Measurements of the diameter, temperature, and birefringence of fibrous materials running from spinneret toward a winding machine during the melt spinning of polyethylene terephthalate (PET) were carried out. A specially designed spinning machine which enables us to measure the above variables was constructed. The measurements were carried out without touching the running fiber by employing various optical devices. Particularly, an infrared radiation microscope was employed successfully for the temperature measurement.
Changes in observed diameter, temperature, and birefringence and in calculated values of velocity and rate of deformation of the running fiber along the spinning line were similar to those reported by other authors. The thinning in the diameter of the running fiber seemed to be completed within a distance of two meters down from the spinneret. An estimation of the magnitude of the two components of dynamic loss compliance
J″ of PET,
Ji″based on the recoverable viscoelastic deformation and
Jη″based on flow, was made for temperatures at different positions along the spinning line. The changes in the diameter and birefringence of the running fiber were explained qualitatively with the relative magnitude of
Ji″and
Jη″. In the zone below and close to the spinneret where
Jη″>>
Ji″, flow is dominant resulting in the rapid thinning in the diameter of the running fiber. On the contrary, in the zone where
Jη″<<
Ji″, recoverable deformation is dominant resulting in the very little change in the diameter of the running fiber. A comparison of the relative contribution of
Ji″and
Jη″and the magnitude of the birefringence leads us to an idea that the inter- and intra-molecular forces which are responsible to the recoverable deformation, may work effectively in molecular orientation. The rate of relaxation of molecular orientation was evaluated by calculating relaxation times according to a Maxwell model. The increase in relaxation time may be a part of the reason for the increase of the birefringence in the zone where cooling proceeds effectively.
An analysis of the change in the diameter and temperature along the spinning line was carried out numerically using equations of force and heat balances. Because the material parameter used in the force balance equation is only extensional viscosity, the agreement between observed and calculated values was limited in the high temperature initial zone of spinning where flow is dominant in the deformation of running fibrous materials.
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