Irreversible Thermal Shrinkage and Fine Structure of Nylon 6 Fiber

Abstract

The irreversible thermal shrinkage of nylon 6 fibers which were cold-drawn or heat-treated was measured by heating them successively from room temperature to 190° C.
The thermal shrinkage occurred in two stages, namely ( 1 ) in the range from room temperature to 60° C, and ( 2 ) starting at 90° C. The former was almost unaffected by the history such as cold-drawing or heat-treating. On the other hand, the latter was sensitively influenced by a difference in fine structure caused by cold-drawing and heat-treating. When these results were compared with temperature dependence of fine structure and of other physical properties, it was found that the thermal shrinkage is closely related to the release of strains and to the relaxation of molecular chains in amorphous region, associated with a breakdown of intermolecular hydrogen bond in this region. As crystallites would act as crosslinking points in crosslinked polymers and inhibit the relaxation and the motion of segments in amorphous region, the behavior of shrinkage seemed to be decided by the network-density in net-structure composed of crystallites as well as amorphous chains and by the extent of tension of amorphous chains. On the basis of this assumption, the mechanism of irreversible thermal-shrinkage for each specimen was discussed.