No abstract

No abstract

SynopsisWide-angle x-ray scattering (WAXS) has been used to characterize the ordered phases of spin-oriented nylon 6 fibers wound a t speeds ranging from 5000 to 8OOO m/min. Quantitative analysis of the radial diffractometer scans by a computerized curve-fitting procedure reveals that the unit-cell geometry of both the a and y crystalline morphologies are highly dependent on winding speed and on annealing conditions. At 800" m/min, there is a particularly large reduction in the intermolecular distance along the van der Waals forces of the a unit cell, which is accompanied by substantial crystal growth in the hydrogen-bond direction. Similar increases in the width and perfection of the a crystals result from water annealing and steam treatment. The perfection of the y crystals increases with winding speed and after annealing in water, but steam treatment increases the intermolecular distance along the hydrogen bonds while reducing it along the van der Waals forces. Using bulk density measurements and the experimentally determined crystalline density p, for each sample, the volume-fraction crystallinity (VFC) is shown to pass through a maximum a t ca. 6500 m/min. This maximum arises from a decrease in a crystallinity with increasing winding speed together with an increase in y crystallinity, which levels off above ca. 7000 m/min. I t is demonstrated that the determination of VFC assuming constants pu would lead to large errors. The onentation of the a crystals is found to be much less than that of the y crystals, but it increases quite rapidly with winding speed. Water and steam treatments cause increases in a orientation and decreases in y orientation.The polymorphic nature of nylon 6 has made microstructural analysis particularly complicated. The number and nature of the crystal forms that

Treatments in highly polar solvents, such as dimethyl formamide, dimethyl acetamide, and dimethyl sulfoxide, under suitable conditions have been found to improve the dyeability of Nomex® yam so that it can be dyed under atmospheric conditions in a reasonable length of time without the aid of a carrier. Essentially, these solvents provide chemical energy to the yam, permitting rearrangements of the polymer chains through breakage and reformation of interchain hydrogen bonding. The changes in dyeability may be attributed to orientation changes or to microvoid formation occurring in the fiber structure during treatment.Nomex*, a commercially available, thermally stable aramid fiber, is difficult to dye because of its extremely high glass transition temperature (Ta ~ 275°C). At present, the recommended method for dyeing Nomex involves relatively high concentrations of a dye carrier in the dyebath and a high dyeing temperature for a long period of time [3]. Such conditions require substantial amounts of energy to maintain dyeing temperature and for the treatment of waste dyebaths.Recent work at TRI has focused on the use of chemical energy provided by a suitable solvent to modify fiber structure and thereby improve dyeability [5,8].In our studies on Nomex, this concept was explored by modifying the Nomex structure with highly polar solvents such as dimethyl formamide, dimethyl acetamide, and dimethyl sulfoxide [4]. Characterization of the extent of interaction between these solvents and Nomex has involved a study of shrinkage phenomena under dynamic (constant heating rate) conditions. In addition, we have examined the effects of the various solvent treatments on the dyeing and mechanical properties and on the structure of Nomex. '

No abstract