The change of structural and physic

The change of structural and physical characteristics of as-spun fibers brought by the introduction of LIB can now be analyzed on the basis of the results obtained from the simulation. As can be seen from the Fig. 16, the solidification stress changes drastically inside the LIB depending on the position at which the crystallization is assumed to occur. The solidification stress increases from a value of 7 MPa at the upper surface of the LIB to a value of 30 MPa at the outlet of the LIB. High level of solidification stress and the consequent increase in the molecular orientation can be realized only when the crystallization is assumed to occur at a position close to the outlet of the LIB. At this position, the solidification stress is significantly higher than that of the standard high-speed spun fibers and such high levels of solidification stress is necessary to account for the significant enhancement of molecular orientation in the LIB fibers. This consideration agrees with the experimental results in which birefringence showed a steep increase in the take-up speed range of 1 to 2 km/min where crystallization started to occur (Figs. 2 and 4). Support for the postulate that th