Abstract
In order to investigate the effects of the concentration of swelling agent and temperature of the immersed bath on the structural stability of the drawn P. E. T. fibers in water with the different oriented properties of their crystallite, the swelling behaviors of thess fibers in the phenol aqueous solution of various concentration are discussed. Changes of their molecular orientation after swelling for 3 hours were observed by the birefringence. The results obtained are as follows:
1) The lower stretched and non-heated P. E. T. fibers (70°C) show a slight shrinkage in dilute phenol aqueous solution at 40°C and smaller elongation in the concentrated solution. The intermediately stretched fibers show smaller elongation in the dilute solution, and these swelling elongation become larger with increased concentration of the phenol aqueous solution. The fiber of draw ratio 2.0 is apt to elongate most. The higher stretched fibers with fiber-like orientation slightly shrink in the concentrated phenol aqueous solution due to the entropical contraction. These heated fibers show a smaller elongation compared with the non-heated, and the fine structure in the amorphous region of these fibers may be stabilized.
2) The swelling behaviors for the stretched fibers at 60°C become almost similar that of the stretched fibers at 70°C with various oriented properties. The stretched fibers at 80°C show same swelling behavior as that of the lower stretched at 70°C. And the stretched fibers at 90°C have swelling behaviors to superpose behaviors of the lower stretched one at 70°C on that of the higher stretched.
3) Generally, swelling elongation is smaller with rising temperature of the phenol aqueous solution.
4) The change of birefringence for the higher stretched (70°C) and non-heated fibers after swelling for 3 hours in the phenol aqueous solution of the various concentrations at 40°C give remarkable oriented effects due to the acceleration of crystallization and swelling elongation. The changes of birefringence for the lower stretched (70°C) and non-heated fibers give only a slight effects and all stretched fibers of the non-heated have positive birefringence. As the structural damage due to the swelling for the higher stretched and heated fibers with fiber-like orientation may be reached down to the higher oriented region. The values of birefringence becomes smaller as compared with non-swollen and heated fibers. The dependence on the concentration of the swelling agent is slightly. The changes of birefringence for the lower stretched and heated fibers do not show so remarkablely as the higher stretched f_??_ibers do, and these fibers have negative birefringence.
