orientation: High Orientation, higher strength and less flexibility

CONTD… 6) Nature of monomer: a) Same monomer (Homopolymer) -More strength, less flexibility b) Same monomer (Co-polymer) -Less strength, more flexibility 7) Internal structure of fiber polymer: a) For ring structure -More strength, less flexibility b) For normal structure -Less strength, more flexibility