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Spin Orientation during Acrylic Fiber Formation by Wet-Spinning
Spin Orientation during Acrylic Fiber Formation by Wet-Spinning JITENDER SINGH2011TT10926GURJINDER SINGH2011TT10917
SPIN ORIENTATION ??? A premature molecular orientation acquired during the fiber formation step itself before any intentional orientation stretch is taken.The level of this orientation influences the Iater drawing processes and final fibre properties.
2The spin bath deformation is very complex, and we cannot calculate a draw ratio from the kinematics of spinning.It cannot be equated to any known velocity such as = Q/hole area or Vf since the deformations involve a large component of viscous flow which produces no molecular orientation
SONIC MODULUSSonic modulus is a measure of spin orientation in a fibre .Sound travel faster along a polymer chain than from one chain to another .So , sonic velocity will be higher for oriented polymer than unoriented polymer.Sonic modulus is related to sonic velocity by ,
E = Sonic Modulus in grams/denierV = Sonic Velocity in kilometers/second
FACTORS AFFECTING SPIN ORIENTATION
Spinneret hole diameter, DSpinning solution flow rate per hole, QGodet Speed, Denier per filament of the fiber (dpf)
C = Polymer Concentration , S = Stretch Ratio
An increase in sonic modulus or orientation as the production rate is increased while producing a filament of a given denier.Spin orientation is higher for the 5.0-mil spinneret than the 3.0-mil spinneretThe slopes of the constant denier lines are larger for the 3.0-mil spinneret .
Sonic modulus initially increases fast with decrease in denier and then levels out to a constant value . Increase in sonic modulus will be more in 5 mil than 3 mil. Capilliary .
Correlation of Results jet stretch ratio, defined as V1/, where is the average solution velocity in the spinneret hole, the spinning solution does not issue from the spinneret with velocity (V), but instead it leaves with a velocity Vf which is normally 4 to 10 times less than. Reason: Barus EffectVf- free velocity
We go for Vf/V, would be a more realistic parameter.
resulting ratio, V1/Vf, might properly be called the filament attenuation, the actual denier reductionVf is the velocity if no tension were applied.This ratio correlates much better.
Argument: V1/ does not depend on Q &, whereas V1/Vf does in just the right way
DISCUSSIONCalculation of An Orientation FactorMoseley related the sonic modulus of solid polymers to molecular orientation.sound travels with a certain velocity down the molecular axis while it travels at a different(slower) velocity between chains, i.e., perpendicular to the chain axes orientation factor ( )
Approximate equation .. . .(a)
, is the sonic modulus of a sample having completely randommolecular orientation.
ranges from 0 for random orientation to 1 when all chains are oriented perfectly.Equation (a) was derived for a solid polymer with no porosity. But we have porous, fibrillar network structure.
Mechanism of OrientationDivided into two classes: One group says the source is in the fluid region before solidification other points to the solid region. In first mechanism, preferential orientation by the perpendicular (shear) velocity gradient in spinneret capillary and/or the parallel (axial) velocity gradient in the fluid outside the capillary and then solidified.In the second,the thread-line tension is considered to cold draw the solidified filaments. The thread-line tension within the fluid filament due to the attenuation from velocity Vf to V1 plus a contribution from the hydrodynamic drag in the bath for wet spinning.alternate mechanism of orientationnot in the well defined fluid or solid regions but in the transition zonea distinct boundary between coagulated and uncoagulated solution This boundary moves into the filament as the filament proceeds away from the spinneret.Boundary motion is controlled by the solvent and non-solvent diffusion rates.
In melt-spinning this boundary controlled by heat transfer. stresses in the threadline must be transmitted across this boundarythey may actually be higher here than anywhere else.(possibility)a large shear gradient may be established on the fluid side of the boundary, and in this way the attenuation could occur by shear gradients rather than axial gradients.Due to the diffusion across the boundary, oriented material created very near this boundary could be immobilized very quickly before relaxation thus leading to spin orientation.
(Another possibility) lies on the solid side of this boundary. Since this material is so freshly formed, its modulus may not be as large as that of the completely coagulated filament leaving the bath. This material would be very easy to orient especially if stress concentration occurs in the annular ring.Another bit of evidence pointing to the importance of this region is that when a certain velocity , the filaments will break.
Thanks . . .Reference:D. R. Paul, J. Appl. Polym. Sci., 13,817-826 (1969).