CHANGE OF FINE STRUCTURES OF POLYVINYL ALCOHOL FIBERS BY DRAWING AND RELAXATION

Abstract

The change in fine structures, by hot-drawing and heat treatment (slack), of polyvinyl alcohol (PVA) fibers spun with aqueous solution of Na₂SO₄ (Fiber G) and NaOH (Fiber C) as coagulant was investigated by means of X-ray diffraction, differential thermal analysis and optical dichroism.
The fiber-forming process, i.e., the change of the solvent coaguelant composition along the spinning line, in NaOH solution is quite different from that in Na₂SO₄ solution. Fiber C has a higher drawability and less shrinkage compared with Fiber G.
By hot-drawing, longer crystalline and shorter amorphous regions are formed in Fiber C, than in Fiber G. The lattice distortions of the second-kind are also low in Fiber C. These difference of fine structure was remarkably reflected in the melting point and dimensional stability. It was assumed that the mobility of the molecular chains during hot-drawing and heat treatment depends on the comformation in as-spun fibers.