Chapter I Overview
I. Process overview
1. Solution spinning process
Solution preparation, preparation before spinning (filtration, deaeration, mixing), spinning, post-treatment (washing, stretching, heat setting, crimping, cutting, packaging)
2. Classification of solution spinning
In the solution spinning method, according to the different coagulation methods, it is divided into:
■ Wet spinning
■ Dry spinning
■ Dry and wet spinning
(1) Wet spinning
The spinning solution squeezed out from the pores of the spinneret enters the coagulation bath, and the polymer is precipitated in the coagulation bath to form nascent fibers.
Figure 1 ~ 4 Schematic diagram of wet spinning
1. Spinneret 2. Coagulating bath 3. Drawing roller 4. Winding device
For the spinneret for AT235 Lab Wet Spinning Machine, we Anytester can customized the hole number and hole size as per customer request. Also for the coagulating bath, the size can be made as per customer request and it also can equipped with heating.
■ Diffusion and coagulation in wet spinning are not only general physical and chemical processes, but also chemical changes occur to some chemical fibers such as viscose fibers. Therefore, the forming process of wet spinning is more complicated, and the spinning speed is affected by solvents. Due to the double diffusion of the coagulant and the fluid resistance of the coagulation bath, the spinning speed is much lower than that of melt spinning. The spinning speed is 5-100 m/min, and the winding speed of melt spinning is several hundred meters to several kilometers per minute.
■ When using wet spinning, it must be equipped with coagulation bath configuration, recycling and recovery equipment. The process is complicated, the plant construction and equipment investment costs are relatively large, the spinning speed is low, the cost is high, and the environmental pollution is severe.
■ At present, aramid, vinylon, chlorinated fiber, spandex, cellulose fiber and certain fiber-forming polymers composed of rigid macromolecules all need to use wet spinning.
(2) Drying Spinning
The spinning solution extruded from the capillary holes of the spinneret enters the spinning shaft. Through the action of the hot air in the tunnel, the solvent in the trickle of the solution is quickly volatilized, and the trickle of the solution is concentrated and solidified to become the nascent fiber while gradually removing the solvent.
When using dry spinning, the primary problem is the choice of solvent. Because the spinning speed mainly depends on the volatilization speed of the solvent, the solvent should be selected so that the polymer concentration in the solution should be as high as possible, and the boiling point and latent heat of evaporation of the solvent should be as low as possible, so as to reduce the conversion of the spinning solution to The amount of solvent volatilized in the fiber process reduces the heat energy consumption and increases the spinning speed. In addition to technical and economic requirements, the flammability of solvents should also be considered to meet safety protection requirements. The most commonly used dry spinning solvents are acetone and dimethylformamide.
■ Present, the dry spinning speed is generally 200~500m/min, and the higher one can reach 1000-1500m/min. However, due to the limitation of the solvent volatilization speed, the dry spinning speed is still lower than that of melt spinning, and it also requires solvent recovery and other processes. , So there are more auxiliary equipment than melt spinning.
■ Dry spinning is generally suitable for spinning chemical fiber filaments. The main varieties produced are aramid, acetate fiber, chlorinated fiber, spandex and so on.
(3) Dry Jet Wet Spinning
The spinning solution extruded from the capillary pores of the spinneret first passes through a section of air layer, and then enters the coagulation bath to form a solidification process. Compared with ordinary wet spinning, the spinning speed is increased by 5 to 10 times.