Wet spinning

Wet spinning

Wet spinning is applied to polymers which do not melt and dissolve only in non-volatile or thermally unstable solvents. In this process, the polymer is dissolved in a suitable solvent, and the solution is extruded through a spinnerene to a liquid bath containing low molecular weight chemicals. This chemical is a non solvent to the polymer but is freely miscible with the solvent used to prepare polymer dope 

In this process, the method of solution preparation, filtration and extrusion i.e., polymer dope preparation is very similar to those used for dry spinning. But more dilute polymer solution is used for complicated solidification process .Polymer contentvaries between (5 % to25 %) it 20 to 5000 poise viscosity.

For extrusion, the same general principles are used for the design of the spinnerettes. But the spacing of the holes in the wet spinning is closer than the dry spinning because the polymer stream he moves in a liquid medium after extrusion. Presence of liquid restricts t coalescing of the filaments during solidification

The spin-block is not a compacted one like that of melt spinning and dry spinning because of the presence of special spin bath with chemicals. Instead, the design of the spin block is such the spinneretter are submerged in spin bath and connected to the spin block by transfer e of pipes. Also, the spinnerette pack present in spin chemically inert material.

The solidification process of the polymer solution consists of extraction of the solvent by the chemicals present in the spin bath. This process is an f spin inward and outward mass transfer process in the polymer stream of bath. Inward and outward mass transfer is more complex phenomenon in wet spinning.


The extracted fibre can be stretching in the spin-bath because of its gel- like structure. The degree of stretching can be as high as 30 times only a slow rate of transition allows higher stretch. Sometimes to have more degree of stretching, the fibre usually passes through several baths containing The extruded fibre ca the co-adulating chemical.

Because of high liquid content in the wet spun fibres, it is difficult to wind them on take-up bobbins. Also, drying of the fibres before drawing
renders difficulties for further processing. So instead of winding in a bobbin in take-up, sometimes centrifugal spinning method is generally adopted to collect the filaments after solidification. 

In this method, the fibre is passed to the inside of a rotating container into which the yarn is collected with the aid of centrifugal force. The material gathered in the rotating container forms a stable package or cake. The cake can be removed v.hen rotation stops. 

An alternative process can be used, where the fibres after solidification can be post-treated continuously. The cakes or the fibres can be washed repeatedly to remove any residual solvent or any other chemical present in the fibre.

The advantages and disadvantages of wet spinning process can be summarized below

 Advantage

(a) It can be used for any polymer. Even polyethylene, polypropylene and nylon can be converted from polymer to their fibre by wet spinning technique.

(b)  Fibre can attain maximum strength, which can be comparable with maximum theoretical strength, particularly for flexible polymers. Comparatively melt spinning process can not result in maximum theoretical strength

(c) The process can be continuous.

Disadvantage

(a) The production rate is low

(b) One or more than one bath is requiredfor completely removal of the solvent from the polymer

(c) Post-spinning operations are morel length

(d) Because of lengthier process, it is more costly.

(e) The formation of exact fibre cross section is difficult to control because of inward and outward mass transfer process.