Gelation in Spinning Chemical Fibres from Solutions of Polymers

Abstract

678.01It was shown that gelation takes place according to a scenario determined by the trajectory of movement of the state of the polymer solution from the initial position to the binodal in the phase separation diagram of the polymer-solvent-precipitant system. The fundamental quantitative characteristics of gelation in spinning of chemical fibres from polymer solutions and their calculation relations were determined.More than 4 million tons of chemical fibres are now manufactured from solutions of polymers by the wet spinning method in the world each year. The common mechanism of fabrication of gel fibres combines the different technologies for these fibres. The present article analyzes gelation in wet spinning of fibres from polymer solutions based on phase diagrams.The gel phase, which is the primary structure of the fibre, determines its properties to a great degree. Beginning with the research of S. P. Papkov [1, 2], gelation in fibre spinning has been considered from the point of view of the phase state of the polymer solutions. In our article, we examine gelation as the basic stage of wet spinning based on a five-dimensional phase-equilibrium diagram of the system polymersolventprecipitator (concentration)mechanical fieldtemperature. The gelation process is considered as movement (kinetics) of the state of the system in phase space, reflected by the phase diagram. It is assumed that the rate of the phase transition (gelation) at each point of phase space is much greater than the rate of movement of the system over this phase space.Traditionally, gelation has only been considered as a diffusion phenomenon in the polymersolventprecipitator system and correspondingly, the change in the concentrations of these components. In this case, gelation takes place according to a scenario defined by the trajectory of movement of the state of the polymer solution from the point of the initial position to the gel region, intersecting the binodal in the phase separation diagram of the polymersolventprecipitator system as a function of both the change in the concentrations and the change in the phase diagram itself when the composition of the solvent changes.The phase diagram of amorphous separation of the polyacrylonitrile (PAN)dimethylformamide (DMF) system and the change when the solvent is replaced by DMFwater mixture (curves 2-5) are shown in Fig. 1. Crystallization equilibrium in the PANDMF system plays an important role in formation of the gel, especially its structure. Crystalline PAN is limitedly soluble in DMF (curve 6). The system located below this line contains undissolved PAN crystallites (crystal nuclei) and the system above the line does not contain these crystallites. The gel formed at a temperature below the crystallization line is [1, 2] a network associated at points by crystallites. The state and mechanical properties of the gel determines the line of the glassy state of the concentrated (with respect to the polymer) phase to a great degree (line 7).However, in the five-dimensional phase equilibrium d...