Abstract
It was found that wet-spun polyvinyl alcohol (PVA) fibers whitened when they were hot-drawn to the constant draw ratio before breaking. In order to investigate the relation between the mechanism of whitening and the fine structure of whitened fibers, PVA fibers were drawn at various temperature and draw ratio, rate of drawing, tensile strength, visible ray transmittance, X-ray small angle scattering power, crystallinity and crystalline orientation of hot-drawn fibers were measured.
1) It was concluded that periodic transverse lines of whitened fibers observed with a optical microscope are row of macrovoids which appear only in dense parts of cross sections. Creases on the surface are observed with a scanning electron microscope.
2) Changes of tensile strength and crystalline orientation by hot-drawing are correlative with that of visible ray transmittance. It was suggested that macrovoids which occured in fiber disturbs the structure.
3) Conditions of hot-drawing, temperature, rate of drawing and medium have a important effects upon the whitening points. From these results, the mechanism of whitening were discussed.
