Wet Spinning – An Overview

 

What is wet spinning?

Wet spinning is a kind of solution spinning and belongs to the spinning method of chemical fiber. Depending on the different property of the polymer fiber. There are two main spinning methods of chemical fibers: melt spinning and solution spinning. In addition, there are special or unconventional methods of spinning, such as electrospinning, solution blow spinning. Among them, according to the different solidification mode, solution spinning method is divided into wet spinning and dry spinning.

In the production of chemical fibers, most of them are produced by melt spinning, followed by wet spinning. And only a few are produced by dry or other unconventional spinning methods.

Dry jet wet spinning

A variant of wet spinning is dry jet wet spinning, which is called dry-wet spinning for short. It is a chemical fiber spinning method which combines the characteristics of dry spinning and wet spinning. This is a new spinning method developed in the 1960s.
After the spinning solution (sometimes called a “spinning dope”) is pressed out of the spinneret. It passes through a space (3 ~ 100 mm, generally less than 20 ~ 30 mm) and then enters the coagulation bath. The gas in space can be air or some other inert gas.
When using dry jet wet spinning, the trickle flow of the spinning solution can undergo significant spinneret stretching in the air. And the length of the stretch zone is far longer than the length of the swell zone of the flow. The axial deformation of the liquid flow occurs over such a long distance, and the velocity gradient is not large. In fact, there is no great deformation in the swelling region. In contrast, in wet spinning, spinneret stretching takes place over a very short distance, the velocity gradient is large, the swelling zone of the liquid flow is severely deformed. And the spinneret stretching causes the filament to break. Therefore, using dry jet wet spinning can improve the stretching ratio and spinning speed of the nozzle.

The spinning speed of dry jet wet spinning can reach 600 ~ 1200 m/min, which is much higher than that of wet spinning. And the spinneret with larger aperture (φ=0.15 ~ 0.3 mm) can be used. However, the concentration and viscosity of the spinning solution can be as high as that of dry spinning. What’s more, the structure formation process of the fiber can be controlled effectively by dry jet wet spinning. In dry spinning, the solidification speed of liquid flow is often very slow due to the limit of solvent evaporation speed. In dry-wet spinning, the flow of liquid (fiber) being drawn enters the coagulating bath. And the solidification rate and fiber structure can be changed over a wide range by adjusting the composition and temperature of the coagulating bath.
Although dry jet wet spinning has the advantages of both dry spinning and wet spinning, the liquid flow tends to flow slowly along the spinneret surface. This phenomenon is related to the elastic viscosity of polymer solution, surface tension, the geometry of spinneret hole and the deformation speed of the liquid flow. Dry jet wet spinning has been used in the production of polyacrylonitrile fiber, aromatic polyamide fiber, polybenzimidazole fiber, etc.

For more information about wet spinning, you can send email to fyia@hkdowell.com or come to this website.