Spin Process and Fiber Structure

Spin Processes and Fiber Structure 38.3.1. Flexible Chain Molecules... 

The mathematical formulation of the fiber-spinning process is meant to simulate and predict the hydrodynamics of the process and the relationship between spinning conditions and fiber structure. It involves rapid extensional deformation, heat transfer to the surrounding quenching environment, air drag on the filament surface, crystallization under rapid axial-orientation, and nonisothermal conditions. 

Polyacrylonitrile (PAN) is produced by the additional polymerization of acrylonitrile always, the second and the third monomers are used for the modihcation of dyeability and spinnability. They can then be spun into fibers by dry or wet spinning methods, such as how Orion with a distinctive dumbbell cross section is spun by dry process produced by DuPont, and Acrilan had circular cross section and is spun by the wet extrusion technique produced by Monsanto. PAN fiber can also get the crimp structure like wool by using the bicomponent spinning process in fiber preparation. Properties of PAN fibers are listed in Table 2.27. 

A network of oriented microfibrils is formed during coagulation in the spinning process of PBT fibers and films. The microfibrils have a typical diameter on the order of 100 A, and have irregularly shaped cross sections. This network is the basis for the structure and the properties of the final material. 

New Developments in Spinning and Drawing. The continual effort by the fiber producers to increase production, lower manufacturing costs, and improve quality has led to a better understanding of the effects of the spinning and drawing process on physical and molecular structure of... 

These solvents include tetrahydrofuran (THF), 1,4-dioxane, chloroform, dichloromethane, and chlorobenzene. The relatively broad solubility characteristics of PSF have been key in the development of solution-based hollow-fiber spinning processes in the manufacture of polysulfone asymmetric membranes (see Hollow-fibermembranes). The solvent list for PES and PPSF is short because of the propensity of these polymers to undergo solvent-induced crystallization in many solvents. When the PES structure contains a small proportion of a second bisphenol comonomer, as in the case of RADEL A (Amoco Corp.) polyethersulfone, solution stability is much improved over that of PES homopolymer. 

As noted in Fig. 14.1 (a), commercial fibers of semicrystallme polymers are always cold-drawn after spinning to achieve further structuring through further macromolecular orientation and crystalline morphological changes, many of which are retained because of the low temperature of the cold-drawing processes. A typical stress-strain curve for a polycrystalline polymer at a temperature Tg < T < Tm appears in Fig. 14.6. 

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