Regulation of the structure of fibres from polymer solutions

Abstract

The properties of fibres wet spun from solutions of polymers can be altered within wide limits by using information on the rheological properties of the spinning solutions, the phase equilibrium diagrams of polymer solventprecipitator systems, and information on the glass transition and crystallization in the system. The homogeneity of the structure and properties of the fibre increase in the order of spinning methods: diffusion, thermotropic, mechanotropic.At present, approximately 5 million tons/year of chemical fibres (polyacrylonitrile, cellulose, polyvinyl chloride, polyaramid, polyvinyl alcohol, and several other kinds) are manufactured worldwide by spinning from solutions of polymers. These are textile fibres for general household applications and also a different kind of industrial fibres high-strength, highmodulus, thermostable, heat-resistant, etc.The manufacturers and developers of chemical fibre technology are attempting to obtain a defined set of physicomechanical properties of the fibres (yarns) for use in different articles in certain conditions, up to production of narrowly specialized fibres. It is sometimes necessary for the fibre to have a uniform structure both in the transverse and in the longitudinal direction and sometimes vice versa. For some articles, it is necessary to realize the maximum breaking strength of the fibres, while for others, it is the maximum elongation, high porosity, or density, smooth or rough surface, different shape of the cross section, etc.The properties of chemical fibres are a function of many factors primarily the chemical composition of the polymer and physical state of the polymer in the fibre, i.e., its structure. The mechanical properties of a fibre the breaking strength and elongation at break, modulus of elasticity, sorption capacity, etc. can differ by more than one order of magnitude even with the same polymer composition. These differences in the properties of a fibre are due to certain organization of the structure of the polymer. The structure of the polymer in a fibre is usually in a nonequilibrium, frozen usually in the amorphouscrystalline state. For this reason, the properties of the fibre are also a function of the composition and morphology of these phases and their interrelationships. Unfortunately, analyzing the structure of a polymer is complex, expensive, and laborious. In addition, there is no unambiguous correlation between the structure and properties of a fibre. The defectiveness of the macrostructure of the fibre also affects this correlation.Let us define the terminology and basic concepts of the structure of the polymer in a fibre.Macrostructure. Structural regions comparable to the transverse dimensions of a fibre, i.e., greater than 0.01 µm, include segments with different density, porosity, orientation of the polymer chains, crystallinity, etc. The size of the segments with a different structure along a fibre can vary from several micrometers to 10 m and more these are layers, fibrils, pores, and void cavities, thickened and thinned ...

Design and Fabrication of Membranes Based on PAN Copolymer Obtained from Solutions in N-methylmorpholine-N-oxide

“…Although the processes described above proceed at a high speed, they can be regulated, for example, by choosing a precipitant [ 29 ] or the temperature of the coagulation bath [ 30 ]. Thus, in [ 31 , 32 ] it was shown that an increase in the content of the solvent (DMSO) in the precipitation water bath allows to obtain fewer defective samples with a uniform cross-section. A decrease in temperature leads to a slowdown in diffusion processes and affects both the morphology and the shape of the resulting fibers [ 33 ].…”