EFFECT OF FINE STRUCTURES ON MECHANICAL PROPERTIES OF POLYVINYL ALCOHOL FIBERS

Abstract

The relation between the fine structures and mechanical properties was investigated on polyvinyl alcohol fibers spun in coagulating baths of Na₂SO₄ (G) or NaOH (C), followed by hotdrawing and relaxation heat treatment.
Three mechanical loss peaks are observed around 20°C, 70°C and 120°C, which are known as β_a, α_a and β_c absorptions, respectively. The intensities of these absorptions decrease with draw ratio, and increase with shrinkage ratio. The α_a absorption is attributed to the microbrownian motion of amorphous chains and disappears when the amorphous orientation function Fa is extrapolated to 1. The fine structures of fiber G and fiber C are reflected on the relation between the peak intensity of α_a absorption and Fa. The β_c absorption is considered to be attributed to the low ordered amorphous region. Dynamic modulus E' increases and the lowering of E' by heating becomes smaller with the increase in the total orientation function Ft. Highly drawn fibers have higher Young's modulus, while highly relaxed fibers have lower modulus. Young's modulus is reasonably explained using a series model of crystalline and amorphous regions. The breaking strength and elongation are remarkably affected by the state of amorphous regions. The breaking strength and elongation strongly depend on Fa. Very high hot-drawing was possible for fiber C than fiber G. This is because for the high molecular orientation and the high modulus, high strength and low elongation.
The behaviours for the knot strength were different between fiber G and fiber C, reflecting the difference of the structures of amorphous region. It should be considered that the knot strength is related to other factors such as the length of amorphous region, in addition to Fa.