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.
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.
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.
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
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.