(164l) A Reappraisal of Typical and Novel Fiber Forming Polymeric Materials

A polymer is made up of many small molecules which have combined to form a single long or large molecule by a process called ‘polymerization’. If drawn into long filament- like materials, whose length is at least 100 times its diameter, polymers are said to have been converted into ‘fibers’.

Fibers are of natural origin such as cotton, wool, flax and silk and man- made or synthetic fibers made of nylon, polyesters, polypropylene, and acrylics. While natural fibers (except silk) occur as staples, synthetic fibers can be produced as continuous filaments or cut to form staples.

From the viewpoint of a consumer, fibers can be classified into three types, viz., comfort fibers, safety fibers and industrial fibers. Comfort fibers are those used for making undergarments and garments. Comfort fibers should have adequate strength and extensibility, softness, good moisture regain, and preferably some flame retardancy, and should be capable of being dyed. For instance, cotton, silk, wool, nylon, polyesters, and acrylics. Safety fibers are those used in making carpets, curtains, seat covers, draperies and so on. Such fibers should be strong, tough, durable, abrasion- resistant, difficult to ignite, flame retardant, liberate minimum heat, smoke and toxic gases if involved in a fire. For instance, aromatic polyamides, polyimides, polybenzimidazoles and polyoxy diazoles. Industrial fibers are used as reinforcing materials in composite structures. These fibers are also called structural fibers as they possess very high modulus, strength, thermal stability, toughness and durability. Structural fibers are used to reinforce articles such as rigid and flexible tubes, pipes & tyres and in composite structures called fiber- reinforced plastics (FRP) used in the construction of boats, cars, planes and even buildings. Uniaxially oriented fibers of aromatic polyamides and polyesters, carbon fibers and silica fibers are examples of industrial fibers.

Nylon 6,6 is a hard and strong fiber forming polymer, highly crystalline and its use temperature is below glass transition temperature (T_g). Polymers extruded from the melt to produce fibers include nylon, and PET (e.g., Terylene, Trevira) and polypropylene.

Fibers are made from polymers by a process called ‘spinning’. There are three principal spinning methods, viz, melt spinning, dry spinning and wet spinning. In the melt- spinning process, the polymer is used in the molten state, while, in the other two cases, the polymer is used as a solution in an appropriate solvent. In all the three cases, however, the polymer (either in the molten or in the solution form) is streamed through a spinneret which is a special kind of plate with extremely fine holes for the fibers to emerge.

This work extends a strengthened knowledgebase regarding classification, structures and processing techniques of fiber forming materials. A detailed account on various fiber forming materials and their structures is accorded and existing as well as novel fiber manufacturing processes are reviewed. The essential attributes of existing fiber forming materials, their limitations and applications, are also discussed. In addition, present work also deals with the current state of the art and latest research status in the field of fiber technology, particularly in fabrication and application of nanofibers in several chemical & allied engineering realms.

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